  Spider silk is biocompatible, biodegradable, and rivals some of the best
synthetic materials in terms of strength and toughness. Despite extensive
research, comprehensive experimental evidence of the formation and morphology
of its internal structure is still limited and controversially discussed. Here,
we report the complete mechanical decomposition of natural silk fibers from the
golden silk orb-weaver Trichonephila clavipes into ~10 nm-diameter nanofibrils,
the material's apparent fundamental building blocks. Furthermore, we produced
nanofibrils of virtually identical morphology by triggering an intrinsic
self-assembly mechanism of the silk proteins. Independent physico-chemical
fibrillation triggers were revealed, enabling fiber assembly from stored
precursors "at-will". This knowledge furthers the understanding of this
exceptional material's fundamentals, and ultimately, leads toward the
realization of silk-based high-performance materials.
