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Biomimetic Carbon Fiber Systems Engineering: A Modular Design Strategy To Generate Biofunctional Composites from Graphene and Carbon Nanofibers

  • Mohammadreza Taale
    Mohammadreza Taale
    Biocompatible Nanomaterials, Institute for Materials Science, Kiel University, Kaiserstraße 2, D-24143 Kiel, Germany
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  • , 
  • Fabian Schütt
    Fabian Schütt
    Functional Nanomaterials, Institute for Materials Science, Kiel University, Kaiserstraße 2, D-24143 Kiel, Germany
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    Orcidhttp://orcid.org/0000-0003-2942-503X
  • , 
  • Tian Carey
    Tian Carey
    Cambridge Graphene Centre, University of Cambridge, 9 JJ Thomson Avenue, Cambridge CB3 0FA, U.K.
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  • , 
  • Janik Marx
    Janik Marx
    Institute of Polymer and Composites, Hamburg University of Technology, Denickestraße 15, D-21073 Hamburg, Germany
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  • , 
  • Yogendra Kumar Mishra
    Yogendra Kumar Mishra
    Functional Nanomaterials, Institute for Materials Science, Kiel University, Kaiserstraße 2, D-24143 Kiel, Germany
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    Orcidhttp://orcid.org/0000-0002-8786-9379
  • , 
  • Norbert Stock
    Norbert Stock
    Institute of Inorganic Chemistry, Kiel University, Max-Eyth Straße 2, D-24118 Kiel, Germany
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    Orcidhttp://orcid.org/0000-0002-0339-7352
  • , 
  • Bodo Fiedler
    Bodo Fiedler
    Institute of Polymer and Composites, Hamburg University of Technology, Denickestraße 15, D-21073 Hamburg, Germany
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  • , 
  • Felice Torrisi
    Felice Torrisi
    Cambridge Graphene Centre, University of Cambridge, 9 JJ Thomson Avenue, Cambridge CB3 0FA, U.K.
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    Orcidhttp://orcid.org/0000-0002-6144-2916
  • , 
  • Rainer Adelung
    Rainer Adelung
    Functional Nanomaterials, Institute for Materials Science, Kiel University, Kaiserstraße 2, D-24143 Kiel, Germany
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  • , and 
  • Christine Selhuber-Unkel*
    Christine Selhuber-Unkel
    Biocompatible Nanomaterials, Institute for Materials Science, Kiel University, Kaiserstraße 2, D-24143 Kiel, Germany
    *E-mail: [email protected]
    More by Christine Selhuber-Unkel
    Orcidhttp://orcid.org/0000-0002-5051-4822
Cite this: ACS Appl. Mater. Interfaces 2019, 11, 5, 5325–5335
Publication Date (Web):January 2, 2019
https://doi.org/10.1021/acsami.8b17627

Copyright © 2019 American Chemical Society. This publication is licensed under these Terms of Use.

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Abstract

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Carbon-based fibrous scaffolds are highly attractive for all biomaterial applications that require electrical conductivity. It is additionally advantageous if such materials resembled the structural and biochemical features of the natural extracellular environment. Here, we show a novel modular design strategy to engineer biomimetic carbon fiber-based scaffolds. Highly porous ceramic zinc oxide (ZnO) microstructures serve as three-dimensional (3D) sacrificial templates and are infiltrated with carbon nanotubes (CNTs) or graphene dispersions. Once the CNTs and graphene coat the ZnO template, the ZnO is either removed by hydrolysis or converted into carbon by chemical vapor deposition. The resulting 3D carbon scaffolds are both hierarchically ordered and free-standing. The properties of the microfibrous scaffolds were tailored with a high porosity (up to 93%), a high Young’s modulus (ca. 0.027–22 MPa), and an electrical conductivity of ca. 0.1–330 S/m, as well as different surface compositions. Cell viability, fibroblast proliferation rate and protein adsorption rate assays have shown that the generated scaffolds are biocompatible and have a high protein adsorption capacity (up to 77.32 ± 6.95 mg/cm3) so that they are able to resemble the extracellular matrix not only structurally but also biochemically. The scaffolds also allow for the successful growth and adhesion of fibroblast cells, showing that we provide a novel, highly scalable modular design strategy to generate biocompatible carbon fiber systems that mimic the extracellular matrix with the additional feature of conductivity.

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1. Introduction

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Regenerative medicine aims at developing microenvironments for the regrowth of damaged or dysfunctional tissue and organs. New promising strategies of regenerative medicine make use of biomaterial scaffolds that resemble the chemical composition, (1) the topographical structure, and the three-dimensional (3D) micro- and nanoenvironments of extracellular matrix (ECM). (2) The ECM consists of interwoven protein fibers, such as collagens, in different ranges of diameters varying from a few (<5 nm) up to several hundred nanometers for bundled collagen fibrils. (3) The chemical, structural, and mechanical features of the ECM significantly control cell migration, as well as tissue development and maintenance (4) such that finding novel ways to mimic the ECM is a highly important task in biomaterials science. As the diameter (<5 nm) and length (<500 nm) of unbundled collagen fibrils are in the range of those of carbon nanotubes (CNTs), (3) CNTs present an interesting substitute for collagen fibrils.
A general goal of artificially fabricated biomaterial scaffolds is to promote cells to differentiate and proliferate in three dimensions so that they fulfill their functions in the artificial tissue and integrate well after implantation. (5) Particularly, the microstructure and porosity of a scaffold are the key to achieve spatially organized cell growth, besides the induction of specific biological functions in the regenerated tissue. Tailoring pore size, shape, and interconnectivity of a scaffold ensures that cell migration, as well as oxygen and nutrient contribution are similar to the conditions of natural tissues. (6) Often, a large pore size in the range of a few micrometers supports cell migration and ensures the transport of nutrition and waste products. (7)
In neural implants and heart tissue engineering, the electrical conductivity of a scaffold material is often a further requirement necessary for cellular signaling and function. (8) For example, conductivities of 0.03–0.6 S/m have been reported for cardiac muscles. (9) Carbon-based nanomaterials can in principle fulfill such requirements for 3D assemblies. (10,11) CNTs have a high electrical conductivity (up to 67 000 S/cm) (12) and chemical stability (e.g., against acids); (13) while graphene (G) offers high surface area (2630 m2/g) (14) and high electrical conductivity (107–108 S/m). (15) Both CNTs and graphene have attracted significant attention in biomedical applications, ranging from biosensors (16) and drug/gene delivery (17) to targeted bioimaging. (17) In addition, compared to other carbon-based nanomaterials, the high physical aspect ratio of CNTs (up to 3750 length/diameter) and graphene provides a sufficient surface area for the attachment of adhesion ligands and cells. (14,18) Regarding neural tissue engineering, 3D graphene foams (19) and graphene films (18) have contributed to enhance neural stem cell differentiation toward astrocytes and neurons. (20)
An important requirement for such carbon-containing scaffolds is biocompatibility. The biocompatibility of CNTs depends on the concentration of CNTs, (21) their degree of purification, synthesis method, (22) aspect ratio, diameter and number of CNT walls, (23) and their surface functionalization. (24) Although many studies have proven the feasibility of CNTs as biocompatible material, (25) the cytotoxicity of CNTs is still a concern due to residual metal catalysts, amorphous carbon, and CNT aggregation that can occur within the cell. (26) In contrast, graphene has been reported to be biocompatible and is readily applicable for a variety of biological applications, including the use of neuronal cells, (18) cardiomyocytes, (27) and osteoblast (28) cells. Graphene oxide (GO) is an interesting graphene derivative, as it consists of a single atomic carbon layer decorated with hydrophilic functional groups such as carboxylic acid, hydroxyl, and epoxide. (29) In particular, GO has shown a strong tendency to interact with peptides and proteins via physical or chemical bonds. (30) Therefore, graphene and GO have great potential in biomedical applications as they can easily be converted into biofunctional, peptide- or protein-coated surfaces. Moreover, carbon microtube materials, specifically aerographite (AG), are of further interest as biomaterials due to their electrical conductivity (0.2–0.8 S/m) (31) and highly porous (up to 99.99%) (32) 3D interconnected network. A recent study has demonstrated the feasibility of AG as a suitable 3D matrix for cell migration and proliferation. (33) However, a clear pathway to generate a highly porous biocompatible ECM-mimetic scaffold with tunable porosity, electrical conductivity, and suitable mechanics for biomedical applications has so far been missing.
Here we demonstrate a novel modular design strategy to generate hierarchically structured carbon-based, microfibrous scaffold materials with adjustable electrical and mechanical properties that mimic the structure of the extracellular matrix. The materials investigated here are biocompatible, support cell proliferation and adhesion, and open the gateway to future biomaterial development, where biocompatibility and electrical conductivity are vital for cell proliferation and stimulation.

2. Results and Discussion

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2.1. Novel Types of Graphitic Scaffolds by CNT and Graphene Infiltration

Different types of fibrous 3D carbon scaffolds have been prepared based on our modular template-mediated method. Figure 1 shows the modular design strategy of our fabrication method. The fabrication uses presintered highly porous (porosity > 93%) ceramic ZnO templates as a sacrificial material. (32) These ZnO templates themselves consist of interconnected tetrapod-shaped ZnO particles. Representative scanning electron microscopy (SEM) images of the ZnO templates are shown in the Supporting Information Figure S2. The highly porous ZnO templates have an interstitial space of approximately 10–100 μm between ZnO filaments, which in turn have diameters between 0.5 and 5 μm. Therefore, the spatial geometry and organization of the microtube-shaped structures of the ZnO template are comparable to that of the ECM. (34)

Figure 1

Figure 1. Schematic illustration of different 3D carbon tube structures. The highly porous ZnO template can be either infiltrated with a nanoparticle dispersion (e.g., graphene, CNT) leading to a homogeneous coating around the tetrapodal particles or converted to a graphitic structure using a chemical vapor deposition (CVD) process (aerographite). The combination of both processes leads to a modular design strategy, especially in terms of conductivity, mechanical stiffness, and surface topography.

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The coating of ZnO templates with carbon nanomaterials (e.g., CNTs, graphene) is performed via a simple process to infiltrate the entire 3D template with a CNT dispersion as described by Schütt et al. (35) In addition, here we demonstrate that the feasibility of this technique can be extended also to graphene dispersions. The infiltration process relies on the superhydrophilicity of the ZnO template, (36) which is a direct result of the combination of the hydrophilic character of the individual tetrapod-shaped ZnO microparticles and the high porosity (>93%) of the template. During water evaporation, the nanomaterials form a widely homogeneous coverage (35) around the ZnO microrods (Supporting Information Figures S3 and S4). The amounts of CNTs and graphene flakes covering the ZnO template can be controlled by cyclically repeating the infiltration process several times (Supporting Information, Figures S3 and S4). SEM images revealed that the infiltrated CNTs form a layer made of self-entangled CNTs around the ZnO network (Supporting Information Figure S4). Similarly to CNTs, a dispersion of graphene flakes also forms a homogeneous layer around the ZnO (Supporting Information Figure S3).
To generate freestanding scaffolds from the ZnO templates after coating them with carbon nanomaterials, the ZnO must be carefully removed. We have used three different processes to remove the sacrificial ZnO network after infiltration (Figure 1): (i) hydrolyzing the sacrificial ZnO template by a HCl solution (35) (Supporting Information Figure S5a), (ii) converting the ZnO template via a CVD process (31) (Supporting Information Figure S5b,c), and (iii) using a carbothermal reduction process (37) in combination with glucose (g) as a carbon source. Each of these processes leads to a specific type of carbon-based scaffold. Therefore, the results of these processes (Supporting Information Figure S5) are discussed in the following sections.

2.2. Freestanding Carbon Nanotube Network (CNTT) Scaffolds from Hydrolysis of the Sacrificial ZnO Template by HCl

When HCl is used to dissolve the ZnO in CNT-coated ZnO templates, hierarchically structured CNTT scaffolds are formed. These structures consist of interconnected hollow tubes, which are composed of self-entangled CNT networks, as reported previously. (35) SEM images of the resulting CNTT scaffolds are presented in Figure 2a–c. The presented structures demonstrate a hierarchical architecture, where the porous scaffold are composed of microtetrapods (Figure 2a,b), which in turn consist of nanoscale CNTs (Figure 2c). The HCl-based ZnO dissolution can only be applied for templates infiltrated with CNTs. Templates infiltrated with graphene only led to collapsing structures (data not shown), presumably as the graphene flakes cannot interweave.

Figure 2

Figure 2. SEM images from low to high magnification of the different 3D carbon structures. (a−c) Carbon nanotube tubes (CNTTs), (d−f) aerographite with incorporated CNTs (AG−CNTT) (the red arrows show the grown CNTs during the CVD process), (g−i) aerographite (AG), (j−l) aerographite with incorporated graphene (AG−G) (the yellow arrows point to nanopores on the surface of aerographite), and (m−o) carbon nanotube tubes incorporated into a thick carbon layer (CNTT−g).

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2.3. ZnO Conversion to AG via CVD Forms Composites with Embedded Nanoparticles

We also use a CVD process to remove the ZnO, resulting in a thin (∼15 nm) film of graphite around the entire template similar to the graphitic shells in AG. (31) The CVD process can be applied if the ZnO is coated with either CNTs or graphene (Supporting Information Figure S6). Then, the AG serves as an additional backbone. This is the case in all of our CVD-based scaffolds, i.e., in composites of graphene and aerographite (AG–G) and in composites of multiwalled CNTs and aerographite (AG–CNTT) (Figure 2d–l). The modular design of the fabrication process allows us to change and tailor the surface topography of the hollow graphitic microtubes. Up to 5 μm long CNTs are formed perpendicular to the surface of microtubes on AG–G and AG–CNTT during the CVD process (Figure 2f). Such CNTs are not formed on pure AG (Figure 2i). (31) The growth of new carbon nanotubes on AG–G networks (Figure 2l, red arrows) is most likely attributed to the adsorption of carbon atom clusters on the active sites of the graphene surface during the CVD process. (38)

2.4. Carbothermal Reduction Process Leads to Novel Types of Graphitic Structures with Embedded CNTs

In the carbothermal reduction reaction, (37) glucose acts as the carbon source enabling the reduction of ZnO in a quartz tube furnace at 950 °C under argon atmosphere. To do so, ZnO templates were infiltrated with a mixture of glucose and CNTs. The carbothermal reduction of ZnO to Zn(g) (37) leads to ZnO removal and to the formation of graphitic shells, thus resulting in the so-called CNTT–g structure (Figure 2m–o). We have confirmed the removal of ZnO by Raman spectroscopy (Figure 3, CNTT–g graph) (see next paragraph). Furthermore, this process results in a scaffold with a microstructure that is comparable to that of the AG–CNTT scaffold (Figure 2e,n). However, the graphitic shells of the CNTT–g scaffold appear to be thicker than those of the AG–CNTT scaffold (Figure 2n,o). Additionally, in contrast to the AG–CNTT structures, no additional CNTs are grown (Figure 2n) in the CNTT–g case.

Figure 3

Figure 3. Raman spectroscopy of aerographite, ZnO, CNTT, AG–CNTT, CNTT–g, AG–G, graphene, and CNT inks.

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Figure 3 shows Raman spectra (Renishaw 1000 InVia) of all of the carbon-based structures. Raman spectroscopy is used to examine the structural fingerprint of each material at a wavelength of 514.5 nm with an incident power of ∼0.1 mW. The graphene and CNT inks were drop-cast onto Si/SiO2 substrates before measurement. For the graphene ink (red curve), the G peak (∼1586) corresponds to the E2g phonon at the Brillouin zone center, and the D peak located at ∼1350 cm–1 corresponds to the breathing modes of the sp2 carbon atoms and requires a defect for its activation. (39) Our graphene inks are produced by liquid-phase exfoliation; therefore we attribute this peak to edge defects rather than to defects in the basal plane. (40) The two-dimensional (2D) peak located at ∼2700 cm–1 is the D peak overtone and can be fitted by a single Lorentzian, indicating electronically decoupled graphene monolayers. (41)
The aerographite (dark blue curve) shows a G peak position Pos(G) ∼ 1600 cm–1 and the absence of a distinct 2D peak, indicating the more defective nature of this sample and a lack of structural order in the aerographite. (42) The AG–G (yellow curve) structure has a similar spectrum to that of aerographite with D and G peaks located at ∼1350 and ∼1600 cm–1, respectively, indicating that the material is mostly composed of aerographite and graphene, given the selective etching of the ZnO scaffold during the CVD reduction. (31) The spectra of the CNT ink (green curve) and CNT ink with glucose (purple curve) show D, G, and 2D peaks at ∼1350, ∼1580, and ∼2700 cm–1, respectively. The peaks from the glucose residue are too weak to be observed. Moreover, the CNTT spectra (gray curve), AG–CNTT (blue curve), and CNTT–g (pink curve) have D, G, and 2D peaks that demonstrate the presence of the CNTs, respectively. Finally, the ZnO spectra (brown curve) display several peaks below 1200 cm–1, predominately created from the intense peak at 1158 cm–1 attributed to the 2A1(LO) and 2E1(LO) modes at the Brillouin zone center. (43) However, no peaks attributed to ZnO are observed in any of the CNTTs or aerographite scaffolds, proving the complete removal of the ZnO template.

2.5. Scaffold Mechanics can be Tailored Over Several Orders of Magnitudes

Figure 4 shows Young’s moduli and electrical conductivities of CNTT, AG–CNTT, CNTT–g, AG, and AG–G. The scaffold with the lowest stiffness is AG with a Young’s modulus of 16 kPa, which is comparable to previously reported values. (31) AG–G has a Young’s modulus of up to 27 kPa, thus adding graphene into the graphitic shells of AG results in a mechanical reinforcement of the scaffold (∼170%). This reinforcement is in a similar range to that of other graphene-reinforced porous networks, e.g., graphene/chitosan composites (44) (∼200%). In contrast to AG–G, AG–CNTT is much stiffer (Figure 4), with Young’s modulus reaching ∼22 MPa.

Figure 4

Figure 4. Young’s modulus (measured under compression) and electrical conductivity of the 3D CNTT, AG–CNTT, CNTT–g, and AG–G scaffolds. All structures containing CNTs have a higher Young’s modulus and conductivity compared to those without CNTs. The values for pure AG and CNTTs were taken from the corresponding publications, (31,35) whereas the other values were measured using a self-built electromechanical testing setup.

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This reinforcement by a factor of about 1000 is presumably due to the reinforcement of CNTs on the nanoscale by self-entanglement. (35) Hence, the mechanical reinforcement of AG by CNTs is higher than in other CNT-reinforced porous biomaterials, including gelatin methacrylate (GelMA)–CNT composites (45) and poly(propylenefumarate)–CNT composites. (46) Young’s modulus of CNTT–g (∼4 MPa) is in between the moduli of AG–G and AG–CNTT. These results confirm that the incorporation of CNTs and graphene into 3D scaffolds compensates for the typically low mechanical Young’s moduli of porous structures (47) and that AG provides a stable backbone for CNTT scaffolds. In addition, the structural integrity of AG–G scaffolds is demonstrated during a long-cycle compression test (Figure S7) (Supporting Information Video S1).

2.6. Tailoring Scaffold Conductivity

We also investigated the electrical properties of our scaffolds (Figure 4, gray squares). AG–G and AG have similar electrical conductivities of around 0.5 and 0.2 S/m, whereas the conductivities of AG–CNTT and CNTT–g are about 120 and 130 S/m, respectively (Figure 4). Hence, AG–CNTT and CNTT–g clearly have higher electrical conductivities than CNT-containing electrospun fibrous composites (3.5 S/m), (48) which are applied in cardiac tissue engineering. The increase in conductivity of the scaffolds can be mainly attributed to the high conductivity of CNTs that are embedded in the graphitic shells of AG. This effect is more pronounced in the case of AG–CNTT and CNTT–g, presumably as a result of the conductive pathways formed by the self-entangled CNT networks. It has already been shown that by adjusting the CNT concentration during the infiltration process, the conductivity of CNTT can be tailored between 10–6 and 130 S/m. (35) Indeed, CNTT–g has the highest conductivity (330 S/m) of our scaffolds.

2.7. Scaffolds Strongly Adsorb Proteins

Albumin is an adhesive protein in plasma and can non-specifically bind to low-dimensional carbon-based materials via electrostatic interactions. (49) Therefore, we checked the albumin adsorption capacity of the scaffolds using the bicinchoninic acid (BCA) assay. As shown in Figure 5, within the first 48 h, albumin adsorption is smaller on AG–G than on AG–CNTT, whereas its adsorption is very similar on all scaffolds later on. The highest absolute protein adsorption mass (30.23–22.6 ± 2.76 mg/cm3) was detected during the first 2 days of incubation, and the adsorption amount reduced to approximately two-thirds (23.69–20.64 ± 2.39 mg/cm3) during the third to fourth day of incubation. Overall, protein adsorption is very similar on all tested scaffolds, although CNTT, CNTT–g, and AG–CNTT scaffolds adsorb slightly higher protein amounts (CNTT–g: 77.32 ± 6.95 mg/cm3; CNTT: 70.77 ± 5.33 mg/cm3; AG–CNTT: 68.08 ± 6.73 mg/cm3) than AG–G (64.92 ± 7.2 mg/cm3) (Figure 5a). This might be attributed to the higher protein adsorption capacity of CNTs than graphene flakes due to van der Waals forces and electrostatic interactions. (30)

Figure 5

Figure 5. Protein adsorption on CNTT, AG–CNTT, CNTT–g, and AG–G during 0–48, 49–96, and 97–144 h of incubation with albumin solution (1 mg/mL). (a) Absolute protein adsorption amount per scaffold volume. (b) Absolute protein adsorption amount per scaffold weight.

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To compare our results of protein adsorption with other studies, we needed to relate them to the weight of the scaffolds by taking into account their density (Table 1). Figure 5b shows that protein adsorption per weight of CNTT, CNTT–g, and AG–CNTT scaffolds is different for different scaffold types (CNTT–g: 147.9 ± 13.42 mg/g; CNTT: 128.9 ± 9.69 mg/g; AG–CNTT: 115.14 ± 11.38 mg/g). It is also higher than on single-walled CNTs and graphene (∼100 mg/g) (30) and on nanoporous silica (∼70 mg/g). (50) In addition, due to its low density, AG–G adsorbs even more protein per weight (1512.25 mg/g) after 144 h, e.g., about 10 times more than our other scaffolds. The albumin adsorption on AG–G even after 48 h (527 mg/g) is comparable to that of graphene oxide (∼500 mg/g). (30)
Table 1. Full Names and Abbreviations of Fabricated Materials and Scaffolds in Our Study
full name abbreviation density (g/cm3) porosity (%)
aerographite AG ∼200 × 10–6  (31) up to ∼99.9 (31)
carbon nanotube tube CNTT ∼0.064 ∼94
carbon nanotube tube–glucose CNTT–g ∼0.061 ∼90
aerographite–carbon nanotube tube AG–CNTT ∼0.069 ∼95
aerographite–graphene AG–G ∼0.005 ∼96

2.8. Biocompatibility of the Carbon-Based Scaffolds

Biocompatibility of the scaffolds is investigated by methylthiazolyldiphenyl-tetrazolium bromide (MTT) metabolic activity and WST-1 assays, as well as by proliferation studies. Figure 6 shows the results for CNTT, CNTT–g, AG–CNTT, and AG–G samples using an MTT assay, demonstrating that all scaffolds are biocompatible, hosting a similar number of viable cells as the negative control. As cell adhesion is not possible on pristine AG without functionalization, (33) biocompatibility of AG is not investigated again in this study.

Figure 6

Figure 6. Percentage of viable cells (rat embryonic fibroblasts wild type, REF52wt) relative to the negative control, as determined in an MTT assay (four independent experiments, five technical repeats in each of them). The error bars denote standard deviation.

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Figure 7 shows the proliferation rate of rat embryonic fibroblast cells (REF52wt) cultured on CNTT, CNTT–g, AG–CNTT, and AG–G samples relative to cells cultured on a culture dish. CNT-containing scaffolds (CNTT, CNTT–g, and AG–CNTT) lead to higher proliferation rates (ca. 300–320%) than graphene-containing structures (AG–G) (∼240%) after 7 days in culture. As fibroblast proliferation depends on matrix stiffness, (51) an increase in stiffness might also lead to an increase in fibroblast proliferation, (52) which can be attributed to the translation of mechanical cues from the matrix into a biochemical one via mechanosensory receptors such as focal adhesions. (53) Specifically, it has been reported that fibroblasts need substrates with a minimum Young’s modulus of 20–30 kPa to spread and 2 MPa to spread and polarize perfectly. (51) Hence, the huge difference in Young’s moduli between CNT-reinforced scaffolds (between 4 MPa in CNTT–g and 23 MPa in CNTT) and graphene-reinforced scaffolds (27 kPa in AG–G) can explain the higher proliferation rate of fibroblast cells on CNTT, AG–CNTT, and CNTT–g compared to AG–G.

Figure 7

Figure 7. Results of WST-1 metabolic tests of cell proliferation rate (REF52wt). Mean values were determined from four independent experiments, each including five technical repeats. The error bars denote standard deviation, the raw data were normalized to the control, and a correction factor was applied to account for unspecific adsorption (see Materials and Methods).

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2.9. Carbon-Based Scaffolds as Porous Structures for Cell Growth

Fibroblast cells (REF52wt) were cultured for 7 days on the scaffolds to investigate cellular growth at the surface and inside. SEM images of critically point-dried cells (Figure 8) revealed that cells (highlighted in green) are attached to the surface of the scaffolds. Fibroblasts do not migrate strongly within a 3D network (54) but proliferate so that we typically observe several cells at one location. Cells are sprawled and elongated between the filaments of scaffolds and have a polygonal shape on all four scaffold types. Close-up images on the adhesion sites reveal tightly anchored membranes of cells to CNTs and graphene on the surface of structures, comparable to fibroblasts on AG functionalized with cyclic arginylglycylaspartic acid (RGD) peptides. (33)

Figure 8

Figure 8. SEM images of REF52wt cells after 7 days of culturing within (a–c) AG–CNTT, (d, e) CNTT–g, (g–i) AG–G, and (j–l) CNTT scaffolds. Left: Medium-sized overview images illustrating the growth of cells between the fibers in different directions and planes; middle: zoomed-in images showing well-stretched cells along the fibers and their elongation; and right: close-up images on the adhesion sites, proving the presence of strong contacts between the materials and the cell membrane (yellow arrows).

