Mimicking the Hierarchical Structure of Spider Silk: Pseudoprotein Nanofiber Yarns with Unprecedented Toughness

Preparing high-performance artificial spider silk with hierarchical structures using purely chemical synthesis methods is challenging, albeit promising. Herein, a high-molecular-weight pseudoprotein material (CPPUU) synthesized by introducing polypeptide fragments (PZLY) and cystine dimethyl ester (CDE) into a polyurethane/urea macromolecular chain is described. Nanofiber yarn is subsequently prepared using an improved electrospinning process. After pre-stretching, the tensile strength of the nanofiber yarn is 286.0 ± 47.1 MPa, and the toughness is an unprecedented 925.4 ± 116.1 MJ m^{- 3}, surpassing that of both natural and synthetic fibers reported to date. Moreover, the nanofiber yarn can lift a weight 100 000 times its mass and withstand the free fall of a weight 25 000 times its mass. Structural analysis indicates that the yarn contains structures such as random coils, α-helices, and β-sheets commonly found in spider silk; additionally, the existence of β-turns in pseudoprotein materials is verified. The hierarchical structural resemblance to spider silk and the stress-strain curve suggest that a self-toughening mechanism is responsible for the excellent mechanical properties displayed by the yarn. This study should promote the production of artificial spider silk, with potential applications in various high-performance materials and industries.