title: Spines of the porcupine fish: Structure, composition, and mechanical properties.
abstract: This paper explores the structure, composition, and mechanical properties of porcupine fish spines for the first time. The spine was found to be composed of nanocrystalline hydroxyapatite, protein (collagen), and water using X-ray diffraction, energy-dispersive X-ray spectroscopy, and thermogravimetric analysis. Microstructures have mineralized fibrillar sheets in the longitudinal direction and in a radial orientation in the transverse direction that were observed using light and electron microscopy. Based on the images, the hierarchical structure of the spine shows both concentric and radial reinforcement. Mechanical properties were obtained using cantilever beam and nanoindentation tests. A tapered cantilever beam model was developed and compared to that of a uniform cantilever beam. The tapered beam model showed that while the stresses experienced were similar to those of the uniform beam, the location of the maximum stress was near the distal region of the beam rather than at the base, which allows the porcupine fish to conserve energy and resources if the spine is fractured.
authors.affiliation: Materials Science and Engineering Program, University of California, San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0418, USA. Electronic address: fysu@eng.ucsd.edu.
authors.forename: Frances Y
authors.initials: FY
authors.lastname: Su
authors.affiliation: National Center for Microscopy and Imaging Research, University of California, San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0608, USA.
authors.forename: Eric A
authors.initials: EA
authors.lastname: Bushong
authors.affiliation: National Center for Microscopy and Imaging Research, University of California, San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0608, USA.
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Deerinck
authors.affiliation: Materials Science and Engineering Program, University of California, San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0418, USA.
authors.forename: Kyungah
authors.initials: K
authors.lastname: Seo
authors.affiliation: Chemical and Environmental Engineering, University of California, Riverside, 900 University Ave., Riverside, CA 92521, USA.
authors.forename: Steven
authors.initials: S
authors.lastname: Herrera
authors.affiliation: Materials Science and Engineering Program, University of California, San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0418, USA; Mechanical and Aerospace Engineering, University of California, San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0411, USA.
authors.forename: Olivia A
authors.initials: OA
authors.lastname: Graeve
authors.affiliation: Chemical and Environmental Engineering, University of California, Riverside, 900 University Ave., Riverside, CA 92521, USA.
authors.forename: David
authors.initials: D
authors.lastname: Kisailus
authors.affiliation: Mechanical and Aerospace Engineering, University of California, San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0411, USA; Department of NanoEngineering, University of California, San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0448, USA.
authors.forename: Vlado A
authors.initials: VA
authors.lastname: Lubarda
authors.affiliation: Materials Science and Engineering Program, University of California, San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0418, USA; Mechanical and Aerospace Engineering, University of California, San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0411, USA.
authors.forename: Joanna
authors.initials: J
authors.lastname: McKittrick
mesh_terms: D000075342:Animal Scales / Q000502:physiology*; D000818:Animals; D001696:Biomechanical Phenomena; D005399:Fishes; D013052:Spectrometry, X-Ray Emission; D013314:Stress, Mechanical; D014961:X-Ray Diffraction
keywords: Mechanical properties; Microstructure; Nanoindentation; Porcupine fish; X-ray microscopy