The degree of functionalization or methacrylation of gelatins was assessed using proton nuclear magnetic resonance ( 1 H NMR) spectroscopy, following a previously reported method. All NMR spectra were recorded using a Bruker Advance 500 spectrometer (Bruker Scientific Inc., USA). To prepare the samples for NMR analysis, 20 mg of freeze-dried functionalized gelatin and unmodified gelatin were dissolved in 1.5 mL of deuterium oxide (D2O) at 40°C.