2.1 Preparation of Silk Fibroin Methacryloyl
2.1.1 Preparation of photoinitiator LAP
The product of SilMA was purchased from Engineering For Life (Suzhou, China). Firstly, we should prepare the solution of LAP according to the instructions. In brief, 20 mL PBS was added into the brown bottle containing 0.05 g photoinitiator LAP in solid state. The solution was dissolved in 40-50 ℃ water bath for 15 min, and be shaken several times during the period. The standard solution of LAP was successfully prepared and stored in the refrigerator (4 ℃), protected against exposure to light.
2.1.2 Preparation of SilMA hydrogel
As recommended, the SilMA with concentration of 10%, 15% and 20% were prepared. The required mass of solid SilMA was taken and put into the centrifuge tube, then the corresponding volume of standard solution of LAP was added. The SilMA solution was dissolved at room temperature for 0.5-1 h, and be shaken several times during the period (avoid violent ultrasound, high temperature and strong shear). The sterile SilMA solution could be prepared by filtered with syringe filter of 0.22 μM pore size (Biosharp, Hefei, China). The mechanical properties, especially the hardness of hydrogel can be readily adjusted by changing the UV irradiation time to meet the needs of different tissues and experimental requirements,[17] so is SilMA hydrogel. In this study, the solution was irradiated with 405 nm light source for 1 min to make SilMA hydrogel.