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Silk is strong, stretchy: Darwin's bark spider


Bark spider web / Lalueza-Fox,.. / LicenseCC-by - Attribution

Silk of the Darwin's bark spider is twice as strong as other spider silk due to extreme extensibility combined with high strength.

Man-made structural fibers are generally coils of simple, homogenous strands. In contrast, spider silk fibrils are constructed with alternating nano-segments that are either extremely flexible (amorphous glycine-rich matrices) or extremely strong (crystalites made of anti-parallel pleated beta sheets). Dozens of fibrils come together to form each thread. As a result, the fibers are nearly as strong as Kevlar yet much more stretchable and tough.
"Combining high strength and elasticity, spider silks are exceptionally tough, i.e., able to absorb massive kinetic energy before breaking. Spider silk is therefore a model polymer for development of high performance biomimetic fibers…We examined the biomechanical properties of silk produced by the remarkable Malagasy 'Darwin's bark spider' (Caerostris darwini), which we predicted would produce exceptional silk based upon its amazing web. The spider constructs its giant orb web (up to 2.8 m2) suspended above streams, rivers, and lakes. It attaches the web to substrates on each riverbank by anchor threads as long as 25 meters. Dragline silk from both Caerostris webs and forcibly pulled silk, exhibits an extraordinary combination of high tensile strength and elasticity previously unknown for spider silk. The toughness of forcibly silked fibers averages 350 MJ m3, with some samples reaching 520 MJ/m3. Thus, C. darwini silk is more than twice tougher than any previously described silk, and over 10 times better than Kevlar®. Caerostris capture spiral silk is similarly exceptionally tough.

Conclusions: Caerostris darwini produces the toughest known biomaterial. We hypothesize that this extraordinary toughness coevolved with the unusual ecology and web architecture of these spiders, decreasing the likelihood of bridgelines breaking and collapsing the web into the river." (Agnarsson et al. 2010:1)

"Spidroin I have previously been characterized by NMR and x-ray diffraction. They were found to be predominantly in b-sheet conformation and to organize into crystallites... These crystallites are interconnected in an amorphous glycine-rich matrix" (Du et al. 2006: 4528)

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About the inspiring organism
Med_caerostris_darwini_web Caerostris

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Organism/taxonomy data provided by:
Species 2000 & ITIS Catalogue of Life: 2008 Annual Checklist

Bioinspired products and application ideas

Application Ideas: Structural materials that are both strong and elastic while maintaining a light weight are invaluable to the myriad applications that require such materials such as super strong ropes and cables. Steel and carbon fiber may someday be supplemented or even supplanted by spider silk-inspired fibers. The natural antiseptic and biologically-compatible composition of spider silk could be utilized to make advanced bandages and sutures. Strong fibers for use in protective clothing, tents, awnings, fish net manufacturing, and rigging. Stronger ropes and cables. Strong polymers.

Industrial Sector(s) interested in this strategy: Manufacturing, Transportation, Construction

Department of Biology
Ingi Agnarsson
Faculty of Natural Sciences, University of Puerto Rico
Agnarsson I; Kuntner M; Blackledge TA. 2010. Bioprospecting finds the toughest biological material: extraordinary silk from a giant riverine orb spider. PLoS ONE [Internet],
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Du N; Liu XY; Narayanan J; Li L; Lim MLM; Li D. 2006. Design of superior spider silk: from nanostructure to mechanical properties. Biophysical Journal. 91(12): 4528-4535.
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