Macroporous silk fibroin cryogels

Silk fibroin cryogels with remarkable properties were obtained from frozen fibroin solutions (4.2-12.6%) at subzero temperatures between -5 and -22 °C. This was achieved by the addition of ethylene glycol diglycidyl ether (EGDE) into the cryogelation system. EGDE triggers the conformational transition of fibroin from random coil to β-sheet structure and hence fibroin gelation. One of the unique features of fibroin cryogels is their elasticity that allows them to resist complete compression without any crack development, during which water inside the cryogel is removed. The compressed cryogel immediately swells during unloading to recover its original shape. The scaffolds obtained by freeze-drying of the cryogels consist of regular, interconnected pores of diameters ranging from 50 to 10 μm that could be regulated by the synthesis parameters. The mechanical compressive strength and the modulus of the scaffolds increase with decreasing pore diameter, that is, with decreasing gelation temperature or, with increasing fibroin or EGDE concentrations in the feed. The scaffolds produced at 12.6% fibroin exhibit a very high compressive modulus (50 MPa) making them good candidates as bone scaffold materials.