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Detection of Posner's clusters during calcium phosphate nucleation: a molecular dynamics study

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Abstract

Hydroxyapatite (HA), the main mineral phase of mammalian tooth enamel and bone, originates in body fluids from amorphous calcium phosphate (ACP). ACP presents short-range order in the form of small domains with size of 0.9 nm and chemical formula Ca9(PO4)6, known as Posner's clusters. In this study, the aggregation and clustering of calcium and phosphate ions in water has been investigated by means of shell-model molecular dynamics simulations. Calcium phosphate aggregates form in solution with compositions and Ca coordination that are similar to those found in Posner's cluster, but the stoichiometry of these species is dependent on the ionic composition of the solution: calcium-deficient clusters in solutions with low Ca : P ratio; cluster containing protonated phosphate groups in neutral solutions; sodium ions partially substituting calcium in solutions containing a mixture of sodium and calcium ions. These Posner-like clusters can be connected by phosphate groups, which act as a bridge between their central calcium ions. The simulations of the aggregation in solution of calcium phosphate clusters are an unbiased and unequivocal validation of Posner's model, and reveal for the first time the structure and composition of the species that form during the early stages of ACP nucleation at a scale still inaccessible to experiment.

Graphical abstract: Detection of Posner's clusters during calcium phosphate nucleation: a molecular dynamics study

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Publication details

The article was received on 02 May 2017, accepted on 21 Jul 2017 and first published on 21 Jul 2017


Article type: Paper
DOI: 10.1039/C7TB01199G
Citation: J. Mater. Chem. B, 2017, Advance Article
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    Detection of Posner's clusters during calcium phosphate nucleation: a molecular dynamics study

    G. Mancardi, C. E. Hernandez Tamargo, D. Di Tommaso and N. H. de Leeuw, J. Mater. Chem. B, 2017, Advance Article , DOI: 10.1039/C7TB01199G

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