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To investigate cell adhesion at the molecular level, we studied the presence of paxillin in adhesion structures. Paxillin is a component of focal adhesion clusters; (55) therefore, it can be assumed that more paxillin in contact with our scaffolds is related to stronger cell adhesion. We used cells that were stably transfected with yellow fluorescent protein (YFP)-paxillin and imaged the paxillin in fluorescence microscopy. Imaging fluorescence in 3D matrices compared to 2D is challenging. (56) Due to the low intensity of paxillin in the cells and the high light absorbance of our scaffolds, (31) imaging the paxillin adhesion sites was only possible by using long acquisition times (5 s), which resulted in background signals. Nevertheless, paxillin-containing adhesion sites can be distinguished around the filaments of the scaffolds. Based on the fluorescence images (Figures 9a–d and S8), more adhesion clusters can be detected on CNT-reinforced scaffolds than on graphene-reinforced scaffolds. This could again result from the different mechanical properties of the scaffolds, but it is also in agreement with cell studies on multiwalled CNTs showing that NIH-3T3 fibroblasts form larger adhesion clusters on CNTs than on graphene. (57)

Figure 9

Figure 9. High-magnification fluorescence images of REF52 YFP-paxillin cells on 3D scaffolds: (a) CNTT, (b) AG–CNTT, (c) CNTT–g, and (d) AG–G. YFP-paxillin is mainly distributed in small clusters (YFP; yellow), the nucleus was stained with Hoechst (4′,6-diamidino-2-phenylindole, DAPI; blue), and actin fibers were visualized by phalloidin (red). Fluorescence imaging took place in optical sections approximately between 50 and 100 μm from the surface of the material. Adhesion sites are detectable (a, b) as tiny yellow spots mainly around the tube-shaped filaments of CNTT and AG–CNTT structures. Due to the low intensity and small size of YFP-paxillin (c, d), they are not clearly observed, which is also obscured by red (actin fibers) and blue (nucleus) channels in multichannel images. The green dashed arrows illustrate the protrusion direction of the cells.

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A further important contribution to cell adhesion is the cytoskeleton, where networks of actin fibers determine cell shape and movements. (58) To investigate cellular actin networks on our scaffolds, we investigated the fluorescence of phalloidin to detect actin fibers. Again, imaging deeply inside the scaffolds was impaired by the strong light absorbance of CNTs and graphene, restricting it to the first 300 μm from the surface. As shown in Figure 9, well-developed actin fibers (in red) are indeed present within the fibroblasts. Furthermore, the cells are polarized and have oriented actin bundles. Figure 9a–c also shows that actin fibers on CNT-reinforced scaffolds (CNTT, AG–CNTT, and CNTT–g) are mainly oriented in the direction of fibroblast protrusions. Although many actin fibers can be detected in cells grown on AG–G (Figure 9d), they are neither well polarized nor elongated like the actin fibers in the cells on CNT-reinforced scaffolds (CNTT, AG–CNTT, and CNTT–g). These results could again originate from the mechanical properties of our materials, similarly to proliferation rate and paxillin clusters.

2.10. ECM-Mimetic Scaffolds

The open porous structure of our scaffolds with large free volumes (>95%) should be highly beneficial for the growth and migration of cells, as the open pores allow the cells to freely migrate and proliferate within the scaffolds. (2) Moreover, in contrast to other studies on 3D porous structures, in which the alignment of CNTs (24) or graphene sheets (59) confined the accessibility of cavities, our carbon framework structures provide accessible interconnected pores from all sides (Figure 2). In addition, the hierarchical organization of structural elements, specifically self-entangled CNTs in the form of microtubes, is reminiscent of the hierarchical nano- and microstructure of the ECM. It should therefore in principle be possible to employ our modular design strategy to generate different composition-dependent structural and mechanical features similar to collagen (60) in the ECM. As our scaffolds strongly adsorb proteins, it should also be possible to adsorb adhesion ligands typically present in ECM proteins, such as RGD. (61) In this way, the scaffolds can be modified such that they finally mimic the ECM structurally and biochemically, but with the additional feature of conductivity.

3. Conclusions

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In summary, we have introduced a novel modular design strategy to produce carbon-based scaffolds that mimic the ECM and allow 3D cellular growth. Biocompatibility studies revealed a high proliferation rate of fibroblasts as well as the ability of fibroblasts to develop paxillin-containing adhesion sites. In addition, the cells sprawl and elongate between single filaments of the scaffolds. Tuning electrical conductivity (ca. 0.1–330 S/m), stiffness (ca. 10–3–0.7 MPa), and protein adsorption and porosity (up to ∼99%) of the scaffold provides great possibilities for culturing cells. Based on the proven protein adsorption capacity of the scaffolds, they are suitable for biofunctionalization and addition of other biochemical cues. This is particularly relevant in tissue engineering of electrically excitable tissue, e.g., heart tissue, as our scaffolds have tunable electrical conductivity. In addition, the fabrication procedure is very simple and can in principle be adopted to develop 3D assemblies from other low-dimensional nanomaterials (e.g., bioactive ceramic nanoparticles, polymeric nanofibers) by only changing the nanoparticle dispersion, as long as the nanoparticles are connected via strong physical contacts such as entanglement, fusion, or physical locks. This makes the scaffolds promising candidates as conductive ECM-mimetic materials in many applications from regenerative medicine to 3D cell culture.

4. Materials and Methods

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4.1. Fabrication of 3D Carbon Scaffold Materials

Templates of tetrapod-shaped ZnO were fabricated by a previously developed flame transport synthesis method. (32) The resulting loose powder was pressed into a cylindrical shape (h = 3 mm, d = 6 mm) at a density of 0.3 g/cm3. The pellets were subsequently sintered for 5 h at 1150 °C to obtain an interconnected 3D ZnO network. (32) This structure is the sacrificial template used for fabrication of carbon-based scaffolds, i.e., freestanding CNTT, AG–CNTT, and AG–G.
For the fabrication of the CNTT scaffolds, the porous ZnO templates were infiltrated with an aqueous dispersion of multiwalled CNTs (1 wt %, CARBOBYK-9810, BYK Additives & Instruments) using a self-built computer-controlled syringe. The length of the CNTs can be on the order of a few micrometers, with diameters in the range of 20–60 nm. (34) After infiltration of ∼90 μL of the CNT solution, the samples were dried under ambient conditions for at least 1 h. The process was repeated six times so that CNTs covered the ZnO template. Then, the ZnO backbone was removed by immersing the composite in a 1 M HCl solution overnight. The HCl solution was replaced by washing with pure ethanol (five times). Finally, the etched structures were dried in a critical point dryer (EMS 3000) by using the automatic mode. The purge time was set to 15 min to ensure that all ethanol was washed out, leaving freestanding CNTTs. (3)
To alter the CNTT structures further, we added glucose (1 wt %) to the CNT ink used for infiltration. The infiltration into a ZnO template was then repeated four times. After that, the samples were transferred into a quartz tube furnace and heated to 950 °C under argon atmosphere for 2 h. During this process, the ZnO was removed by carbothermal reduction, (45) leading to CNTT–g, which contains both the remnants of the glucose and embedded CNTs.
For the synthesis of AG–CNTT scaffolds, the CNT-coated ZnO templates were exposed to a CVD process, as reported previously. (31) Briefly, the ZnO template was replicated into aerographite at ∼760 °C under a hydrogen and argon atmosphere in the presence of toluene as the source of carbon. (62) Thereby, the CNTs were embedded into the graphite microtubes of aerographite while the ZnO was simultaneously etched by H2.
A similar process was used to generate composites of graphene and aerographite (AG–G). The graphene ink was made by dispersing graphite flakes (12 mg/mL, Sigma-Aldrich No. 332461) and Triton X-100 stabilization agent (1.7 mg/mL) in deionized water, followed by sonication (Fisherbrand FB15069, Max power 800 W) for 9 h. (63,64) The dispersion was then centrifuged (Sorvall WX100 mounting a TH-641 swinging bucket rotor) at 5k rpm for 1 h to remove the thick flakes. The supernatant (i.e., the top 70%) of the dispersion was then decanted to produce the final graphene ink. In Figure S1, optical absorption spectroscopy (Cary 7000) is used to estimate the flake concentration. (65) The flake concentration in the graphene ink is obtained via the Beer–Lambert law, which links the absorbance A = αcl with the beam path length l (m), the flake concentration c (g/L), and the absorption coefficient α (L/(g m)). The graphene ink was diluted 1:20 with water/Triton X-100. An absorption coefficient of α ∼ 1390 L/(g m) for the graphene ink at 660 nm was utilized, (66) estimating a graphene flake concentration of ∼0.09 mg/mL, consistent with previous reports of graphene-based inks. (40,67) The spectrum of the graphene ink is mostly featureless due to the linear dispersion of the Dirac electrons, while the peak in the UV region is a signature of the van Hove singularity in the graphene density of states. (68) The ZnO scaffold was infiltrated 50 times to achieve coverage of graphene around the ZnO tetrapods, due to the low concentration of the ink (0.09 mg/mL). After infiltration, the CVD process (see process specification above) was used to embed the graphene flakes into aerographite microtubes and to remove the ZnO template.

4.2. Mechanical and Electrical Characterizations of 3D Carbon Scaffold Materials

Mechanical and electrical characterizations were performed using a self-built setup consisting of a Maerzhaeuser Wetzlar HS 6.3 micromanipulator, which is driven by a stepper motor, a Kern PLE 310-3N precision balance, and a Keithley 6400 source meter. A self-written LabView program controls all components. To avoid any vibration damping, the whole setup is located on a very rigid aluminum plate in a box filled with sand, which is mounted on a vibration-isolated table. Stress–strain curves were measured by placing the sample in between the micromanipulator and the precision balance. For compression tests, the micromanipulator deforms the sample by a user-defined step size. After each step, the program measures the force of the balance after a short settling time has been elapsed. These steps are repeated until the maximum deformation defined by the user is reached. Afterwards, the direction of the deformation is inverted until the micromanipulator comes back to its original position. Finally, the stress–strain curves are evaluated and Young’s modulus is determined. With respect to the cyclic compression test, the same procedure was repeated several times. The wait time between each compression step was set to 0 s, and the deformation speed was set to 40 μm/s. To demonstrate the structural integrity, a video was recorded during the long-cycle compression test with a USB camera. Furthermore, the same setup also allows to record the current–voltage characteristics using a Keithley 6400 source meter in the four-wire sense mode. For electrical measurements, the carbon structures were connected to thin copper plates on both sides by using conductive silver paste. It is noteworthy that only a thin layer of paste was needed to ensure good electrical connection of the porous material to the measurement setup. Current–voltage curves were measured in a voltage range of up to 5 V. Finally, the resistance was calculated from the obtained data and converted to conductivity to give meaningful values for each structure.

4.3. Cell Culture and Cell Seeding on Scaffolds

Rat embryonic fibroblasts (REF52), both as wild type and stably transfected with YFP-paxillin (REF YFP-Pax), (69) were cultured in Dulbecco’s modification of Eagle medium (Biochrom, Germany) at 37 °C, 5% CO2 at ∼90% humidity. The medium was supplemented with 10% fetal bovine serum (Biochrom, Germany) and 1% penicillin/streptomycin (Sigma-Aldrich, Germany). To expel any traces of remaining zinc from the scaffold fabrication process prior to cell experiments, all samples were immersed in culture medium for 14 days after autoclaving at 121 °C. Shortly before the cell experiments, the cells were immersed in a fresh culture medium, counted with a cell counter (Scepter, Merck Millipore, Germany), and ∼20 000 cells were seeded on each scaffold in 24-well plates. The cells were incubated on the scaffolds for 1, 3, or 7 days.

4.4. Cell Staining

To investigate the cell morphology, proliferation, and adhesion on the scaffolds, cell nuclei were stained with DAPI (Thermo Fisher, Germany), and actin stress fibers were stained with phalloidin (Alexa Fluor 647 phalloidin, Thermo Fisher, Germany). Imaging was carried out using fluorescence microscopy (IX81, Olympus, Germany), and images were processed with cellSens Dimension (Olympus, Germany). For electron microscopy investigations, the cells were fixed by paraformaldehyde (Thermo Fisher, Germany) and dried using critical point drying (EMS 3000). A thin layer of gold was sputtered (Bal-Tec SCD 050, 30 mA, 30 s) onto the sample prior to scanning electron microscopy (SEM) (Ultra Plus Zeiss SEM, 5 kV). The cells in SEM images were highlighted in green (via Adobe Photoshop CC 2017) to distinguish them more easily.

4.5. Viability and Proliferation Assay

The number of living cells on the scaffolds was quantified by a WST-1 proliferation assay after 1, 3, and 7 days of incubation. In this assay, the number of living cells can be acquired from the amount of dye produced via bioreduction of stable tetrazolium salt WST-1 (Sigma-Aldrich, Germany). The amount of formazan is proportional to the number of cells (Cell Proliferation Reagent WST-1 Protocol, Sigma-Aldrich, Germany). The experiments were carried out as follows: After seeding the cells onto each sample (see specification above), the scaffolds were first washed with phosphate buffered saline and then incubated with a WST-1-containing medium for 4 h. The concentration of the formazan dye was quantified by a multiwell spectrophotometer (Bio-Tek μQuant) after removal of the samples from the wells. CNTs tend to react with tetrazolium salts; (70) thus, the proliferation rates were normalized to the absorption of the detected tetrazolium on control samples without cells. The amount of tetrazolium reacting with the scaffolds was determined for each sample as explained in the following: 10 000 cells were cultured for 24 h in 96-well plates prior to adding scaffolds to half of the wells, with the other half serving as scaffold-free control. Then, all of the wells were incubated for an additional time of 4 h with the WST-1 reagent before quantification of the formazan (i.e., product of tetrazolium cell reaction) amount in each well by a multiwell spectrophotometer. The amount of tetrazolium that reacted with the scaffold was calculated for each specimen by subtracting the amount of formazan of scaffold-containing wells from scaffold-free control wells. The difference in absorbance between the scaffolds and controls was used as a correction factor for the data generated with the WST-1 assay.
In addition, the viability of cells was tested according to the ISO 10993 norm. Briefly, 10 000 cells/100 μL REF52 cells were cultured in a 96-well plate for 24 h. For medium extraction, the scaffolds were incubated in a culture medium at 37 °C for 72 h. The cultured cells were incubated with either untreated medium or extracted medium for a further 24 h. To determine cell viability, the colorimetric methylthiazolyldiphenyl-tetrazolium bromide metabolic activity assay (MTT; Sigma-Aldrich, Germany) was used. The cells in untreated medium served as the negative control, and the cells in 20% dimethyl sulfoxide were the positive control. The absorbance was measured at 490 nm (absorption wavelength of formazan) and 600 nm as a reference. The results from the cultured cells with extracted medium were normalized to the values measured for the negative control.

4.6. Protein Adsorption Rate

The protein adsorption rate on the scaffolds was measured by using bovine serum albumin (Pierce; Thermo Fisher, Germany) as a model protein. Protein solution (1 mL, 1 mg/mL) was added per scaffold and incubated at 37 °C in a humidified incubator (CO2 5%, humidity 95%). After 48 h, nonadhered proteins were carefully removed by a pipette and saved for recording. The scaffolds were washed with saline and incubated for a further 48 h after addition of 1 mL of protein solution. The same procedure was repeated after 48 h. The concentration of protein in the supernatant was measured using a Micro BCA protein assay (Pierce; Thermo Fisher, Germany). To do so, 10 μL of supernatant was mixed with 200 μL of working reagent and incubated for 30 min. The absorbance was measured using a microplate reader (Bio-Tek μQuant) at 570 nm. After calibrating the results with a standard curve provided by the BCA protein assay kit (Pierce; Thermo Fisher, Germany), the protein adsorption rate was calculated by subtracting the residual protein concentration from the initial protein concentration.

Supporting Information

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The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.8b17627.

  • Optical absorption spectrum of graphene ink (Figure S1); SEM images of ZnO templates (Figures S2–S4); different 3D carbon tube structures (Figure S5); SEM images of AG–CNTT structures (Figure S6); long-cycle compression test graph of AG–G scaffold (Figure S7); high-magnification fluorescence image of REF52 YFP-paxillin cells (Figure S8); supporting discussion (PDF)

  • Structural integrity of AG–G scaffold (AVI)

Terms & Conditions

Most electronic Supporting Information files are available without a subscription to ACS Web Editions. Such files may be downloaded by article for research use (if there is a public use license linked to the relevant article, that license may permit other uses). Permission may be obtained from ACS for other uses through requests via the RightsLink permission system: http://pubs.acs.org/page/copyright/permissions.html.

Author Information

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  • Corresponding Author
  • Authors
    • Mohammadreza Taale - Biocompatible Nanomaterials, Institute for Materials Science and , Kiel University, Kaiserstraße 2, D-24143 Kiel, Germany
    • Fabian Schütt - Functional Nanomaterials, Institute for Materials Science and , Kiel University, Kaiserstraße 2, D-24143 Kiel, Germany;  Orcidhttp://orcid.org/0000-0003-2942-503X
    • Tian Carey - Cambridge Graphene Centre, University of Cambridge, 9 JJ Thomson Avenue, Cambridge CB3 0FA, U.K.
    • Janik Marx - Institute of Polymer and Composites, Hamburg University of Technology, Denickestraße 15, D-21073 Hamburg, Germany
    • Yogendra Kumar Mishra - Functional Nanomaterials, Institute for Materials Science and , Kiel University, Kaiserstraße 2, D-24143 Kiel, Germany;  Orcidhttp://orcid.org/0000-0002-8786-9379
    • Norbert Stock - Institute of Inorganic Chemistry, Kiel University, Max-Eyth Straße 2, D-24118 Kiel, Germany;  Orcidhttp://orcid.org/0000-0002-0339-7352
    • Bodo Fiedler - Institute of Polymer and Composites, Hamburg University of Technology, Denickestraße 15, D-21073 Hamburg, Germany
    • Felice Torrisi - Cambridge Graphene Centre, University of Cambridge, 9 JJ Thomson Avenue, Cambridge CB3 0FA, U.K.;  Orcidhttp://orcid.org/0000-0002-6144-2916
    • Rainer Adelung - Functional Nanomaterials, Institute for Materials Science and , Kiel University, Kaiserstraße 2, D-24143 Kiel, Germany
  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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R.A. gratefully acknowledges partial project funding by the Deutsche Forschungsgemeinschaft under contract FOR2093. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. GrapheneCore2 785219. C.S.-U. was supported by the European Research Council (ERC StG 336104 CELLINSPIRED, ERC PoC 768740 CHANNELMAT) and the German Research Foundation (RTG 2154, SFB 1261 project B7). M.T. acknowledges support from the German Academic Exchange Service (DAAD) through a research grant for doctoral candidates (91526555-57048249). The authors acknowledge funding from EPSRC grants EP/P02534X/1, ERC grant 319277 (Hetero2D), the Trinity College, Cambridge, and the Isaac Newton Trust. We also acknowledge Galen Ream for critical proofreading.

