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Thin "shells" resist impact loading: sea urchins


Sea urchin test showing joints / J Brew / LicenseCC-by-nc-sa - Attribution Non-commercial Share Alike

The hard outer coverings of some sea urchins, called 'tests', allow local deformation that may resist impact loading by incorporating collagen-swathed sutures.

"Some of the few relatively large shells with thin walls are those of sea urchins and other echinoid echinoderms. They resemble pressure-supported structures…but they lack the requisite internal pressures (Ellers and Telford 1992), so they have to have proper shells, at least in the engineering sense. For the biologist, they have 'tests' rather than 'shells,' and the latter distinction isn't just our usual terminological proliferation. Tests, unlike shells, are growing structures of articulated hard elements. For some, at least, collagen-swathed sutures permit significant local deformation, which should reduce impact loading and thus offset some of the hazards of a thin shell (Telford 1985). Nonetheless, they do smash easily…The best rationalization I can offer for why sea urchins tolerate such fragility is that the wave forces don't provide either piercing loads or a sudden hammering impact." (Vogel 2003:388)
About the inspiring organism

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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: Strengthening ceramics, mimicking function of sutures in glass to reduce fracture, using fewer materials to manufacture or protect underwater infrastructure.

Industrial Sector(s) interested in this strategy: Ceramics, glass, marine infrastructure

Vogel S. 2003. Comparative Biomechanics: Life's Physical World. Princeton: Princeton University Press. 580 p.
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Ellers, O; Telford, M. 1992. Causes and consequences of fluctuating coelomic pressure in sea urchins. The Biological Bulletin. 182(3): 424-434.
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Telford, M. 1985. Domes, arches and urchins: the skeletal architecture of echinoids (Echinodermata). Zoomorphology. 105: 125-134.
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Ellers, O; Johnson, AS; Mober, PE. 1998. Structural strengthening of urchin skeletons by collagenous sutural ligaments. The Biological Bulletin. 195(2): 136-144.
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over 7 years ago
Great example of Life's Principle "Resourceful and opportunistic by using shape rather than material" Sutures down the side make it very strong. Instead of using a lot of material, it stays impact-resistant with it's structure.
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