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The formation of a biologically equivalent carbonated apatite on the surface of synthetic calcium phosphate ceramics (CPC) may be an important step leading to bonding with bone. Reactions of several single phase CPCs upon immersion into a simulated physiological solution (SPS) with an electrolyte composition of human plasma were determined.The CPCs covered a wide range of stabilities from hydroxyapatites (HA) to metastable tricalcium phosphates (TCP) and tetracalcium phosphate (TTCP). Changes in chemical compositions of SPS and infrared spectral features after CPC immersion were analyzed. New phase formation was observed on all the CPCs. However, kinetics, compositions, and structures of the new phases were significantly different.
The studied CPCs can be characterized by the time to new phase formation in vitro: it was found to increase in the order: not well crystallized (wc) HAS <well crystallized (wc) HAs <α-TCP, TTCP <β-TCP. Only calcium-deficient HA (CDHA) and nwc stoichiometric HAs (s-HA) led to immediate new phase formation. The phase was identified as carbonated apatite. The wc HAs and β-TCP did not elicit carbonated apatite formation within the time frame of the experiment. TTCP transformed intensively to poorly crystallized carbonated apatite after 2 days of immersion.
calcium phosphate, phase transformation, precipitation
Professor, University of Pennsylvania, Philadelphia, PA
Research Specialist, University of Pennsylvania, Philadelphia, PA