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Articles by V Sahni
Total Records ( 2 ) for V Sahni
  T. A Blackledge , C Boutry , S. C Wong , A Baji , A Dhinojwala , V Sahni and I. Agnarsson
  Todd A. Blackledge, Cecilia Boutry, Shing-Chung Wong, Avinash Baji, Ali Dhinojwala, Vasav Sahni, and Ingi Agnarsson

Spider dragline silk has enormous potential for the development of biomimetic fibers that combine strength and elasticity in low density polymers. These applications necessitate understanding how silk reacts to different environmental conditions. For instance, spider dragline silk `supercontracts' in high humidity. During supercontraction, unrestrained dragline silk contracts up to 50% of its original length and restrained fibers generate substantial stress. Here we characterize the response of dragline silk to changes in humidity before, during and after supercontraction. Our findings demonstrate that dragline silk exhibits two qualitatively different responses to humidity. First, silk undergoes a previously unknown cyclic relaxation–contraction response to wetting and drying. The direction and magnitude of this cyclic response is identical both before and after supercontraction. By contrast, supercontraction is a `permanent' tensioning of restrained silk in response to high humidity. Here, water induces stress, rather than relaxation and the uptake of water molecules results in a permanent change in molecular composition of the silk, as demonstrated by thermogravimetric analysis (TGA). Even after drying,...

  I Agnarsson , A Dhinojwala , V Sahni and T. A. Blackledge
  Ingi Agnarsson, Ali Dhinojwala, Vasav Sahni, and Todd A. Blackledge

The abrupt halt of a bumble bee's flight when it impacts the almost invisible threads of an orb web provides an elegant example of the amazing strength and toughness of spider silk. Spiders depend upon these properties for survival, yet the impressive performance of silk is not limited solely to tensile mechanics. Here, we show that silk also exhibits powerful cyclic contractions, allowing it to act as a high performance mimic of biological muscles. These contractions are actuated by changes in humidity alone and repeatedly generate work 50 times greater than the equivalent mass of human muscle. Although we demonstrate that this response is general and occurs weakly in diverse hydrophilic materials, the high modulus of spider silk is such that it generates exceptional force. Furthermore, because this effect already operates at the level of single silk fibers, only 5 µm in diameter, it can easily be scaled across the entire size range at which biological muscles operate. By contrast, the most successful...

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