Serum-hydroxyapatite interaction in vitro

Abstract

In a project to develop hydroxyapatites for bone replacement, biological and synthetic types were prepared at 600°C, ground to 300–600μm and immersed in a pooled human serum for periods up to 1 month at 4°C to assess material interaction. It was found that the levels of calcium in the serum were reduced at 6h immersion, followed by an increase to reach maximum at 48h and then stability up to 1 month. Phosphorus levels showed the opposite behaviour. Both apatites showed similar trends, although higher values were recorded for the synthetic type, suggesting higher activity. Infrared spectral analysis complemented the biochemical values, where the optical densities (O.D.) of phosphate groups were reduced, reflecting the increased phosphorus in serum and denoting leaching. Also O.D. values of both CO 3 2− and OH − groups were reduced at 10h, then returned to original levels. Scanning electron microscopy revealed a spongy appearance parallel with reduced O.D. and higher levels of serum Ca 2+. At longer periods (48h) the concentric needles of hydroxyapatite are clearly shown to be deposited on biological apatite. Differences in responses were attributed to their original crystalline structure assessed by X-ray diffraction analysis, as well as pore analysis using a mercury porosimeter.