The Photocleavable Protein PhoCl-Based Dynamic Hydrogels.

Dynamic protein hydrogels have attracted increasing attention owing to their tunable physiochemical and mechanical properties, customized functionality, and biocompatibility. Among the different types of dynamic hydrogels, photoresponsive hydrogels are of particular interest. Here, we report the engineering of a photoresponsive protein hydrogel by using the photocleavable protein PhoCl. We employed the well-developed SpyTag and SpyCatcher chemistry to engineer PhoCl-containing covalently cross-linked hydrogels. In the hydrogel network, PhoCl, which can be cleaved into two fragments upon violet irradiation, is employed as a dynamic structural motif to regulate the cross-linking density of the hydrogel network. The resultant PhoCl-containing hydrogels showed photoresponsive viscoelastic properties. Upon violet irradiation, the PhoCl hydrogels soften, leading to an irreversible reduction in the storage moduli. However, no gel-sol transition was observed. Leveraging this light-induced stiffness change, we employed this hydrogel as a cell culture substrate to investigate the mechanobiological response of NIH-3T3 fibroblast cells. Our results showed that 3T3 cells can change their morphologies in response to the stiffness change of the PhoCl hydrogel substrate dynamically, rendering PhoCl-based hydrogels a useful substrate for other mechanobiological studies.