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    Advanced bifunctional electrocatalysts for the O redn. reaction (ORR) and O evolution reaction (OER) are promising to improve the efficiency of fuel cells and metal-air batteries. Among the state-of-the-art efficient O electrocatalysts, heteroatom-doped C materials are favorable candidates. However, the enriched doping requires a highly exposed C skeleton. Here, we report a scalable route to prep. C nanotubes (CNTs) loaded on graphene microfolds (CGFs) by a low-temp. spray-drying procedure. Mol.-level assembly of graphene and CNTs, mesoporous structures, and large sp. surface areas permit the C skeleton of CGFs to be highly exposed. After doping with abundant N and P (5.58 at% for N, 0.1 at% for P), CGFs exhibit excellent bifunctional electrocatalytic activity for both the ORR and OER, with superb durability and methanol tolerance. The measured variance of the ORR and OER metrics (ΔE=Ej=10-E1/2) was low at 0.9 V vs. reversible hydrogen electrode (vs. RHE), being within only 20 mV of Pt- and Ru-based electrodes, and superior to transition-metal-based catalysts and other C catalysts. Such efficient overall electrocatalytic activity allows CGFs to be used for high-performance O electrodes in renewable energy devices.
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  11. 11
    Li, Z.; Liu, Z.; Sun, H.; Gao, C. Superstructured Assembly of Nanocarbons: Fullerenes, Nanotubes, and Graphene. Chem. Rev. 2015, 115, 7046– 7117,  DOI: 10.1021/acs.chemrev.5b00102
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    11
    Superstructured Assembly of Nanocarbons: Fullerenes, Nanotubes, and Graphene
    Li, Zheng; Liu, Zheng; Sun, Haiyan; Gao, Chao
    Chemical Reviews (Washington, DC, United States) (2015), 115 (15), 7046-7117CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    A review. The development on fullerenes, CNTs and graphene is currently enjoying a rapid pace, with enormous research achievements emerging every day. In this review, we focused on the tailored assembly of these sp2-hybridized nanocarbons into various macroscopic superstructures covering 1D fibers/yarns,2D films/papers, and 3D porous/dense monoliths.
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  12. 12
    Lekawa-Raus, A.; Patmore, J.; Kurzepa, L.; Bulmer, J.; Koziol, K. Electrical Properties of Carbon Nanotube Based Fibers and Their Future Use in Electrical Wiring. Adv. Funct. Mater. 2014, 24, 3661– 3682,  DOI: 10.1002/adfm.201303716
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    12
    Electrical Properties of Carbon Nanotube Based Fibers and Their Future Use in Electrical Wiring
    Lekawa-Raus, Agnieszka; Patmore, Jeff; Kurzepa, Lukasz; Bulmer, John; Koziol, Krzysztof
    Advanced Functional Materials (2014), 24 (24), 3661-3682CODEN: AFMDC6; ISSN:1616-301X. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A review. The prodn. of continuous fibers made purely of C nanotubes has paved the way for new macro-scale applications which use the superior properties of individual C nanotubes. These wire-like macroscopic assemblies of C nanotubes were recognized to have a potential to be used in elec. wiring. C nanotube wiring may be extremely light and mech. stronger and more efficient in transferring high frequency signals than any conventional conducting material, being cost-effective simultaneously. However, transfer of the unique properties of individual CNTs to the macro-scale proves to be quite challenging. This Feature Article gives an overview of the potential of using C nanotube fibers as next generation wiring, state of the art developments in this field, and goals to be achieved before C nanotubes may be transformed into competitive products.
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  13. 13
    Sahebian, S.; Zebarjad, S. M.; vahdati Khaki, J.; Lazzeri, A. A Study on the Dependence of Structure of Multi-Walled Carbon Nanotubes on Acid Treatment. J. Nanostruct. Chem. 2015, 5, 287– 293,  DOI: 10.1007/s40097-015-0160-3
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    There is no corresponding record for this reference.
  14. 14
    Aliofkhazraei, M.; Ali, N.; Milne, W. I.; Ozkan, C. S.; Mitura, S.; Gervasoni, J. L. Graphene Science Handbook: Electrical and Optical Properties; CRC Press, 2016; p 715.
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    There is no corresponding record for this reference.
  15. 15
    Chen, J. H.; Jang, C.; Xiao, S.; Ishigami, M.; Fuhrer, M. S. Intrinsic and Extrinsic Performance Limits of Graphene Devices on SiO2. Nat. Nanotechnol. 2008, 3, 206– 209,  DOI: 10.1038/nnano.2008.58
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    15
    Intrinsic and extrinsic performance limits of graphene devices on SiO2
    Chen, Jian-Hao; Jang, Chaun; Xiao, Shudong; Ishigami, Masa; Fuhrer, Michael S.
    Nature Nanotechnology (2008), 3 (4), 206-209CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)
    The linear dispersion relation in graphene gives rise to a surprising prediction: the resistivity due to isotropic scatterers, such as white-noise disorder or phonons, is independent of carrier d., n. Here we show that electron-acoustic phonon scattering is indeed independent of n, and contributes only 30 Ω to graphene's room-temp. resistivity. At a technol. relevant carrier d. of 1 × 1012 cm-2, we infer a mean free path for electron-acoustic phonon scattering of >2 μm and an intrinsic mobility limit of 2 × 105 cm2 V-1 s-1. If realized, this mobility would exceed that of InSb, the inorg. semiconductor with the highest known mobility (∼7.7 × 104 cm2 V-1 s-1) and that of semiconducting carbon nanotubes (∼1 × 105 cm2 V-1 s-1). A strongly temp.-dependent resistivity contribution is obsd. above ∼200 K; its magnitude, temp. dependence and carrier-d. dependence are consistent with extrinsic scattering by surface phonons at the SiO2 substrate and limit the room-temp. mobility to ∼4 × 104 cm2 V-1 s-1, indicating the importance of substrate choice for graphene devices.
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  16. 16
    Gorityala, B. K.; Ma, J.; Wang, X.; Chen, P.; Liu, X. W. Carbohydrate Functionalized Carbon Nanotubes and Their Applications. Chem. Soc. Rev. 2010, 39, 2925– 2934,  DOI: 10.1039/b919525b
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    16
    Carbohydrate functionalized carbon nanotubes and their applications
    Gorityala, Bala Kishan; Ma, Jimei; Wang, Xin; Chen, Peng; Liu, Xue-Wei
    Chemical Society Reviews (2010), 39 (8), 2925-2934CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
    A review. Carbon nanotubes (CNTs) have attracted tremendous attention in biomedical applications due to their mol. size and unique properties. This tutorial review summarizes the strategies to functionalize CNTs with bioactive carbohydrates, which improve their soly., biocompatibility, and biofunctionalities while preserving their desired properties. In addn., studies on the usage of carbohydrate functionalized CNTs to detect bacteria, to bind to specific lectins, to deliver glyco-mimetic drug mols. into cells and to probe cellular activities as biosensors are reviewed. Improvement in biocompatibility and introduction of bio-functionalities by integration of carbohydrate with CNTs are paving the way to glyco-nanotechnol. and may provide new tools for glycobiol. studies.
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  17. 17
    Bhunia, S. K.; Saha, A.; Maity, A. R.; Ray, S. C.; Jana, N. R. Carbon Nanoparticle-Based Fluorescent Bioimaging Probes. Sci. Rep. 2013, 3, 1473,  DOI: 10.1038/srep01473
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    17
    Carbon nanoparticle-based fluorescent bioimaging probes
    Bhunia, Susanta Kumar; Saha, Arindam; Maity, Amit Ranjan; Ray, Sekhar C.; Jana, Nikhil R.
    Scientific Reports (2013), 3 (), 1473, 7 pp.CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)
    Fluorescent nanoparticle-based imaging probes have advanced current labeling technol. and are expected to generate new medical diagnostic tools based on their superior brightness and photostability compared with conventional mol. probes. Although significant progress has been made in fluorescent semiconductor nanocrystal-based biol. labeling and imaging, the presence of heavy metals and the toxicity issues assocd. with heavy metals have severely limited the application potential of these nanocrystals. Here, we report a fluorescent carbon nanoparticle-based, alternative, nontoxic imaging probe that is suitable for biol. staining and diagnostics. We have developed a chem. method to synthesize highly fluorescent carbon nanoparticles 1-10 nm in size; these particles exhibit size-dependent, tunable visible emission. These carbon nanoparticles have been transformed into various functionalised nanoprobes with hydrodynamic diams. of 5-15 nm and have been used as cell imaging probes.
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  18. 18
    Fabbro, A.; Scaini, D.; León, V.; Vázquez, E.; Cellot, G.; Privitera, G.; Lombardi, L.; Torrisi, F.; Tomarchio, F.; Bonaccorso, F.; Bosi, S.; Ferrari, A. C.; Ballerini, L.; Prato, M. Graphene-Based Interfaces Do Not Alter Target Nerve Cells. ACS Nano 2016, 10, 615– 623,  DOI: 10.1021/acsnano.5b05647
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    18
    Graphene-Based Interfaces Do Not Alter Target Nerve Cells
    Fabbro, Alessandra; Scaini, Denis; Leon, Veronica; Vazquez, Ester; Cellot, Giada; Privitera, Giulia; Lombardi, Lucia; Torrisi, Felice; Tomarchio, Flavia; Bonaccorso, Francesco; Bosi, Susanna; Ferrari, Andrea C.; Ballerini, Laura; Prato, Maurizio
    ACS Nano (2016), 10 (1), 615-623CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    Neural-interfaces rely on the ability of electrodes to transduce stimuli into elec. patterns delivered to the brain. In addn. to sensitivity to the stimuli, stability in the operating conditions and efficient charge transfer to neurons, the electrodes should not alter the physiol. properties of the target tissue. Graphene is emerging as a promising material for neuro-interfacing applications, given its outstanding physico-chem. properties. Here, we use graphene-based substrates (GBSs) to interface neuronal growth. We test our GBSs on brain cell cultures by measuring functional and synaptic integrity of the emerging neuronal networks. We show that GBSs are permissive interfaces, even when uncoated by cell adhesion layers, retaining unaltered neuronal signaling properties, thus being suitable for carbon-based neural prosthetic devices.
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  19. 19
    Call, T. P.; Carey, T.; Bombelli, P.; Lea-Smith, D. J.; Hooper, P.; Howe, C. J.; Torrisi, F. Platinum-Free, Graphene Based Anodes and Air Cathodes for Single Chamber Microbial Fuel Cells. J. Mater. Chem. A 2017, 5, 23872– 23886,  DOI: 10.1039/C7TA06895F
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    19
    Platinum-free, graphene based anodes and air cathodes for single chamber microbial fuel cells
    Call, Toby P.; Carey, Tian; Bombelli, Paolo; Lea-Smith, David J.; Hooper, Philippa; Howe, Christopher J.; Torrisi, Felice
    Journal of Materials Chemistry A: Materials for Energy and Sustainability (2017), 5 (45), 23872-23886CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)
    Microbial fuel cells (MFCs) exploit the ability of microorganisms to generate elec. power during metab. of substrates. However, the low efficiency of extracellular electron transfer from cells to the anode and the use of expensive rare metals as catalysts, such as platinum, limit their application and scalability. In this study we investigate the use of pristine graphene based electrodes at both the anode and the cathode of a MFC for efficient elec. energy prodn. from the metabolically versatile bacterium Rhodopseudomonas palustris CGA009. We achieve a volumetric peak power output (PV) of up to 3.51 ± 0.50 W m-3 using graphene based aerogel anodes with a surface area of 8.2 m2 g-1. We demonstrate that enhanced MFC output arises from the interplay of the improved surface area, enhanced cond., and catalytic surface groups of the graphene based electrode. In addn., we show a 500-fold increase in PV to 1.3 ± 0.23 W m-3 when using a graphene coated stainless steel (SS) air cathode, compared to an uncoated SS cathode, demonstrating the feasibility of a platinum-free, graphene catalyzed MFCs. Finally, we show a direct application for microwatt-consuming electronics by connecting several of these coin sized devices in series to power a digital clock.
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  20. 20
    Li, N.; Zhang, Q.; Gao, S.; Song, Q.; Huang, R.; Wang, L.; Liu, L.; Dai, J.; Tang, M.; Cheng, G. Three-Dimensional Graphene Foam as a Biocompatible and Conductive Scaffold for Neural Stem Cells. Sci. Rep. 2013, 3, 1604,  DOI: 10.1038/srep01604
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    20
    Three-dimensional graphene foam as a biocompatible and conductive scaffold for neural stem cells
    Li, Ning; Zhang, Qi; Gao, Song; Song, Qin; Huang, Rong; Wang, Long; Liu, Liwei; Dai, Jianwu; Tang, Mingliang; Cheng, Guosheng
    Scientific Reports (2013), 3 (), 1604, 6 pp.CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)
    Neural stem cell (NSC) based therapy provides a promising approach for neural regeneration. For the success of NSC clin. application, a scaffold is required to provide 3-dimensional (3D) cell growth microenvironments and appropriate synergistic cell guidance cues. Here, the authors report the first utilization of graphene foam, a 3D porous structure, as a novel scaffold for NSCs in vitro. It was found that 3-dimensional graphene foams (3D-GFs) can not only support NSC growth, but also keep cell at an active proliferation state with upregulation of Ki67 expression than that of 2-dimensional graphene films. Meanwhile, phenotypic anal. indicated that 3D-GFs can enhance the NSC differentiation towards astrocytes and esp. neurons. Furthermore, a good elec. coupling of 3D-GFs with differentiated NSCs for efficient elec. stimulation was obsd. The authors' findings implicate 3D-GFs could offer a powerful platform for NSC research, neural tissue engineering and neural prostheses.
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  21. 21
    Mooney, E.; Dockery, P.; Greiser, U.; Murphy, M.; Barron, V. Carbon Nanotubes and Mesenchymal Stem Cells: Biocompatibility, Proliferation and Differentiation. Nano Lett. 2008, 8, 2137– 2143,  DOI: 10.1021/nl073300o
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    There is no corresponding record for this reference.
  22. 22
    Yang, S. T.; Luo, J.; Zhou, Q.; Wang, H. Pharmacokinetics, Metabolism and Toxicity of Carbon Nanotubes for Bio-Medical Purposes. Theranostics 2012, 2, 271– 282,  DOI: 10.7150/thno.3618
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    22
    Pharmacokinetics, metabolism and toxicity of carbon nanotubes for biomedical purposes
    Yang, Sheng-Tao; Luo, Jianbin; Zhou, Qinghan; Wang, Haifang
    Theranostics (2012), 2 (3), 271-282CODEN: THERDS; ISSN:1838-7640. (Ivyspring International Publisher)
    A review. Carbon nanotubes (CNTs) have attracted great interest of the nano community and beyond. However, the biomedical applications of CNTs arouse serious concerns for their unknown in vivo consequence, in which the information of pharmacokinetics, metab. and toxicity of CNTs is essential. In this review, we summarize the updated data of CNTs from the biomedical view. The information shows that surface chem. is crucial in regulating the in vivo behaviors of CNTs. Among the functionalization methods, PEGylation is the most efficient one to improve the pharmacokinetics and biocompatibility of CNTs. The guiding effects of the pharmacokinetics, metab. and toxicity information on the biomedical applications of CNTs are discussed.
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  23. 23
    Jia, G.; Wang, H.; Yan, L.; Wang, X.; Pei, R.; Yan, T.; Zhao, Y.; Guo, X. Cytotoxicity of Carbon Nanomaterials: Single-Wall Nanotube, Multi-Wall Nanotube, and Fullerene. Environ. Sci. Technol. 2005, 39, 1378– 1383,  DOI: 10.1021/es048729l
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    23
    Cytotoxicity of Carbon Nanomaterials: Single-Wall Nanotube, Multi-Wall Nanotube, and Fullerene
    Jia, Guang; Wang, Haifang; Yan, Lei; Wang, Xiang; Pei, Rongjuan; Yan, Tao; Zhao, Yuliang; Guo, Xinbiao
    Environmental Science and Technology (2005), 39 (5), 1378-1383CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    A cytotoxicity test protocol for single-wall nanotubes (SWNTs), multi-wall nanotubes (with diams. ranging from 10 to 20 nm, MWNT10), and fullerene (C60) was tested. Profound cytotoxicity of SWNTs was obsd. in alveolar macrophage (AM) after a 6-h exposure in vitro. The cytotoxicity increases by as high as ∼35% when the dosage of SWNTs was increased by 11.30 μg/cm2. No significant toxicity was obsd. for C60 up to a dose of 226.00 μg/cm2. The cytotoxicity apparently follows a sequence order on a mass basis: SWNTs > MWNT10 > quartz > C60. SWNTs significantly impaired phagocytosis of AM at the low dose of 0.38 μg/cm2, whereas MWNT10 and C60 induced injury only at the high dose of 3.06 μg/cm2. The macrophages exposed to SWNTs or MWNT10 of 3.06 μg/cm2 showed characteristic features of necrosis and degeneration. A sign of apoptotic cell death likely existed. Carbon nanomaterials with different geometric structures exhibit quite different cytotoxicity and bioactivity in vitro, although they may not be accurately reflected in the comparative toxicity in vivo.
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  24. 24
    Correa-Duarte, M. A.; Wagner, N.; Rojas-Chapana, J.; Morsczeck, C.; Thie, M.; Giersig, M. Fabrication and Biocompatibility of Carbon Nanotube-Based 3D Networks as Scaffolds for Cell Seeding and Growth. Nano Lett. 2004, 4, 2233– 2236,  DOI: 10.1021/nl048574f
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    24
    Fabrication and Biocompatibility of Carbon Nanotube-Based 3D Networks as Scaffolds for Cell Seeding and Growth
    Correa-Duarte, Miguel A.; Wagner, Nicholas; Rojas-Chapana, Jose; Morsczeck, Christian; Thie, Michael; Giersig, Michael
    Nano Letters (2004), 4 (11), 2233-2236CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    Thin film networks of multi-walled carbon nanotubes (MWCNTs) were prepd. by exerting chem. induced capillary forces upon the nanotubes. During this process MWCNTs undergo a transformation from being a vertically aligned structure to an interlocking resistive network of interconnected nanotubes, whose main feature is a regular three-dimensional (3D) sieve architecture. Due to their structural characteristics at the nanoscale level, 3D-MWCNT-based networks are in principle ideal candidates for scaffolds/matrixes in tissue engineering. Their potential application in this field was confirmed by extensive growth, spreading, and adhesion of the common mouse fibroblast cell line L929.
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  25. 25
    Edwards, S. L.; Church, J. S.; Werkmeister, J. A.; Ramshaw, J. A. M. Tubular Micro-Scale Multiwalled Carbon Nanotube-Based Scaffolds for Tissue Engineering. Biomaterials 2009, 30, 1725– 1731,  DOI: 10.1016/j.biomaterials.2008.12.031
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    25
    Tubular micro-scale multiwalled carbon nanotube-based scaffolds for tissue engineering
    Edwards, Sharon L.; Church, Jeffrey S.; Werkmeister, Jerome A.; Ramshaw, John A. M.
    Biomaterials (2009), 30 (9), 1725-1731CODEN: BIMADU; ISSN:0142-9612. (Elsevier Ltd.)
    In this study we have prepd. a tubular knitted scaffold from a 9 ply multiwalled carbon nanotube (MWCNT) yarn and a composite scaffold, formed by electrospinning poly(lactic-co-glycolic acid) (PLGA) nanofibres onto the knitted scaffold. Both structures were assessed for in vitro biocompatibility with NR6 mouse fibroblast cells for up to 22 days and their suitability as tissue engineering scaffolds considered. The MWCNT yarn was found to support cell growth throughout the culture period, with fibroblasts attaching to, and proliferating on, the yarn surface. The knitted tubular scaffold contained large pores that inhibited cell spanning, leading to the formation of cell clusters on the yarn, and an uneven cell distribution on the scaffold surface. The smaller pores, created through electrospinning, were found to promote cell spanning, leading to a uniform distribution of cells on the composite scaffold surface. Evaluation of the elec. and mech. properties of the knitted scaffold detd. resistance levels of 0.9 kΩ/cm, with a breaking load and extension to break approaching 0.7 N and 8%, resp. The PLGA/MWCNT composite scaffold presented in this work not only supports cell growth, but also has the potential to utilize the full range of elec. and mech. properties that carbon nanotubes have to offer.
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  26. 26
    Liu, Y.; Zhao, Y.; Sun, B.; Chen, C. Understanding the Toxicity of Carbon Nanotubes. Acc. Chem. Res. 2013, 46, 702– 713,  DOI: 10.1021/ar300028m
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    26
    Understanding the toxicity of carbon nanotubes
    Liu, Ying; Zhao, Yuliang; Sun, Baoyun; Chen, Chunying
    Accounts of Chemical Research (2013), 46 (3), 702-713CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
    A review. Because of their unique phys., chem., elec., and mech. properties, carbon nanotubes (CNTs) have attracted a great deal of research interest and have many potential applications. As large-scale prodn. and application of CNTs increases, the general population is more likely to be exposed to CNTs either directly or indirectly, which has prompted considerable attention about human health and safety issues related to CNTs. Although considerable exptl. data related to CNT toxicity at the mol., cellular, and whole animal levels have been published, the results are often conflicting. Therefore, a systematic understanding of CNT toxicity is needed but has not yet been developed. In this Account, we highlight recent investigations into the basis of CNT toxicity carried out by our team and by other labs. We focus on several important factors that explain the disparities in the exptl. results of nanotoxicity, such as impurities, amorphous carbon, surface charge, shape, length, agglomeration, and layer nos. The exposure routes, including inhalation, i.v. injection, or dermal or oral exposure, can also influence the in vivo behavior and fate of CNTs. The underlying mechanisms of CNT toxicity include oxidative stress, inflammatory responses, malignant transformation, DNA damage and mutation (errors in chromosome no. as well as disruption of the mitotic spindle), the formation of granulomas, and interstitial fibrosis. These findings provide useful insights for de novo design and safe application of carbon nanotubes and their risk assessment to human health. To obtain reproducible and accurate results, researchers must establish stds. and reliable detection methods, use std. CNT samples as a ref. control, and study the impact of various factors systematically. In addn., researchers need to examine multiple types of CNTs, different cell lines and animal species, multidimensional evaluation methods, and exposure conditions. To make results comparable among different institutions and countries, researchers need to standardize choices in toxicity testing such as that of cell line, animal species, and exposure conditions. The knowledge presented here should lead to a better understanding of the key factors that can influence CNT toxicity so that their unwanted toxicity might be avoided.
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  27. 27
    Cohen-Karni, T.; Qing, Q.; Li, Q.; Fang, Y.; Lieber, C. M. Graphene and Nanowire Transistors for Cellular Interfaces and Electrical Recording. Nano Lett. 2010, 10, 1098– 1102,  DOI: 10.1021/nl1002608
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    27
    Graphene and Nanowire Transistors for Cellular Interfaces and Electrical Recording
    Cohen-Karni, Tzahi; Qing, Quan; Li, Qiang; Fang, Ying; Lieber, Charles M.
    Nano Letters (2010), 10 (3), 1098-1102CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    Nanowire field-effect transistors (NW-FETs) have been shown to be powerful building blocks for nanoscale bioelectronic interfaces with cells and tissue due to their excellent sensitivity and their capability to form strongly coupled interfaces with cell membranes. Graphene has also been shown to be an attractive building block for nanoscale electronic devices, although little is known about its interfaces with cells and tissue. Here we report the first studies of graphene field effect transistors (Gra-FETs) as well as combined Gra- and NW-FETs interfaced to electrogenic cells. Gra-FET conductance signals recorded from spontaneously beating embryonic chicken cardiomyocytes yield well-defined extracellular signals with signal-to-noise ratio routinely >4. The conductance signal amplitude was tuned by varying the Gra-FET working region through changes in water gate potential, Vwg. Signals recorded from cardiomyocytes for different Vwg result in const. calibrated extracellular voltage, indicating a robust graphene/cell interface. Significantly, variations in Vwg across the Dirac point demonstrate the expected signal polarity flip, thus allowing, for the first time, both n- and p-type recording to be achieved from the same Gra-FET simply by offsetting Vwg. In addn., comparisons of peak-to-peak recorded signal widths made as a function of Gra-FET device sizes and vs. NW-FETs allowed an assessment of relative resoln. in extracellular recording. Specifically, peak-to-peak widths increased with the area of Gra-FET devices, indicating an averaged signal from different points across the outer membrane of the beating cells. One-dimensional silicon NW- FETs incorporated side by side with the two-dimensional Gra-FET devices further highlighted limits in both temporal resoln. and multiplexed measurements from the same cell for the different types of devices. The distinct and complementary capabilities of Gra- and NW-FETs could open up unique opportunities in the field of bioelectronics in the future.
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  28. 28
    Akhavan, O.; Ghaderi, E.; Shahsavar, M. Graphene Nanogrids for Selective and Fast Osteogenic Differentiation of Human Mesenchymal Stem Cells. Carbon 2013, 59, 200– 211,  DOI: 10.1016/j.carbon.2013.03.010
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    Graphene nanogrids for selective and fast osteogenic differentiation of human mesenchymal stem cells
    Akhavan, Omid; Ghaderi, Elham; Shahsavar, Mahla
    Carbon (2013), 59 (), 200-211CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
    Graphene nanogrids (fabricated by graphene nanoribbons obtained through oxidative unzipping of multi-walled carbon nanotubes) were used as two-dimensional selective templates for accelerated differentiation of human mesenchymal stem cells (hMSCs), isolated from umbilical cord blood, into osteogenic lineage. The biocompatible and hydrophilic graphene nanogrids showed high actin cytoskeleton proliferations coinciding with patterns of the nanogrids. The amts. of proliferations were found slightly better than proliferation on hydrophilic graphene oxide (GO) sheets, and significantly higher than non-uniform proliferations on hydrophobic reduced graphene oxide (rGO) sheets and polydimethylsiloxane substrate. In the presence of chem. inducers, the reduced graphene oxide nanoribbon (rGONR) grid showed a highly accelerated osteogenic differentiation of the hMSCs (a patterned differentiation) in short time of 7 days in which the amt. of the osteogenesis was ∼2.2 folds greater than the differentiation (a uniform differentiation) on the rGO sheets. We found that although in the absence of any chem. inducers the graphene nanogrids showed slight patterned osteogenic differentiations, the graphene sheets could not present any differentiation. Therefore, the highly accelerated differentiation on the rGONR grid was assigned to both its excellent capability in adsorption of the chem. inducers and phys. stresses induced by the surface topog. features of the nanogrids.
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  29. 29
    Shin, S. R.; Li, Y. C.; Jang, H. L.; Khoshakhlagh, P.; Akbari, M.; Nasajpour, A.; Zhang, Y. S.; Tamayol, A.; Khademhosseini, A. Graphene-Based Materials for Tissue Engineering. Adv. Drug Delivery Rev. 2016, 105, 255– 274,  DOI: 10.1016/j.addr.2016.03.007
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    Graphene-based materials for tissue engineering
    Shin, Su Ryon; Li, Yi-Chen; Jang, Hae Lin; Khoshakhlagh, Parastoo; Akbari, Mohsen; Nasajpour, Amir; Zhang, Yu Shrike; Tamayol, Ali; Khademhosseini, Ali
    Advanced Drug Delivery Reviews (2016), 105 (Part_B), 255-274CODEN: ADDREP; ISSN:0169-409X. (Elsevier B.V.)
    Graphene and its chem. derivs. have been a pivotal new class of nanomaterials and a model system for quantum behavior. The material's excellent elec. cond., biocompatibility, surface area and thermal properties are of much interest to the scientific community. Two-dimensional graphene materials have been widely used in various biomedical research areas such as bioelectronics, imaging, drug delivery, and tissue engineering. In this review, we will highlight the recent applications of graphene-based materials in tissue engineering and regenerative medicine. In particular, we will discuss the application of graphene-based materials in cardiac, neural, bone, cartilage, skeletal muscle, and skin/adipose tissue engineering. We will also discuss the potential risk factors of graphene-based materials in tissue engineering. In conclusion, we will outline the opportunities in the usage of graphene-based materials for clin. applications.
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  30. 30
    Smith, S. C.; Ahmed, F.; Gutierrez, K. M.; Frigi Rodrigues, D. A Comparative Study of Lysozyme Adsorption with Graphene, Graphene Oxide, and Single-Walled Carbon Nanotubes: Potential Environmental Applications. Chem. Eng. J. 2014, 240, 147– 154,  DOI: 10.1016/j.cej.2013.11.030
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    A comparative study of lysozyme adsorption with graphene, graphene oxide, and single-walled carbon nanotubes: Potential environmental applications
    Smith, Sean C.; Ahmed, Farid; Gutierrez, Krystal M.; Frigi Rodrigues, Debora
    Chemical Engineering Journal (Amsterdam, Netherlands) (2014), 240 (), 147-154CODEN: CMEJAJ; ISSN:1385-8947. (Elsevier B.V.)
    Wastewater contains numerous classes of org. mols., primarily different types of sol. microbial products, e.g., polysaccharides, nucleic acids, proteins. The presence of these compds. in effluent increases the risk of toxic byproduct formation during chlorination. In recent years, studies demonstrated the power of C-based nanomaterials to remove many chem. compds. and pollutants from aq. solns. This work examd. the protein absorption capacity and adsorption mechanisms of 3 C-based nanomaterials: graphene (G), graphene oxide (GO), and single-walled C nanotubes (SWNT) in various water chemistries, using lysozyme as a model protein. Results showed GO exhibited the highest lysozyme adsorption capacity (∼500 mg protein/g nanomaterial) in adsorption isotherm assays. Adsorption data were fitted to Langmuir, Freundlich, and Temkin models and relevant parameters were detd. Lysozyme adsorption by GO and SWNT was strongly affected by the presence of mono- and di-valent salts; however, no significant pH dependence was obsd. for protein adsorption to studied nanomaterial. Results also showed the GO adsorption mechanism was mainly electrostatic, while the G and SWNT mechanisms were attributed to van der Waals forces and some electrostatic interactions. Adsorption expts. of proteins present in wastewater were performed to test the efficacy of G, GO, and SWNT as sorbents for complex environmental samples. All 3 nanomaterials removed more protein from wastewater than conventional sorbents reported in the literature.
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  31. 31
    Mecklenburg, M.; Schuchardt, A.; Mishra, Y. K.; Kaps, S.; Adelung, R.; Lotnyk, A.; Kienle, L.; Schulte, K. Aerographite: Ultra Lightweight, Flexible Nanowall, Carbon Microtube Material with Outstanding Mechanical Performance. Adv. Mater. 2012, 24, 3486– 3490,  DOI: 10.1002/adma.201200491
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    Aerographite: Ultra Lightweight, Flexible Nanowall, Carbon Microtube Material with Outstanding Mechanical Performance
    Mecklenburg, Matthias; Schuchardt, Arnim; Mishra, Yogendra Kumar; Kaps, Soeren; Adelung, Rainer; Lotnyk, Andriy; Kienle, Lorenz; Schulte, Karl
    Advanced Materials (Weinheim, Germany) (2012), 24 (26), 3486-3490, S3486/1-S3486/26CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
    We present a novel synthesis of an ultralightwt., elec. conductive, mech. robust, and flexible graphite-based material, Aerographite. In contrast to already established synthesis for other carbon nanostructures like carbon nanotubes (CNTs) or graphene, this CVD process uses ZnO as template for the synthesis of bulk samples on the centimeter scale. This inorg. semiconductor is a suitable substrate/template material for sp2 hybridized carbons, e.g., CNTs and graphene. The common structural motive of the Aerographite family is the completely interconnected network of microstructures with a nanoscopic wall thickness. Variants come as filled and unfilled, corrugated walls, or as a superlightwt. example of a hollow framework of struts from amorphous carbon. The at. structure can be tuned from graphitic to glass-like pyrolytic carbon, with the advantage of remarkable mech. properties. This most lightwt. material reaches the highest merit indexes for sp. moduli obsd. until now. Further optimization of parameters, e.g., pore size and vol. d. of sintering bridges keeps the opportunity for future improvements of the mech performance of Aerographite. Further properties such as cond., flexibility and compressibility without losing structural integrity, high optical adsorption and x-ray opacity, a high-temp. stability and chem. resistance, the bearing of tensile and compressive loads, and the super hydrophobicity make it a remarkable multifunctional material. Next to others, potential applications might be electrode materials for increasing demand of batteries and high surface area supercapacitor materials. Proper designed carbon materials from the Aerographites family could avoid typical problems of electrode materials like low mech. cycling stability, degenerating elec. contacts, or non-optimized electrolyte-to-surface ratio which might be tuned by simple compression due to the negligible Poisson's ration of these sponge-like structures.
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  32. 32
    Mishra, Y. K.; Kaps, S.; Schuchardt, A.; Paulowicz, I.; Jin, X.; Gedamu, D.; Freitag, S.; Claus, M.; Wille, S.; Kovalev, A.; Gorb, S. N.; Adelung, R. Fabrication of Macroscopically Flexible and Highly Porous 3D Semiconductor Networks from Interpenetrating Nanostructures by a Simple Flame Transport Approach. Part. Part. Syst. Charact. 2013, 30, 775– 783,  DOI: 10.1002/ppsc.201300197
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    Fabrication of Macroscopically Flexible and Highly Porous 3D Semiconductor Networks from Interpenetrating Nanostructures by a Simple Flame Transport Approach
    Mishra, Yogendra K.; Kaps, Soeren; Schuchardt, Arnim; Paulowicz, Ingo; Jin, Xin; Gedamu, Dawit; Freitag, Stefan; Claus, Maria; Wille, Sebastian; Kovalev, Alexander; Gorb, Stanislav N.; Adelung, Rainer
    Particle & Particle Systems Characterization (2013), 30 (9), 775-783CODEN: PPCHEZ; ISSN:1521-4117. (Wiley-VCH Verlag GmbH & Co. KGaA)
    We have demonstrated that the FTS approach and its variants offer versatile fabrication of various kinds of large 3D interconnected networks of high porosity using nano-microscopic building blocks from metal oxides. Properties of these networks can be tailored by using different types of building blocks, their d., and the type of interconnections. For example, the Young's modulus of these 3D networks can be tuned from wool-type behavior to rubber elastic regime of several MPa. The flexibility and high-temp. stability of these conducting and highly porous networks could be used for various technol. applications. Apart from 3D networks, a large variety of 1D structures can be synthesized in sized ranging from nanometers to centimeters. Features including simplicity, low cost, mass-scale prodn., and versatility of structures produced by the FTS approach and its variants open numerous areas not only in basic research but also for industrial applications.
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    Lamprecht, C.; Taale, M.; Paulowicz, I.; Westerhaus, H.; Grabosch, C.; Schuchardt, A.; Mecklenburg, M.; Böttner, M.; Lucius, R.; Schulte, K.; Adelung, R.; Selhuber-Unkel, C. A Tunable Scaffold of Microtubular Graphite for 3D Cell Growth. ACS Appl. Mater. Interfaces 2016, 8, 14980– 14985,  DOI: 10.1021/acsami.6b00778
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    Mouw, J. K.; Ou, G.; Weaver, V. M. Extracellular Matrix Assembly: A Multiscale Deconstruction. Nat. Rev. Mol. Cell Biol. 2014, 15, 771– 785,  DOI: 10.1038/nrm3902
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    Extracellular matrix assembly: a multiscale deconstruction
    Mouw, Janna K.; Ou, Guanqing; Weaver, Valerie M.
    Nature Reviews Molecular Cell Biology (2014), 15 (12), 771-785CODEN: NRMCBP; ISSN:1471-0072. (Nature Publishing Group)
    The biochem. and biophys. properties of the extracellular matrix (ECM) dictate tissue-specific cell behavior. The mols. that are assocd. with the ECM of each tissue, including collagens, proteoglycans, laminins and fibronectin, and the manner in which they are assembled det. the structure and the organization of the resultant ECM. The product is a specific ECM signature that is comprised of unique compositional and topog. features that both reflect and facilitate the functional requirements of the tissue.
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    Schütt, F.; Signetti, S.; Krüger, H.; Röder, S.; Smazna, D.; Kaps, S.; Gorb, S. N.; Mishra, Y. K.; Pugno, N. M.; Adelung, R. Hierarchical Self-Entangled Carbon Nanotube Tube Networks. Nat. Commun. 2017, 8, 1215  DOI: 10.1038/s41467-017-01324-7
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    Feng, X.; Feng, L.; Jin, M.; Zhai, J.; Jiang, L.; Zhu, D. Reversible Super-Hydrophobicity to Super-Hydrophilicity Transition of Aligned ZnO Nanorod Films. J. Am. Chem. Soc. 2004, 126, 62– 63,  DOI: 10.1021/ja038636o
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    Reversible Super-hydrophobicity to Super-hydrophilicity Transition of Aligned ZnO Nanorod Films
    Feng, Xinjian; Feng, Lin; Jin, Meihua; Zhai, Jin; Jiang, Lei; Zhu, Daoben
    Journal of the American Chemical Society (2004), 126 (1), 62-63CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Remarkable surface wettability transition occurs with an inducement of UV for aligned ZnO nanorod films. The inorg. oxide films, which show super-hydrophobicity (left), become super-hydrophilic (right) when exposed to UV illumination. After the films are placed in the dark, the wettability evolves back to super-hydrophobicity. This reversible effect is ascribed to the cooperation of the surface photosensitivity and the aligned nanostructure. Such special property will greatly extend the applications of ZnO films.
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    Chen, H.-K. Kinetic Study on the Carbothermic Reduction of Zinc Oxide. Scand. J. Metall. 2001, 30, 292– 296,  DOI: 10.1034/j.1600-0692.2001.300503.x
