Porous cylindrical (L = 10 mm, Ø = 6 mm) titanium (Ti6-Al-4V) implants were used (Biomet, Warsaw, IN). Additionally, half of the implants had their surfaces coated with gold, as follows. The implants were electrolytically cleaned by cathodic polarization of the implant for a heavy formation of hydrogen gas at the surface. The treatment14 ,15 was carried out in a strong alkaline solution containing NaOH. Each implant was afterward immersed in a weak acid solution (5% H2SO4), neutralizing the alkaline film at the surface. Initial electrolytic strike plating with gold (~0.5 μm) was carried out in an acid gold electrolyte based upon a gold tetrachloride complex AuCl4− to improve the adhesion of the following gold layer. After assuring that the initial strike plating was made properly upon the titanium surface, a 100% pure gold coating with low mechanical stress was applied by deposition of a 3- to 4-μm-thick gold layer from a weak acid gold bath based upon AuCN. Between each of the process steps, careful rinse in pure water was carried out to avoid contamination. The gold plating was carried out in The Technical University of Denmark.
Figure 2 shows that this plating process guaranteed that the electrolytic gold layer was applied on the surface and also in the porous interlocks without disturbing the porosity of the implant. Holes in the gold plating were, however, quite common.
Scanning electron microscopy and energy dispersive spectroscopy confirmed the base implant characterization stated by the supplier, and that the gold layer was correctly plated at the surface of half of the implants (data not shown).