Sequentially-crosslinked bioactive hydrogels as nano-patterned substrates with customizable stiffness and degradation for corneal tissue engineering applications

Naturally-bioactive hydrogels like gelatin provide favorable properties for tissue-engineering but lack sufficient mechanical strength for use as implantable tissue engineering substrates. Complex fabrication or multi-component additives can improve material strength, but often compromises other properties. Studies have shown gelatin methacrylate (GelMA) as a bioactive hydrogel with diverse tissue growth applications. We hypothesize that, with suitable material modifications, GelMA could be employed for growth and implantation of tissue-engineered human corneal endothelial cell (HCEC) monolayer. Tissue-engineered HCEC monolayer could potentially be used to treat corneal blindness due to corneal endothelium dysfunction. Here, we exploited a sequential hybrid (physical followed by UV) crosslinking to create an improved material, named as GelMA+, with over 8-fold increase in mechanical strength as compared to regular GelMA. The presence of physical associations increased the subsequent UV-crosslinking efficiency resulting in robust materials able to withstand standard endothelium insertion surgical device loading. Favorable biodegradation kinetics were also measured in vitro and in vivo. We achieved hydrogels patterning with nano-scale resolution by use of oxygen impermeable stamps that overcome the limitations of PDMS based molding processes. Primary HCEC monolayers grown on GelMA+ carrier patterned with pillars of optimal dimension demonstrated improved zona-occludin-1 expression, higher cell density and cell size homogeneity, which are indications of functionally-superior transplantable monolayers. The hybrid crosslinking and fabrication approach offers potential utility for development of implantable tissue-engineered cell-carrier constructs with enhanced bio-functional properties.