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    Kinetic study on the carbothermic reduction of zinc oxide
    Chen, Hsi-Kuei
    Scandinavian Journal of Metallurgy (2001), 30 (5), 292-296CODEN: SJMLAG; ISSN:0371-0459. (Munksgaard International Publishers Ltd.)
    The kinetics of carbothermic redn. of zinc oxide with carbon powder under a nitrogen atm. (at 1 atm). The exptl. results indicated that the redn. rate could be increased by increasing the molar ratio of C/ZnO, height of solid sample, d. of solid sample or reaction temp. The rate was also found to be increased by reducing the grain size of zinc oxide and carbon or the nitrogen gas flow rate. The empirical expressions of conversion rates of zinc oxide and carbon as well as the prodn. rate of zinc were detd. from the regression of the exptl. data.
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    Zhao, J.; Xing, B.; Yang, H.; Pan, Q.; Li, Z.; Liu, Z. Growth of Carbon Nanotubes on Graphene by Chemical Vapor Deposition. New Carbon Mater. 2016, 31, 31– 36,  DOI: 10.1016/S1872-5805(16)60002-1
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    Ferrari, A. C.; Robertson, J. Resonant Raman Spectroscopy of Disordered, Amorphous, and Diamondlike Carbon. Phys. Rev. B: Condens. Matter Mater. Phys. 2001, 64, 075414,  DOI: 10.1103/PhysRevB.64.075414
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    Resonant Raman spectroscopy of disordered, amorphous, and diamondlike carbon
    Ferrari, A. C.; Robertson, J.
    Physical Review B: Condensed Matter and Materials Physics (2001), 64 (7), 075414/1-075414/13CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)
    The Raman spectra of a wide range of disordered and amorphous carbons were measured under excitation from 785 to 229 nm. The dispersion of peak positions and intensities with excitation wavelength is used to understand the nature of resonant Raman scattering in C and how to derive the local bonding and disorder from the Raman spectra. The spectra show 3 basic features, the D and G around 1600 and 1350 cm-1 for visible excitation and an extra T peak, for UV excitation, at ∼1060 cm-1. The G peak, due to the stretching motion of sp2 pairs, is a good indicator of disorder. It shows dispersion only in amorphous networks, with a dispersion rate proportional to the degree of disorder. Its shift well >1600 cm-1 under UV excitation indicates sp2 chains. The dispersion of the D peak is strongest in ordered carbons. It shows little dispersion in amorphous C, so that in UV excitation it becomes like a d.-of-states feature of vibrations of sp2 ringlike structures. The intensity ratio I(D)/I(G) falls with increasing UV excitation in all forms of C, with a faster decrease in more ordered carbons, so that it is generally small for UV excitation. The T peak, due to sp3 vibrations, only appears in UV Raman, lying around 1060 cm-1 for H-free carbons and around 980 cm-1 in hydrogenated carbons. In hydrogenated carbons, the sp3 C-Hx stretching modes around 2920 cm-1 can be clearly detected for UV excitation. This assignment is confirmed by D substitution.
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    Carey, T.; Cacovich, S.; Divitini, G.; Ren, J.; Mansouri, A.; Kim, J. M.; Wang, C.; Ducati, C.; Sordan, R.; Torrisi, F. Fully Inkjet-Printed Two-Dimensional Material Field-Effect Heterojunctions for Wearable and Textile Electronics. Nat. Commun. 2017, 8, 1202,  DOI: 10.1038/s41467-017-01210-2
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    Fully inkjet-printed two-dimensional material field-effect heterojunctions for wearable and textile electronics
    Carey Tian; Ren Jiesheng; Kim Jong M; Torrisi Felice; Cacovich Stefania; Divitini Giorgio; Ducati Caterina; Ren Jiesheng; Wang Chaoxia; Mansouri Aida; Sordan Roman
    Nature communications (2017), 8 (1), 1202 ISSN:.
    Fully printed wearable electronics based on two-dimensional (2D) material heterojunction structures also known as heterostructures, such as field-effect transistors, require robust and reproducible printed multi-layer stacks consisting of active channel, dielectric and conductive contact layers. Solution processing of graphite and other layered materials provides low-cost inks enabling printed electronic devices, for example by inkjet printing. However, the limited quality of the 2D-material inks, the complexity of the layered arrangement, and the lack of a dielectric 2D-material ink able to operate at room temperature, under strain and after several washing cycles has impeded the fabrication of electronic devices on textile with fully printed 2D heterostructures. Here we demonstrate fully inkjet-printed 2D-material active heterostructures with graphene and hexagonal-boron nitride (h-BN) inks, and use them to fabricate all inkjet-printed flexible and washable field-effect transistors on textile, reaching a field-effect mobility of ~91 cm(2) V(-1) s(-1), at low voltage (<5 V). This enables fully inkjet-printed electronic circuits, such as reprogrammable volatile memory cells, complementary inverters and OR logic gates.
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    Ferrari, A. C.; Meyer, J. C.; Scardaci, V.; Casiraghi, C.; Lazzeri, M.; Mauri, F.; Piscanec, S.; Jiang, D.; Novoselov, K. S.; Roth, S. Raman Spectrum of Graphene and Graphene Layers. Phys. Rev. Lett. 2006, 97, 187401,  DOI: 10.1103/PhysRevLett.97.187401
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    Raman Spectrum of Graphene and Graphene Layers
    Ferrari, A. C.; Meyer, J. C.; Scardaci, V.; Casiraghi, C.; Lazzeri, M.; Mauri, F.; Piscanec, S.; Jiang, D.; Novoselov, K. S.; Roth, S.; Geim, A. K.
    Physical Review Letters (2006), 97 (18), 187401/1-187401/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
    Graphene is the 2-dimensional building block for C allotropes of every other dimensionality. Its electronic structure is captured in its Raman spectrum that clearly evolves with the no. of layers. The D peak 2nd order changes in shape, width, and position for an increasing no. of layers, reflecting the change in the electron bands via a double resonant Raman process. The G peak slightly down-shifts. This allows unambiguous, high-throughput, nondestructive identification of graphene layers, which is critically lacking in this emerging research area.
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    Ferrari, A.; Robertson, J. Interpretation of Raman Spectra of Disordered and Amorphous Carbon. Phys. Rev. B: Condens. Matter Mater. Phys. 2000, 61, 14095– 14107,  DOI: 10.1103/PhysRevB.61.14095
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    Interpretation of Raman spectra of disordered and amorphous carbon
    Ferrari, A. C.; Robertson, J.
    Physical Review B: Condensed Matter and Materials Physics (2000), 61 (20), 14095-14107CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)
    The model and theor. understanding of the Raman spectra in disordered and amorphous C are given. The nature of the G and D vibration modes in graphite is analyzed in terms of the resonant excitation of π states and the long-range polarizability of π bonding. Visible Raman data on disordered, amorphous, and diamondlike C are classified in a 3-stage model to show the factors that control the position, intensity, and widths of the G and D peaks. The visible Raman spectra depend formally on the configuration of the sp2 sites in sp2-bonded clusters. In cases where the sp2 clustering is controlled by the sp3 fraction, such as in as-deposited tetrahedral amorphous C (ta-C) or hydrogenated amorphous C (a-C:H) films, the visible Raman parameters can be used to derive the sp3 fraction.
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    Cuscó, R.; Alarcón-Lladó, E.; Ibáñez, J.; Artús, L.; Jiménez, J.; Wang, B.; Callahan, M. Temperature Dependence of Raman Scattering in ZnO. Phys. Rev. B: Condens. Matter Mater. Phys. 2007, 75, 165202,  DOI: 10.1103/PhysRevB.75.165202
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    Temperature dependence of Raman scattering in ZnO
    Cusco, Ramon; Alarcon-Llado, Esther; Ibanez, Jordi; Artus, Luis; Jimenez, Juan; Wang, Buguo; Callahan, Michael J.
    Physical Review B: Condensed Matter and Materials Physics (2007), 75 (16), 165202/1-165202/11CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
    The authors present a Raman scattering study of wurtzite ZnO at 80-750 K. Second-order Raman features are interpreted in the light of recent ab initio phonon d. of states calcns. The temp. dependence of the Raman intensities allows the assignment of difference modes to be made unambiguously. Some weak, sharp Raman peaks are detected whose temp. dependence suggests they may be due to impurity modes. High-resoln. spectra of the Ehigh2, A1(LO), and E1(LO) modes were recorded, and an anal. of the anharmonicity and lifetimes of these phonons is carried out. The Ehigh2 mode displays a visibly asym. line shape. This can be attributed to anharmonic interaction with transverse and longitudinal acoustic phonon combinations in the vicinity of the K point, where the 2-phonon d. of states displays a sharp edge around the Ehigh2 frequency. The temp. dependence of the linewidth and frequency of the Ehigh2 mode is well described by a perturbation-theory renormalization of the harmonic Ehigh2 frequency resulting from the interaction with the acoustic 2-phonon d. of states. But the A1(LO) and E1(LO) frequencies lie in a region of nearly flat 2-phonon d. of states, and they exhibit a nearly sym. Lorentzian line shape with a temp. dependence that is well accounted for by a dominating asym. decay channel.
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    Fan, H.; Wang, L.; Zhao, K.; Li, N.; Shi, Z.; Ge, Z.; Jin, Z. Fabrication, Mechanical Properties, and Biocompatibility of Graphene-Reinforced Chitosan Composites. Biomacromolecules 2010, 11, 2345– 2351,  DOI: 10.1021/bm100470q
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    Fabrication, Mechanical Properties, and Biocompatibility of Graphene-Reinforced Chitosan Composites
    Fan, Hailong; Wang, Lili; Zhao, Keke; Li, Nan; Shi, Zujin; Ge, Zigang; Jin, Zhaoxia
    Biomacromolecules (2010), 11 (9), 2345-2351CODEN: BOMAF6; ISSN:1525-7797. (American Chemical Society)
    Few-layered graphene sheets, synthesized by d.c. arc-discharge method using NH3 as one of the buffer gases, were dispersed in chitosan/acetic acid solns. FTIR and XPS showed the presence of oxygen-contg. functional groups on the surface of graphene sheets that may assist the good dispersion of graphene in chitosan soln. Graphene/chitosan films were produced by soln. casting method. The mech. properties of composite films were tested by nanoindentation method. With the addn. of a small amt. of graphene in chitosan (0.1-0.3 wt. %), the elastic modulus of chitosan increased over ∼200%. The biocompatibility of graphene/chitosan composite films was checked by tetrazolium-based colorimetric assays in vitro. The cell adhesion result showed that the L929 cell can adhere to and develop on the graphene/chitosan composite films as well as on pure chitosan film, indicating that graphene/chitosan composites have good biocompatibility. Because there is no metallic impurity in graphene raw materials, the time-consuming purifn. process for removing metal nanoparticles entrapped in carbon nanotubes is thus avoided when graphene is used to prep. biomedical materials. Graphene/chitosan composites are potential candidates as scaffold materials in tissue engineering.
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    Ahadian, S.; Ramón-Azcón, J.; Estili, M.; Liang, X.; Ostrovidov, S.; Shiku, H.; Ramalingam, M.; Nakajima, K.; Sakka, Y.; Bae, H. H.; Matsue, T.; Khademhosseini, A. Hybrid Hydrogels Containing Vertically Aligned Carbon Nanotubes with Anisotropic Electrical Conductivity for Muscle Myofiber Fabrication. Sci. Rep. 2015, 4, 4271,  DOI: 10.1038/srep04271
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    Shi, X.; Sitharaman, B.; Pham, Q. P.; Liang, F.; Wu, K.; Edward Billups, W.; Wilson, L. J.; Mikos, A. G. Fabrication of Porous Ultra-Short Single-Walled Carbon Nanotube Nanocomposite Scaffolds for Bone Tissue Engineering. Biomaterials 2007, 28, 4078– 4090,  DOI: 10.1016/j.biomaterials.2007.05.033
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    Fabrication of porous ultra-short single-walled carbon nanotube nanocomposite scaffolds for bone tissue engineering
    Shi, Xinfeng; Sitharaman, Balaji; Pham, Quynh P.; Liang, Feng; Wu, Katherine; Edward Billups, W.; Wilson, Lon J.; Mikos, Antonios G.
    Biomaterials (2007), 28 (28), 4078-4090CODEN: BIMADU; ISSN:0142-9612. (Elsevier Ltd.)
    We investigated the fabrication of highly porous scaffolds made of three different materials [poly(propylene fumarate) (PPF) polymer, an ultra-short single-walled carbon nanotube (US-tube) nanocomposite, and a dodecylated US-tube (F-US-tube) nanocomposite] in order to evaluate the effects of material compn. and porosity on scaffold pore structure, mech. properties, and marrow stromal cell culture. All scaffolds were produced by a thermal-crosslinking particulate-leaching technique at specific porogen contents of 75, 80, 85, and 90 vol%. Scanning electron microcopy, microcomputed tomog., and mercury intrusion porosimetry were used to analyze the pore structures of scaffolds. The porogen content was found to dictate the porosity of scaffolds. There was no significant difference in porosity, pore size, and interconnectivity among the different materials for the same porogen fraction. Nearly 100% of the pore vol. was interconnected through 20 μm or larger connections for all scaffolds. While interconnectivity through larger connections improved with higher porosity, compressive mech. properties of scaffolds declined at the same time. However, the compressive modulus, offset yield strength, and compressive strength of F-US-tube nanocomposites were higher than or similar to the corresponding properties for the PPF polymer and US-tube nanocomposites for all the porosities examd. As for in vitro osteocond., marrow stromal cells demonstrated equally good cell attachment and proliferation on all scaffolds made of different materials at each porosity. These results indicate that functionalized ultra-short single-walled carbon nanotube nanocomposite scaffolds with tunable porosity and mech. properties hold great promise for bone tissue engineering applications.
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    Chen, Z.; Ren, W.; Gao, L.; Liu, B.; Pei, S.; Cheng, H. M. Three-Dimensional Flexible and Conductive Interconnected Graphene Networks Grown by Chemical Vapour Deposition. Nat. Mater. 2011, 10, 424– 428,  DOI: 10.1038/nmat3001
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    Three-dimensional flexible and conductive interconnected graphene networks grown by chemical vapor deposition
    Chen, Zongping; Ren, Wencai; Gao, Libo; Liu, Bilu; Pei, Songfeng; Cheng, Hui-Ming
    Nature Materials (2011), 10 (6), 424-428CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)
    Integration of individual two-dimensional graphene sheets into macroscopic structures is essential for the application of graphene. Graphene-based composites and macroscopic structures were recently fabricated using chem. derived graphene sheets. However, these composites and structures suffer from poor elec. cond. because of the low quality and/or high inter-sheet junction contact resistance of the chem. derived graphene sheets. Here the authors report the direct synthesis of three-dimensional foam-like graphene macrostructures, which the authors call graphene foams (GFs), by template-directed CVD. A GF consists of an interconnected flexible network of graphene as the fast transport channel of charge carriers for high elec. cond. Even with a GF loading as low as ∼0.5%, GF/poly(di-Me siloxane) composites show a very high elec. cond. of ∼10 S cm-1, which is ∼6 orders of magnitude higher than chem. derived graphene-based composites. Using this unique network structure and the outstanding elec. and mech. properties of GFs, as an example, the authors demonstrate the great potential of GF/poly(di-Me siloxane) composites for flexible, foldable and stretchable conductors.
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    Zhao, G.; Zhang, X.; Lu, T. J.; Xu, F. Recent Advances in Electrospun Nanofibrous Scaffolds for Cardiac Tissue Engineering. Adv. Funct. Mater. 2015, 25, 5726– 5738,  DOI: 10.1002/adfm.201502142
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    Recent Advances in Electrospun Nanofibrous Scaffolds for Cardiac Tissue Engineering
    Zhao, Guoxu; Zhang, Xiaohui; Lu, Tian Jian; Xu, Feng
    Advanced Functional Materials (2015), 25 (36), 5726-5738CODEN: AFMDC6; ISSN:1616-301X. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Cardiovascular diseases remain the leading cause of human mortality worldwide. Some severe symptoms, including myocardial infarction and heart failure, are difficult to heal spontaneously or under systematic treatment due to the limited regenerative capacity of the native myocardium. Cardiac tissue engineering has emerged as a practical strategy to culture functional cardiac tissues and relieve the disorder in myocardium when implanted. In cardiac tissue engineering, the design of a scaffold is closely relevant to the function of the regenerated cardiac tissues. Nanofibrous materials fabricated by electrospinning have been developed as desirable scaffolds for tissue engineering applications because of the biomimicking structure of protein fibers in native extra cellular matrix. The versatilities of electrospinning on the polymer component, the fiber structure, and the functionalization with bioactive mols. have made the fabrication of nanofibrous scaffolds with suitable mech. strength and biol. properties for cardiac tissue engineering feasible. Here, an overview of recent advances in various electrospun scaffolds for engineering cardiac tissues, including the design of advanced electrospun scaffolds and the performance of the scaffolds in functional cardiac tissue regeneration, is provided with the aim to offer guidance in the innovation of novel electrospun scaffolds and methods for improving their potential for cardiac tissue engineering applications.
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    Zuo, G.; Kang, S. G.; Xiu, P.; Zhao, Y.; Zhou, R. Interactions between Proteins and Carbon-Based Nanoparticles: Exploring the Origin of Nanotoxicity at the Molecular Level. Small 2013, 9, 1546– 1556,  DOI: 10.1002/smll.201201381
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    49
    Interactions between proteins and carbon-based nanoparticles: Exploring the origin of nanotoxicity at the molecular level
    Zuo, Guanghong; Kang, Seung-gu; Xiu, Peng; Zhao, Yuliang; Zhou, Ruhong
    Small (2013), 9 (9-10), 1546-1556CODEN: SMALBC; ISSN:1613-6810. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A review. The widespread application of nanomaterials has spurred an interest in the study of interactions between nanoparticles and proteins due to the biosafety concerns of these nanomaterials. In this review, a summary is presented of some of the recent studies on this important subject, esp. on the interactions of proteins with carbon nanotubes (CNTs) and metallofullerenols. Two potential mol. mechanisms have been proposed for CNTs' inhibition of protein functions. The driving forces of CNTs' adsorption onto proteins are found to be mainly hydrophobic interactions and the so-called π-π stacking between CNTs' carbon rings and proteins' arom. residues. However, there is also recent evidence showing that endohedral metallofullerenol Gd@C82(OH)22 can be used to inhibit tumor growth, thus acting as a potential nanomedicine. These recent findings have provided a better understanding of nanotoxicity at the mol. level and also suggested therapeutic potential by using nanoparticles' cytotoxicity against cancer cells.
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    Suh, C. W.; Kim, M. Y.; Choo, J. B.; Kim, J. K.; Kim, H. K.; Lee, E. K. Analysis of Protein Adsorption Characteristics to Nano-Pore Silica Particles by Using Confocal Laser Scanning Microscopy. J. Biotechnol. 2004, 112, 267– 277,  DOI: 10.1016/j.jbiotec.2004.05.005
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    50
    Analysis of protein adsorption characteristics to nano-pore silica particles by using confocal laser scanning microscopy
    Suh, Chang Woo; Kim, Min Young; Choo, Jae Bum; Kim, Jong Kil; Kim, Ho Kun; Lee, Eun Kyu
    Journal of Biotechnology (2004), 112 (3), 267-277CODEN: JBITD4; ISSN:0168-1656. (Elsevier B.V.)
    The effect of av. pore size of nanopore silica particles on protein adsorption characteristics was detd. exptl. by the dissocn. const. and the adsorption capacity detd. from the Langmuir equation. As the av. pore size was increased from 2.2 to 45 nm, the BSA adsorption capacity increased from 16.8 to 84.3 mg/g-silica so as the equil. const. (from 2.6 to 9.4 mg/mL). Using confocal microscopy with fluorescence labeling, we could visualize the protein adsorption in situ and det. the min. pore size required for efficient intraparticle adsorption. The confocal microscopy anal. revealed that BSA was adsorbed mainly on the surface of the particles with a smaller pore size, but diffused further into the interstitial surface when it was sufficiently large. It was concluded that for BSA whose Stoke's diam. is ∼3.55 nm the min. pore size of about 45 nm or larger was required for a sufficient adsorption capacity.
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    Prager-Khoutorsky, M.; Lichtenstein, A.; Krishnan, R.; Rajendran, K.; Mayo, A.; Kam, Z.; Geiger, B.; Bershadsky, A. D. Fibroblast Polarization Is a Matrix-Rigidity-Dependent Process Controlled by Focal Adhesion Mechanosensing. Nat. Cell Biol. 2011, 13, 1457– 1465,  DOI: 10.1038/ncb2370
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    Fibroblast polarization is a matrix-rigidity-dependent process controlled by focal adhesion mechanosensing
    Prager-Khoutorsky, Masha; Lichtenstein, Alexandra; Krishnan, Ramaswamy; Rajendran, Kavitha; Mayo, Avi; Kam, Zvi; Geiger, Benjamin; Bershadsky, Alexander D.
    Nature Cell Biology (2011), 13 (12), 1457-1465CODEN: NCBIFN; ISSN:1465-7392. (Nature Publishing Group)
    Cell elongation and polarization are basic morphogenetic responses to extracellular matrix adhesion. The authors demonstrate here that human cultured fibroblasts readily polarize when plated on rigid, but not on compliant, substrates. On rigid surfaces, large and uniformly oriented focal adhesions are formed, whereas cells plated on compliant substrates form numerous small and radially oriented adhesions. Live-cell monitoring showed that focal adhesion alignment precedes the overall elongation of the cell, indicating that focal adhesion orientation may direct cell polarization. SiRNA-mediated knockdown of 85 human protein tyrosine kinases (PTKs) induced distinct alterations in the cell polarization response, as well as diverse changes in cell traction force generation and focal adhesion formation. Remarkably, changes in rigidity-dependent traction force development, or focal adhesion mechanosensing, were consistently accompanied by abnormalities in the cell polarization response. The authors propose that the different stages of cell polarization are regulated by multiple, PTK-dependent mol. checkpoints that jointly control cell contractility and focal-adhesion-mediated mechanosensing.
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    El-Mohri, H.; Wu, Y.; Mohanty, S.; Ghosh, G. Impact of Matrix Stiffness on Fibroblast Function. Mater. Sci. Eng., C 2017, 74, 146– 151,  DOI: 10.1016/j.msec.2017.02.001
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    Impact of matrix stiffness on fibroblast function
    El-Mohri, Hichem; Wu, Yang; Mohanty, Swetaparna; Ghosh, Gargi
    Materials Science & Engineering, C: Materials for Biological Applications (2017), 74 (), 146-151CODEN: MSCEEE; ISSN:0928-4931. (Elsevier B.V.)
    Chronic non-healing wounds, caused by impaired prodn. of growth factors and reduced vascularization, represent a significant burden to patients, health care professionals, and health care system. While several wound dressing biomaterials have been developed, the impact of the mech. properties of the dressings on the residing cells and consequently on the healing of the wounds is largely overlooked. The primary focus of this study is to explore whether manipulation of the substrate mechanics can regulate the function of fibroblasts, particularly in the context of their angiogenic activity. A photocrosslinkable hydrogel platform with orthogonal control over gel modulus and cell adhesive sites was developed to explore the quant. relationship between ECM compliance and fibroblast function. Increase in matrix stiffness resulted in enhanced fibroblast proliferation and stress fiber formation. However, the angiogenic activity of fibroblasts was found to be optimum when the cells were seeded on compliant matrixes. Thus, the observations suggest that the stiffness of the wound dressing material may play an important role in the progression of wound healing.
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    Sun, Y.; Chen, C. S.; Fu, J. Forcing Stem Cells to Behave: A Biophysical Perspective of the Cellular Microenvironment. Annu. Rev. Biophys. 2012, 41, 519– 542,  DOI: 10.1146/annurev-biophys-042910-155306
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    Forcing stem cells to behave: a biophysical perspective of the cellular microenvironment
    Sun, Yubing; Chen, Christopher S.; Fu, Jianping
    Annual Review of Biophysics (2012), 41 (), 519-542CODEN: ARBNCV; ISSN:1936-122X. (Annual Reviews Inc.)
    A review. Phys. factors in the local cellular microenvironment, including cell shape and geometry, matrix mechanics, external mech. forces, and nanotopog. features of the extracellular matrix, can all have strong influences on regulating stem cell fate. Stem cells sense and respond to these insol. biophys. signals through integrin-mediated adhesions and the force balance between intracellular cytoskeletal contractility and the resistant forces originated from the extracellular matrix. Importantly, these mechanotransduction processes can couple with many other potent growth-factor-mediated signaling pathways to regulate stem cell fate. Different bioengineering tools and microscale/nanoscale devices have been successfully developed to engineer the phys. aspects of the cellular microenvironment for stem cells, and these tools and devices have proven extremely powerful for identifying the extrinsic phys. factors and their downstream intracellular signaling pathways that control stem cell functions.
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    Moreno-Arotzena, O.; Borau, C.; Movilla, N.; Vicente-Manzanares, M.; García-Aznar, J. M. Fibroblast Migration in 3D Is Controlled by Haptotaxis in a Non-Muscle Myosin II-Dependent Manner. Ann. Biomed. Eng. 2015, 43, 3025– 3039,  DOI: 10.1007/s10439-015-1343-2
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    Fibroblast Migration in 3D is Controlled by Haptotaxis in a Non-muscle Myosin II-Dependent Manner
    Moreno-Arotzena O; Borau C; Movilla N; Garcia-Aznar J M; Vicente-Manzanares M
    Annals of biomedical engineering (2015), 43 (12), 3025-39 ISSN:.
    Cell migration in 3D is a key process in many physiological and pathological processes. Although valuable knowledge has been accumulated through analysis of various 2D models, some of these insights are not directly applicable to migration in 3D. In this study, we have confined biomimetic hydrogels within microfluidic platforms in the presence of a chemoattractant (platelet-derived growth factor-BB). We have characterized the migratory responses of human fibroblasts within them, particularly focusing on the role of non-muscle myosin II. Our results indicate a prominent role for myosin II in the integration of chemotactic and haptotactic migratory responses of fibroblasts in 3D confined environments.
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    Turner, C. E. Paxillin and Focal Adhesion Signalling. Nat. Cell Biol. 2000, 2, E231– E236,  DOI: 10.1038/35046659
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    Paxillin and focal adhesion signalling
    Turner, Christopher E.
    Nature Cell Biology (2000), 2 (12), E231-E236CODEN: NCBIFN; ISSN:1465-7392. (Nature Publishing Group)
    A review with 78 refs. To facilitate a rapid response to environmental change, cells use scaffolding-or adaptor-proteins to recruit key components of their signal-transduction machinery to specific subcellular locations. Paxillin is a multi-domain adaptor found at the interface between the plasma membrane and the actin cytoskeleton. Here it provides a platform for the integration and process of adhesion- and growth factor-related signals.
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    Chiu, C.-L.; Aguilar, J. S.; Tsai, C. Y.; Wu, G.; Gratton, E.; Digman, M. M. A.; Kuo, J.; Han, X.; Hsiao, C.; Iii, J. Y. Nanoimaging of Focal Adhesion Dynamics in 3D. PLoS One 2014, 9, e99896,  DOI: 10.1371/journal.pone.0099896
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    Nanoimaging of focal adhesion dynamics in 3D
    Chiu, Chi-Li; Aguilar, Jose S.; Tsai, Connie Y.; Wu, GuiKai; Gratton, Enrico; Digman, Michelle A.
    PLoS One (2014), 9 (6), e99896/1-e99896/10, 10 pp.CODEN: POLNCL; ISSN:1932-6203. (Public Library of Science)
    Organization and dynamics of focal adhesion proteins have been well characterized in cells grown on two-dimensional (2D) cell culture surfaces. However, much less is known about the dynamic assocn. of these proteins in the 3D microenvironment. Limited imaging technologies capable of measuring protein interactions in real time and space for cells grown in 3D is a major impediment in understanding how proteins function under different environmental cues. In this study, we applied the nano-scale precise imaging by rapid beam oscillation (nSPIRO) technique and combined the scaning-fluorescence correlation spectroscopy (sFCS) and the no. and mol. brightness (N&B) methods to investigate paxillin and actin dynamics at focal adhesions in 3D. Both MDA-MB-231 cells and U2OS cells produce elongated protrusions with high intensity regions of paxillin in cell grown in 3D collagen matrixes. Using sFCS we found higher percentage of slow diffusing proteins at these focal spots, suggesting assembling/disassembling processes. In addn., the N&B anal. shows paxillin aggregated predominantly at these focal contacts which are next to collagen fibers. At those sites, actin showed slower apparent diffusion rate, which indicated that actin is either polymg. or binding to the scaffolds in these locals. Our findings demonstrate that by multiplexing these techniques we have the ability to spatially and temporally quantify focal adhesion assembly and disassembly in 3D space and allow the understanding tumor cell invasion in a more complex relevant environment.
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    Ryoo, S. R.; Kim, Y. K.; Kim, M. H.; Min, D. H. Behaviors of NIH-3T3 Fibroblasts on Graphene/Carbon Nanotubes: Proliferation, Focal Adhesion, and Gene Transfection Studies. ACS Nano 2010, 4, 6587– 6598,  DOI: 10.1021/nn1018279
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    Behaviors of NIH-3T3 Fibroblasts on Graphene/Carbon Nanotubes: Proliferation, Focal Adhesion, and Gene Transfection Studies
    Ryoo, Soo-Ryoon; Kim, Young-Kwan; Kim, Mi-Hee; Min, Dal-Hee
    ACS Nano (2010), 4 (11), 6587-6598CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    Carbon-based materials, including graphene and carbon nanotubes, have been considered attractive candidates for biomedical applications such as scaffolds in tissue engineering, substrates for stem cell differentiation, and components of implant devices. Despite the potential biomedical applications of these materials, only limited information is available regarding the cellular events, including cell viability, adhesion, and spreading, that occur when mammalian cells interface with carbon-based nanomaterials. Here, we report behaviors of mammalian cells, specifically NIH-3T3 fibroblast cells, grown on supported thin films of graphene and carbon nanotubes to investigate biocompatibility of the artificial surface. Proliferation assay, cell shape anal., focal adhesion study, and quant. measurements of cell adhesion-related gene expression levels by RT-PCR reveal that the fibroblast cells grow well, with different nos. and sizes of focal adhesions, on graphene- and carbon nanotube-coated substrates. Interestingly, the gene transfection efficiency of cells grown on the substrates was improved up to 250% that of cells grown on a cover glass. The present study suggests that these nanomaterials hold high potential for bioapplications showing high biocompatibility, esp. as surface coating materials for implants, without inducing notable deleterious effects while enhancing some cellular functions (i.e., gene transfection and expression).
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    Cooper, G. M. The Cell: A Molecular Approach; ASM Press, 2000; Vol. 10.
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    Serrano, M. C.; Patiño, J.; García-Rama, C.; Ferrer, M. L.; Fierro, J. L. G.; Tamayo, A.; Collazos-Castro, J. E.; Del Monte, F.; Gutiérrez, M. C. 3D Free-Standing Porous Scaffolds Made of Graphene Oxide as Substrates for Neural Cell Growth. J. Mater. Chem. B 2014, 2, 5698– 5706,  DOI: 10.1039/C4TB00652F
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    3D free-standing porous scaffolds made of graphene oxide as substrates for neural cell growth
    Serrano, M. C.; Patino, J.; Garcia-Rama, C.; Ferrer, M. L.; Fierro, J. L. G.; Tamayo, A.; Collazos-Castro, J. E.; del Monte, F.; Gutierrez, M. C.
    Journal of Materials Chemistry B: Materials for Biology and Medicine (2014), 2 (34), 5698-5706CODEN: JMCBDV; ISSN:2050-7518. (Royal Society of Chemistry)
    The absence of efficient therapies for the treatment of lesions affecting the central nervous system encourages scientists to explore new materials in an attempt to enhance neural tissue regeneration while preventing inhibitory fibroglial scars. In recent years, the superlative properties of graphene-based materials have provided a strong incentive for their application in biomedicine. Nonetheless, a few attempts to date have envisioned the use of graphene for the fabrication of three-dimensional (3D) substrates for neural repair, but none of these involve graphene oxide (GOx) despite some attractive features such as higher hydrophilicity and versatility of functionalization. In this paper, we report novel, free-standing, porous and flexible 3D GOx-based scaffolds, produced by the biocompatible freeze-casting procedure named ISISA, with potential utility in neural tissue regeneration. The resulting materials were thoroughly characterized by Fourier-transform IR, Raman, and X-ray photoelectron spectroscopies and SEM, as well as flexibility testing. Embryonic neural progenitor cells were then used to investigate adhesion, morphol., viability, and neuronal/glial differentiation. Highly viable and interconnected neural networks were formed on these 3D scaffolds, contg. both neurons and glial cells and rich in dendrites, axons and synaptic connections, and the results are in agreement with those obtained in initial studies performed with two-dimensional GOx films. These results encourage further investigation in vivo on the use of these scaffolds as guide substrates to promote the repair of neural injuries.
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    LeBaron, R. G.; Athanasiou, K. A. Extracellular Matrix Cell Adhesion Peptides: Functional Applications in Orthopedic Materials. Tissue Eng. 2000, 6, 85– 103,  DOI: 10.1089/107632700320720
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    Extracellular matrix cell adhesion peptides: functional applications in orthopedic materials
    Lebaron, Richard G.; Athanasiou, Kyriacos A.
    Tissue Engineering (2000), 6 (2), 85-103CODEN: TIENFP; ISSN:1076-3279. (Mary Ann Liebert, Inc.)
    A review with 147 refs. This review describes research on selected peptide sequences that affect cell adhesion as it applies in orthopedic applications. Of particular interest are the integrin-binding RGD peptides and heparin-binding peptides. The influence of these peptides on cell adhesion is described. Cell adhesion is defined as a sequence of four steps: cell attachment, cell spreading, organization of an actin cytoskeleton, and formation of focal adhesions. RGD sequences clearly influence cell attachment and spreading, whereas heparin-binding sequences appear to be less efficient. Collectively, these sequences appear to promote all steps of cell adhesion in certain cell types. This review also addresses issues related to peptide immobilization, as well as potential complexities that may develop as a result of using these versatile cell-binding sequences. Also described are future directions in the field concerning use of existing and more sophisticated peptide substrata.
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    Marx, J.; Lewke, M. R. D.; Smazna, D.; Mishra, Y. K.; Adelung, R.; Schulte, K.; Fiedler, B. Processing, Growth Mechanism and Thermodynamic Calculations of Carbon Foam with a Hollow Tetrapodal Morphology – Aerographite. Appl. Surf. Sci. 2019, 470, 535– 542,  DOI: 10.1016/j.apsusc.2018.11.016
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    Processing, growth mechanism and thermodynamic calculations of carbon foam with a hollow tetrapodal morphology - Aerographite
    Marx, J.; Lewke, M. R. D.; Smazna, D.; Mishra, Y. K.; Adelung, R.; Schulte, K.; Fiedler, B.
    Applied Surface Science (2019), 470 (), 535-542CODEN: ASUSEE; ISSN:0169-4332. (Elsevier B.V.)
    Aerographite is a 3D interconnected carbon foam with a tetrapodal morphol. The synthesis of Aerographite is based on a 2-step process: first the prodn. of a zinc oxide (ZnO) template in a flame transport synthesis (FTS) followed by the replication into the carbon structure in a chem. vapor deposition process (CVD). This study presents a growth model of this 3D carbon foam via analyzing the newly formed carbon structure in an interrupted synthesis by SEM, transmission electron microscopy (TEM), and Raman spectroscopy. Moreover, the Gibbs free energy of the occurred replica CVD (rCVD) process, based on the redn. of ZnO and the formation of carbon layers, was calcd. During the CVD process the injected carbon deposits on the surfaces of the ZnO tetrapods, while simultaneously the replication into the carbon structure takes place, as a result of the redn. of ZnO into gaseous zinc and water vapor, which is due to the reaction of ZnO with the hydrogen (H2) from the injected source. This replication of the ZnO template into a carbon structure is based on an epitaxial controlled process combined with a catalytic graphitization, whereby the morphol. of the template structure is replicated by the carbon. Furthermore, the influence of the growth process on the arrangement of carbon in layers and formation of defects was explained.
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    Wang, F.; Torrisi, F.; Jiang, Z.; Popa, D.; Hasan, T.; Sun, Z.; Cho, W.; Ferrari, A. C. Graphene Passively Q-Switched Two-Micron Fiber Lasers. In Conference on Lasers and Electro-Optics (CLEO); OSA Technical Digest (Optical Society of America): San Jose, CA, 2012; p JW2A 72.
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    Purdie, D. G.; Popa, D.; Wittwer, V. J.; Jiang, Z.; Bonacchini, G.; Torrisi, F.; Milana, S.; Lidorikis, E.; Ferrari, A. C. Few-Cycle Pulses from a Graphene Mode-Locked All-Fiber Laser. Appl. Phys. Lett. 2015, 106, 253101,  DOI: 10.1063/1.4922397
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  • Abstract

