Fig. 1: Keratin/BSA composite fiber produced using protein chain entanglement strategy.

a Schematic of the protein unfolding. Urea breaks hydrogen bonds (H-bonds) while DTT cleaves disulfide bonds (S-S), leading to the unfolding of keratin from nano-aggregates into single molecules and BSA from spherical structures into random structures, respectively, thus causing protein chain entanglement in protein composite solution. b Schematic of the fiber formation process of the composite proteins. The unfolded proteins are aligned and squeezed into coagulation, leading to S-S crosslinking through the reoxidation of thiol groups. Simultaneously, protein refolding occurs through dehydration, followed by fiber formation through drawing collection. c Mass protein composite fibers are collected in a rotor collector. d Representative scanning electron microscopy (SEM) images of a drawn keratin/BSA composite fiber (DKBF) in longitudinal and (e) cross sections show a uniform diameter of ~12 μm and a smooth surface (n = 3). f A representative polarized optical microscopy (POM) image of a DKBF shows strong birefringence, indicating an ordered arrangement of proteins within the fiber (n = 3). g A SEM image of a knotted DKBF (n = 3). h A summary of the mechanical properties of keratin-based fibers under different treatments indicates that DKBFs have balanced mechanical performance. Note: PKFs denote pure keratin fibers; UKBFs denote undrawn keratin/BSA composite fibers; DKBFs denote drawn keratin/BSA composite fibers.