title: Protective role of Arapaima gigas fish scales: structure and mechanical behavior.
abstract: The scales of the arapaima (Arapaima gigas), one of the largest freshwater fish in the world, can serve as inspiration for the design of flexible dermal armor. Each scale is composed of two layers: a laminate composite of parallel collagen fibrils and a hard, highly mineralized surface layer. We review the structure of the arapaima scales and examine the functions of the different layers, focusing on the mechanical behavior, including tension and penetration of the scales, with and without the highly mineralized outer layer. We show that the fracture of the mineral and the stretching, rotation and delamination of collagen fibrils dissipate a significant amount of energy prior to catastrophic failure, providing high toughness and resistance to penetration by predator teeth. We show that the arapaima's scale has evolved to minimize damage from penetration by predator teeth through a Bouligand-like arrangement of successive layers, each consisting of parallel collagen fibrils with different orientations. This inhibits crack propagation and restricts damage to an area adjoining the penetration. The flexibility of the lamellae is instrumental to the redistribution of the compressive stresses in the underlying tissue, decreasing the severity of the concentrated load produced by the action of a tooth. The experimental results, combined with small-angle X-ray scattering characterization and molecular dynamics simulations, provide a complete picture of the mechanisms of deformation, delamination and rotation of the lamellae during tensile extension of the scale.
authors.affiliation: Materials Science & Engineering Program, University of California, San Diego, La Jolla, CA 92093, USA.
authors.forename: Wen
authors.initials: W
authors.lastname: Yang
authors.affiliation: Materials Science & Engineering Program, University of California, San Diego, La Jolla, CA 92093, USA.
authors.forename: Vincent R
authors.initials: VR
authors.lastname: Sherman
authors.affiliation: Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
authors.forename: Bernd
authors.initials: B
authors.lastname: Gludovatz
authors.affiliation: National Center for Microscopy and Imaging Research Facility, University of California, San Diego, La Jolla, CA 92093, USA.
authors.forename: Mason
authors.initials: M
authors.lastname: Mackey
authors.affiliation: Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Zimmermann
authors.affiliation: Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
authors.forename: Edwin H
authors.initials: EH
authors.lastname: Chang
authors.affiliation: Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
authors.forename: Eric
authors.initials: E
authors.lastname: Schaible
authors.affiliation: Department of Civil & Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
authors.forename: Zhao
authors.initials: Z
authors.lastname: Qin
authors.affiliation: Department of Civil & Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
authors.forename: Markus J
authors.initials: MJ
authors.lastname: Buehler
authors.affiliation: Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA; Department of Materials Science & Engineering, University of California, Berkeley, CA 94720, USA. Electronic address: roritchie@lbl.gov.
authors.forename: Robert O
authors.initials: RO
authors.lastname: Ritchie
authors.affiliation: Materials Science & Engineering Program, University of California, San Diego, La Jolla, CA 92093, USA; Department of Mechanical & Aerospace Engineering, University of California, San Diego, La Jolla, CA 92093, USA; Department of NanoEngineering, University of California, San Diego, La Jolla, CA 92093, USA. Electronic address: mameyers@eng.ucsd.edu.
authors.forename: Marc A
authors.initials: MA
authors.lastname: Meyers
mesh_terms: D000818:Animals; D019245:Compressive Strength / Q000502:physiology; D055119:Elastic Modulus / Q000502:physiology; D005399:Fishes / Q000033:anatomy & histology* / Q000502:physiology*; D006244:Hardness / Q000502:physiology; D008422:Materials Testing; D012867:Skin / Q000737:chemistry* / Q000648:ultrastructure*; D012879:Skin Physiological Phenomena; D013329:Structure-Activity Relationship; D013499:Surface Properties; D013718:Tensile Strength / Q000502:physiology
keywords: Arapaima; Armor; Collagen; Delamination; Fish scales