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arXiv · 1507.04321

Insights into the Hierarchical Structure of Spider Dragline Silk Fibers: Evidence for Fractal Clustering of $\beta$-Sheet Nano-Crystallites

Qiushi Mou·Chris J. Benmore·Warner S. Weber·Jeffery L. Yarger
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Abstract

Spider dragline silk is one of the toughest materials known and understanding the hierarchical structure is a critical component in the efforts to connect structure to function. In this paper, we take the first step in elucidating the hierarchical fractal structure of $\beta$-sheet nano-crystallites, which form a robust self-similar network exhibiting an non-linear mechanical property. A combined small angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) study of the nano-crystalline component in dragline silk fibers from several species of spiders including, Latrodectus hesperus, Nephila clavipes, Argiope aurantia and Araneus gemmoides is presented. SAXS structure factors exhibit a `lamellar peak' in the q-range from 0.60 to 0.82 nm$^{-1}$ for various spider dragline silk fibers, indicating the presence of strong nano-crystal ordering on the $>$10 nm length-scale. The stochastically reconstructed electron density maps indicate that the $\beta$-sheet crystals are hierarchically structured as mass fractals and that nano-crystals tend to form 10 to 50 nm sized clusters with long-range crystalline ordering. This nano-crystal ordering along the fiber axis also helps to explain the difference between axial and radial sound velocities recently measured by Brillouin spectroscopy.

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Qiushi Mou, Chris J. Benmore, Warner S. Weber, Jeffery L. Yarger. 2015-07-15. Insights into the Hierarchical Structure of Spider Dragline Silk Fibers: Evidence for Fractal Clustering of $\beta$-Sheet Nano-Crystallites. https://arxiv.org/abs/1507.04321

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