Microstructures of the crosslinked silk fibroin hydrogels: (A) SEM images of the freeze-dried hydrogels, the insets were the magnified surface morphologies of the porous walls; (B) AFM images of the different hydrogels. The samples were as follows: (a) R3-SN1, the ratio of RSF and SNF was 3:1; (b) R4-SN1, the ratio of RSF and SNF was 4:1; (c) R6-SN1, the ratio of RSF and SNF was 6:1; (d) R12-SN1, the ratio of RSF and SNF was 12:1; (e) R100, pure RSF hydrogel.