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

• DOI: 10.1038/ncomms3634
• Publication Date: 2013-10-15T15:01:57Z
• Authors: Elizabeth A. Zimm...; Bernd Gludovatz; Eric Schaible; Neil K. N. Dave; Wen Yang; Marc A. Meyers; Robert O. Ritchie
• Keywords: Food Chain; Compressive Strength; Adaptation, Biological; Fishes; 02 engineering and technology; X-Ray Diffraction; Hardness; Predatory Behavior; Tensile Strength; Scattering, Small Angle; Animals; Collagen; Characiformes; 0210 nano-technology; Brazil; Synchrotrons; Skin

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.