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Coherently aligned nanoparticles within a biogenic single crystal: A biological prestressing strategy

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Science  08 Dec 2017:
Vol. 358, Issue 6368, pp. 1294-1298
DOI: 10.1126/science.aaj2156

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Many roads to being tough

A number of routes exist to increase toughness in both natural and human-made materials—for example, using secondary phases and precipitates or exploiting tailored architectures and shaped crystals. Polishchuk et al. detail the nanoscale internal structure of calcitic microlenses formed by a brittlestar (see the Perspective by Duffy). The segregation of magnesium-rich particles forms a secondary phase that places compressive stresses on the host matrix. This toughening mechanism resembles Guinier-Preston zones known in classical metallurgy.

Science, this issue p. 1294 see also p. 1254

Abstract

In contrast to synthetic materials, materials produced by organisms are formed in ambient conditions and with a limited selection of elements. Nevertheless, living organisms reveal elegant strategies for achieving specific functions, ranging from skeletal support to mastication, from sensors and defensive tools to optical function. Using state-of-the-art characterization techniques, we present a biostrategy for strengthening and toughening the otherwise brittle calcite optical lenses found in the brittlestar Ophiocoma wendtii. This intriguing process uses coherent nanoprecipitates to induce compressive stresses on the host matrix, functionally resembling the Guinier–Preston zones known in classical metallurgy. We believe that these calcitic nanoparticles, being rich in magnesium, segregate during or just after transformation from amorphous to crystalline phase, similarly to segregation behavior from a supersaturated quenched alloy.

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