Ionic interaction with bone mineral vi response of the calcium phosphate mineral to calcifying solutions

Four synthetic calcium phosphate samples with different Ca/P or cation/P ratios were submitted to ⁴⁵Ca²⁺ and ³²PO₄^3- exchange for seven days in a standard solution approximating the 'physiologic' concentrations for Ca PO₄ Na and Cl. The samples exhibited different affinities for Ca²⁺ and PO₄^3- directly dependent on the composition of the solid. Optical and x-ray diffraction techniques were employed to detect changes in the solid phases. Variations directly related to the partition of Ca²⁺ and PO₄^3- into the solids and kinetics of isotope exchange were observed. Relative changes (before and after chemical treatment) were measured after pyrolysis of the samples. Interpretation of the data required knowledge of the phase equilibria in the CaO-P₂O₅-H₂O and CaO-P₂O₅ systems and the crystal chemistry of calcium phosphate apatites. Bone mineral is subject to long term exchange and equilibration with the surrounding serum. Maturation of bone crystallites may parallel the exchange reactions of the synthetic calcium phosphates.