Stretchable silk fibroin hydrogels

Hydrogels derived from silk fibroin (SF) are attractive soft materials in biomedical applications such as drug delivery and tissue engineering. However, SF hydrogels reported so far are generally brittle in tension limiting their load-bearing applications. We present here a novel strategy for preparing stretchable SF hydrogels by incorporating flexible polymer chains into the brittle SF network, which strengthen the interconnections between SF globules. We included N, N-dimethylacrylamide (DMAA) monomer and ammonium persulfate initiator into an aqueous SF solution containing a diepoxide cross-linker to in situ generate flexible poly (N,N-dimethylacrylamide) (PDMAA) chains. Moreover, instead of SF, methacrylated SF was used for the gel preparation to create an interconnected SF/PDMAA network. The free-radical polymerization of DMAA leads to the formation of PDMAA chains interconnecting globular SF molecules via their pendant vinyl groups. Incorporation of 2 w/v% DMAA into the SF network turns the brittle hydrogel into a stretchable one sustaining up to 370% elongation ratio. The mechanical properties of SF hydrogels could be adjusted by the amount of PDMAA incorporated into the SF network. The stretchable and tough SF hydrogels thus developed are suitable as a scaffold in tissue engineering and offer an advantage as a biomaterial over other SF-based biomaterials.