(713f) Microbially Synthesized Polymeric Amyloid Fiber Promotes ?-Nanocrystal Formation and Displays Gigapascal Tensile Strength

Dragline spider silk stands out as one of the strongest and toughest natural materials and has motivated decades of research to produce recombinant silk fibers at macroscales. Despite these efforts, achieving gigapascal tensile strength with higher than 150 MJ*m^-3 toughness in recombinant fibers remained challenging. On the other hand, the ability of amyloid peptides to self-assemble into stable β-sheet nanofibrils had made them potential candidates for material innovation in nanotechnology. However, such nanoscale feature was rarely translated into attractive macroscopic properties. Inspired by the structure of natural spidroins, we propose a strategy that combines the mechanical superiorities of spider silk and amyloid nanofibrils by fusing amyloid peptides with spidroin-derived flexible linkers. These microbially synthesized polymeric amyloid proteins could be wet-spun into macroscopic fibers, and structural analyses unveiled a high degree of crystallinity with the presence of β-nanocrystals that resembled the cross-β structure of amyloid nanofibrils. These polymeric amyloid fibers displayed strong and molecular-weight-dependent mechanical properties. Fibers made from the high molecular weight protein containing 128 repeats of the FGAILSS sequence exhibited an average ultimate tensile strength of 0.98 ± 0.08 GPa and an average toughness of 161 ± 26 MJ*m^-3, surpassing most recombinant protein fibers and even some natural spider silk fibers. The design strategy and the biosynthetic approach presented in this study can be generalized to create numerous functional materials, and the macroscopic amyloid fibers will enable a wide range of mechanically demanding applications.