Formation of Amorphous TiO2 Film on Ti Using Anodizing in Concentrated H3PO4 Aqueous Solution and Its Osteoconductivity

Anodizing of Ti specimens were performed in concentrated H3PO4 aqueous solutions with a purpose to incorporate a large amount of phosphate ion into anodized coatings, and their osteoconductivity was evaluated in in vivo test. Ti specimens were anodized in 0.1­11M H3PO4 aqueous solutions up to 200V at a rate of 0.1V s11. Anodized coatings were evaluated with SEM, TEM, XRD, XPS, and laser microscope. Anodized specimens were implanted in rats’ tibia for 14 d, and then extracted. When anodized in concentrated (22M) H3PO4 aqueous solutions under spark discharge, crystallized anatase transformed to amorphous anatase by containing a large amount of PO4 in crystal lattice of TiO2. The amorphous anatase coatings had better osteoconductivity than the crystallized anatase coatings. It is not exactly clear what was the intrinsic factor for the high osteoconductivity, but the crystallinity of anatase and/or PO4 in the film is considered to be responsible for the difference in bone-forming ability of TiO2 films. [doi:10.2320/matertrans.M2011234]