Anodic TiO₂ nanotubes from stirred baths: Hydroxyapatite growth & osteoblast responses

Self-organized porous nano-tubular TiO₂ was anodically formed on titanium from electrolyte containing 1 M Na₂SO₄ and 0.5 wt.% NaF. The oxidation was carried out for 2 h at 20 V and the electrolytes were stirred using (i) magnetic pellet and (ii) ultrasonic waves. The nanotubes have single-pore diameter of 50-90 nm under the magnetic pellet stirring and 75-110 nm under the ultrasonic agitation. The coatings were amorphous in this condition. Amorphous coatings cannot nucleate apatite easily and require crystallization heat-treatments for inducting apatite. The current nanotubes were heated for 2 h at 500 °C. This treatment converted them to crystalline mixed anatase and rutile. These heat-treated coatings were then immersed in simulated body fluid (SBF) for 5, 168 and 504 h to nucleate apatite. Apatite produced on ultrasonically obtained nanotube contained finer crystals. Cell culture studies were done on the control non-oxidized titanium and SBF-treated coatings using MG63 human osteosarcoma cells. Studies of total protein assay were done using the Pierce BCA protein assay. Ultrasonic stirring and 504 h of exposure to SBF has the best combination of apatite induction and protein activity. The higher bioactivity of this condition is attributed chiefly to the thicker apatite layer and finer apatite crystallite size.