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Liquid crystallinity of natural silk secretions

Nature volume 349, pages 596–598 (1991)Cite this article

Abstract

NATURAL silk exhibits a strength and stiffness similar to, and a toughness up to ten times greater than, that of artificial high-performance fibres1–5. These exceptional tensile properties, the optical birefringence of some silk secretions6–9 and the molecular order exhibited by some synthetic polypeptides in solution10 all suggest that natural silk secretions might form liquid-crystalline phases. We have now used polarized-light microscopy to study the secretions from major ampullae of spiders (Nephila clavipes) and from silk glands of silkworms (Bombyx mori). As the concentration is increased by evaporation of water, nematic liquid-crystalline microstructures develop. We deduce that natural silk secretions become liquid crystalline after leaving the gland but before solidifying into a fibre, thus promoting global molecular alignment in the fibre. Our hand-drawn fibres from droplets of secretion, as well as sheared thin films, show a banded microstructure which is indicative of a periodic variation in the direction of molecular alignment11. Both B. mori and N. clavipes, on the other hand, have apparently developed processing routes that ensure uniform molecular alignment: the threads and draglines, respectively, of these species do not show banded microstructures.

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Authors and Affiliations

  1. Department of Materials Science and Engineering FB-10, University of Washington, Seattle, Washington, 98195, USA

    Keven Kerkam & Christopher Viney

  2. US Army Research, Development and Engineering Center, Natick, Massachusetts, 01760, USA

    David Kaplan & Stephen Lombardi

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  1. Keven Kerkam
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  2. Christopher Viney
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  3. David Kaplan
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  4. Stephen Lombardi
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Kerkam, K., Viney, C., Kaplan, D. et al. Liquid crystallinity of natural silk secretions. Nature 349, 596–598 (1991). https://doi.org/10.1038/349596a0

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