Relationships between supercontraction and mechanical properties of spider silk.
Typical spider dragline silk tends to outperform other natural fibres and most man-made filaments. However, even small changes in spinning conditions can have large effects on the mechanical properties of a silk fibre as well as on its water uptake. Absorbed water leads to significant shrinkage in an unrestrained dragline fibre and reversibly converts the material into a rubber. This process is known as supercontraction and may be a functional adaptation for the silk's role in the spider's web. Supercontraction is thought to be controlled by specific motifs in the silk proteins and to be induced by the entropy-driven recoiling of molecular chains. In analogy, in man-made fibres thermal shrinkage induces changes in mechanical properties attributable to the entropy-driven disorientation of 'unfrozen' molecular chains (as in polyethylene terephthalate) or the 'broken' intermolecular hydrogen bonds (as in nylons). 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.
Liu
Yi
Y
Department of Macromolecular Science and The Key Laboratory of Molecular Engineering of Polymers of Ministry of Education, Fudan University, Shanghai 200433, PR China.
Shao
Zhengzhong
Z
Vollrath
Fritz
F
D000818:Animals; D005260:Female; D005349:Fibroins / Q000737:chemistry* / Q000648:ultrastructure; D019476:Insect Proteins / Q000737:chemistry* / Q000648:ultrastructure; D013112:Spiders / Q000737:chemistry*; D013314:Stress, Mechanical
D019476:Insect Proteins; D005349:Fibroins