Preferred growth orientation of biomimetic apatite crystals

Simulated body fluid (SBF) solutions are widely used for in vitro bioactivity tests and to coat bioinert materials with biomimetic calcium phosphates. In this study, a SBF solution was used to precipitate hydroxy carbonated apatite (HCA) with a general formula Ca10−x(HPO4)x−y(CO3)y(PO4)6−x(OH)2−x on a bioactive titanium surface. X-ray diffraction (XRD) as well as cross-sectional transmission electron microscopy (TEM) analyses revealed that the biomimetically derived crystallites show a preferred growth orientation in direction of their c-axis and perpendicular to the surface of the bioactive substrate. This growth behaviour as well as the measured crystal dimensions ranging from 5×10×20 to 5×20×100 nm are very similar to that found in the mineral part of mammalian bone, where the c-axes of plate-shaped apatite crystals are well aligned with the long axes of the collagen fibrils.