Photopolymerization has been a favorable method to prepare hydrogels for in situ cell encapsulation for tissue engineering applications. The major benefits of light-mediated gelation include rapid and ambient gelation conditions, as well as high tunability in polymerization kinetics.  A widely adopted method to prepare cell-laden hydrogels is through cross-linking of hydrophilic vinyl polymers (e.g., poly(ethylene glycol) diacrylate or PEGDA) with a cleavage-type photoinitiator (e.g., Irgacure 2959) and ultraviolet light (UV) exposure. However, the use of UV light sources for cell encapsulation often invites critics regarding biosafety. Although a visible light source can be used to eliminate the risks associated with UV light, conventional visible light gelation systems often involve the use of photosensitizer (e.g., eosin-Y, rose bengal), cytotoxic co-initiators (e.g., triethanolamine), and co-monomers (e.g., N-vinylpyrrolidone). The additional co-initiators or co-monomers components often offset the benefits of visible light. In this contribution, we report innovative visible light mediated hydrogel systems formed by step-growth thiol-vinyl photopolymerizations. A non-cleavage type visible light photosensitizer eosin-Y was used to generate thiyl radicals from thiol-containing cross-linkers and initiates rapid gelation. Various cytocompatible vinyl macromers (e.g., PEG-tetra-norbornene, PEG-tetra-acrylate, and PEG-tetra-acrylamide) and thiol-containing cross-linkers (e.g., dithiothreitol, bis-cysteine bearing peptides) were explored for synthesizing highly cytocompatible cell-laden and responsive hydrogels. No cytotoxic components are required in our rapid step-growth gelation systems. In addition to characterizing gelation kinetics, we have demonstrated the utility of these new visible light mediated gelation systems in several biomaterials and tissue engineering applications, including synthesis of multi-structural and photodegradable hydrogels, as well as promoting the survival and differentiation of human mesenchymal stem cells.

Visible light mediated thiol-vinyl photopolymerized hydrogels for 3D cell culture

246th National Meeting (2013)

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