Phase transformation of octacalcium phosphate in vivo and in vitro.

Octacalcium phosphate (OCP) was implanted in both thigh muscle pouches of ddY mice for 3 weeks, and was soaked in a simulated body fluid (SBF) and 1% NaCl solution maintained at 37 degrees C for 1 day, 1 week and 3 weeks. After implantation or soaking, the specimens were characterized by scanning electron microscopic analyses, X-ray diffractometry, and infrared absorption spectroscopy. X-ray diffraction study showed that OCP had been completely transformed to apatite with low crystallinity such as the mouse's femur after a 3-week implantation in the mouse body, and an apatic crystal was formed after soaking in the NaCl solution. The IR absorption spectra revealed that CO3 was incorporated in the apatite formed from OCP in both the mouse body and the NaCl solution, while OCP changed little after soaking in the SBF. It seems that the magnesium ion retards the transformation of OCP to apatite.