Abstract
Microstructural factors may play a role in the osseointegration of calcium phosphates. In this paper, direct microstructural interactions between crystalline calcium phosphates and the biological milieu are reported. Degradation via exposure to osteoblast culture closely resembles in vivo interactions with subcutaneous tissues in a bovine model at early time periods. That these interactions were common to both experiments constitutes one of the few known examples of in vitroโin vivo correspondence. Interestingly, the degradation of phase pure hydroxyapatite (HA) in vitro was more rapid than that of biphasic HA in vivo. In both cases, grain extraction/pullout was frequently observed. This suggests a connection to smallerโscale observations of epitaxial CHA nucleation and growth on preโexisting HA grains. A microstructure in which the grain boundary is dissolving/corroding can apparently be disassembled by forces transmitted through biological structures. These observations are distinct from those of simple nonโbiological solutions and prove that biological environments can interact with the material beneath the ceramicโcell/ceramicโtissue interface. Many often ignored microstructural factorsโgrain size, shape, grain boundary strength and the presence of impurity phasesโmay in fact control degradation. We also suggest that even relatively modest initial grain sizes will, in combination with the mild/absent foreign body response to calcium phosphates, result in lengthy in vivo particle resistence. ยฉ 2003 Wiley Periodicals, Inc. J Biomed Mater Res 68A: 61โ70, 2004