Interfaces in graded coatings on titanium-based implants

Graded bilayered glass-ceramic composite coatings on Ti6Al4V substrates were fabricated using an enameling technique. The layers consisted of a mixture of glasses in the CaO-MgO-Na2O-K2O-P2O5 system with different amounts of calcium phosphates (CPs). Optimum firing conditions have been determined for the fabrication of coatings having good adhesion to the metal, while avoiding deleterious reactions between the glass and the ceramic particles. The final coatings do not crack or delaminate. The use of high-silica layers (> 60 wt % SiO2) in contact with the alloy promotes long-term stability of the coating; glass-metal adhesion is achieved through the formation of a nanostructured Ti5Si3 layer. A surface layer containing a mixture of a low-silica glass (similar to 53 wt % SiO2) and synthetic hydroxyapatite particles promotes the precipitation of new apatite during tests in vitro. The in vitro behavior of the coatings in simulated body fluid depends both on the composition of the glass matrix and the CP particles, and is strongly affected by the coating design and the firing conditions. (c) 2008 Wiley Periodicals, Inc. J Biomed Mater Res 88A: 1010-1021, 2009