The hidden link between supercontraction and mechanical behavior of spider silks

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

doi:10.1016/j.jmbbm.2010.09.008

Cited by 82 publications

(80 citation statements)

References 52 publications

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“…The average elongation to break was 26·7 ± 3·9% at 30% RH, 30·8 ± 3·8% at 70% RH and 26·7 ± 5·1% in water (Table 1). The fi ndings are in excellent agreement with other studies on the infl uence of humidity on mechanical properties of silk from other spider species (Elices et al, 2011b;Plaza et al, 2006;Vehoff et al, 2007). The tests in presence of water, however, revealed different results, as supercontraction was tried to be avoided during the measurement using a pretreatment.…”

Section: Infl Uence Of Humidity As Well As Presence Of Water On Mechasupporting

confidence: 89%

“…The tests in presence of water, however, revealed different results, as supercontraction was tried to be avoided during the measurement using a pretreatment. In previous studies, the tested silk fi bers were either exposed to high humidity conditions or were completely wetted, but all were dried before being mechanically tested (Elices et al, 2011b;Gosline et al, 1984;Guinea et al, 2003;PerezRigueiro et al, 2003;Work, 1985;Work and Morosoff, 1982). In contrast, the mechanical properties of the fi bers under water was directly tested.…”

Section: Infl Uence Of Humidity As Well As Presence Of Water On Mechamentioning

confidence: 99%

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Characterization of natural and biomimetic spider silk fibers

Keerl

Scheibel

2012

Bioinspired, Biomimetic and Nanobiomaterials

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List of notations FS= forced silking RH = relative humidity % w/v = weight per volume percentage % v/v = volume per volume percentage IntroductionSpider silk produced by orb-weaving spiders reveals fascinating mechanical properties, in particular, its unique combination of high tensile strength and elasticity, distinguishing it from most other natural or man-made fi bers (Cunniff et al., 1994;Denny, 1976;Eisoldt et al., 2011;Gosline et al., 1984Gosline et al., , 1999Heim et al., 2009;Kaplan et al., 1991;Ko and Jovicic, 2004). Of the fi ve different silks produced by an orb-weaving spider for web building, dragline silk, serving as frame and radial fi ber in the web and as the spider's lifeline, is the best characterized one, as it is the easiest accessible one Vollrath, 2000). A common method to obtain dragline silk for mechanical and structural analysis is the application of forced silking of captive spiders, that is, forcibly pulling the fi ber from a spider's spinneret (e.g. by winding it on a rotating mandrel) (Ortlepp and Gosline, 2004;Perez-Rigueiro et al., 2005;Work and Emerson, 1982). Earlier studies have revealed that spinning speeds have an impact on resilience, strain at breaking, breaking energy, initial Young's modulus, yield point and ductility (most likely related to the variation in diameter of a single fi ber; Chen et al., 2006; PerezRigueiro et al., 2005;Romer and Scheibel, 2008;Scheibel, 2004;). Furthermore, it was shown that forcibly silked fi bers have higher storage moduli and lower loss moduli than native silks (Blackledge et al., 2005; Work, 1976). Despite their intriguing mechanical properties, the use of these fi bers in various industrial or medical applications is limited because of constraints in farming of spiders which are based on their territorial and cannibalistic nature (Fox, 1975). Thus, the focus of silk research has recently shifted towards biotechnologically producing the underlying proteins as well as mimicking the spinning process to produce a new class of high-performance fi bers (Hardy et al., 2008;O'Brien et al., 1998;Omenetto and Kaplan, 2010;Scheibel, 2004).Artifi cial spider silk fi bers can be obtained by two different approaches: (a) spinning from regenerated silk dopes and (b) spinning from solutions of recombinant silk proteins. Regenerated silk solutions from silk fi bers are usually prepared by dissolving a large amount of natural silk fi bers in harsh solvents, such as highly concentrated lithium bromide solutions, hexafl uoroisopropanol (HFIP) or hexafl uoroacetone hydrate (Hardy et al., 2008). However, the number of studies on spider silk is limited as most Pages 83-94 http://dx

