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.