In vitro and in vivo behaviour of Ca- and P-enriched anodized titanium

The influence of different surface preparations on titanium biocompatibility and bone integration was evaluated. Commercially grade 2 titanium rods (diameter 2 mm, length: 3 mm), vacuum annealed and hydrofluoric acid etched was selected for its promising surface characteristics to achieve good direct osseointegration. Some rods were surface modified by Anodic Spark Discharge anodization and a thin layer (approximately 5 microm) of amorphous TiO2 containing Ca and P (Ti/AM) was obtained. Some of the Ti/AM specimens underwent a further hydrothermal treatment to produce a thin outermost layer (approximately 1 microm) of hydroxyapatite (Ti/AM/HA). Cytotoxicity tests (direct contact: ISO 10993-5) showed good cytocompatibility for all tested samples. Ti and tissue culture substrate + DMEM control, respectively, were associated with a significant higher proportion of attached cells than Ti/AM and Ti/AM/HA (P < 0.0005), but this was in the normal range of 10-20% of unattached cells for cytocompatible materials. Histomorphometric analysis conducted on samples inserted in the cancellous bone of distal femoral epiphysis of Sprague-Dawley rats gave the following results at 4 and 8 weeks: Affinity index (AI%) data proving the surface osteconductive properties of non-anodized acid etched Ti (AI-4 weeks: 67.1 +/- 17.0%; AI-8 weeks: 74.8 +/- 11.5%). Ti/AM samples showed the lowest values (AI-4 weeks: 45.8 +/- 15.9%; AI-8 weeks: 68.5 +/- 13.6%) while the best performances of the Ti/AM/HA samples (AI-4 weeks: 60.4 +/- 21.8%; AI-8 weeks: 79.5 + 9.37%) indicated that hydroxyapatite allowed a higher bone to implant contact respect to Ti only. Further investigations should be performed in order to better understand the mechanism of observed in vitro behaviour and to achieve information on long-term osseointegration process.