Solution-Mediated Transformation of Octacalcium Phosphate (OCP) to Apatite

Authors

R. Z. LeGeros, New York University
G. Daculsi, INSERM
I. Orly, INSERM
T. Abergas, New York University
W. Torres, New York University

Abstract

OCP crystals were hydrolyzed in solutions containing Ca²⁺, Mg²⁺, HPO₄^2-, CO₃^2-, F^-, citrate or P₂O₇ ions. Products of hydrolysis were analyzed using scanning (SEM) and transmission (TEM) electron microscopy, infrared spectroscopy and x-ray diffraction.

Results demonstrated that the OCP to Apatite (AP) transformation is influenced by: (1) types of ions in solution: inhibited by Mg²⁺, citrate or P₂O₇^4-; facilitated by F^-, CO₃^2-, HPO₄^2- or Ca²⁺ ions; (2) ionic concentrations; (3) solution pH; (4) OCP crystal size. SEM showed needle-like micro-crystals on the surfaces and ends of OCP macrocrystals. TEM showed side-to-side and end-to-end arrangements and presence of central defects in the apatite crystals. IR spectra showed the incorporation of CO₃, or HPO₄, the HPO₄ incorporation being least from F-containing solutions. These results suggest that OCP to AP transformation occurred by the process of dissolution of OCP and subsequent precipitation of Ca-deficient apatites, incorporating CO₃^2-, HPO₄^2- or F^- present in solution.

These results indicate that the observed stabilty of OCP in pathological calcifications may be due to the presence of Mg²⁺, citrate and/or P₂O₇^4- and/or low levels of CO₃^2-, F^-, Ca²⁺, HPO₄^2- ions in the biological fluids.

Recommended Citation

LeGeros, R. Z.; Daculsi, G.; Orly, I.; Abergas, T.; and Torres, W. (1989) "Solution-Mediated Transformation of Octacalcium Phosphate (OCP) to Apatite," Scanning Microscopy: Vol. 3: No. 1, Article 16.
Available at: https://digitalcommons.usu.edu/microscopy/vol3/iss1/16