SERUM-HYDROXYAPATITE INTERACTION IN-VITRO

In a project to develop hydroxyapatites for bone replacement, biologic al and synthetic types were prepared at 600 degrees C, ground to 300-6 00 mu m and immersed in a pooled human serum for periods up to 1 month at 4 degrees C to assess material interaction. It was found that the levels of calcium in the serum were reduced at 6 h immersion, followed by an increase to reach maximum at 48 h and then stability up to 1 mo nth. Phosphorus levels showed the opposite behaviour. Both apatites sh owed similar trends, although higher values were recorded for the synt hetic type, suggesting higher activity. Infrared spectral analysis com plemented the biochemical values, where the optical densities (O.D.) o f phosphate groups were reduced, reflecting the increased phosphorus i n serum and denoting leaching. Also, O.D. values of both CO32- and OH- groups were reduced at 10 h, then returned to original levels. Scanni ng electron microscopy revealed a spongy appearance parallel with redu ced O.D. and higher levels of serum Ca2+. At longer periods (48 h) the concentric needles pf hydroxyapatite are clearly shown to be deposite d on biological apatite. Differences in responses were attributed to t heir original crystalline structure assessed by X-ray diffraction anal ysis, as well as pore analysis using a mercury porosimeter.