In vitro bioactivity evaluation of nano- and micro-crystalline anodic TiO ₂: HA formation, cellular affinity and organ culture

Anodization is an easily viable technique useful for producing TiO ₂ coatings on titanium substrates. Nano-crystalline anodic TiO ₂ structure was produced on titanium at 20 V using 1 M Na ₂SO ₄ and 0.5% NaF and consolidated by a further heat-treatment. Micro-crystalline anodic TiO ₂ was produced on titanium by applying a galvanostatic current density of 70 A/m ² in water medium. To assess the usefulness of these nano- and micro-oxides for bone implant stability, physical properties and bone in vitro bioactivity including HA formation, cellular affinity and mouse-tissue morphogenesis, were evaluated. Bioactivity of the different anodic surfaces was evaluated by treating them in a simulated body fluid (SBF) to form hydroxyapatite (HA) and the rates of HA formation were compared. Deposits of HA could be seen on the nano-oxide surface within 7 days, whereas HA was detected only after 14 days on the micro-oxide surface. In vitro cell culture tests done using mouse osteoblasts indicated that the nano-oxides showed statistically significant cell activity than the micro-oxides and the machined titanium. Branching morphogenesis test done for 72 h on these surfaces showed more branching on the micro- and nano-oxides as compared with titanium surface.