Spider Silk: Rapid, Bottom-Up Self-Assembly of MaSp1 into Hierarchically Structured Fibers Through Biomimetic Processing

Abstract

Spider dragline silk's exceptional mechanical performance, coupled with its benign production pathway, have inspired the design of diverse smart materials. Remarkably, relatively little is known about the self-assembly process of major ampullate spidroin 1 (MaSp1) – the main protein constituent of dragline fiber – during its rapid conversion from soluble precursor protein into hierarchically structured mature silk fibers. Herein, the biomimetic potential of MaSp1 is explored using a new recombinant platform with full domain representation. MaSp1 is found to undergo efficient liquid-liquid phase separation (LLPS) in response to kosmotropic ions, with notably higher propensity compared to MaSp2, and with MaSp1 exhibiting a more complex solubility profile relative to levels of sodium chloride. To further the understanding of silk spinning, the rapid assembly of mesoscale structures is monitored in real-time in response to ion and pH gradients, revealing a progression from LLPS droplets toward aligned hierarchical fibers. Furthermore, using this biomimetic system, insoluble macroscopic MaSp1 fibers can be readily generated, wherein the application of mechanical deformation triggers the emergence of β-sheet secondary structures. The insights gained from this study can have broader application in efforts to mimic the formation of biomaterials with spatially organized features across multiple length scales.