Aqueous spinning system with a citrate buffer for highly extensible silk fibers

Inspired by the natural spinning process, we developed an aqueous wet spinning system using a citrate buffer with polyethylene glycol (PEG), where the citrate buffer served for ion exchange and acidification and the PEG functioned for dehydration. This biomimetic condition induced the formation of solid fibers with a core–shell structure. The PEG layer could be subsequently removed by the equipped water bath, resulting in amorphous silk fibers. Due to the amorphous state, the silk fibers could be stretched at up to 12 times the original reel speed. Eventually, the mechanical properties featured an extraordinary extension of ~100% and a toughness of ~70 MJ/m³. The crystalline state of the resultant fibers was characterized by synchrotron WAXS to determine the degree of crystallinity and orientation of the beta-sheet structure. Interestingly, the citrate buffer-mediated spinning system enabled tuning of the induction of crystallization by changing the citrate buffer concentrations and coagulation time. The current amorphous spinning of regenerated silk fibers provided in-depth insights into the green and sustainable fabrication of artificial capture-silk-like fibers with unique extensibility and toughness.