The effect of structural characteristics on the in vitro bioactivity of hydroxyapatite

In previous studies a film of hydroxylapatite (HA) was coated onto the inner pore surfaces of reticulated alumina for bone substitutes with the use of a so‐called thermal deposition method. In this process, the HA films must be sintered at high temperatures for a strong adhesion to the alumina substrate. It has been found that high‐temperature sintering inevitably changes the crystallinity of the coated HA, and in turn affects its bioactivity. Therefore, in this study, in vitro experiments were carried out to investigate the effects of structural changes on the in vitro bioactivity. The factors dominating in vitro bioactivity of HA, including surface area, degree of crystallinity, and temperature, were identified. The activation energy for volume diffusion was calculated for different in vitro solution temperatures. Also discussed is the underlying mechanism of growth and dissolution processes during the in vitro test. © 2002 Wiley Periodicals, Inc. J Biomed Mater Res (Appl Biomater) 63: 71–78, 2002