Enhancing Mechanical Properties of Silk Fibroin Hydrogel through Restricting the Growth of β-Sheet Domains

Usually, regenerated silk fibroin (RSF) hydrogels cross-linked by chemical agents such as horseradish peroxide (HRP)/H₂O₂ perform elastic properties, while display unsatisfactory strength for practical applications especially as load-bearing materials, and inadequate stability when incubated in a simulated in vivo environment. Here, the RSF hydrogel with both excellent strength and elasticity was prepared by inducing the conformation transition from random coil to β-sheet in a restricted RSF network precross-linked by HRP/H₂O₂. Such "dual-networked" hydrogels, regarding the one with 10 wt % RSF (Mw: 220 kDa) as a representative, show around 100% elongation, as well as the compressive modulus and tensile modulus up to 3.0 and 2.5 MPa respectively, which are much higher than those of physically cross-linked natural polymer hydrogels (commonly within 0.01-0.1 MPa at the similar solid content). It has been shown that the enhanced comprehensive mechanical properties of RSF hydrogels derive from the formation of small-sized and uniformly distributed β-sheet domains in the hydrogel during the conformation transition of RSF whose size is limited by the first network formed by cross-linkers with HRP/H₂O₂. Importantly, the tough RSF hydrogel changes the normally weak recognition of various RSF hydrogels and holds a great potential to be the material in biomedical field because it seems to be very promising regarding its biocompatibility, biodegradability, etc.