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Relationships between supercontraction and mechanical properties of spider silk

Nature Materials volume 4, pages 901–905 (2005)Cite this article

Abstract

Typical spider dragline silk tends to outperform other natural fibres and most man-made filaments1. However, even small changes in spinning conditions can have large effects on the mechanical properties of a silk fibre2,3,4,5,6 as well as on its water uptake. Absorbed water leads to significant shrinkage in an unrestrained dragline fibre7,8 and reversibly converts the material into a rubber9. This process is known as supercontraction10 and may be a functional adaptation for the silk’s role in the spider’s web11. Supercontraction is thought to be controlled by specific motifs in the silk proteins12,13 and to be induced by the entropy-driven recoiling of molecular chains9,14. In analogy, in man-made fibres thermal shrinkage induces changes in mechanical properties15,16,17 attributable to the entropy-driven disorientation of ‘unfrozen’ molecular chains (as in polyethylene terephthalate)15,18 or the ‘broken’ intermolecular hydrogen bonds (as in nylons)17. Here we show for Nephila major-ampullate silk how in a biological fibre the spinning conditions affect the interplay between shrinkage and mechanical characteristics. This interaction reveals design principles linking the exceptional properties of silk to its molecular orientation.

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Figure 1: Comparisons of stress–strain curves of spider silks spun under different conditions.
Figure 2: General correlations between mechanical properties and the Csh of spider silk.
Figure 3: General correlations between mechanical properties and the breaking strain of spider silk.
Figure 4: The two states S1 and S2 and the stress–strain curves of their representative spider silks.

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Acknowledgements

For funding we thank the British EPSRC (grant GR/NO1538/01) as well as the European Commission (grant G5RD-CT-2002-00738), the National Natural Science Foundation of China (NSFC 20434010), the Science and Technology Development Foundation of Shanghai (grant 05JC14009) and the AFSOR of the United States of America (grant F49620-03-1-0111). We thank C. Holland and D. Porter for constructive criticism.

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Authors and Affiliations

  1. Department of Macromolecular Science and The Key Laboratory of Molecular Engineering of Polymers of Ministry of Education, Fudan University, Shanghai, 200433, P.R. China

    Yi Liu & Zhengzhong Shao

  2. Department of Zoology, University of Oxford, South Parks Road, Oxford, OX1 3PS, UK

    Yi Liu & Fritz Vollrath

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Correspondence to Yi Liu, Zhengzhong Shao or Fritz Vollrath.

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Liu, Y., Shao, Z. & Vollrath, F. Relationships between supercontraction and mechanical properties of spider silk. Nature Mater 4, 901–905 (2005). https://doi.org/10.1038/nmat1534

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