Theoretical Defect Energetics in Calcium Phosphate Bioceramics

Abstract

Vacancies, impurities, and foreign ions dissolving in calcium phosphate bioceramics play an important role in the biological properties of the materials. However, little is known about the thermodynamic stability of the defects. In this regard, point defects in hydroxyapatite (HAp) and octacalcium phosphate (OCP) were calculated in a first-principles manner, and the chemical-potential dependence of the defect formation energies was revealed. In particular, because calcium phosphates are usually subjected to an aqueous solution, a methodology to evaluate ionic chemical potentials under chemical equilibrium of the solid-aqueous solution was introduced. In the present article, recent results based on such a methodology (the solution pH dependence of Ca/P molar ratio of HAp and the ion-exchange ability with foreign cations in HAp and OCP) were reviewed. Feature D. J. Green-contributing editor

First-principles calculations of divalent substitution of Ca2+ in tricalcium phosphates

“…In this regard, however, details were already described in our preceding papers [23][24][25]. Therefore, only some important points are briefly described as follows.…”

Surface properties of biomimetic nanocrystalline apatites; applications in biomaterials

“…Non-stoichiometry is related to vacancies in Me sites and Y sites. Significant number of vacancies in XO 4 sites have never been reported and theoretical calculations have shown that the creation of PO 4 vacancies in calcium phosphate hydroxyapatite would be associated with strong destabilization of the structure [17]. In other terms, the creation of large defects like XO 4 vacancies in the apatite structure would produce a collapse of the structure and the formation of other phases, whereas small defects like those corresponding to Me and Y vacancies allow preservation of the structure, although they are associated with a loss of cohesion and stability.…”

Quantification of trace metals in deciduous tooth enamel using energy dispersive X-ray fluorescence spectrometry

“…Divalent zinc and magnesium are known to adsorb onto the HAP crystals but with lower affinity than calcium (7). In a more recent work, Matsunaga measured ionic substitution energies of various divalent cations in saturated hydroxyapatite solutions, with some findings shown in figure 1.2 (8). Although the exact energies from Matsunaga's work are specific to the controlled conditions of the experiment, the pattern of decreasing substitution energy is understood to be related to the increasing electronegativity of the cations and also to their ionic radius (8).…”