Swelling behaviours and mechanical properties of silk fibroin–polyurethane composite hydrogels

Silk fibroin–polyurethane (SF–PU) hydrogels combining advantages of the natural/synthetic materials were fabricated. FTIR was applied to characterize the structure of hydrogels. It was found that cross-linking network formed through chemical reactions between NCO groups on PU chain and NH2, OH groups on SF chains, in addition to the hydrogen bonding interactions. SEM was taken to observe the morphology of hydrogels, which exhibited a porous structure. Hydrogels demonstrated impressive swelling–deswelling behaviours and good sensitivities to temperature, ionic strength and pH. The swelling ratio of hydrogel could be as high as 4.37 and it decreased with the increase of SF contents. Due to that the diffusion exponent (n) was about 0.45, the initial swelling stage was thought to be controlled by the Fickian diffusion. For the whole swelling process, experimental results well fitted into the Schott second-order kinetic equation. Mechanical tests showed that the elastic modulus of hydrogels were about 0.558 MPa. Properties of hydrogels could be finely controlled so as to fulfill these potential biomedical applications, such as in Nucleus Pulposus Replacement or controlled drug release.