Injectable hydrogels have previously demonstrated potential as a temporary scaffold for tissue regeneration or as a delivery vehicle for cells, growth factors, or drugs. However, most injectable hydrogel systems lack a microporous structure, preventing host cell migration into the hydrogel interior and limiting spreading and proliferation of encapsulated cells. Herein, an injectable microporous hydrogel assembled from gelatin/gelatin methacryloyl (GelMA) composite microgels is described. Microgels are produced by a water-in-oil emulsion using a gelatin/GelMA aqueous mixture. These microgels show improved thermal stability compared to GelMA-only microgels and benefit from combined photopolymerization using UV irradiation (365 nm) in the presence of a photoinitiator (PI) and enzymatic reaction by microbial transglutaminase (mTG), which together enable fast curing and tissue adhesion of the hydrogel. The dual-crosslinking approach also allows for the reduction of PI concentration and minimizes cytotoxicity during photopolymerization. When applied for in situ cell encapsulation, encapsulated human dermal fibroblasts and human mesenchymal stem cells (hMSCs) are able to rapidly spread and proliferate in the pore space of the hydrogel. This hydrogel has the potential to enhance hMSC anti-inflammatory behavior through the demonstrated secretion of prostaglandin E2 (PGE2) and interleukin-6 (IL-6) by encapsulated cells. Altogether, this injectable formulation has the potential to be used as a cell delivery vehicle for various applications in regenerative medicine.
