Effect of fluoride and hydroxyl group on bioactivity of the anodized films prepared by two-step anodization at low current density

Titanium and its alloys are promising dental implant materials. In order to improve the bioactivity of the anodized films, the two-step anodization was performed to produce the films. The steps were performed at 0.2 mA/cm² for 30 min in electrolytes containing H₃PO₄/C₂H₅OH and H₃PO₄/C₂H₅OH/NH₄F, respectively. The anodized films were soaked in a simulated body fluid (SBF). The effects of surface roughness, hydroxyl groups, fluoride, and hydrophilicity groups on the bioactivity were investigated and were found on the anodized films formed under two-step anodization using 1 M H₃PO₄ + 80% V/V C₂H₅OH + 0.75 wt% NH₄F. The bioactivity evaluation showed that the combination of two-step anodization in NH₄F as an electrolyte induced a formation of apatite on the anodized films. The surface roughness, hydroxyl groups, and fluoride formed on the hydrophilic anodized films are found to be responsible for the rapid formation of hydroxyapatite during SBF soaking. This will be useful in various biomedical applications especially in dental implant procedures.