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    Figure 1

    Figure 1. Schematic illustration of different 3D carbon tube structures. The highly porous ZnO template can be either infiltrated with a nanoparticle dispersion (e.g., graphene, CNT) leading to a homogeneous coating around the tetrapodal particles or converted to a graphitic structure using a chemical vapor deposition (CVD) process (aerographite). The combination of both processes leads to a modular design strategy, especially in terms of conductivity, mechanical stiffness, and surface topography.

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    Figure 2

    Figure 2. SEM images from low to high magnification of the different 3D carbon structures. (a−c) Carbon nanotube tubes (CNTTs), (d−f) aerographite with incorporated CNTs (AG−CNTT) (the red arrows show the grown CNTs during the CVD process), (g−i) aerographite (AG), (j−l) aerographite with incorporated graphene (AG−G) (the yellow arrows point to nanopores on the surface of aerographite), and (m−o) carbon nanotube tubes incorporated into a thick carbon layer (CNTT−g).

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    Figure 3

    Figure 3. Raman spectroscopy of aerographite, ZnO, CNTT, AG–CNTT, CNTT–g, AG–G, graphene, and CNT inks.

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    Figure 4

    Figure 4. Young’s modulus (measured under compression) and electrical conductivity of the 3D CNTT, AG–CNTT, CNTT–g, and AG–G scaffolds. All structures containing CNTs have a higher Young’s modulus and conductivity compared to those without CNTs. The values for pure AG and CNTTs were taken from the corresponding publications, (31,35) whereas the other values were measured using a self-built electromechanical testing setup.

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    Figure 5

    Figure 5. Protein adsorption on CNTT, AG–CNTT, CNTT–g, and AG–G during 0–48, 49–96, and 97–144 h of incubation with albumin solution (1 mg/mL). (a) Absolute protein adsorption amount per scaffold volume. (b) Absolute protein adsorption amount per scaffold weight.

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    Figure 6

    Figure 6. Percentage of viable cells (rat embryonic fibroblasts wild type, REF52wt) relative to the negative control, as determined in an MTT assay (four independent experiments, five technical repeats in each of them). The error bars denote standard deviation.

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    Figure 7

    Figure 7. Results of WST-1 metabolic tests of cell proliferation rate (REF52wt). Mean values were determined from four independent experiments, each including five technical repeats. The error bars denote standard deviation, the raw data were normalized to the control, and a correction factor was applied to account for unspecific adsorption (see Materials and Methods).

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    Figure 8

    Figure 8. SEM images of REF52wt cells after 7 days of culturing within (a–c) AG–CNTT, (d, e) CNTT–g, (g–i) AG–G, and (j–l) CNTT scaffolds. Left: Medium-sized overview images illustrating the growth of cells between the fibers in different directions and planes; middle: zoomed-in images showing well-stretched cells along the fibers and their elongation; and right: close-up images on the adhesion sites, proving the presence of strong contacts between the materials and the cell membrane (yellow arrows).

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    Figure 9

    Figure 9. High-magnification fluorescence images of REF52 YFP-paxillin cells on 3D scaffolds: (a) CNTT, (b) AG–CNTT, (c) CNTT–g, and (d) AG–G. YFP-paxillin is mainly distributed in small clusters (YFP; yellow), the nucleus was stained with Hoechst (4′,6-diamidino-2-phenylindole, DAPI; blue), and actin fibers were visualized by phalloidin (red). Fluorescence imaging took place in optical sections approximately between 50 and 100 μm from the surface of the material. Adhesion sites are detectable (a, b) as tiny yellow spots mainly around the tube-shaped filaments of CNTT and AG–CNTT structures. Due to the low intensity and small size of YFP-paxillin (c, d), they are not clearly observed, which is also obscured by red (actin fibers) and blue (nucleus) channels in multichannel images. The green dashed arrows illustrate the protrusion direction of the cells.

