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Synthetic nacre by predesigned matrix-directed mineralization

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Science  07 Oct 2016:
Vol. 354, Issue 6308, pp. 107-110
DOI: 10.1126/science.aaf8991

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Making nacre shine in the lab

Many of the materials that animals use to make shells and skeletons are built with brittle or soft molecules. They owe their amazing mechanical properties to their layered construction, which is a challenge for synthetic fabrication. Pearly nacre, for example, has proved challenging to make owing to its complex structure of aragonite crystals in an organic matrix. Using an assembly-and-mineralization approach, Mao et al. have managed to fabricate nacre in the laboratory (see the Perspective by Barthelat). First, a layered, three-dimensional chitosan matrix is made, within which aragonite nanocrystals are precipitated from a solution containing calcium bicarbonate.

Science, this issue p. 107; see also p. 32

Abstract

Although biomimetic designs are expected to play a key role in exploring future structural materials, facile fabrication of bulk biomimetic materials under ambient conditions remains a major challenge. Here, we describe a mesoscale “assembly-and-mineralization” approach inspired by the natural process in mollusks to fabricate bulk synthetic nacre that highly resembles both the chemical composition and the hierarchical structure of natural nacre. The millimeter-thick synthetic nacre consists of alternating organic layers and aragonite platelet layers (91 weight percent) and exhibits good ultimate strength and fracture toughness. This predesigned matrix-directed mineralization method represents a rational strategy for the preparation of robust composite materials with hierarchically ordered structures, where various constituents are adaptable, including brittle and heat-labile materials.

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