Spider silk softening by water uptake: an AFM study

Schäfer, Arne; Vehoff, Thorsten; Glišović, Anja; Salditt, Tim

doi:10.1007/s00249-007-0216-5

Cited by 30 publications

(37 citation statements)

References 37 publications

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“…First, supercontraction occurs through an irreversible uptake of water when silk first encounters humidity above a critical value of ~70%. Supercontraction permanently alters the molecular organization of restrained silk, even after it is dried, as demonstrated by the differences in thermal stability and mechanical performance of dry supercontracted (WS 0.5% ) silk compared with dry virgin silk (Figs 5-8) Guinea et al, 2005;Jelinski et al, 1999;Savage et al, 2004;Schafer et al, 2008;Vollrath and Porter, 2006b;Yang et al, 2000). Second, cyclic contraction occurs reversibly and in proportion to drying or wetting of silk, both before and after supercontraction.…”

Section: Discussionmentioning

confidence: 99%

“…During supercontraction, water is hypothesized to plasticize silk fibers by breaking hydrogen bonds between proteins thereby allowing re-orientation of silk molecules to lower energy levels Guinea et al, 2005;Jelinski et al, 1999;Savage et al, 2004;Schafer et al, 2008;Yang et al, 2000). Recent studies have focused on the importance of disrupting secondary structure in the glycine-rich blocks for mobilization of proteins within the amorphous network (Savage and Gosline, 2008a;Savage and Gosline, 2008b;van Beek et al, 2002).…”

Section: Introductionmentioning

confidence: 99%

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

Blackledge

Boutry

Wong

et al. 2009

Journal of Experimental Biology

107

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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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

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

107

114

View full text Add to dashboard Cite

show abstract

“…As a result, only a few techniques can provide structural information about silk monofilaments, including microscopic methods (atomic force microscopy, [1][2][3][4][5][6] scanning 3,5 and transmission electron microscopy, 7,8 and scanning transmission X-ray microscopy 9,10 ) and synchrotron X-ray diffraction. 11,12 Nevertheless, some of these techniques require a certain degree of treatment of the fiber that might affect its structure and/or they provide no molecular (i.e., spectroscopic) information.…”

Section: Introductionmentioning

confidence: 99%

Structure of silk by raman spectromicroscopy: From the spinning glands to the fibers

et al. 2011

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Raman spectroscopy has long been proved to be a useful tool to study the conformation of protein‐based materials such as silk. Thanks to recent developments, linearly polarized Raman spectromicroscopy has appeared very efficient to characterize the molecular structure of native single silk fibers and spinning dopes because it can provide information relative to the protein secondary structure, molecular orientation, and amino acid composition. This review will describe recent advances in the study of the structure of silk by Raman spectromicroscopy. A particular emphasis is put on the spider dragline and silkworm cocoon threads, other fibers spun by orb‐weaving spiders, the spinning dope contained in their silk glands and the effect of mechanical deformation. Taken together, the results of the literature show that Raman spectromicroscopy is particularly efficient to investigate all aspects of silk structure and production. The data provided can lead to a better understanding of the structure of the silk dope, transformations occurring during the spinning process, and structure and mechanical properties of native fibers. © 2011 Wiley Periodicals, Inc. Biopolymers 97: 322–336, 2012.

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“…Water infiltrates the silk, disrupting hydrogen bonding within the amorphous region of the proteins (Jelinski et al, 1999;Schafer et al, 2008). This increases molecular mobility such that entropy can drive the proteins into a less organized configuration (Gosline et al, 1984).…”

Section: Introductionmentioning

confidence: 99%

Spider silk as a novel high performance biomimetic muscle driven by humidity

Agnarsson

Dhinojwala

Sahni

et al. 2009

Journal of Experimental Biology

136

129

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SUMMARYThe 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 synthetic muscles developed so far are driven by electric voltage, such that they cannot scale easily across large ranges in cross-sectional areas. The potential applicability of silk muscles is further enhanced by our finding that silkworm fibers also exhibit cyclic contraction because they are already available in commercial quantities. The simplicity of using wet or dry air to drive the biomimetic silk muscle fibers and the incredible power generated by silk offer unique possibilities in designing lightweight and compact actuators for robots and micro-machines, new sensors, and green energy production.

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Spider silk softening by water uptake: an AFM study

Cited by 30 publications

References 37 publications

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

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

Structure of silk by raman spectromicroscopy: From the spinning glands to the fibers

Spider silk as a novel high performance biomimetic muscle driven by humidity

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