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Mechanical adaptability of the Bouligand-type structure in natural dermal armour

2013; Nature Portfolio; Volume: 4; Issue: 1 Linguagem: Inglês

10.1038/ncomms3634

2041-1723

Elizabeth A. Zimmermann, Bernd Gludovatz, Eric Schaible, Neil K. N. Dave, Wen Yang, Marc A. Meyers, Robert O. Ritchie,

Calcium Carbonate Crystallization and Inhibition

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. The scales of Arapaima gigas, a fresh water fish found in the Amazon Basin, act as effective armour against predators. Here, Zimmermann et al. elucidate the deformation mechanisms that allow for this resistance, concluding that lamellae in the scales reorient under an applied load, preventing fracture.