Tuning hardness in calcite by incorporation of amino acids

Yi-Yeoun Kim, Joseph Carloni, Beatrice Demarchi, David Sparks, David Reid, Miki Kunitake, Chiu Tang, Melinda Duer, Colin Freeman, Boaz Pokroy, Kirsty Elizabeth Helena Penkman, John Harding, Lara Estroff, Shefford Baker, Fiona C. Meldrum

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Structural biominerals are inorganic/organic composites that exhibit remarkable mechanical properties. However, the structure–property relationships of even the simplest building unit—mineral single crystals containing embedded macromolecules—remain poorly understood. Here, by means of a model biomineral made from calcite single crystals containing glycine (0–7 mol%) or aspartic acid (0–4 mol%), we elucidate the origin of the superior hardness of biogenic calcite. We analysed lattice distortions in these model crystals by using X-ray diffraction and molecular dynamics simulations, and by means of solid-state nuclear magnetic resonance show that the amino acids are incorporated as individual molecules.We also demonstrate that nanoindentation hardness increased with amino acid content, reaching values equivalent to their biogenic counterparts. A dislocation pinning model reveals that the enhanced hardness is determined by the force required to cut covalent bonds in the molecules.
Original languageEnglish
Pages (from-to)903-910
Number of pages8
JournalNature Materials
Issue number8
Early online date2 May 2016
Publication statusPublished - 1 Aug 2016

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