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Updated: May 6, 2026

A Millimeter Scale Flexural Testing System for Measuring the Mechanical Properties of Marine Sponge Spicules
Published on: October 11, 2017
Mechanical adaptability of the Bouligand-type structure in natural dermal armour
Elizabeth A Zimmermann1, Bernd Gludovatz, Eric Schaible
1Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
Abstract:
Arapaima gigas, a fresh water fish found in the Amazon Basin, resist predation by piranhas through the strength and toughness of their scales, which act as natural dermal armour. Arapaima scales consist of a hard, mineralized outer shell surrounding a more ductile core. This core region is composed of aligned mineralized collagen fibrils arranged in distinct lamellae. Here we show how the Bouligand-type (twisted plywood) arrangement of collagen fibril lamellae has a key role in developing their unique protective properties, by using in situ synchrotron small-angle X-ray scattering during mechanical tensile tests to observe deformation mechanisms in the fibrils. Specifically, the Bouligand-type structure allows the lamellae to reorient in response to the loading environment; remarkably, most lamellae reorient towards the tensile axis and deform in tension through stretching/sliding mechanisms, whereas other lamellae sympathetically rotate away from the tensile axis and compress, thereby enhancing the scale's ductility and toughness to prevent fracture.
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