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      Friedl, Peter; Wolf, Katarina
      Journal of Cell Biology (2010), 188 (1), 11-19CODEN: JCLBA3; ISSN:0021-9525. (Rockefeller University Press)
      A review. Cell migration underlies tissue formation, maintenance, and regeneration as well as pathol. conditions such as cancer invasion. Structural and mol. determinants of both tissue environment and cell behavior define whether cells migrate individually (through amoeboid or mesenchymal modes) or collectively. Here, using a multi-parameter tuning model, the authors describe how dimension, d., stiffness, and orientation of the extracellular matrix together with cell determinants, including cell-cell and cell-matrix adhesion, cytoskeletal polarity and stiffness, and pericellular proteolysis, interdependently control migration mode and efficiency. Motile cells integrate variable inputs to adjust interactions among themselves and with the matrix to dictate the migration mode. The tuning model provides a matrix of parameters that control cell movement as an adaptive and interconvertible process with relevance to different physiol. and pathol. contexts.
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    5. 5
      Langer, R.; Vacanti, J. P. Tissue Engineering. Science 1993, 260, 920– 926,  DOI: 10.1126/science.8493529
      5
      Tissue engineering
      Langer, Robert; Vacanti, Joseph P.
      Science (Washington, DC, United States) (1993), 260 (5110), 920-6CODEN: SCIEAS; ISSN:0036-8075.
      A review with 72 refs. The loss or failure of an organ or tissue is one of the most frequent, devastating, and costly problems in human health care. A new field, tissue engineering, applies the principles of biol. and engineering to the development of functional substitutes for damaged tissue. The foundations and challenges of this interdisciplinary field and its attempts to provide solns. to tissue creation and repair are discussed.
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      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3sXis1Sktrs%253D&md5=7216d2fc547382becf42126c0bfcc490
    6. 6
      Place, E. S.; Evans, N. D.; Stevens, M. M. Complexity in Biomaterials for Tissue Engineering. Nat. Mater. 2009, 8, 457– 470,  DOI: 10.1038/nmat2441
      6
      Complexity in biomaterials for tissue engineering
      Place, Elsie S.; Evans, Nicholas D.; Stevens, Molly M.
      Nature Materials (2009), 8 (6), 457-470CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)
      A review. The mol. and phys. information coded within the extracellular milieu is informing the development of a new generation of biomaterials for tissue engineering. Several powerful extracellular influences have already found their way into cell-instructive scaffolds, while others remain largely unexplored. Yet for com. success tissue engineering products must be not only efficacious but also cost-effective, introducing a potential dichotomy between the need for sophistication and ease of prodn. This is spurring interest in recreating extracellular influences in simplified forms, from the redn. of biopolymers into short functional domains, to the use of basic chemistries to manipulate cell fate. In the future these exciting developments are likely to help reconcile the clin. and com. pressures on tissue engineering.
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    7. 7
      Loh, Q. L.; Choong, C. Three-Dimensional Scaffolds for Tissue Engineering Applications: Role of Porosity and Pore Size. Tissue Eng., Part B 2013, 19, 485– 502,  DOI: 10.1089/ten.teb.2012.0437
      7
      Three-Dimensional Scaffolds for Tissue Engineering Applications: Role of Porosity and Pore Size
      Loh, Qiu Li; Choong, Cleo
      Tissue Engineering, Part B: Reviews (2013), 19 (6), 485-502CODEN: TEPBAB; ISSN:1937-3368. (Mary Ann Liebert, Inc.)
      A review. Tissue engineering applications commonly encompass the use of three-dimensional (3D) scaffolds to provide a suitable microenvironment for the incorporation of cells or growth factors to regenerate damaged tissues or organs. These scaffolds serve to mimic the actual in vivo microenvironment where cells interact and behave according to the mech. cues obtained from the surrounding 3D environment. Hence, the material properties of the scaffolds are vital in detg. cellular response and fate. These 3D scaffolds are generally highly porous with interconnected pore networks to facilitate nutrient and oxygen diffusion and waste removal. This review focuses on the various fabrication techniques (e.g., conventional and rapid prototyping methods) that have been employed to fabricate 3D scaffolds of different pore sizes and porosity. The different pore size and porosity measurement methods will also be discussed. Scaffolds with graded porosity have also been studied for their ability to better represent the actual in vivo situation where cells are exposed to layers of different tissues with varying properties. In addn., the ability of pore size and porosity of scaffolds to direct cellular responses and alter the mech. properties of scaffolds will be reviewed, followed by a look at nature's own scaffold, the extracellular matrix. Overall, the limitations of current scaffold fabrication approaches for tissue engineering applications and some novel and promising alternatives will be highlighted.
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    8. 8
      Ganji, Y.; Li, Q.; Quabius, E. S.; Böttner, M.; Selhuber-Unkel, C.; Kasra, M. Cardiomyocyte Behavior on Biodegradable Polyurethane/Gold Nanocomposite Scaffolds under Electrical Stimulation. Mater. Sci. Eng., C 2016, 59, 10– 18,  DOI: 10.1016/j.msec.2015.09.074
      8
      Cardiomyocyte behavior on biodegradable polyurethane/gold nanocomposite scaffolds under electrical stimulation
      Ganji, Yasaman; Li, Qian; Quabius, Elgar Susanne; Bottner, Martina; Selhuber-Unkel, Christine; Kasra, Mehran
      Materials Science & Engineering, C: Materials for Biological Applications (2016), 59 (), 10-18CODEN: MSCEEE; ISSN:0928-4931. (Elsevier B.V.)
      Following a myocardial infarction (MI), cardiomyocytes are replaced by scar tissue, which decreases ventricular contractile function. Tissue engineering is a promising approach to regenerate such damaged cardiomyocyte tissue. Engineered cardiac patches can be fabricated by seeding a high d. of cardiac cells onto a synthetic or natural porous polymer. In this study, nanocomposite scaffolds made of gold nanotubes/nanowires incorporated into biodegradable castor oil-based polyurethane were employed to make micro-porous scaffolds. H9C2 cardiomyocyte cells were cultured on the scaffolds for one day, and elec. stimulation was applied to improve cell communication and interaction in neighboring pores. Cells on scaffolds were examd. by fluorescence microscopy and SEM, revealing that the combination of scaffold design and elec. stimulation significantly increased cell confluency of H9C2 cells on the scaffolds. Furthermore, we showed that the gene expression levels of Nkx2.5, atrial natriuretic peptide (ANF) and natriuretic peptide precursor B (NPPB), which are functional genes of the myocardium, were up-regulated by the incorporation of gold nanotubes/nanowires into the polyurethane scaffolds, in particular after elec. stimulation.
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    9. 9
      Potse, M.; Dubé, B.; Vinet, A. Cardiac Anisotropy in Boundary-Element Models for the Electrocardiogram. Med. Biol. Eng. Comput. 2009, 47, 719– 729,  DOI: 10.1007/s11517-009-0472-x
      9
      Cardiac anisotropy in boundary-element models for the electrocardiogram
      Potse Mark; Dube Bruno; Vinet Alain
      Medical & biological engineering & computing (2009), 47 (7), 719-29 ISSN:.
      The boundary-element method (BEM) is widely used for electrocardiogram (ECG) simulation. Its major disadvantage is its perceived inability to deal with the anisotropic electric conductivity of the myocardial interstitium, which led researchers to represent only intracellular anisotropy or neglect anisotropy altogether. We computed ECGs with a BEM model based on dipole sources that accounted for a "compound" anisotropy ratio. The ECGs were compared with those computed by a finite-difference model, in which intracellular and interstitial anisotropy could be represented without compromise. For a given set of conductivities, we always found a compound anisotropy value that led to acceptable differences between BEM and finite-difference results. In contrast, a fully isotropic model produced unacceptably large differences. A model that accounted only for intracellular anisotropy showed intermediate performance. We conclude that using a compound anisotropy ratio allows BEM-based ECG models to more accurately represent both anisotropies.
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    10. 10
      Fang, B.; Yang, J.; Chen, C.; Zhang, C.; Chang, D.; Xu, H.; Gao, C. Carbon Nanotubes Loaded on Graphene Microfolds as Efficient Bifunctional Electrocatalysts for the Oxygen Reduction and Oxygen Evolution Reactions. ChemCatChem 2017, 9, 4520– 4528,  DOI: 10.1002/cctc.201700985
      10
      Carbon Nanotubes Loaded on Graphene Microfolds as Efficient Bifunctional Electrocatalysts for the Oxygen Reduction and Oxygen Evolution Reactions
      Fang, Bo; Yang, Jia; Chen, Chen; Zhang, Chunxiao; Chang, Dan; Xu, Hangxun; Gao, Chao
      ChemCatChem (2017), 9 (24), 4520-4528CODEN: CHEMK3; ISSN:1867-3880. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Advanced bifunctional electrocatalysts for the O redn. reaction (ORR) and O evolution reaction (OER) are promising to improve the efficiency of fuel cells and metal-air batteries. Among the state-of-the-art efficient O electrocatalysts, heteroatom-doped C materials are favorable candidates. However, the enriched doping requires a highly exposed C skeleton. Here, we report a scalable route to prep. C nanotubes (CNTs) loaded on graphene microfolds (CGFs) by a low-temp. spray-drying procedure. Mol.-level assembly of graphene and CNTs, mesoporous structures, and large sp. surface areas permit the C skeleton of CGFs to be highly exposed. After doping with abundant N and P (5.58 at% for N, 0.1 at% for P), CGFs exhibit excellent bifunctional electrocatalytic activity for both the ORR and OER, with superb durability and methanol tolerance. The measured variance of the ORR and OER metrics (ΔE=Ej=10-E1/2) was low at 0.9 V vs. reversible hydrogen electrode (vs. RHE), being within only 20 mV of Pt- and Ru-based electrodes, and superior to transition-metal-based catalysts and other C catalysts. Such efficient overall electrocatalytic activity allows CGFs to be used for high-performance O electrodes in renewable energy devices.
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    11. 11
      Li, Z.; Liu, Z.; Sun, H.; Gao, C. Superstructured Assembly of Nanocarbons: Fullerenes, Nanotubes, and Graphene. Chem. Rev. 2015, 115, 7046– 7117,  DOI: 10.1021/acs.chemrev.5b00102
      11
      Superstructured Assembly of Nanocarbons: Fullerenes, Nanotubes, and Graphene
      Li, Zheng; Liu, Zheng; Sun, Haiyan; Gao, Chao
      Chemical Reviews (Washington, DC, United States) (2015), 115 (15), 7046-7117CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
      A review. The development on fullerenes, CNTs and graphene is currently enjoying a rapid pace, with enormous research achievements emerging every day. In this review, we focused on the tailored assembly of these sp2-hybridized nanocarbons into various macroscopic superstructures covering 1D fibers/yarns,2D films/papers, and 3D porous/dense monoliths.
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    12. 12
      Lekawa-Raus, A.; Patmore, J.; Kurzepa, L.; Bulmer, J.; Koziol, K. Electrical Properties of Carbon Nanotube Based Fibers and Their Future Use in Electrical Wiring. Adv. Funct. Mater. 2014, 24, 3661– 3682,  DOI: 10.1002/adfm.201303716
      12
      Electrical Properties of Carbon Nanotube Based Fibers and Their Future Use in Electrical Wiring
      Lekawa-Raus, Agnieszka; Patmore, Jeff; Kurzepa, Lukasz; Bulmer, John; Koziol, Krzysztof
      Advanced Functional Materials (2014), 24 (24), 3661-3682CODEN: AFMDC6; ISSN:1616-301X. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A review. The prodn. of continuous fibers made purely of C nanotubes has paved the way for new macro-scale applications which use the superior properties of individual C nanotubes. These wire-like macroscopic assemblies of C nanotubes were recognized to have a potential to be used in elec. wiring. C nanotube wiring may be extremely light and mech. stronger and more efficient in transferring high frequency signals than any conventional conducting material, being cost-effective simultaneously. However, transfer of the unique properties of individual CNTs to the macro-scale proves to be quite challenging. This Feature Article gives an overview of the potential of using C nanotube fibers as next generation wiring, state of the art developments in this field, and goals to be achieved before C nanotubes may be transformed into competitive products.
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    13. 13
      Sahebian, S.; Zebarjad, S. M.; vahdati Khaki, J.; Lazzeri, A. A Study on the Dependence of Structure of Multi-Walled Carbon Nanotubes on Acid Treatment. J. Nanostruct. Chem. 2015, 5, 287– 293,  DOI: 10.1007/s40097-015-0160-3
      There is no corresponding record for this reference.
    14. 14
      Aliofkhazraei, M.; Ali, N.; Milne, W. I.; Ozkan, C. S.; Mitura, S.; Gervasoni, J. L. Graphene Science Handbook: Electrical and Optical Properties; CRC Press, 2016; p 715.
      There is no corresponding record for this reference.
    15. 15
      Chen, J. H.; Jang, C.; Xiao, S.; Ishigami, M.; Fuhrer, M. S. Intrinsic and Extrinsic Performance Limits of Graphene Devices on SiO2. Nat. Nanotechnol. 2008, 3, 206– 209,  DOI: 10.1038/nnano.2008.58
      15
      Intrinsic and extrinsic performance limits of graphene devices on SiO2
      Chen, Jian-Hao; Jang, Chaun; Xiao, Shudong; Ishigami, Masa; Fuhrer, Michael S.
      Nature Nanotechnology (2008), 3 (4), 206-209CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)
      The linear dispersion relation in graphene gives rise to a surprising prediction: the resistivity due to isotropic scatterers, such as white-noise disorder or phonons, is independent of carrier d., n. Here we show that electron-acoustic phonon scattering is indeed independent of n, and contributes only 30 Ω to graphene's room-temp. resistivity. At a technol. relevant carrier d. of 1 × 1012 cm-2, we infer a mean free path for electron-acoustic phonon scattering of >2 μm and an intrinsic mobility limit of 2 × 105 cm2 V-1 s-1. If realized, this mobility would exceed that of InSb, the inorg. semiconductor with the highest known mobility (∼7.7 × 104 cm2 V-1 s-1) and that of semiconducting carbon nanotubes (∼1 × 105 cm2 V-1 s-1). A strongly temp.-dependent resistivity contribution is obsd. above ∼200 K; its magnitude, temp. dependence and carrier-d. dependence are consistent with extrinsic scattering by surface phonons at the SiO2 substrate and limit the room-temp. mobility to ∼4 × 104 cm2 V-1 s-1, indicating the importance of substrate choice for graphene devices.
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    16. 16
      Gorityala, B. K.; Ma, J.; Wang, X.; Chen, P.; Liu, X. W. Carbohydrate Functionalized Carbon Nanotubes and Their Applications. Chem. Soc. Rev. 2010, 39, 2925– 2934,  DOI: 10.1039/b919525b
      16
      Carbohydrate functionalized carbon nanotubes and their applications
      Gorityala, Bala Kishan; Ma, Jimei; Wang, Xin; Chen, Peng; Liu, Xue-Wei
      Chemical Society Reviews (2010), 39 (8), 2925-2934CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
      A review. Carbon nanotubes (CNTs) have attracted tremendous attention in biomedical applications due to their mol. size and unique properties. This tutorial review summarizes the strategies to functionalize CNTs with bioactive carbohydrates, which improve their soly., biocompatibility, and biofunctionalities while preserving their desired properties. In addn., studies on the usage of carbohydrate functionalized CNTs to detect bacteria, to bind to specific lectins, to deliver glyco-mimetic drug mols. into cells and to probe cellular activities as biosensors are reviewed. Improvement in biocompatibility and introduction of bio-functionalities by integration of carbohydrate with CNTs are paving the way to glyco-nanotechnol. and may provide new tools for glycobiol. studies.
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    17. 17
      Bhunia, S. K.; Saha, A.; Maity, A. R.; Ray, S. C.; Jana, N. R. Carbon Nanoparticle-Based Fluorescent Bioimaging Probes. Sci. Rep. 2013, 3, 1473,  DOI: 10.1038/srep01473
      17
      Carbon nanoparticle-based fluorescent bioimaging probes
      Bhunia, Susanta Kumar; Saha, Arindam; Maity, Amit Ranjan; Ray, Sekhar C.; Jana, Nikhil R.
      Scientific Reports (2013), 3 (), 1473, 7 pp.CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)
      Fluorescent nanoparticle-based imaging probes have advanced current labeling technol. and are expected to generate new medical diagnostic tools based on their superior brightness and photostability compared with conventional mol. probes. Although significant progress has been made in fluorescent semiconductor nanocrystal-based biol. labeling and imaging, the presence of heavy metals and the toxicity issues assocd. with heavy metals have severely limited the application potential of these nanocrystals. Here, we report a fluorescent carbon nanoparticle-based, alternative, nontoxic imaging probe that is suitable for biol. staining and diagnostics. We have developed a chem. method to synthesize highly fluorescent carbon nanoparticles 1-10 nm in size; these particles exhibit size-dependent, tunable visible emission. These carbon nanoparticles have been transformed into various functionalised nanoprobes with hydrodynamic diams. of 5-15 nm and have been used as cell imaging probes.
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    18. 18
      Fabbro, A.; Scaini, D.; León, V.; Vázquez, E.; Cellot, G.; Privitera, G.; Lombardi, L.; Torrisi, F.; Tomarchio, F.; Bonaccorso, F.; Bosi, S.; Ferrari, A. C.; Ballerini, L.; Prato, M. Graphene-Based Interfaces Do Not Alter Target Nerve Cells. ACS Nano 2016, 10, 615– 623,  DOI: 10.1021/acsnano.5b05647
      18
      Graphene-Based Interfaces Do Not Alter Target Nerve Cells
      Fabbro, Alessandra; Scaini, Denis; Leon, Veronica; Vazquez, Ester; Cellot, Giada; Privitera, Giulia; Lombardi, Lucia; Torrisi, Felice; Tomarchio, Flavia; Bonaccorso, Francesco; Bosi, Susanna; Ferrari, Andrea C.; Ballerini, Laura; Prato, Maurizio
      ACS Nano (2016), 10 (1), 615-623CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      Neural-interfaces rely on the ability of electrodes to transduce stimuli into elec. patterns delivered to the brain. In addn. to sensitivity to the stimuli, stability in the operating conditions and efficient charge transfer to neurons, the electrodes should not alter the physiol. properties of the target tissue. Graphene is emerging as a promising material for neuro-interfacing applications, given its outstanding physico-chem. properties. Here, we use graphene-based substrates (GBSs) to interface neuronal growth. We test our GBSs on brain cell cultures by measuring functional and synaptic integrity of the emerging neuronal networks. We show that GBSs are permissive interfaces, even when uncoated by cell adhesion layers, retaining unaltered neuronal signaling properties, thus being suitable for carbon-based neural prosthetic devices.
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    19. 19
      Call, T. P.; Carey, T.; Bombelli, P.; Lea-Smith, D. J.; Hooper, P.; Howe, C. J.; Torrisi, F. Platinum-Free, Graphene Based Anodes and Air Cathodes for Single Chamber Microbial Fuel Cells. J. Mater. Chem. A 2017, 5, 23872– 23886,  DOI: 10.1039/C7TA06895F
      19
      Platinum-free, graphene based anodes and air cathodes for single chamber microbial fuel cells
      Call, Toby P.; Carey, Tian; Bombelli, Paolo; Lea-Smith, David J.; Hooper, Philippa; Howe, Christopher J.; Torrisi, Felice
      Journal of Materials Chemistry A: Materials for Energy and Sustainability (2017), 5 (45), 23872-23886CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)
      Microbial fuel cells (MFCs) exploit the ability of microorganisms to generate elec. power during metab. of substrates. However, the low efficiency of extracellular electron transfer from cells to the anode and the use of expensive rare metals as catalysts, such as platinum, limit their application and scalability. In this study we investigate the use of pristine graphene based electrodes at both the anode and the cathode of a MFC for efficient elec. energy prodn. from the metabolically versatile bacterium Rhodopseudomonas palustris CGA009. We achieve a volumetric peak power output (PV) of up to 3.51 ± 0.50 W m-3 using graphene based aerogel anodes with a surface area of 8.2 m2 g-1. We demonstrate that enhanced MFC output arises from the interplay of the improved surface area, enhanced cond., and catalytic surface groups of the graphene based electrode. In addn., we show a 500-fold increase in PV to 1.3 ± 0.23 W m-3 when using a graphene coated stainless steel (SS) air cathode, compared to an uncoated SS cathode, demonstrating the feasibility of a platinum-free, graphene catalyzed MFCs. Finally, we show a direct application for microwatt-consuming electronics by connecting several of these coin sized devices in series to power a digital clock.
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    20. 20
      Li, N.; Zhang, Q.; Gao, S.; Song, Q.; Huang, R.; Wang, L.; Liu, L.; Dai, J.; Tang, M.; Cheng, G. Three-Dimensional Graphene Foam as a Biocompatible and Conductive Scaffold for Neural Stem Cells. Sci. Rep. 2013, 3, 1604,  DOI: 10.1038/srep01604
      20
      Three-dimensional graphene foam as a biocompatible and conductive scaffold for neural stem cells
      Li, Ning; Zhang, Qi; Gao, Song; Song, Qin; Huang, Rong; Wang, Long; Liu, Liwei; Dai, Jianwu; Tang, Mingliang; Cheng, Guosheng
      Scientific Reports (2013), 3 (), 1604, 6 pp.CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)
      Neural stem cell (NSC) based therapy provides a promising approach for neural regeneration. For the success of NSC clin. application, a scaffold is required to provide 3-dimensional (3D) cell growth microenvironments and appropriate synergistic cell guidance cues. Here, the authors report the first utilization of graphene foam, a 3D porous structure, as a novel scaffold for NSCs in vitro. It was found that 3-dimensional graphene foams (3D-GFs) can not only support NSC growth, but also keep cell at an active proliferation state with upregulation of Ki67 expression than that of 2-dimensional graphene films. Meanwhile, phenotypic anal. indicated that 3D-GFs can enhance the NSC differentiation towards astrocytes and esp. neurons. Furthermore, a good elec. coupling of 3D-GFs with differentiated NSCs for efficient elec. stimulation was obsd. The authors' findings implicate 3D-GFs could offer a powerful platform for NSC research, neural tissue engineering and neural prostheses.
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    21. 21
      Mooney, E.; Dockery, P.; Greiser, U.; Murphy, M.; Barron, V. Carbon Nanotubes and Mesenchymal Stem Cells: Biocompatibility, Proliferation and Differentiation. Nano Lett. 2008, 8, 2137– 2143,  DOI: 10.1021/nl073300o
      There is no corresponding record for this reference.
    22. 22
      Yang, S. T.; Luo, J.; Zhou, Q.; Wang, H. Pharmacokinetics, Metabolism and Toxicity of Carbon Nanotubes for Bio-Medical Purposes. Theranostics 2012, 2, 271– 282,  DOI: 10.7150/thno.3618
      22
      Pharmacokinetics, metabolism and toxicity of carbon nanotubes for biomedical purposes
      Yang, Sheng-Tao; Luo, Jianbin; Zhou, Qinghan; Wang, Haifang
      Theranostics (2012), 2 (3), 271-282CODEN: THERDS; ISSN:1838-7640. (Ivyspring International Publisher)
      A review. Carbon nanotubes (CNTs) have attracted great interest of the nano community and beyond. However, the biomedical applications of CNTs arouse serious concerns for their unknown in vivo consequence, in which the information of pharmacokinetics, metab. and toxicity of CNTs is essential. In this review, we summarize the updated data of CNTs from the biomedical view. The information shows that surface chem. is crucial in regulating the in vivo behaviors of CNTs. Among the functionalization methods, PEGylation is the most efficient one to improve the pharmacokinetics and biocompatibility of CNTs. The guiding effects of the pharmacokinetics, metab. and toxicity information on the biomedical applications of CNTs are discussed.
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    23. 23
      Jia, G.; Wang, H.; Yan, L.; Wang, X.; Pei, R.; Yan, T.; Zhao, Y.; Guo, X. Cytotoxicity of Carbon Nanomaterials: Single-Wall Nanotube, Multi-Wall Nanotube, and Fullerene. Environ. Sci. Technol. 2005, 39, 1378– 1383,  DOI: 10.1021/es048729l
      23
      Cytotoxicity of Carbon Nanomaterials: Single-Wall Nanotube, Multi-Wall Nanotube, and Fullerene
      Jia, Guang; Wang, Haifang; Yan, Lei; Wang, Xiang; Pei, Rongjuan; Yan, Tao; Zhao, Yuliang; Guo, Xinbiao
      Environmental Science and Technology (2005), 39 (5), 1378-1383CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      A cytotoxicity test protocol for single-wall nanotubes (SWNTs), multi-wall nanotubes (with diams. ranging from 10 to 20 nm, MWNT10), and fullerene (C60) was tested. Profound cytotoxicity of SWNTs was obsd. in alveolar macrophage (AM) after a 6-h exposure in vitro. The cytotoxicity increases by as high as ∼35% when the dosage of SWNTs was increased by 11.30 μg/cm2. No significant toxicity was obsd. for C60 up to a dose of 226.00 μg/cm2. The cytotoxicity apparently follows a sequence order on a mass basis: SWNTs > MWNT10 > quartz > C60. SWNTs significantly impaired phagocytosis of AM at the low dose of 0.38 μg/cm2, whereas MWNT10 and C60 induced injury only at the high dose of 3.06 μg/cm2. The macrophages exposed to SWNTs or MWNT10 of 3.06 μg/cm2 showed characteristic features of necrosis and degeneration. A sign of apoptotic cell death likely existed. Carbon nanomaterials with different geometric structures exhibit quite different cytotoxicity and bioactivity in vitro, although they may not be accurately reflected in the comparative toxicity in vivo.
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    24. 24
      Correa-Duarte, M. A.; Wagner, N.; Rojas-Chapana, J.; Morsczeck, C.; Thie, M.; Giersig, M. Fabrication and Biocompatibility of Carbon Nanotube-Based 3D Networks as Scaffolds for Cell Seeding and Growth. Nano Lett. 2004, 4, 2233– 2236,  DOI: 10.1021/nl048574f
      24
      Fabrication and Biocompatibility of Carbon Nanotube-Based 3D Networks as Scaffolds for Cell Seeding and Growth
      Correa-Duarte, Miguel A.; Wagner, Nicholas; Rojas-Chapana, Jose; Morsczeck, Christian; Thie, Michael; Giersig, Michael
      Nano Letters (2004), 4 (11), 2233-2236CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      Thin film networks of multi-walled carbon nanotubes (MWCNTs) were prepd. by exerting chem. induced capillary forces upon the nanotubes. During this process MWCNTs undergo a transformation from being a vertically aligned structure to an interlocking resistive network of interconnected nanotubes, whose main feature is a regular three-dimensional (3D) sieve architecture. Due to their structural characteristics at the nanoscale level, 3D-MWCNT-based networks are in principle ideal candidates for scaffolds/matrixes in tissue engineering. Their potential application in this field was confirmed by extensive growth, spreading, and adhesion of the common mouse fibroblast cell line L929.
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    25. 25
      Edwards, S. L.; Church, J. S.; Werkmeister, J. A.; Ramshaw, J. A. M. Tubular Micro-Scale Multiwalled Carbon Nanotube-Based Scaffolds for Tissue Engineering. Biomaterials 2009, 30, 1725– 1731,  DOI: 10.1016/j.biomaterials.2008.12.031
      25
      Tubular micro-scale multiwalled carbon nanotube-based scaffolds for tissue engineering
      Edwards, Sharon L.; Church, Jeffrey S.; Werkmeister, Jerome A.; Ramshaw, John A. M.
      Biomaterials (2009), 30 (9), 1725-1731CODEN: BIMADU; ISSN:0142-9612. (Elsevier Ltd.)
      In this study we have prepd. a tubular knitted scaffold from a 9 ply multiwalled carbon nanotube (MWCNT) yarn and a composite scaffold, formed by electrospinning poly(lactic-co-glycolic acid) (PLGA) nanofibres onto the knitted scaffold. Both structures were assessed for in vitro biocompatibility with NR6 mouse fibroblast cells for up to 22 days and their suitability as tissue engineering scaffolds considered. The MWCNT yarn was found to support cell growth throughout the culture period, with fibroblasts attaching to, and proliferating on, the yarn surface. The knitted tubular scaffold contained large pores that inhibited cell spanning, leading to the formation of cell clusters on the yarn, and an uneven cell distribution on the scaffold surface. The smaller pores, created through electrospinning, were found to promote cell spanning, leading to a uniform distribution of cells on the composite scaffold surface. Evaluation of the elec. and mech. properties of the knitted scaffold detd. resistance levels of 0.9 kΩ/cm, with a breaking load and extension to break approaching 0.7 N and 8%, resp. The PLGA/MWCNT composite scaffold presented in this work not only supports cell growth, but also has the potential to utilize the full range of elec. and mech. properties that carbon nanotubes have to offer.
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    26. 26
      Liu, Y.; Zhao, Y.; Sun, B.; Chen, C. Understanding the Toxicity of Carbon Nanotubes. Acc. Chem. Res. 2013, 46, 702– 713,  DOI: 10.1021/ar300028m
      26
      Understanding the toxicity of carbon nanotubes
      Liu, Ying; Zhao, Yuliang; Sun, Baoyun; Chen, Chunying
      Accounts of Chemical Research (2013), 46 (3), 702-713CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
      A review. Because of their unique phys., chem., elec., and mech. properties, carbon nanotubes (CNTs) have attracted a great deal of research interest and have many potential applications. As large-scale prodn. and application of CNTs increases, the general population is more likely to be exposed to CNTs either directly or indirectly, which has prompted considerable attention about human health and safety issues related to CNTs. Although considerable exptl. data related to CNT toxicity at the mol., cellular, and whole animal levels have been published, the results are often conflicting. Therefore, a systematic understanding of CNT toxicity is needed but has not yet been developed. In this Account, we highlight recent investigations into the basis of CNT toxicity carried out by our team and by other labs. We focus on several important factors that explain the disparities in the exptl. results of nanotoxicity, such as impurities, amorphous carbon, surface charge, shape, length, agglomeration, and layer nos. The exposure routes, including inhalation, i.v. injection, or dermal or oral exposure, can also influence the in vivo behavior and fate of CNTs. The underlying mechanisms of CNT toxicity include oxidative stress, inflammatory responses, malignant transformation, DNA damage and mutation (errors in chromosome no. as well as disruption of the mitotic spindle), the formation of granulomas, and interstitial fibrosis. These findings provide useful insights for de novo design and safe application of carbon nanotubes and their risk assessment to human health. To obtain reproducible and accurate results, researchers must establish stds. and reliable detection methods, use std. CNT samples as a ref. control, and study the impact of various factors systematically. In addn., researchers need to examine multiple types of CNTs, different cell lines and animal species, multidimensional evaluation methods, and exposure conditions. To make results comparable among different institutions and countries, researchers need to standardize choices in toxicity testing such as that of cell line, animal species, and exposure conditions. The knowledge presented here should lead to a better understanding of the key factors that can influence CNT toxicity so that their unwanted toxicity might be avoided.
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    27. 27
      Cohen-Karni, T.; Qing, Q.; Li, Q.; Fang, Y.; Lieber, C. M. Graphene and Nanowire Transistors for Cellular Interfaces and Electrical Recording. Nano Lett. 2010, 10, 1098– 1102,  DOI: 10.1021/nl1002608
      27
      Graphene and Nanowire Transistors for Cellular Interfaces and Electrical Recording
      Cohen-Karni, Tzahi; Qing, Quan; Li, Qiang; Fang, Ying; Lieber, Charles M.