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Section: Infl Uence Of Humidity As Well As Presence Of Water On Mechasupporting

confidence: 89%

Section: Infl Uence Of Humidity As Well As Presence Of Water On Mechamentioning

confidence: 99%

Characterization of natural and biomimetic spider silk fibers

Keerl

Scheibel

2012

Bioinspired, Biomimetic and Nanobiomaterials

View full text Add to dashboard Cite

show abstract

“…a post-tensioning mechanism controlled by wetting. Supercontraction is thought to be controlled by specific motifs in the silk proteins [71,77] and induced by the entropy-driven recoiling of molecular chains [78,79], and has a scaling effect on mechanical properties [12,70,73,74]. To trigger the proposed molecular response, solvent must penetrate the protein structure, enhanced by the presence of fibril globules due to an increase in free volume (and thus exposed surface area).…”

Section: Voids and Free Volumementioning

confidence: 99%

“…supercontraction increases strength and stiffness [70,73,82] and may supersede the benefits of shear interlock alone).…”

Section: Voids and Free Volumementioning

confidence: 99%

Increasing silk fibre strength through heterogeneity of bundled fibrils

Cranford

2013

J. R. Soc. Interface.

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Can naturally arising disorder in biological materials be beneficial? Materials scientists are continuously attempting to replicate the exemplary performance of materials such as spider silk, with detailed techniques and assembly procedures. At the same time, a spider does not precisely machine silk-imaging indicates that its fibrils are heterogeneous and irregular in cross section. While past investigations either focused on the building material (e.g. the molecular scale protein sequence and behaviour) or on the ultimate structural component (e.g. silk threads and spider webs), the bundled structure of fibrils that compose spider threads has been frequently overlooked. Herein, I exploit a molecular dynamics-based coarse-grain model to construct a fully three-dimensional fibril bundle, with a length on the order of micrometres. I probe the mechanical behaviour of bundled silk fibrils with variable density of heterogenic protrusions or globules, ranging from ideally homogeneous to a saturated distribution. Subject to stretching, the model indicates that cooperativity is enhanced by contact through low-force deformation and shear 'locking' between globules, increasing shear stress transfer by up to 200 per cent. In effect, introduction of a random and disordered structure can serve to improve mechanical performance. Moreover, addition of globules allows a tuning of free volume, and thus the wettability of silk (with implications for supercontraction). These findings support the ability of silk to maintain near-molecular-level strength at the scale of silk threads, and the mechanism could be easily adopted as a strategy for synthetic fibres.

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“…This is especially critical for spider webs in situ, wherein changes in humidity and silk moisture content can imbue significant pre-tension in silk threadlines (a phenomenon known as supercontraction [34][35][36][37]). Stresses owing to supercontraction have been measured and found to be of the order of 10-100 MPa [38].…”

Section: Introductionmentioning

confidence: 99%

Compliant threads maximize spider silk connection strength and toughness

Pugno

Cranford

2014

J. R. Soc. Interface.

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Millions of years of evolution have adapted spider webs to achieve a range of functionalities, including the well-known capture of prey, with efficient use of material. One feature that has escaped extensive investigation is the silk-on-silk connection joints within spider webs, particularly from a structural mechanics perspective. We report a joint theoretical and computational analysis of an idealized silk-on-silk fibre junction. By modifying the theory of multiple peeling, we quantitatively compare the performance of the system while systematically increasing the rigidity of the anchor thread, by both scaling the stress-strain response and the introduction of an applied pre-strain. The results of our study indicate that compliance is a virtue-the more extensible the anchorage, the tougher and stronger the connection becomes. In consideration of the theoretical model, in comparison with rigid substrates, a compliant anchorage enormously increases the effective adhesion strength (work required to detach), independent of the adhered thread itself, attributed to a nonlinear alignment between thread and anchor (contact peeling angle). The results can direct novel engineering design principles to achieve possible load transfer from compliant fibre-to-fibre anchorages, be they silk-on-silk or another, as-yet undeveloped, system.

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The hidden link between supercontraction and mechanical behavior of spider silks

Cited by 82 publications

References 52 publications

Characterization of natural and biomimetic spider silk fibers

Characterization of natural and biomimetic spider silk fibers

Increasing silk fibre strength through heterogeneity of bundled fibrils

Compliant threads maximize spider silk connection strength and toughness

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