Injectable gelatin-PEG hydrogels obtained via cytochrome C-mediated polymerization.

Injectable hydrogels capable of in situ gelation under physiological conditions are highly attractive for minimally invasive surgery and locoregional drug delivery. We herein report three novel injectable hydrogels composed of gelatin methacrylate (GelMA) and poly(ethyleneglycol) dimethacrylate (PEGDA), crosslinked through a Fenton-like radical polymerization mediated by cytochrome C (CyC) in the presence of H2O2 and L-ascorbic acid. To the best of our knowledge, this is the first example of an injectable hydrogel formulation in which CyC is used as a redox mediator for radical polymerization. CyC enables the replacement of transition metals while maintaining polymerization kinetics comparable to those of hydrogels synthesized via traditional Fenton systems. The resulting hydrogels, undergoing a sol-gel transition within 1.0 and 2.0 minutes, are biocompatible, and their properties are highly tunable. Indeed, rheological analysis showed that mechanical properties and the linear viscoelastic region (LVR) can be easily modulated by varying the concentrations of the starting methacryl-functionalized gelatin and the crosslinker. Structural characterization and biodegradation studies revealed that enzymatic degradation is strongly dependent on the degree of crosslinking. All hydrogels were readily injectable and showed no detectable cytotoxicity in conditioned-medium assays. Sustained release of rhodamine 101, as a drug-mimicking system, reached ∼70% over 7 days.