2.5 Preparation sample of GelMA solutions
GelMA solutions consisted of 50 mg/ml GelMA, 30 mg/ml Gelatin, 3.5 mg/ml sodium hyaluronate (HA), 10% v/v glycerol, and 1% m/v Irgacure 2959 in DPBS water. Gelatin and glycerol could increase the printability and HA could increase the biocompatibility of GelMA hydrogel(Xu et al., 2020). The mixture was cast in a mold and crosslinked for 5, 10, 20, 40, 60, 80, 100s under the UV light with a wavelength of 365 nm and the intensity of 200 mV/cm2 to make a sample with 1 cm in diameter and 2 mm in thickness.