2.4 FTIR analysis
GelMA was dissolved in DPBS at a concentration of 50 mg/ml for 2 hours
at 37 ℃. After GelMA was completely dissolved, 1 m/v
2-Hydroxy-4’-(2-hydroxyethoxy)-2-methylpropiophenone (irgacure 2959,
Sigma-Aldrich, USA) was added. The mixture was crosslinked for 5, 10,
20, 40, 60, 80 and 100s with the wavelength of 365 mm and the intensity
of 200 mV/cm2 to get different samples with different
crosslinking time. The samples were lyophilized and analyzed by FTIR-ATR
spectroscopy (Frontier, PerkinElmer, Rodgau, UK). All samples were
scanned 5 times at 400-4000 cm-1 with a resolution of
4 cm-1. Gelatin was used as a control.