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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.
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Multi‐Point Nanoindentation Method to Determine Mechanical Anisotropy in Nanofibrillar Thin Films
Biomaterials with outstanding mechanical properties including spider silk, wood, and cartilage, often feature an oriented nanofibrillar structure. The orientation of nanofibrils gives rise to a significant mechanical anisotropy which is extremely challenging to characterize, especially for microscopically small or inhomogeneous samples. Here we report a technique utilizing atomic force microscope indentation at multiple points combined with finite element analysis to sample the mechanical anisotropy of a thin film in a microscopically small area. The system we study is the tape-like silk of the Chilean recluse spider, which entirely consists of strictly oriented nanofibrils giving rise to a large mechanical anisotropy. We present the most detailed directional nanoscale structure–property characterization of spider silk to date, revealing the tensile and transverse elastic moduli as 9 GPa and 1 GPa, respectively, and the binding strength between silk nanofibrils as 159 ± 13 MPa. Furthermore, based on this binding strength, we derive the nanofibrils’ surface energy, as 37 mJ/m2, and conclude that van der Waals forces play a decisive role in inter-fibrillar binding. Due to its versatility, this technique has many potential applications including early diseases diagnostics, as underlying pathological conditions can alter the local mechanical properties of tissues.
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- PAR ID:
- 10342545
- Date Published:
- Journal Name:
- Small
- ISSN:
- 1613-6810
- Page Range / eLocation ID:
- 2202065
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1002/smll.202202065
