Predation versus protection: Fish teeth and scales evaluated by nanoindentation
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Jeffrey Schirer, Amanda Simpson, and Richard Nay Hysitron Inc., Minneapolis, Minnesota 55344
Yen-Shan Lin Department of Mechanical and Aerospace Engineering, University of California, San Diego, La Jolla, California 92093; and Department of Mechanical Engineering, San Diego State University, San Diego, California 92182
Wen Yang and Maria I. Lopez Materials Science and Engineering Program, University of California, San Diego, La Jolla, California 92093
Jianan Li School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, People’s Republic of China
Eugene A. Olevsky Department of Mechanical Engineering, San Diego State University, San Diego, California 92182
Marc A. Meyers Department of Mechanical and Aerospace Engineering and Department of Nanoengineering, University of California, San Diego, La Jolla, California 92093 (Received 5 May 2011; accepted 26 August 2011)
Most biological materials are hierarchically structured composites that often possess exceptional mechanical properties. We show that nanoindentation can be a powerful tool for understanding the structure‑mechanical property relationship of biological materials and illustrate this for fish teeth and scales, not heretofore investigated at the nanoscale. Piranha and shark teeth consist of enameloid and dentin. Nanoindentation measurements show that the reduced modulus and hardness of enameloid are 4‑5 times higher than those of dentin. Arapaima scales are multilayered composites that consist of mineralized collagen fibers. The external layer is more highly mineralized, resulting in a higher modulus and hardness compared with the internal layer. Alligator gar scales are composed of a highly mineralized external ganoin layer and an internal bony layer. Similar design strategies, gradient structures, and a hard external layer backed by a more compliant inner layer are exhibited by fish teeth and scales and seem to fulfill their functional purposes. I. INTRODUCTION
Through hundreds of millions of years of evolution, organisms have developed a myriad of ingenious solutions to ensure and optimize survival and success. Many biological (natural) materials are composites of organic (proteins and/or polysaccharides) and inorganic (minerals) components hierarchically assembled into complex structures at ambient temperature and pressure and usually in an aqueous environment.1,2 These natural composites have exceptional mechanical properties that are far beyond their relative weak constituents and are often multifunctional and possess self-healing ability. Some examples are abalone nacre,3,4 crab exoskeletons,5 a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2011.332 100
J. Mater. Res., Vol. 27, No. 1, Jan 14, 2012
http://journals.cambridge.org
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chiton radular teeth,6 and squid beaks.7 In this study, we investigate teeth and scales from four unique fish species, piranha (Serrasalmus manueli), great white shark (GWS, Carcharodon carcharias), arapaima (Arapaima gi
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