Abstract
Double-layered calcium phosphate coating films consisting of layers with different crystallinity and composition were fabricated on titanium substrates by RF magnetron sputtering. The first layer of the double-layered coating film, i.e., the inner layer, was made of calcium phosphate having high crystallinity, the second layer, i.e., the outer layer, was made of calcium phosphate having low crystallinity. A double-layered HAp/OAp coating film was fabricated on the titanium substrate; as an inner layer, an HAp film was prepared on the titanium substrate by heat treatment of an OAp film in air at 873 K for 7.2 ks, and then, the HAp layer was coated with the OAp film. In the fabrication of a double-layered OAp/ACP coating film, the inner OAp and the outer ACP films were coated on the titanium substrate under different sputtering conditions. The thickness of the single layer was controlled to be 0.5 μm, and the total thickness of these double-layered coating films was around 1 μm. The coating film that comprises the double-layer was dense with a uniform thickness, and the two layers were in close contact with each other. The bonding strength of the HAp/OAp coating film was greater than 50 MPa. As in vivo evaluation, the removal torque of HAp/OAp-coated titanium implants from the femur of Japanese white rabbits was measured. The value of this torque was considerably higher than that of the removal torque of non-coated titanium implants. The outer OAp layer with low crystallinity appeared to dissolve after the 4-week implantation, while the inner HAp layer remained intact and was directly attached to the new bone.
