title: Mechanical adaptability of the Bouligand-type structure in natural dermal armour.
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.
authors.affiliation: Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Zimmermann
authors.forename: Bernd
authors.initials: B
authors.lastname: Gludovatz
authors.forename: Eric
authors.initials: E
authors.lastname: Schaible
authors.forename: Neil K N
authors.initials: NK
authors.lastname: Dave
authors.forename: Wen
authors.initials: W
authors.lastname: Yang
authors.forename: Marc A
authors.initials: MA
authors.lastname: Meyers
authors.forename: Robert O
authors.initials: RO
authors.lastname: Ritchie
mesh_terms: D000220:Adaptation, Biological; D000818:Animals; D001938:Brazil; D060125:Characiformes / Q000502:physiology; D003094:Collagen / Q000648:ultrastructure*; D019245:Compressive Strength; D005399:Fishes / Q000033:anatomy & histology*; D020387:Food Chain; D006244:Hardness; D011235:Predatory Behavior; D053838:Scattering, Small Angle; D012867:Skin / Q000648:ultrastructure*; D017356:Synchrotrons; D013718:Tensile Strength; D014961:X-Ray Diffraction
chemical_list: D003094:Collagen