Preparation of biphasic brushite-apatite orthopedic cement powders by chemical precipitation

Brushite (CaHPO₄·2H₂O, dicalcium phosphate dihydrate) is known to be the precursor to the mineralized portion (HA: calcium hydroxyapatite, Ca₁₀(PO₄)₆(OH)₂) of hard tissues in the biological crystallization processes. In other words, it can be readily asserted that there must be a point of equilibrium (within the three-dimensional pH, temperature and concentration space) between brushite and hydroxyapatite phases in physiological solutions. While brushite is acidic, hydroxyapatite is a basic phase. It is also known that mixtures which contain these phases, in appropriate mixing ratios, could undergo a neutralization reaction in aqueous solutions at the human body temperature of 36.5°C. Based on these facts, it would be possible to produce bone cements, for orthopedic applications, from the biphasic powder mixtures of brushite and apatite. The feasability of synthesizing these biphasic powder mixtures in variable phase ratios have been tested, for the first time in this study, by using a single-step chemical precipitation process. This paper explains this novel process and analyzes the X-ray diffraction and infrared spectroscopy data obtained from these powders.