IONIC INTERACTION WITH BONE MINERAL .4. VARYING AFFINITY OF SYNTHETIC CALCIUM PHOSPHATES FOR CA2+

The concentration of Ca2+ and PO43- in the liquid film surrounding the crystals of several synthetic calcium phosphates suspended in an aqueous medium was calculated from 45Ca2+ and 32PO43- exchange studies performed under physiological conditions. This permitted an estimation of the uptake of Ca2+ and PO43- from solution by the solid phase alone, exclusive of the uptake by the adherent liquid film. The compounds with low calcium-to-phosphate molar ratio (Ca/P) showed a greater affinity for Ca2+ than those with higher Ca/P. Octacalcium phosphate (Ca/P = 1.33) incorporated considerably more Ca2+ than PO43-. Tricalcium phosphate (Ca/P = 1.5), Bio-Rad apatite (Ca/P = 1.51), G-D apatite (Ca/P = 1.63), and L-apatite (Ca/P = 1.67), all of which gave apatitic X-ray diffraction patterns, demonstrated an uptake of Ca2+ in decreasing order, and an uptake of PO43- in increasing order. © 1968.