2.2 1H-Nuclear Magnetic Resonance (1H-NMR) analysis
GelMA was confirmed by 1H-NMR. 30 mg/ml GelMA was dissolved in deuterium oxide (D2O) (Sigma-Aldrich, USA) at 40℃. 1H-NMR spectra were obtained by NMR spectroscopy with a single axis gradient at 400 MHz (1H-NMR, Bruker, Billerica, MA). Gelatin was used as a control.