Thermo‐hygro‐mechanical behavior of spider dragline silk: Glassy and rubbery states

Plaza, Gustavo R.; Guinea, Gustavo V.; Pérez‐Rigueiro, José; Calafat, Manuel Elices

doi:10.1002/polb.20751

Cited by 100 publications

(108 citation statements)

References 40 publications

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“…As orb webs rely on radial silk to dissipate the energy received during prey impact, capture success should increase with hysteresis for silk of a given toughness (Sensenig et al, 2012). However, as silk becomes rubberlike when wet, it is likely than hysteresis decreases at high humidity (Gosline et al, 1984;Plaza et al, 2006) (C.B., unpublished data). Therefore, if anything, water-induced changes in hysteresis should decrease capture success.…”

Section: Discussionmentioning

confidence: 99%

Wet webs work better: Humidity, supercontraction and the performance of spider orb webs

Boutry

Blackledge

2013

Journal of Experimental Biology

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SUMMARYLike many biomaterials, spider silk responds to water through softening and swelling. Major ampullate silk, the main structural element of most prey capture webs, also shrinks dramatically if unrestrained or develops high tension if restrained, a phenomenon called 'supercontraction'. While supercontraction has been investigated for over 30years, its consequences for web performance remain controversial. Here, we measured prey capture performance of dry and wet (supercontracted) orb webs of Argiope and Nephila using small wood blocks as prey. Prey capture performance significantly increased at high humidity for Argiope while the improvement was less dramatic for Nephila. This difference is likely due to Argiope silk supercontracting more than Nephila silk. Web deflection, measured as the extension of the web upon prey impact, also increased at high humidity in Argiope, suggesting that silk softening upon supercontraction explains the improved performance of wet webs. These results strongly argue that supercontraction is not detrimental to web performance.

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Section: Discussionmentioning

confidence: 99%

Wet webs work better: Humidity, supercontraction and the performance of spider orb webs

Boutry

Blackledge

2013

Journal of Experimental Biology

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“…At the reeling speed of 100 mm s 21 , the crystallite size is decreased to 2.7 nm in width, 6.4 nm in length and 2.1 nm in thickness [9], showing the influence of the reeling speed on the crystallite size. Besides the reeling speed, the mechanical properties of silk were also found to be negatively influenced by humidity [10]. These studies show that one is able to tune and improve the mechanical properties of silk by controlling the silk harvesting or processing conditions.…”

Section: Introductionmentioning

confidence: 89%

On the strength of β-sheet crystallites of Bombyx mori silk fibroin

Cheng

Koh

et al. 2014

J. R. Soc. Interface.

169

116

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Silk fibroin, a natural multi-domain protein, has attracted great attention due to its superior mechanical properties such as ultra-high strength and stretchability, biocompatibility, as well as its versatile biodegradability and processability. It is mainly composed of b-sheet crystallites and amorphous domains. Although its strength is well known to be controlled by the dissociation of protein chains from b-sheet crystallites, the way that water as the solvent affects its strength and the reason that its theoretically predicted strength is several times higher than experimental measurement remain unclear. We perform all-atom molecular dynamics simulations on a b-sheet crystallite of Bombyx mori silk. We find that water solvent reduces the number and strength of hydrogen bonds between b-chains, and thus greatly weakens the strength of silk fibroin. By dissociating protein chains at different locations from the crystallite, we also find that the pulling strength for the interior chains is several times higher than that for the surface/corner chains, with the former being consistent with the theoretically predicted value, while the latter on par with the experimental value. It is shown that the weakest rupture strength controls the failure strength of silk fibre. Hence, this work sheds light on the role of water in the strength of silk fibroin and also provides clues on the origin of the strength difference between theory and experiment.

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“…Second, cyclic contraction occurs reversibly and in proportion to drying or wetting of silk, both before and after supercontraction. Although previous studies characterized basic aspects of supercontraction (Bell et al, 2002;Elices et al, 2006;Liu et al, 2008;Pérez-Rigueiro et al, 2003;Pérez-Rigueiro et al, 2005;Pérez-Rigueiro et al, 2007;Plaza et al, 2006;van Beek et al, 1999;Vollrath and Porter, 2006b), the cyclic response of silk to relative humidity is novel. This cyclic response is unique in that it can potentially generate more stress than supercontraction, but does so as humidity decreases.…”

Section: Discussionmentioning

confidence: 99%

How super is supercontraction? Persistent versus cyclic responses to humidity in spider dragline silk

Blackledge

Boutry

Wong

et al. 2009

Journal of Experimental Biology

109

114

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SUMMARYSpider 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, silk mass increased by ~1% after supercontraction. By contrast, the cyclic response to humidity involves a reversible uptake of water. Dried, post-supercontraction silk also differs mechanically from virgin silk. Post-supercontraction silk exhibits reduced stiffness and stress at yield, as well as changes in dynamic energy storage and dissipation. In addition to advancing understanding supercontraction, our findings open up new applications for synthetic silk analogs. For example, dragline silk emerges as a model for a biomimetic muscle, the contraction of which is precisely controlled by humidity alone.

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Thermo‐hygro‐mechanical behavior of spider dragline silk: Glassy and rubbery states

Cited by 100 publications

References 40 publications

Wet webs work better: Humidity, supercontraction and the performance of spider orb webs

Wet webs work better: Humidity, supercontraction and the performance of spider orb webs

On the strength of β-sheet crystallites of Bombyx mori silk fibroin

How super is supercontraction? Persistent versus cyclic responses to humidity in spider dragline silk

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