Synthesis of Porcine and Fish Skin GelMA

The synthesis of GelMA was performed based on our previously reported method [33 (link), 34 (link)].First, 10.0 g of porcine gelatin (Sigma-Aldrich, USA) was dissolved in 100 mL of phosphate-buffered saline (PBS, Sigma-Aldrich) solution with heated stirring (50 °C), and then 5 mL of methacrylic anhydride (Sigma-Aldrich) was added dropwise with an extra 2 hours (h) of reaction. This reaction was stopped by the addition of 100 mL of warm PBS for 10 minutes (min). The final solution was dialyzed for up to 5 days using 12–14-kDa dialysis tubes (Spectrum Laboratories, USA) at 40 °C, followed by lyophilization with a freeze-dryer (Labconco, USA). The GelMA derived from porcine was termed pGelMA. By contrast, the GelMA derived from gelatin of cold-water fish skin (Sigma-Aldrich), termed as fGelMA, was synthesized using the same process, except that the addition amount of methacrylic anhydride was 8 mL [35 (link)].