Calcium-deficient hydroxyapatite (HA) with a calorimetric peak. Variations in calcium, magnesium, and Ca/P molar ratio of 1.50 was synthesized in various concen-phosphate concentrations and pH with time were detertrations (0.01-75 mM) of MgCl 2 at 37.4ЊC by reaction between mined. Increasing the magnesium concentration resulted in particulate CaHPO 4 и 2H 2 O and Ca 4 (PO 4 ) 2 O. The effects of elevated calcium concentrations. After an initial decrease in magnesium on the kinetics of HA formation were determined magnesium owing to its adsorption onto HA nuclei and using isothermal calorimetry. All reactions completely con-precursor(s), a period of slow reaction at constant magnesium sumed the precursor phases as indicated by X-ray diffraction concentration was observed. Both the magnesium concentraanalysis and a constant enthalpy of reaction (240 kJ/mol).
tion in solution and the proportions of precursors present Magnesium concentrations below 1 mM had no effect on the decreased prior to any evidence of a crystalline product kinetics of HA formation. Magnesium concentrations be-phase. This is attributed to the formation of NCP capable tween 1 and 2.5 mM affected the reaction path but did not of incorporating magnesium. This noncrystalline phase affect the time required for complete reaction. Higher concen-persisted for more than 1 year for reactions in magnesium trations extended the times of complete reaction due to mag-concentrations about 2.5 mM. Its conversion to HA renesium adsorption on the precursor phase(s) and HA nuclei, sulted in the release of magnesium to the solution. © 1997 and stabilization of a noncrystalline calcium phosphate John Wiley & Sons, Inc. J Biomed Mater Res, 36, 306-314, 1997. (NCP). HA formation in the presence of magnesium resulted in separation of the following two events: initial formation Key words: magnesium; hydroxyapatite; calcium phosphate of HA nuclei and NCP, and consumption of CaHPO 4 и 2H 2 O. cement; inhibition; amorphous calcium phosphate; nucle-This was indicated by the appearance of an additional ation and growth
Correspondence to: P. W. Brown cipitation of HA from low supersaturation