Gelatin methacrylate was synthesized according to an earlier protocol.[56 (link)] Briefly, a 10% w/v gelatin (porcine skin, Sigma) solution in phosphate buffered saline (PBS) was prepared and heated to 60 °C with constant mixing. After the gelatin was dissolved completely, the temperature was reduced to 50 °C and allowed to reach steady state. After the solution temperature reached 50 °C, methacrylic anhydride (Sigma) was slowly added to the solution to achieve a 5:1 volumetric ratio of gelatin solution : methacrylic anhydride solution. The typical basis reaction volume consisted of 50 ml gelatin solution. Subsequently, the mixture was allowed to react for one hour at 50 °C with continual mixing. After one hour, warmed PBS (40 °C) heated in a secondary beaker was added at a 4:1 volume ratio to the gelatin-methacrylic anhydride solution to deactivate the reaction. Subsequently, the resulting mixture was added to 10 kDa dialysis tubing and the tubing was placed in reverse osmosis water and allowed to dialyze for one week. To ensure effective separation, the dialysis solution was replaced with fresh solution daily. Following the dialysis procedure, the gelatin mixture was lyophilized until dry.