In vivo dissolution behavior of various RF magnetron-sputtered Ca-P coatings on roughened titanium implants

RF magnetron sputter deposition was used to produce 0.1, 1.0 and 4.0 μm thick Ca-P coatings on TiO2-blasted titanium discs. Half of the as-sputtered coated specimens were subjected to an additional infrared heat treatment for 30 s at 425–475°C. X-ray diffraction demonstrated that infrared radiation changed the amorphous 4 μm sputtered coatings into an amorphous–crystalline structure, while the amorphous 0.1 and 1 μm changed in a crystalline apatite structure with the presents of tetracalciumphosphate as a second phase. Scanning electron microscopically examination of the sputtered coatings revealed that annealing of the 4 μm thick coatings resulted in the appearance of small cracks. Subsequently, the discs were implanted subcutaneous into the back of rabbits. After 1, 4, 8 and 12 weeks of implantation, the implants were retrieved and prepared for histological and physicochemical evaluation. Histological evaluation revealed that the tissue response to all coated implants was very uniform. A very thin connective tissue capsule surrounded all implants. The capsule was usually free of inflammatory cells. At the interface, there was a close contact between the capsule and implant surface and no inflammatory cells were seen. Physicochemical evaluation showed that the 0.1 and 1 μm thick amorphous coatings had disappeared within 1 week of implantation. On the other hand, the 4 μm thick amorphous phase disappeared during the implantation periods, which was followed by the precipitation of a crystalline carbonate apatite. Further, at all implantation periods the heat-treated 1 and 4 μm thick coatings could be detected. Occasionally, a granular precipitate was deposited on the heat-treated 4 μm thick coating. Fourier transform infrared spectroscopy showed the formation of carbonate apatite (CO3-AP) on the 4 μm thick amorphous coating and on the heat-treated specimens. On basis of our findings, we conclude that 1 μm thick heat-treated Ca-P sputter coating on roughened titanium implants appear to be of sufficient thickness to show bioactive properties, under in vivo conditions.