Metformin-Loaded Silkworm Silk Fibers with Stable Mechanical Performance and Bioactivity

Abstract Natural silk fibers hold considerable promise for implant applications. However, how to enhance bioactivity while preserving mechanical performance remains a challenge. Herein, a strategy combining soaking with secondary washing was employed to achieve loading of metformin while largely retaining the mechanical properties of silk fibers. Multiscale structural characterization revealed the noncovalent interactions between metformin and silk in the amorphous regions and a slight decrease in fiber orientation and β-sheet nanocrystals. Owing to the stable structure, the metformin-loaded silk fibers retained excellent mechanical properties, exhibiting a tensile strength of 407.8 MPa and a toughness of 36.7 MJ·m–3. Notably, the Weibull shape parameter for tensile strength reached 28.53, indicating mechanical reliability. Furthermore, the metformin-loaded silk fibers demonstrated favorable cytocompatibility and enhanced osteogenic activity. This study provides a facile and mild strategy for the bioactive modification of natural silk fibers while preserving their structural and mechanical properties.