      Nano Letters (2010), 10 (3), 1098-1102CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      Nanowire field-effect transistors (NW-FETs) have been shown to be powerful building blocks for nanoscale bioelectronic interfaces with cells and tissue due to their excellent sensitivity and their capability to form strongly coupled interfaces with cell membranes. Graphene has also been shown to be an attractive building block for nanoscale electronic devices, although little is known about its interfaces with cells and tissue. Here we report the first studies of graphene field effect transistors (Gra-FETs) as well as combined Gra- and NW-FETs interfaced to electrogenic cells. Gra-FET conductance signals recorded from spontaneously beating embryonic chicken cardiomyocytes yield well-defined extracellular signals with signal-to-noise ratio routinely >4. The conductance signal amplitude was tuned by varying the Gra-FET working region through changes in water gate potential, Vwg. Signals recorded from cardiomyocytes for different Vwg result in const. calibrated extracellular voltage, indicating a robust graphene/cell interface. Significantly, variations in Vwg across the Dirac point demonstrate the expected signal polarity flip, thus allowing, for the first time, both n- and p-type recording to be achieved from the same Gra-FET simply by offsetting Vwg. In addn., comparisons of peak-to-peak recorded signal widths made as a function of Gra-FET device sizes and vs. NW-FETs allowed an assessment of relative resoln. in extracellular recording. Specifically, peak-to-peak widths increased with the area of Gra-FET devices, indicating an averaged signal from different points across the outer membrane of the beating cells. One-dimensional silicon NW- FETs incorporated side by side with the two-dimensional Gra-FET devices further highlighted limits in both temporal resoln. and multiplexed measurements from the same cell for the different types of devices. The distinct and complementary capabilities of Gra- and NW-FETs could open up unique opportunities in the field of bioelectronics in the future.
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    28. 28
      Akhavan, O.; Ghaderi, E.; Shahsavar, M. Graphene Nanogrids for Selective and Fast Osteogenic Differentiation of Human Mesenchymal Stem Cells. Carbon 2013, 59, 200– 211,  DOI: 10.1016/j.carbon.2013.03.010
      28
      Graphene nanogrids for selective and fast osteogenic differentiation of human mesenchymal stem cells
      Akhavan, Omid; Ghaderi, Elham; Shahsavar, Mahla
      Carbon (2013), 59 (), 200-211CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
      Graphene nanogrids (fabricated by graphene nanoribbons obtained through oxidative unzipping of multi-walled carbon nanotubes) were used as two-dimensional selective templates for accelerated differentiation of human mesenchymal stem cells (hMSCs), isolated from umbilical cord blood, into osteogenic lineage. The biocompatible and hydrophilic graphene nanogrids showed high actin cytoskeleton proliferations coinciding with patterns of the nanogrids. The amts. of proliferations were found slightly better than proliferation on hydrophilic graphene oxide (GO) sheets, and significantly higher than non-uniform proliferations on hydrophobic reduced graphene oxide (rGO) sheets and polydimethylsiloxane substrate. In the presence of chem. inducers, the reduced graphene oxide nanoribbon (rGONR) grid showed a highly accelerated osteogenic differentiation of the hMSCs (a patterned differentiation) in short time of 7 days in which the amt. of the osteogenesis was ∼2.2 folds greater than the differentiation (a uniform differentiation) on the rGO sheets. We found that although in the absence of any chem. inducers the graphene nanogrids showed slight patterned osteogenic differentiations, the graphene sheets could not present any differentiation. Therefore, the highly accelerated differentiation on the rGONR grid was assigned to both its excellent capability in adsorption of the chem. inducers and phys. stresses induced by the surface topog. features of the nanogrids.
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    29. 29
      Shin, S. R.; Li, Y. C.; Jang, H. L.; Khoshakhlagh, P.; Akbari, M.; Nasajpour, A.; Zhang, Y. S.; Tamayol, A.; Khademhosseini, A. Graphene-Based Materials for Tissue Engineering. Adv. Drug Delivery Rev. 2016, 105, 255– 274,  DOI: 10.1016/j.addr.2016.03.007
      29
      Graphene-based materials for tissue engineering
      Shin, Su Ryon; Li, Yi-Chen; Jang, Hae Lin; Khoshakhlagh, Parastoo; Akbari, Mohsen; Nasajpour, Amir; Zhang, Yu Shrike; Tamayol, Ali; Khademhosseini, Ali
      Advanced Drug Delivery Reviews (2016), 105 (Part_B), 255-274CODEN: ADDREP; ISSN:0169-409X. (Elsevier B.V.)
      Graphene and its chem. derivs. have been a pivotal new class of nanomaterials and a model system for quantum behavior. The material's excellent elec. cond., biocompatibility, surface area and thermal properties are of much interest to the scientific community. Two-dimensional graphene materials have been widely used in various biomedical research areas such as bioelectronics, imaging, drug delivery, and tissue engineering. In this review, we will highlight the recent applications of graphene-based materials in tissue engineering and regenerative medicine. In particular, we will discuss the application of graphene-based materials in cardiac, neural, bone, cartilage, skeletal muscle, and skin/adipose tissue engineering. We will also discuss the potential risk factors of graphene-based materials in tissue engineering. In conclusion, we will outline the opportunities in the usage of graphene-based materials for clin. applications.
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    30. 30
      Smith, S. C.; Ahmed, F.; Gutierrez, K. M.; Frigi Rodrigues, D. A Comparative Study of Lysozyme Adsorption with Graphene, Graphene Oxide, and Single-Walled Carbon Nanotubes: Potential Environmental Applications. Chem. Eng. J. 2014, 240, 147– 154,  DOI: 10.1016/j.cej.2013.11.030
      30
      A comparative study of lysozyme adsorption with graphene, graphene oxide, and single-walled carbon nanotubes: Potential environmental applications
      Smith, Sean C.; Ahmed, Farid; Gutierrez, Krystal M.; Frigi Rodrigues, Debora
      Chemical Engineering Journal (Amsterdam, Netherlands) (2014), 240 (), 147-154CODEN: CMEJAJ; ISSN:1385-8947. (Elsevier B.V.)
      Wastewater contains numerous classes of org. mols., primarily different types of sol. microbial products, e.g., polysaccharides, nucleic acids, proteins. The presence of these compds. in effluent increases the risk of toxic byproduct formation during chlorination. In recent years, studies demonstrated the power of C-based nanomaterials to remove many chem. compds. and pollutants from aq. solns. This work examd. the protein absorption capacity and adsorption mechanisms of 3 C-based nanomaterials: graphene (G), graphene oxide (GO), and single-walled C nanotubes (SWNT) in various water chemistries, using lysozyme as a model protein. Results showed GO exhibited the highest lysozyme adsorption capacity (∼500 mg protein/g nanomaterial) in adsorption isotherm assays. Adsorption data were fitted to Langmuir, Freundlich, and Temkin models and relevant parameters were detd. Lysozyme adsorption by GO and SWNT was strongly affected by the presence of mono- and di-valent salts; however, no significant pH dependence was obsd. for protein adsorption to studied nanomaterial. Results also showed the GO adsorption mechanism was mainly electrostatic, while the G and SWNT mechanisms were attributed to van der Waals forces and some electrostatic interactions. Adsorption expts. of proteins present in wastewater were performed to test the efficacy of G, GO, and SWNT as sorbents for complex environmental samples. All 3 nanomaterials removed more protein from wastewater than conventional sorbents reported in the literature.
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    31. 31
      Mecklenburg, M.; Schuchardt, A.; Mishra, Y. K.; Kaps, S.; Adelung, R.; Lotnyk, A.; Kienle, L.; Schulte, K. Aerographite: Ultra Lightweight, Flexible Nanowall, Carbon Microtube Material with Outstanding Mechanical Performance. Adv. Mater. 2012, 24, 3486– 3490,  DOI: 10.1002/adma.201200491
      31
      Aerographite: Ultra Lightweight, Flexible Nanowall, Carbon Microtube Material with Outstanding Mechanical Performance
      Mecklenburg, Matthias; Schuchardt, Arnim; Mishra, Yogendra Kumar; Kaps, Soeren; Adelung, Rainer; Lotnyk, Andriy; Kienle, Lorenz; Schulte, Karl
      Advanced Materials (Weinheim, Germany) (2012), 24 (26), 3486-3490, S3486/1-S3486/26CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
      We present a novel synthesis of an ultralightwt., elec. conductive, mech. robust, and flexible graphite-based material, Aerographite. In contrast to already established synthesis for other carbon nanostructures like carbon nanotubes (CNTs) or graphene, this CVD process uses ZnO as template for the synthesis of bulk samples on the centimeter scale. This inorg. semiconductor is a suitable substrate/template material for sp2 hybridized carbons, e.g., CNTs and graphene. The common structural motive of the Aerographite family is the completely interconnected network of microstructures with a nanoscopic wall thickness. Variants come as filled and unfilled, corrugated walls, or as a superlightwt. example of a hollow framework of struts from amorphous carbon. The at. structure can be tuned from graphitic to glass-like pyrolytic carbon, with the advantage of remarkable mech. properties. This most lightwt. material reaches the highest merit indexes for sp. moduli obsd. until now. Further optimization of parameters, e.g., pore size and vol. d. of sintering bridges keeps the opportunity for future improvements of the mech performance of Aerographite. Further properties such as cond., flexibility and compressibility without losing structural integrity, high optical adsorption and x-ray opacity, a high-temp. stability and chem. resistance, the bearing of tensile and compressive loads, and the super hydrophobicity make it a remarkable multifunctional material. Next to others, potential applications might be electrode materials for increasing demand of batteries and high surface area supercapacitor materials. Proper designed carbon materials from the Aerographites family could avoid typical problems of electrode materials like low mech. cycling stability, degenerating elec. contacts, or non-optimized electrolyte-to-surface ratio which might be tuned by simple compression due to the negligible Poisson's ration of these sponge-like structures.
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    32. 32
      Mishra, Y. K.; Kaps, S.; Schuchardt, A.; Paulowicz, I.; Jin, X.; Gedamu, D.; Freitag, S.; Claus, M.; Wille, S.; Kovalev, A.; Gorb, S. N.; Adelung, R. Fabrication of Macroscopically Flexible and Highly Porous 3D Semiconductor Networks from Interpenetrating Nanostructures by a Simple Flame Transport Approach. Part. Part. Syst. Charact. 2013, 30, 775– 783,  DOI: 10.1002/ppsc.201300197
      32
      Fabrication of Macroscopically Flexible and Highly Porous 3D Semiconductor Networks from Interpenetrating Nanostructures by a Simple Flame Transport Approach
      Mishra, Yogendra K.; Kaps, Soeren; Schuchardt, Arnim; Paulowicz, Ingo; Jin, Xin; Gedamu, Dawit; Freitag, Stefan; Claus, Maria; Wille, Sebastian; Kovalev, Alexander; Gorb, Stanislav N.; Adelung, Rainer
      Particle & Particle Systems Characterization (2013), 30 (9), 775-783CODEN: PPCHEZ; ISSN:1521-4117. (Wiley-VCH Verlag GmbH & Co. KGaA)
      We have demonstrated that the FTS approach and its variants offer versatile fabrication of various kinds of large 3D interconnected networks of high porosity using nano-microscopic building blocks from metal oxides. Properties of these networks can be tailored by using different types of building blocks, their d., and the type of interconnections. For example, the Young's modulus of these 3D networks can be tuned from wool-type behavior to rubber elastic regime of several MPa. The flexibility and high-temp. stability of these conducting and highly porous networks could be used for various technol. applications. Apart from 3D networks, a large variety of 1D structures can be synthesized in sized ranging from nanometers to centimeters. Features including simplicity, low cost, mass-scale prodn., and versatility of structures produced by the FTS approach and its variants open numerous areas not only in basic research but also for industrial applications.
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    33. 33
      Lamprecht, C.; Taale, M.; Paulowicz, I.; Westerhaus, H.; Grabosch, C.; Schuchardt, A.; Mecklenburg, M.; Böttner, M.; Lucius, R.; Schulte, K.; Adelung, R.; Selhuber-Unkel, C. A Tunable Scaffold of Microtubular Graphite for 3D Cell Growth. ACS Appl. Mater. Interfaces 2016, 8, 14980– 14985,  DOI: 10.1021/acsami.6b00778
      There is no corresponding record for this reference.
    34. 34
      Mouw, J. K.; Ou, G.; Weaver, V. M. Extracellular Matrix Assembly: A Multiscale Deconstruction. Nat. Rev. Mol. Cell Biol. 2014, 15, 771– 785,  DOI: 10.1038/nrm3902
      34
      Extracellular matrix assembly: a multiscale deconstruction
      Mouw, Janna K.; Ou, Guanqing; Weaver, Valerie M.
      Nature Reviews Molecular Cell Biology (2014), 15 (12), 771-785CODEN: NRMCBP; ISSN:1471-0072. (Nature Publishing Group)
      The biochem. and biophys. properties of the extracellular matrix (ECM) dictate tissue-specific cell behavior. The mols. that are assocd. with the ECM of each tissue, including collagens, proteoglycans, laminins and fibronectin, and the manner in which they are assembled det. the structure and the organization of the resultant ECM. The product is a specific ECM signature that is comprised of unique compositional and topog. features that both reflect and facilitate the functional requirements of the tissue.
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    35. 35
      Schütt, F.; Signetti, S.; Krüger, H.; Röder, S.; Smazna, D.; Kaps, S.; Gorb, S. N.; Mishra, Y. K.; Pugno, N. M.; Adelung, R. Hierarchical Self-Entangled Carbon Nanotube Tube Networks. Nat. Commun. 2017, 8, 1215  DOI: 10.1038/s41467-017-01324-7
      There is no corresponding record for this reference.
    36. 36
      Feng, X.; Feng, L.; Jin, M.; Zhai, J.; Jiang, L.; Zhu, D. Reversible Super-Hydrophobicity to Super-Hydrophilicity Transition of Aligned ZnO Nanorod Films. J. Am. Chem. Soc. 2004, 126, 62– 63,  DOI: 10.1021/ja038636o
      36
      Reversible Super-hydrophobicity to Super-hydrophilicity Transition of Aligned ZnO Nanorod Films
      Feng, Xinjian; Feng, Lin; Jin, Meihua; Zhai, Jin; Jiang, Lei; Zhu, Daoben
      Journal of the American Chemical Society (2004), 126 (1), 62-63CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Remarkable surface wettability transition occurs with an inducement of UV for aligned ZnO nanorod films. The inorg. oxide films, which show super-hydrophobicity (left), become super-hydrophilic (right) when exposed to UV illumination. After the films are placed in the dark, the wettability evolves back to super-hydrophobicity. This reversible effect is ascribed to the cooperation of the surface photosensitivity and the aligned nanostructure. Such special property will greatly extend the applications of ZnO films.
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    37. 37
      Chen, H.-K. Kinetic Study on the Carbothermic Reduction of Zinc Oxide. Scand. J. Metall. 2001, 30, 292– 296,  DOI: 10.1034/j.1600-0692.2001.300503.x
      37
      Kinetic study on the carbothermic reduction of zinc oxide
      Chen, Hsi-Kuei
      Scandinavian Journal of Metallurgy (2001), 30 (5), 292-296CODEN: SJMLAG; ISSN:0371-0459. (Munksgaard International Publishers Ltd.)
      The kinetics of carbothermic redn. of zinc oxide with carbon powder under a nitrogen atm. (at 1 atm). The exptl. results indicated that the redn. rate could be increased by increasing the molar ratio of C/ZnO, height of solid sample, d. of solid sample or reaction temp. The rate was also found to be increased by reducing the grain size of zinc oxide and carbon or the nitrogen gas flow rate. The empirical expressions of conversion rates of zinc oxide and carbon as well as the prodn. rate of zinc were detd. from the regression of the exptl. data.
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    38. 38
      Zhao, J.; Xing, B.; Yang, H.; Pan, Q.; Li, Z.; Liu, Z. Growth of Carbon Nanotubes on Graphene by Chemical Vapor Deposition. New Carbon Mater. 2016, 31, 31– 36,  DOI: 10.1016/S1872-5805(16)60002-1
      There is no corresponding record for this reference.
    39. 39
      Ferrari, A. C.; Robertson, J. Resonant Raman Spectroscopy of Disordered, Amorphous, and Diamondlike Carbon. Phys. Rev. B: Condens. Matter Mater. Phys. 2001, 64, 075414,  DOI: 10.1103/PhysRevB.64.075414
      39
      Resonant Raman spectroscopy of disordered, amorphous, and diamondlike carbon
      Ferrari, A. C.; Robertson, J.
      Physical Review B: Condensed Matter and Materials Physics (2001), 64 (7), 075414/1-075414/13CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)
      The Raman spectra of a wide range of disordered and amorphous carbons were measured under excitation from 785 to 229 nm. The dispersion of peak positions and intensities with excitation wavelength is used to understand the nature of resonant Raman scattering in C and how to derive the local bonding and disorder from the Raman spectra. The spectra show 3 basic features, the D and G around 1600 and 1350 cm-1 for visible excitation and an extra T peak, for UV excitation, at ∼1060 cm-1. The G peak, due to the stretching motion of sp2 pairs, is a good indicator of disorder. It shows dispersion only in amorphous networks, with a dispersion rate proportional to the degree of disorder. Its shift well >1600 cm-1 under UV excitation indicates sp2 chains. The dispersion of the D peak is strongest in ordered carbons. It shows little dispersion in amorphous C, so that in UV excitation it becomes like a d.-of-states feature of vibrations of sp2 ringlike structures. The intensity ratio I(D)/I(G) falls with increasing UV excitation in all forms of C, with a faster decrease in more ordered carbons, so that it is generally small for UV excitation. The T peak, due to sp3 vibrations, only appears in UV Raman, lying around 1060 cm-1 for H-free carbons and around 980 cm-1 in hydrogenated carbons. In hydrogenated carbons, the sp3 C-Hx stretching modes around 2920 cm-1 can be clearly detected for UV excitation. This assignment is confirmed by D substitution.
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    40. 40
      Carey, T.; Cacovich, S.; Divitini, G.; Ren, J.; Mansouri, A.; Kim, J. M.; Wang, C.; Ducati, C.; Sordan, R.; Torrisi, F. Fully Inkjet-Printed Two-Dimensional Material Field-Effect Heterojunctions for Wearable and Textile Electronics. Nat. Commun. 2017, 8, 1202,  DOI: 10.1038/s41467-017-01210-2
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      Fully inkjet-printed two-dimensional material field-effect heterojunctions for wearable and textile electronics
      Carey Tian; Ren Jiesheng; Kim Jong M; Torrisi Felice; Cacovich Stefania; Divitini Giorgio; Ducati Caterina; Ren Jiesheng; Wang Chaoxia; Mansouri Aida; Sordan Roman
      Nature communications (2017), 8 (1), 1202 ISSN:.
      Fully printed wearable electronics based on two-dimensional (2D) material heterojunction structures also known as heterostructures, such as field-effect transistors, require robust and reproducible printed multi-layer stacks consisting of active channel, dielectric and conductive contact layers. Solution processing of graphite and other layered materials provides low-cost inks enabling printed electronic devices, for example by inkjet printing. However, the limited quality of the 2D-material inks, the complexity of the layered arrangement, and the lack of a dielectric 2D-material ink able to operate at room temperature, under strain and after several washing cycles has impeded the fabrication of electronic devices on textile with fully printed 2D heterostructures. Here we demonstrate fully inkjet-printed 2D-material active heterostructures with graphene and hexagonal-boron nitride (h-BN) inks, and use them to fabricate all inkjet-printed flexible and washable field-effect transistors on textile, reaching a field-effect mobility of ~91 cm(2) V(-1) s(-1), at low voltage (<5 V). This enables fully inkjet-printed electronic circuits, such as reprogrammable volatile memory cells, complementary inverters and OR logic gates.
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    41. 41
      Ferrari, A. C.; Meyer, J. C.; Scardaci, V.; Casiraghi, C.; Lazzeri, M.; Mauri, F.; Piscanec, S.; Jiang, D.; Novoselov, K. S.; Roth, S. Raman Spectrum of Graphene and Graphene Layers. Phys. Rev. Lett. 2006, 97, 187401,  DOI: 10.1103/PhysRevLett.97.187401
      41
      Raman Spectrum of Graphene and Graphene Layers
      Ferrari, A. C.; Meyer, J. C.; Scardaci, V.; Casiraghi, C.; Lazzeri, M.; Mauri, F.; Piscanec, S.; Jiang, D.; Novoselov, K. S.; Roth, S.; Geim, A. K.
      Physical Review Letters (2006), 97 (18), 187401/1-187401/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
      Graphene is the 2-dimensional building block for C allotropes of every other dimensionality. Its electronic structure is captured in its Raman spectrum that clearly evolves with the no. of layers. The D peak 2nd order changes in shape, width, and position for an increasing no. of layers, reflecting the change in the electron bands via a double resonant Raman process. The G peak slightly down-shifts. This allows unambiguous, high-throughput, nondestructive identification of graphene layers, which is critically lacking in this emerging research area.
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    42. 42
      Ferrari, A.; Robertson, J. Interpretation of Raman Spectra of Disordered and Amorphous Carbon. Phys. Rev. B: Condens. Matter Mater. Phys. 2000, 61, 14095– 14107,  DOI: 10.1103/PhysRevB.61.14095
      42
      Interpretation of Raman spectra of disordered and amorphous carbon
      Ferrari, A. C.; Robertson, J.
      Physical Review B: Condensed Matter and Materials Physics (2000), 61 (20), 14095-14107CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)
      The model and theor. understanding of the Raman spectra in disordered and amorphous C are given. The nature of the G and D vibration modes in graphite is analyzed in terms of the resonant excitation of π states and the long-range polarizability of π bonding. Visible Raman data on disordered, amorphous, and diamondlike C are classified in a 3-stage model to show the factors that control the position, intensity, and widths of the G and D peaks. The visible Raman spectra depend formally on the configuration of the sp2 sites in sp2-bonded clusters. In cases where the sp2 clustering is controlled by the sp3 fraction, such as in as-deposited tetrahedral amorphous C (ta-C) or hydrogenated amorphous C (a-C:H) films, the visible Raman parameters can be used to derive the sp3 fraction.
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    43. 43
      Cuscó, R.; Alarcón-Lladó, E.; Ibáñez, J.; Artús, L.; Jiménez, J.; Wang, B.; Callahan, M. Temperature Dependence of Raman Scattering in ZnO. Phys. Rev. B: Condens. Matter Mater. Phys. 2007, 75, 165202,  DOI: 10.1103/PhysRevB.75.165202
      43
      Temperature dependence of Raman scattering in ZnO
      Cusco, Ramon; Alarcon-Llado, Esther; Ibanez, Jordi; Artus, Luis; Jimenez, Juan; Wang, Buguo; Callahan, Michael J.
      Physical Review B: Condensed Matter and Materials Physics (2007), 75 (16), 165202/1-165202/11CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
      The authors present a Raman scattering study of wurtzite ZnO at 80-750 K. Second-order Raman features are interpreted in the light of recent ab initio phonon d. of states calcns. The temp. dependence of the Raman intensities allows the assignment of difference modes to be made unambiguously. Some weak, sharp Raman peaks are detected whose temp. dependence suggests they may be due to impurity modes. High-resoln. spectra of the Ehigh2, A1(LO), and E1(LO) modes were recorded, and an anal. of the anharmonicity and lifetimes of these phonons is carried out. The Ehigh2 mode displays a visibly asym. line shape. This can be attributed to anharmonic interaction with transverse and longitudinal acoustic phonon combinations in the vicinity of the K point, where the 2-phonon d. of states displays a sharp edge around the Ehigh2 frequency. The temp. dependence of the linewidth and frequency of the Ehigh2 mode is well described by a perturbation-theory renormalization of the harmonic Ehigh2 frequency resulting from the interaction with the acoustic 2-phonon d. of states. But the A1(LO) and E1(LO) frequencies lie in a region of nearly flat 2-phonon d. of states, and they exhibit a nearly sym. Lorentzian line shape with a temp. dependence that is well accounted for by a dominating asym. decay channel.
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    44. 44
      Fan, H.; Wang, L.; Zhao, K.; Li, N.; Shi, Z.; Ge, Z.; Jin, Z. Fabrication, Mechanical Properties, and Biocompatibility of Graphene-Reinforced Chitosan Composites. Biomacromolecules 2010, 11, 2345– 2351,  DOI: 10.1021/bm100470q
      44
      Fabrication, Mechanical Properties, and Biocompatibility of Graphene-Reinforced Chitosan Composites
      Fan, Hailong; Wang, Lili; Zhao, Keke; Li, Nan; Shi, Zujin; Ge, Zigang; Jin, Zhaoxia
      Biomacromolecules (2010), 11 (9), 2345-2351CODEN: BOMAF6; ISSN:1525-7797. (American Chemical Society)
      Few-layered graphene sheets, synthesized by d.c. arc-discharge method using NH3 as one of the buffer gases, were dispersed in chitosan/acetic acid solns. FTIR and XPS showed the presence of oxygen-contg. functional groups on the surface of graphene sheets that may assist the good dispersion of graphene in chitosan soln. Graphene/chitosan films were produced by soln. casting method. The mech. properties of composite films were tested by nanoindentation method. With the addn. of a small amt. of graphene in chitosan (0.1-0.3 wt. %), the elastic modulus of chitosan increased over ∼200%. The biocompatibility of graphene/chitosan composite films was checked by tetrazolium-based colorimetric assays in vitro. The cell adhesion result showed that the L929 cell can adhere to and develop on the graphene/chitosan composite films as well as on pure chitosan film, indicating that graphene/chitosan composites have good biocompatibility. Because there is no metallic impurity in graphene raw materials, the time-consuming purifn. process for removing metal nanoparticles entrapped in carbon nanotubes is thus avoided when graphene is used to prep. biomedical materials. Graphene/chitosan composites are potential candidates as scaffold materials in tissue engineering.
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    45. 45
      Ahadian, S.; Ramón-Azcón, J.; Estili, M.; Liang, X.; Ostrovidov, S.; Shiku, H.; Ramalingam, M.; Nakajima, K.; Sakka, Y.; Bae, H. H.; Matsue, T.; Khademhosseini, A. Hybrid Hydrogels Containing Vertically Aligned Carbon Nanotubes with Anisotropic Electrical Conductivity for Muscle Myofiber Fabrication. Sci. Rep. 2015, 4, 4271,  DOI: 10.1038/srep04271
      There is no corresponding record for this reference.
    46. 46
      Shi, X.; Sitharaman, B.; Pham, Q. P.; Liang, F.; Wu, K.; Edward Billups, W.; Wilson, L. J.; Mikos, A. G. Fabrication of Porous Ultra-Short Single-Walled Carbon Nanotube Nanocomposite Scaffolds for Bone Tissue Engineering. Biomaterials 2007, 28, 4078– 4090,  DOI: 10.1016/j.biomaterials.2007.05.033
      46
      Fabrication of porous ultra-short single-walled carbon nanotube nanocomposite scaffolds for bone tissue engineering
      Shi, Xinfeng; Sitharaman, Balaji; Pham, Quynh P.; Liang, Feng; Wu, Katherine; Edward Billups, W.; Wilson, Lon J.; Mikos, Antonios G.
      Biomaterials (2007), 28 (28), 4078-4090CODEN: BIMADU; ISSN:0142-9612. (Elsevier Ltd.)
      We investigated the fabrication of highly porous scaffolds made of three different materials [poly(propylene fumarate) (PPF) polymer, an ultra-short single-walled carbon nanotube (US-tube) nanocomposite, and a dodecylated US-tube (F-US-tube) nanocomposite] in order to evaluate the effects of material compn. and porosity on scaffold pore structure, mech. properties, and marrow stromal cell culture. All scaffolds were produced by a thermal-crosslinking particulate-leaching technique at specific porogen contents of 75, 80, 85, and 90 vol%. Scanning electron microcopy, microcomputed tomog., and mercury intrusion porosimetry were used to analyze the pore structures of scaffolds. The porogen content was found to dictate the porosity of scaffolds. There was no significant difference in porosity, pore size, and interconnectivity among the different materials for the same porogen fraction. Nearly 100% of the pore vol. was interconnected through 20 μm or larger connections for all scaffolds. While interconnectivity through larger connections improved with higher porosity, compressive mech. properties of scaffolds declined at the same time. However, the compressive modulus, offset yield strength, and compressive strength of F-US-tube nanocomposites were higher than or similar to the corresponding properties for the PPF polymer and US-tube nanocomposites for all the porosities examd. As for in vitro osteocond., marrow stromal cells demonstrated equally good cell attachment and proliferation on all scaffolds made of different materials at each porosity. These results indicate that functionalized ultra-short single-walled carbon nanotube nanocomposite scaffolds with tunable porosity and mech. properties hold great promise for bone tissue engineering applications.
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    47. 47
      Chen, Z.; Ren, W.; Gao, L.; Liu, B.; Pei, S.; Cheng, H. M. Three-Dimensional Flexible and Conductive Interconnected Graphene Networks Grown by Chemical Vapour Deposition. Nat. Mater. 2011, 10, 424– 428,  DOI: 10.1038/nmat3001
      47
      Three-dimensional flexible and conductive interconnected graphene networks grown by chemical vapor deposition
      Chen, Zongping; Ren, Wencai; Gao, Libo; Liu, Bilu; Pei, Songfeng; Cheng, Hui-Ming
      Nature Materials (2011), 10 (6), 424-428CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)
      Integration of individual two-dimensional graphene sheets into macroscopic structures is essential for the application of graphene. Graphene-based composites and macroscopic structures were recently fabricated using chem. derived graphene sheets. However, these composites and structures suffer from poor elec. cond. because of the low quality and/or high inter-sheet junction contact resistance of the chem. derived graphene sheets. Here the authors report the direct synthesis of three-dimensional foam-like graphene macrostructures, which the authors call graphene foams (GFs), by template-directed CVD. A GF consists of an interconnected flexible network of graphene as the fast transport channel of charge carriers for high elec. cond. Even with a GF loading as low as ∼0.5%, GF/poly(di-Me siloxane) composites show a very high elec. cond. of ∼10 S cm-1, which is ∼6 orders of magnitude higher than chem. derived graphene-based composites. Using this unique network structure and the outstanding elec. and mech. properties of GFs, as an example, the authors demonstrate the great potential of GF/poly(di-Me siloxane) composites for flexible, foldable and stretchable conductors.
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    48. 48
      Zhao, G.; Zhang, X.; Lu, T. J.; Xu, F. Recent Advances in Electrospun Nanofibrous Scaffolds for Cardiac Tissue Engineering. Adv. Funct. Mater. 2015, 25, 5726– 5738,  DOI: 10.1002/adfm.201502142
      48
      Recent Advances in Electrospun Nanofibrous Scaffolds for Cardiac Tissue Engineering
      Zhao, Guoxu; Zhang, Xiaohui; Lu, Tian Jian; Xu, Feng
      Advanced Functional Materials (2015), 25 (36), 5726-5738CODEN: AFMDC6; ISSN:1616-301X. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Cardiovascular diseases remain the leading cause of human mortality worldwide. Some severe symptoms, including myocardial infarction and heart failure, are difficult to heal spontaneously or under systematic treatment due to the limited regenerative capacity of the native myocardium. Cardiac tissue engineering has emerged as a practical strategy to culture functional cardiac tissues and relieve the disorder in myocardium when implanted. In cardiac tissue engineering, the design of a scaffold is closely relevant to the function of the regenerated cardiac tissues. Nanofibrous materials fabricated by electrospinning have been developed as desirable scaffolds for tissue engineering applications because of the biomimicking structure of protein fibers in native extra cellular matrix. The versatilities of electrospinning on the polymer component, the fiber structure, and the functionalization with bioactive mols. have made the fabrication of nanofibrous scaffolds with suitable mech. strength and biol. properties for cardiac tissue engineering feasible. Here, an overview of recent advances in various electrospun scaffolds for engineering cardiac tissues, including the design of advanced electrospun scaffolds and the performance of the scaffolds in functional cardiac tissue regeneration, is provided with the aim to offer guidance in the innovation of novel electrospun scaffolds and methods for improving their potential for cardiac tissue engineering applications.
