Accessible Unlicensed Requires Authentication Published by De Gruyter March 31, 2018

Nanocrystalline apatites: The fundamental role of water

Christophe Drouet, Maëlenn Aufray, Sabrina Rollin-Martinet, Nicolas Vandecandelaère, David Grossin, Fabrice Rossignol, Eric Champion, Alexandra Navrotsky and Christian Rey
From the journal American Mineralogist


Bone is a natural nanocomposite. Its mineral component is nanocrystalline calcium phosphate apatite, whose synthetic biomimetic analogs can be prepared by wet chemistry. The initially formed crystals, whether biological or synthetic, exhibit very peculiar physicochemical features. In particular, they are nanocrystalline, nonstoichiometric, and hydrated. The surface of the nanocrystals is covered by a non-apatitic hydrated layer containing mobile ions, which may explain their exceptional surface reactivity. For their precipitation in vivo or in vitro, for their evolution in solution, for the 3D organization of the nanocrystals, and for their consolidation to obtain bulk ceramic materials, water appears to be a central component that has not received much attention. In this mini-review, we explore these key roles of water on the basis of physicochemical and thermodynamic data obtained by complementary tools including FTIR, XRD, ion titrations, oxide melt solution calorimetry, and cryo-FEG-SEM. We also report new data obtained by DSC, aiming to explore the types of water molecules associated with the nanocrystals. These data support the existence of two main types of water molecules associated with the nanocrystals, with different characteristics and probably different roles and functions. These findings improve our understanding of the behavior of bioinspired apatite-based systems for biomedicine and also of biomineralization processes taking place in vivo, at present and in the geologic past. This paper is thus intended to give an overview of the specificities of apatite nanocrystals and their close relationship with water.

†Special collection papers can be found online at


The authors thank the Agence Nationale de la Recherche (ANR) for funding in the scope of the NanoBiocer and BioCapabili projects (ANR-07-BLAN-0373 and PICF 2009). The thermodynamic work at Davis was supported by the France Berkeley Fund (FBF) and the Institut National Polytechnique de Toulouse (INPT).

The authors also thank the GdR CNRS no. 3584 TherMatHT ( and the Thermodynamics Consortium ( for fruitful discussion and collaborative work on the present contribution.

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Received: 2017-11-29
Accepted: 2018-1-9
Published Online: 2018-3-31
Published in Print: 2018-4-25

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