PARTICLE MICROELECTROPHORESIS OF CALCIUM-DEFICIENT HYDROXYAPATITE - SOLUTION COMPOSITION AND KINETIC EFFECTS

Concurrent work demonstrates that the zeta potential of bone is multiv alued and systematically alterable by changes in sample preparation, s teeping fluid composition, and steeping time. Since bone mineral is a mixture of carbonated calcium-deficient hydroxyapatites, and since the zeta potential of calcium-deficient hydroxyapatite (CDHA) is altered by pH and time in HNO3-KOH solutions, the zeta potential of CDHA in ph ysiologic Neuman's fluid (NF) compared with that seen in bone could re veal important information on the contribution of the mineral phase to the zeta potential of bone. In addition, such information may be valu able in designing and evaluating calcium-phosphate ceramics for increa sed bone ingrowth. Results demonstrate that the zeta potential of CDHA in NF is negative. With increasing calcium in NF, the zeta potential magnitude of CDHA decreases and inverts to positiVe values given suffi cient calcium concentration and steeping time. This result is opposite to that seen in bone, suggesting that exposed CDHA is not the predomi nant bone microsurface and implicating a bone surface protein componen t. With increasing phosphate in NF, the zeta potential magnitude incre ases to more negative values. While low concentrations of fluoride sho wed no effect, the possibility of an effect with higher concentrations is still to be determined.