CHARACTERIZATION OF THIN HYDROXYAPATITE LAYERS FORMED ON ANODIC TITANIUM-OXIDE FILMS CONTAINING CA AND P BY HYDROTHERMAL TREATMENT

An anodic titanium oxide film containing Ca and P (AOFCP) was formed o n commercially pure titanium which was anodized in an electrolytic sol ution of dissolved beta-glycerophosphate (beta-GP) and calcium acetate (CA). Hydroxyapatite (HA) crystals were precipitated by hydrothermall y heating the AOFCP at 300 degrees C. After hydrothermal treatment, th e film was characterized by scanning electron microscopy (SEM), energy -dispersive X-ray microanalysis (EDX), and tensile tests. The morpholo gy, composition, and amount of HA crystals precipitated were significa ntly affected by the composition of the electrolytes. Near-stoichiomet ric HA crystals with high crystallinity were precipitated completely c overing the AOFCP surface at specific electrolyte concentrations. The HA layers were thin at 1-2 mu m in thickness. The adhesive strength of the film increased with decreasing electrolyte concentration and the maximum value was about 40 MPa. In vitro tests for 300 days suggested that the stability of the film was high. The high adhesive strength ma y result from the AOFCP existing as an intermediate layer between the HA layer and a titanium substrate. The intervention of the AOFCP may h ave prevented abrupt changes in Ca and P content at an HA coating-tita nium interface as seen in a plasma-sprayed one. The porous TiO2 matrix of the AOFCP may be suitable for nucleation sites of HA crystals, as well as SiO2 matrix of silicate bioactive glasses or glass ceramics. ( C) 1995 John Wiley and Sons, Inc.