Chemical etching of micro-plasma oxidized titania film on titanium alloy and apatite deposited on the surface of modified titania film in vitro

TiO2 film was deposited on titanium alloy by micro-plasma oxidization (MPO) in an electrolyte containing (NaPO3)6 and NaOH. A chemical etching (NaOH aqueous solution) was used to modify the surface of the MPO film to form specific surface structure favorable for apatite deposition. The surface of the MPO film was mainly composed of anatase, while that of the chemically etched MPO (CE-MPO) film shows anatase phase containing Na, Ti and O. Moreover, ribbon-like products with an interlaced morphology were found on the surface of the CE-MPO film. During the chemical etching process, phosphorus of the surface of the MPO film dissolved into the NaOH aqueous solution. Negatively charged HTiO3− ions are formed on the MPO film surface due to the attack of OH− ions on TiO2 phase of the MPO film. The negatively charged HTiO3− ions could incorporate sodium ions from the NaOH aqueous solution to form sodium titanate. When incubated in a simulated body fluid (SBF) for 7 and 14 days, the MPO film does not exhibit apatite-forming ability; however, apatite was deposited on the CE-MPO film probably due to the formation of hydroxyl functionalized surface via an ionic exchange between Na+ ions of the CE-MPO film and H3O+ ions of the SBF.