Role of Silk Fibroin in Modulating Thermo-responsive Behavior of PNIPAM Hydrogels

Abstract

Thermo-responsive hydrogels based on poly(N-isopropylacrylamide) (PNIPAM) have attracted significant attention for advanced biomedical applications due to their smart response near physiological temperature. In this study, silk fibroin (SF) was incorporated into PNIPAM hydrogels to develop a tunable composite system with enhanced physicochemical properties. The hydrogels were successfully synthesized via free radical polymerization, and the effect of SF content (0–15 wt%) on the thermo-responsive behavior, swelling characteristics, deswelling kinetics, and network stability was systematically investigated. The results demonstrated that the incorporation of SF led to a gradual increase in the Lower Critical Solution Temperature, shifting from 32.1 °C for pure PNIPAM to 34.6 °C for the highest SF content. Swelling studies revealed a reduction in equilibrium swelling ratio with increasing SF concentration at 25 °C, while maintaining controlled water retention above LCST. Deswelling analysis showed a more gradual water release behavior in SF-containing hydrogels compared to pure PNIPAM, indicating improved regulation of thermo-responsive collapse. Additionally, gel fraction results confirmed enhanced network stability and crosslinking efficiency with increasing SF content, reaching up to 90.3%. Overall, the incorporation of silk fibroin effectively modulated the structural and thermo-responsive properties of PNIPAM hydrogels, resulting in a more stable and controllable hydrogel system. These findings highlight the potential of PNIPAM/SF composite hydrogels for biomedical applications such as controlled drug delivery, tissue engineering, and smart biomaterials.