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Relationships between supercontraction and mechanical properties of spider silk


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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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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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).

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