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    49. 49
      Zuo, G.; Kang, S. G.; Xiu, P.; Zhao, Y.; Zhou, R. Interactions between Proteins and Carbon-Based Nanoparticles: Exploring the Origin of Nanotoxicity at the Molecular Level. Small 2013, 9, 1546– 1556,  DOI: 10.1002/smll.201201381
      49
      Interactions between proteins and carbon-based nanoparticles: Exploring the origin of nanotoxicity at the molecular level
      Zuo, Guanghong; Kang, Seung-gu; Xiu, Peng; Zhao, Yuliang; Zhou, Ruhong
      Small (2013), 9 (9-10), 1546-1556CODEN: SMALBC; ISSN:1613-6810. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A review. The widespread application of nanomaterials has spurred an interest in the study of interactions between nanoparticles and proteins due to the biosafety concerns of these nanomaterials. In this review, a summary is presented of some of the recent studies on this important subject, esp. on the interactions of proteins with carbon nanotubes (CNTs) and metallofullerenols. Two potential mol. mechanisms have been proposed for CNTs' inhibition of protein functions. The driving forces of CNTs' adsorption onto proteins are found to be mainly hydrophobic interactions and the so-called π-π stacking between CNTs' carbon rings and proteins' arom. residues. However, there is also recent evidence showing that endohedral metallofullerenol Gd@C82(OH)22 can be used to inhibit tumor growth, thus acting as a potential nanomedicine. These recent findings have provided a better understanding of nanotoxicity at the mol. level and also suggested therapeutic potential by using nanoparticles' cytotoxicity against cancer cells.
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      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhsVKksbjI&md5=ebed653bdf1ae22f93abc68bf0f0850c
    50. 50
      Suh, C. W.; Kim, M. Y.; Choo, J. B.; Kim, J. K.; Kim, H. K.; Lee, E. K. Analysis of Protein Adsorption Characteristics to Nano-Pore Silica Particles by Using Confocal Laser Scanning Microscopy. J. Biotechnol. 2004, 112, 267– 277,  DOI: 10.1016/j.jbiotec.2004.05.005
      50
      Analysis of protein adsorption characteristics to nano-pore silica particles by using confocal laser scanning microscopy
      Suh, Chang Woo; Kim, Min Young; Choo, Jae Bum; Kim, Jong Kil; Kim, Ho Kun; Lee, Eun Kyu
      Journal of Biotechnology (2004), 112 (3), 267-277CODEN: JBITD4; ISSN:0168-1656. (Elsevier B.V.)
      The effect of av. pore size of nanopore silica particles on protein adsorption characteristics was detd. exptl. by the dissocn. const. and the adsorption capacity detd. from the Langmuir equation. As the av. pore size was increased from 2.2 to 45 nm, the BSA adsorption capacity increased from 16.8 to 84.3 mg/g-silica so as the equil. const. (from 2.6 to 9.4 mg/mL). Using confocal microscopy with fluorescence labeling, we could visualize the protein adsorption in situ and det. the min. pore size required for efficient intraparticle adsorption. The confocal microscopy anal. revealed that BSA was adsorbed mainly on the surface of the particles with a smaller pore size, but diffused further into the interstitial surface when it was sufficiently large. It was concluded that for BSA whose Stoke's diam. is ∼3.55 nm the min. pore size of about 45 nm or larger was required for a sufficient adsorption capacity.
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    51. 51
      Prager-Khoutorsky, M.; Lichtenstein, A.; Krishnan, R.; Rajendran, K.; Mayo, A.; Kam, Z.; Geiger, B.; Bershadsky, A. D. Fibroblast Polarization Is a Matrix-Rigidity-Dependent Process Controlled by Focal Adhesion Mechanosensing. Nat. Cell Biol. 2011, 13, 1457– 1465,  DOI: 10.1038/ncb2370
      51
      Fibroblast polarization is a matrix-rigidity-dependent process controlled by focal adhesion mechanosensing
      Prager-Khoutorsky, Masha; Lichtenstein, Alexandra; Krishnan, Ramaswamy; Rajendran, Kavitha; Mayo, Avi; Kam, Zvi; Geiger, Benjamin; Bershadsky, Alexander D.
      Nature Cell Biology (2011), 13 (12), 1457-1465CODEN: NCBIFN; ISSN:1465-7392. (Nature Publishing Group)
      Cell elongation and polarization are basic morphogenetic responses to extracellular matrix adhesion. The authors demonstrate here that human cultured fibroblasts readily polarize when plated on rigid, but not on compliant, substrates. On rigid surfaces, large and uniformly oriented focal adhesions are formed, whereas cells plated on compliant substrates form numerous small and radially oriented adhesions. Live-cell monitoring showed that focal adhesion alignment precedes the overall elongation of the cell, indicating that focal adhesion orientation may direct cell polarization. SiRNA-mediated knockdown of 85 human protein tyrosine kinases (PTKs) induced distinct alterations in the cell polarization response, as well as diverse changes in cell traction force generation and focal adhesion formation. Remarkably, changes in rigidity-dependent traction force development, or focal adhesion mechanosensing, were consistently accompanied by abnormalities in the cell polarization response. The authors propose that the different stages of cell polarization are regulated by multiple, PTK-dependent mol. checkpoints that jointly control cell contractility and focal-adhesion-mediated mechanosensing.
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    52. 52
      El-Mohri, H.; Wu, Y.; Mohanty, S.; Ghosh, G. Impact of Matrix Stiffness on Fibroblast Function. Mater. Sci. Eng., C 2017, 74, 146– 151,  DOI: 10.1016/j.msec.2017.02.001
      52
      Impact of matrix stiffness on fibroblast function
      El-Mohri, Hichem; Wu, Yang; Mohanty, Swetaparna; Ghosh, Gargi
      Materials Science & Engineering, C: Materials for Biological Applications (2017), 74 (), 146-151CODEN: MSCEEE; ISSN:0928-4931. (Elsevier B.V.)
      Chronic non-healing wounds, caused by impaired prodn. of growth factors and reduced vascularization, represent a significant burden to patients, health care professionals, and health care system. While several wound dressing biomaterials have been developed, the impact of the mech. properties of the dressings on the residing cells and consequently on the healing of the wounds is largely overlooked. The primary focus of this study is to explore whether manipulation of the substrate mechanics can regulate the function of fibroblasts, particularly in the context of their angiogenic activity. A photocrosslinkable hydrogel platform with orthogonal control over gel modulus and cell adhesive sites was developed to explore the quant. relationship between ECM compliance and fibroblast function. Increase in matrix stiffness resulted in enhanced fibroblast proliferation and stress fiber formation. However, the angiogenic activity of fibroblasts was found to be optimum when the cells were seeded on compliant matrixes. Thus, the observations suggest that the stiffness of the wound dressing material may play an important role in the progression of wound healing.
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    53. 53
      Sun, Y.; Chen, C. S.; Fu, J. Forcing Stem Cells to Behave: A Biophysical Perspective of the Cellular Microenvironment. Annu. Rev. Biophys. 2012, 41, 519– 542,  DOI: 10.1146/annurev-biophys-042910-155306
      53
      Forcing stem cells to behave: a biophysical perspective of the cellular microenvironment
      Sun, Yubing; Chen, Christopher S.; Fu, Jianping
      Annual Review of Biophysics (2012), 41 (), 519-542CODEN: ARBNCV; ISSN:1936-122X. (Annual Reviews Inc.)
      A review. Phys. factors in the local cellular microenvironment, including cell shape and geometry, matrix mechanics, external mech. forces, and nanotopog. features of the extracellular matrix, can all have strong influences on regulating stem cell fate. Stem cells sense and respond to these insol. biophys. signals through integrin-mediated adhesions and the force balance between intracellular cytoskeletal contractility and the resistant forces originated from the extracellular matrix. Importantly, these mechanotransduction processes can couple with many other potent growth-factor-mediated signaling pathways to regulate stem cell fate. Different bioengineering tools and microscale/nanoscale devices have been successfully developed to engineer the phys. aspects of the cellular microenvironment for stem cells, and these tools and devices have proven extremely powerful for identifying the extrinsic phys. factors and their downstream intracellular signaling pathways that control stem cell functions.
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      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38Xpt1yhsLg%253D&md5=6cd350069a081e65d8e2e130b20b43d1
    54. 54
      Moreno-Arotzena, O.; Borau, C.; Movilla, N.; Vicente-Manzanares, M.; García-Aznar, J. M. Fibroblast Migration in 3D Is Controlled by Haptotaxis in a Non-Muscle Myosin II-Dependent Manner. Ann. Biomed. Eng. 2015, 43, 3025– 3039,  DOI: 10.1007/s10439-015-1343-2
      54
      Fibroblast Migration in 3D is Controlled by Haptotaxis in a Non-muscle Myosin II-Dependent Manner
      Moreno-Arotzena O; Borau C; Movilla N; Garcia-Aznar J M; Vicente-Manzanares M
      Annals of biomedical engineering (2015), 43 (12), 3025-39 ISSN:.
      Cell migration in 3D is a key process in many physiological and pathological processes. Although valuable knowledge has been accumulated through analysis of various 2D models, some of these insights are not directly applicable to migration in 3D. In this study, we have confined biomimetic hydrogels within microfluidic platforms in the presence of a chemoattractant (platelet-derived growth factor-BB). We have characterized the migratory responses of human fibroblasts within them, particularly focusing on the role of non-muscle myosin II. Our results indicate a prominent role for myosin II in the integration of chemotactic and haptotactic migratory responses of fibroblasts in 3D confined environments.
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    55. 55
      Turner, C. E. Paxillin and Focal Adhesion Signalling. Nat. Cell Biol. 2000, 2, E231– E236,  DOI: 10.1038/35046659
      55
      Paxillin and focal adhesion signalling
      Turner, Christopher E.
      Nature Cell Biology (2000), 2 (12), E231-E236CODEN: NCBIFN; ISSN:1465-7392. (Nature Publishing Group)
      A review with 78 refs. To facilitate a rapid response to environmental change, cells use scaffolding-or adaptor-proteins to recruit key components of their signal-transduction machinery to specific subcellular locations. Paxillin is a multi-domain adaptor found at the interface between the plasma membrane and the actin cytoskeleton. Here it provides a platform for the integration and process of adhesion- and growth factor-related signals.
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      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXptFShtbw%253D&md5=44337121595d2137d9a1a3496ea46b80
    56. 56
      Chiu, C.-L.; Aguilar, J. S.; Tsai, C. Y.; Wu, G.; Gratton, E.; Digman, M. M. A.; Kuo, J.; Han, X.; Hsiao, C.; Iii, J. Y. Nanoimaging of Focal Adhesion Dynamics in 3D. PLoS One 2014, 9, e99896,  DOI: 10.1371/journal.pone.0099896
      56
      Nanoimaging of focal adhesion dynamics in 3D
      Chiu, Chi-Li; Aguilar, Jose S.; Tsai, Connie Y.; Wu, GuiKai; Gratton, Enrico; Digman, Michelle A.
      PLoS One (2014), 9 (6), e99896/1-e99896/10, 10 pp.CODEN: POLNCL; ISSN:1932-6203. (Public Library of Science)
      Organization and dynamics of focal adhesion proteins have been well characterized in cells grown on two-dimensional (2D) cell culture surfaces. However, much less is known about the dynamic assocn. of these proteins in the 3D microenvironment. Limited imaging technologies capable of measuring protein interactions in real time and space for cells grown in 3D is a major impediment in understanding how proteins function under different environmental cues. In this study, we applied the nano-scale precise imaging by rapid beam oscillation (nSPIRO) technique and combined the scaning-fluorescence correlation spectroscopy (sFCS) and the no. and mol. brightness (N&B) methods to investigate paxillin and actin dynamics at focal adhesions in 3D. Both MDA-MB-231 cells and U2OS cells produce elongated protrusions with high intensity regions of paxillin in cell grown in 3D collagen matrixes. Using sFCS we found higher percentage of slow diffusing proteins at these focal spots, suggesting assembling/disassembling processes. In addn., the N&B anal. shows paxillin aggregated predominantly at these focal contacts which are next to collagen fibers. At those sites, actin showed slower apparent diffusion rate, which indicated that actin is either polymg. or binding to the scaffolds in these locals. Our findings demonstrate that by multiplexing these techniques we have the ability to spatially and temporally quantify focal adhesion assembly and disassembly in 3D space and allow the understanding tumor cell invasion in a more complex relevant environment.
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      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhs1aqsLzF&md5=451079bcae5fc01b08969af791e9ae3c
    57. 57
      Ryoo, S. R.; Kim, Y. K.; Kim, M. H.; Min, D. H. Behaviors of NIH-3T3 Fibroblasts on Graphene/Carbon Nanotubes: Proliferation, Focal Adhesion, and Gene Transfection Studies. ACS Nano 2010, 4, 6587– 6598,  DOI: 10.1021/nn1018279
      57
      Behaviors of NIH-3T3 Fibroblasts on Graphene/Carbon Nanotubes: Proliferation, Focal Adhesion, and Gene Transfection Studies
      Ryoo, Soo-Ryoon; Kim, Young-Kwan; Kim, Mi-Hee; Min, Dal-Hee
      ACS Nano (2010), 4 (11), 6587-6598CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      Carbon-based materials, including graphene and carbon nanotubes, have been considered attractive candidates for biomedical applications such as scaffolds in tissue engineering, substrates for stem cell differentiation, and components of implant devices. Despite the potential biomedical applications of these materials, only limited information is available regarding the cellular events, including cell viability, adhesion, and spreading, that occur when mammalian cells interface with carbon-based nanomaterials. Here, we report behaviors of mammalian cells, specifically NIH-3T3 fibroblast cells, grown on supported thin films of graphene and carbon nanotubes to investigate biocompatibility of the artificial surface. Proliferation assay, cell shape anal., focal adhesion study, and quant. measurements of cell adhesion-related gene expression levels by RT-PCR reveal that the fibroblast cells grow well, with different nos. and sizes of focal adhesions, on graphene- and carbon nanotube-coated substrates. Interestingly, the gene transfection efficiency of cells grown on the substrates was improved up to 250% that of cells grown on a cover glass. The present study suggests that these nanomaterials hold high potential for bioapplications showing high biocompatibility, esp. as surface coating materials for implants, without inducing notable deleterious effects while enhancing some cellular functions (i.e., gene transfection and expression).
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    58. 58
      Cooper, G. M. The Cell: A Molecular Approach; ASM Press, 2000; Vol. 10.
      There is no corresponding record for this reference.
    59. 59
      Serrano, M. C.; Patiño, J.; García-Rama, C.; Ferrer, M. L.; Fierro, J. L. G.; Tamayo, A.; Collazos-Castro, J. E.; Del Monte, F.; Gutiérrez, M. C. 3D Free-Standing Porous Scaffolds Made of Graphene Oxide as Substrates for Neural Cell Growth. J. Mater. Chem. B 2014, 2, 5698– 5706,  DOI: 10.1039/C4TB00652F
      59
      3D free-standing porous scaffolds made of graphene oxide as substrates for neural cell growth
      Serrano, M. C.; Patino, J.; Garcia-Rama, C.; Ferrer, M. L.; Fierro, J. L. G.; Tamayo, A.; Collazos-Castro, J. E.; del Monte, F.; Gutierrez, M. C.
      Journal of Materials Chemistry B: Materials for Biology and Medicine (2014), 2 (34), 5698-5706CODEN: JMCBDV; ISSN:2050-7518. (Royal Society of Chemistry)
      The absence of efficient therapies for the treatment of lesions affecting the central nervous system encourages scientists to explore new materials in an attempt to enhance neural tissue regeneration while preventing inhibitory fibroglial scars. In recent years, the superlative properties of graphene-based materials have provided a strong incentive for their application in biomedicine. Nonetheless, a few attempts to date have envisioned the use of graphene for the fabrication of three-dimensional (3D) substrates for neural repair, but none of these involve graphene oxide (GOx) despite some attractive features such as higher hydrophilicity and versatility of functionalization. In this paper, we report novel, free-standing, porous and flexible 3D GOx-based scaffolds, produced by the biocompatible freeze-casting procedure named ISISA, with potential utility in neural tissue regeneration. The resulting materials were thoroughly characterized by Fourier-transform IR, Raman, and X-ray photoelectron spectroscopies and SEM, as well as flexibility testing. Embryonic neural progenitor cells were then used to investigate adhesion, morphol., viability, and neuronal/glial differentiation. Highly viable and interconnected neural networks were formed on these 3D scaffolds, contg. both neurons and glial cells and rich in dendrites, axons and synaptic connections, and the results are in agreement with those obtained in initial studies performed with two-dimensional GOx films. These results encourage further investigation in vivo on the use of these scaffolds as guide substrates to promote the repair of neural injuries.
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    60. 60
      Avery, N. C.; Bailey, A. J.; Fratzl, P. Collagen: Structure and Mechanics; Springer, 2008.
      There is no corresponding record for this reference.
    61. 61
      LeBaron, R. G.; Athanasiou, K. A. Extracellular Matrix Cell Adhesion Peptides: Functional Applications in Orthopedic Materials. Tissue Eng. 2000, 6, 85– 103,  DOI: 10.1089/107632700320720
      61
      Extracellular matrix cell adhesion peptides: functional applications in orthopedic materials
      Lebaron, Richard G.; Athanasiou, Kyriacos A.
      Tissue Engineering (2000), 6 (2), 85-103CODEN: TIENFP; ISSN:1076-3279. (Mary Ann Liebert, Inc.)
      A review with 147 refs. This review describes research on selected peptide sequences that affect cell adhesion as it applies in orthopedic applications. Of particular interest are the integrin-binding RGD peptides and heparin-binding peptides. The influence of these peptides on cell adhesion is described. Cell adhesion is defined as a sequence of four steps: cell attachment, cell spreading, organization of an actin cytoskeleton, and formation of focal adhesions. RGD sequences clearly influence cell attachment and spreading, whereas heparin-binding sequences appear to be less efficient. Collectively, these sequences appear to promote all steps of cell adhesion in certain cell types. This review also addresses issues related to peptide immobilization, as well as potential complexities that may develop as a result of using these versatile cell-binding sequences. Also described are future directions in the field concerning use of existing and more sophisticated peptide substrata.
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    62. 62
      Marx, J.; Lewke, M. R. D.; Smazna, D.; Mishra, Y. K.; Adelung, R.; Schulte, K.; Fiedler, B. Processing, Growth Mechanism and Thermodynamic Calculations of Carbon Foam with a Hollow Tetrapodal Morphology – Aerographite. Appl. Surf. Sci. 2019, 470, 535– 542,  DOI: 10.1016/j.apsusc.2018.11.016
      62
      Processing, growth mechanism and thermodynamic calculations of carbon foam with a hollow tetrapodal morphology - Aerographite
      Marx, J.; Lewke, M. R. D.; Smazna, D.; Mishra, Y. K.; Adelung, R.; Schulte, K.; Fiedler, B.
      Applied Surface Science (2019), 470 (), 535-542CODEN: ASUSEE; ISSN:0169-4332. (Elsevier B.V.)
      Aerographite is a 3D interconnected carbon foam with a tetrapodal morphol. The synthesis of Aerographite is based on a 2-step process: first the prodn. of a zinc oxide (ZnO) template in a flame transport synthesis (FTS) followed by the replication into the carbon structure in a chem. vapor deposition process (CVD). This study presents a growth model of this 3D carbon foam via analyzing the newly formed carbon structure in an interrupted synthesis by SEM, transmission electron microscopy (TEM), and Raman spectroscopy. Moreover, the Gibbs free energy of the occurred replica CVD (rCVD) process, based on the redn. of ZnO and the formation of carbon layers, was calcd. During the CVD process the injected carbon deposits on the surfaces of the ZnO tetrapods, while simultaneously the replication into the carbon structure takes place, as a result of the redn. of ZnO into gaseous zinc and water vapor, which is due to the reaction of ZnO with the hydrogen (H2) from the injected source. This replication of the ZnO template into a carbon structure is based on an epitaxial controlled process combined with a catalytic graphitization, whereby the morphol. of the template structure is replicated by the carbon. Furthermore, the influence of the growth process on the arrangement of carbon in layers and formation of defects was explained.
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    63. 63
      Wang, F.; Torrisi, F.; Jiang, Z.; Popa, D.; Hasan, T.; Sun, Z.; Cho, W.; Ferrari, A. C. Graphene Passively Q-Switched Two-Micron Fiber Lasers. In Conference on Lasers and Electro-Optics (CLEO); OSA Technical Digest (Optical Society of America): San Jose, CA, 2012; p JW2A 72.
      There is no corresponding record for this reference.
    64. 64
      Purdie, D. G.; Popa, D.; Wittwer, V. J.; Jiang, Z.; Bonacchini, G.; Torrisi, F.; Milana, S.; Lidorikis, E.; Ferrari, A. C. Few-Cycle Pulses from a Graphene Mode-Locked All-Fiber Laser. Appl. Phys. Lett. 2015, 106, 253101,  DOI: 10.1063/1.4922397
      There is no corresponding record for this reference.
    65. 65
      Bianchi, V.; Carey, T.; Viti, L.; Li, L.; Linfield, E. H.; Davies, A. G.; Tredicucci, A.; Yoon, D.; Karagiannidis, P. G.; Lombardi, L.; Tomarchio, F.; Ferrari, A. C.; Torrisi, F.; Vitiello, M. S. Terahertz Saturable Absorbers from Liquid Phase Exfoliation of Graphite. Nat. Commun. 2017, 8, 15763,  DOI: 10.1038/ncomms15763
      65
      Terahertz saturable absorbers from liquid phase exfoliation of graphite
      Bianchi, Vezio; Carey, Tian; Viti, Leonardo; Li, Lianhe; Linfield, Edmund H.; Davies, A. Giles; Tredicucci, Alessandro; Yoon, Duhee; Karagiannidis, Panagiotis G.; Lombardi, Lucia; Tomarchio, Flavia; Ferrari, Andrea C.; Torrisi, Felice; Vitiello, Miriam S.
      Nature Communications (2017), 8 (), 15763CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
      Saturable absorbers (SA) operating at terahertz (THz) frequencies can open new frontiers in the development of passively mode-locked THz micro-sources. Here we report the fabrication of THz SAs by transfer coating and inkjet printing single and few-layer graphene films prepd. by liq. phase exfoliation of graphite. Open-aperture z-scan measurements with a 3.5 THz quantum cascade laser show a transparency modulation ∼80%, almost one order of magnitude larger than that reported to date at THz frequencies. Fourier-transform IR spectroscopy provides evidence of intraband-controlled absorption bleaching. These results pave the way to the integration of graphene-based SA with elec. pumped THz semiconductor micro-sources, with prospects for applications where excitation of specific transitions on short time scales is essential, such as time-of-flight tomog., coherent manipulation of quantum systems, time-resolved spectroscopy of gases, complex mols. and cold samples and ultra-high speed communications, providing unprecedented compactness and resoln.
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    66. 66
      Lotya, M.; Hernandez, Y.; King, P. J.; Smith, R. J.; Nicolosi, V.; Karlsson, L. S.; Blighe, F. M.; De, S.; Wang, Z.; McGovern, I. T.; Duesberg, G. S.; Coleman, J. N. Liquid Phase Production of Graphene by Exfoliation of Graphite in Surfactant/Water Solutions. J. Am. Chem. Soc. 2009, 131, 3611– 3620,  DOI: 10.1021/ja807449u
      66
      Liquid Phase Production of Graphene by Exfoliation of Graphite in Surfactant/Water Solutions
      Lotya, Mustafa; Hernandez, Yenny; King, Paul J.; Smith, Ronan J.; Nicolosi, Valeria; Karlsson, Lisa S.; Blighe, Fiona M.; De, Sukanta; Wang, Zhiming; McGovern, I. T.; Duesberg, Georg S.; Coleman, Jonathan N.
      Journal of the American Chemical Society (2009), 131 (10), 3611-3620CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      The authors demonstrated a method to disperse and exfoliate graphite to give graphene suspended in water-surfactant solns. Optical characterization of these suspensions allowed the partial optimization of the dispersion process. TEM showed the dispersed phase to consist of small graphitic flakes. More than 40% of these flakes had <5 layers with ∼3% of flakes consisting of monolayers. At. resoln. TEM shows the monolayers to be generally free of defects. The dispersed graphitic flakes are stabilized against reaggregation by Coulomb repulsion due to the adsorbed surfactant. The authors use DLVO and Hamaker theory to describe this stabilization. However, the larger flakes tend to sediment out over ∼6 wk, leaving only small flakes dispersed. It is possible to form thin films by vacuum filtration of these dispersions. Raman and IR spectroscopic anal. of these films suggests the flakes to be largely free of defects and oxides, although XPS shows evidence of a small oxide population. Individual graphene flakes can be deposited onto mica by spray coating, allowing statistical anal. of flake size and thickness. Vacuum filtered films are reasonably conductive and are semitransparent. Further improvements may result in the development of cheap transparent conductors.
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    67. 67
      Carey, T.; Jones, C.; Le Moal, F.; Deganello, D.; Torrisi, F. Spray Coating Thin Films on Three-Dimensional Surfaces for a Semi-Transparent Capacitive Touch Device. ACS Appl. Mater. Interfaces 2018, 10, 19948– 19956,  DOI: 10.1021/acsami.8b02784
      There is no corresponding record for this reference.
    68. 68
      Kravets, V. G.; Grigorenko, A. N.; Nair, R. R.; Blake, P.; Anissimova, S.; Novoselov, K. S.; Geim, A. K. Spectroscopic Ellipsometry of Graphene and an Exciton-Shifted van Hove Peak in Absorption. Phys. Rev. B: Condens. Matter Mater. Phys. 2010, 81, 155413,  DOI: 10.1103/PhysRevB.81.155413
      68
      Spectroscopic ellipsometry of graphene and an exciton-shifted van Hove peak in absorption
      Kravets, V. G.; Grigorenko, A. N.; Nair, R. R.; Blake, P.; Anissimova, S.; Novoselov, K. S.; Geim, A. K.
      Physical Review B: Condensed Matter and Materials Physics (2010), 81 (15), 155413/1-155413/6CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
      The authors demonstrate that optical transparency of any two-dimensional system with a sym. electronic spectrum is governed by the fine structure const. and suggest a simple formula that relates a quasiparticle spectrum to an optical absorption of such a system. These results are applied to graphene deposited on a surface of oxidized silicon for which the authors measure ellipsometric spectra, ext. optical consts. of a graphene layer, and reconstruct the electronic dispersion relation near the K point using optical transmission spectra. The authors also present spectroscopic ellipsometry anal. of graphene placed on amorphous quartz substrates and report a pronounced peak in UV absorption at 4.6 eV because of a van Hove singularity in graphene's d. of states. The peak is asym. and down-shifted by 0.5 eV, probably due to excitonic effects.
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    69. 69
      Selhuber-Unkel, C.; Erdmann, T.; López-García, M.; Kessler, H.; Schwarz, U. S.; Spatz, J. P. Cell Adhesion Strength Is Controlled by Intermolecular Spacing of Adhesion Receptors. Biophys. J. 2010, 98, 543– 551,  DOI: 10.1016/j.bpj.2009.11.001
      69
      Cell adhesion strength is controlled by intermolecular spacing of adhesion receptors
      Selhuber-Unkel, C.; Erdmann, T.; Lopez-Garcia, M.; Kessler, H.; Schwarz, U. S.; Spatz, J. P.
      Biophysical Journal (2010), 98 (4), 543-551CODEN: BIOJAU; ISSN:0006-3495. (Cell Press)
      Spatial patterning of biochem. cues on the micro- and nanometer scale controls numerous cellular processes such as spreading, adhesion, migration, and proliferation. Using force microscopy the authors show that the lateral spacing of individual integrin receptor-ligand bonds dets. the strength of cell adhesion. For spacings ≥90 nm, focal contact formation was inhibited and the detachment forces as well as the stiffness of the cell body were significantly decreased compared to spacings ≤50 nm. Analyzing cell detachment at the subcellular level revealed that rupture forces of focal contacts increase with loading rate as predicted by a theor. model for adhesion clusters. Furthermore, the authors show that the weak link between the intra- and extracellular space is at the intracellular side of a focal contact. The authors' results show that cells can amplify small differences in adhesive cues to large differences in cell adhesion strength.
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    70. 70
      Wörle-Knirsch, J. M.; Pulskamp, K.; Krug, H. F. Oops They Did It Again! Carbon Nanotubes Hoax Scientists in Viability Assays. Nano Lett. 2006, 6, 1261– 1268,  DOI: 10.1021/nl060177c
      70
      Oops they did it again! Carbon nanotubes hoax scientists in viability assays
      Worle-Knirsch J M; Pulskamp K; Krug H F
      Nano letters (2006), 6 (6), 1261-8 ISSN:1530-6984.
      New materials of emerging technological importance are single-walled carbon nanotubes (SWCNTs). Because SWCNTs will be used in commercial products in huge amounts, their effects on human health and the environment have been addressed in several studies. Inhalation studies in vivo and submerse applications in vitro have been described with diverging results. Why some indicate a strong cytotoxicity and some do not is what we report on here. Data from A549 cells incubated with carbon nanotubes fake a strong cytotoxic effect within the MTT assay after 24 h that reaches roughly 50%, whereas the same treatment with SWCNTs, but detection with WST-1, reveals no cytotoxicity. LDH, FACS-assisted mitochondrial membrane potential determination, and Annexin-V/PI staining also reveal no cytotocicity. SWCNTs appear to interact with some tetrazolium salts such as MTT but not with others (such as WST-1, INT, XTT). This interference does not seem to affect the enzymatic reaction but lies rather in the insoluble nature of MTT-formazan. Our findings strongly suggest verifying cytotoxicity data with at least two or more independent test systems for this new class of materials (nanomaterials). Moreover, we intensely recommend standardizing nanotoxicological assays with regard to the material used: there is a clear need for reference materials. MTT-formazan crystals formed in the MTT reaction are lumped with nanotubes and offer a potential mechanism to guide bioremediation and clearance for SWCNTs from "contaminated" tissue. SWCNTs are good supporting materials for tissue growth, as attachment of focal adhesions and connections to the cytoskeleton suggest.
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  • Supporting Information

    Supporting Information

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    The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.8b17627.

    • Optical absorption spectrum of graphene ink (Figure S1); SEM images of ZnO templates (Figures S2–S4); different 3D carbon tube structures (Figure S5); SEM images of AG–CNTT structures (Figure S6); long-cycle compression test graph of AG–G scaffold (Figure S7); high-magnification fluorescence image of REF52 YFP-paxillin cells (Figure S8); supporting discussion (PDF)

    • Structural integrity of AG–G scaffold (AVI)


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