Organic Acid-Based Anodization Process to Produce Bioactive Oxides on Titanium Implants

Titanium implants are widely used in medicine because of their favorable mechanical properties and biocompatibility; however, the rapidly forming titanium oxide coatings do not provide an ideal bioactive surface to stimulate osseointegration. This study aims to enhance titanium implant osseointegration through anodization processes designed to incorporate elements and compounds present within human bone into the surface oxides. Commercially pure titanium grade 4 (CPTi) discs were anodized in either oxalic, malic, or ascorbic acid-based electrolytes. Each resulting oxide exhibited complex surface topographies. EDS analyses revealed that Ca, P, and Mg bone chemistry dopant elements were incorporated into each of the oxide coatings. X-ray diffraction analyses revealed combinations of anatase and calcium titanate compounds present in each oxide. Additionally, two of the anodized oxides showed calcium oxide formation, and one oxide also revealed tricalcium phosphate (α-TCP) and hydroxyapatite (HA) formation. Subsequent FTIR spectroscopy analyses revealed carbonate substitution peaks to be present in two of the oxides. This finding indicated that the TCP and HA compounds shown in the XRD analyses of one oxide represented the formation of bone-like carbonated calcium phosphate compounds. A 21-day cell culture study showed favorable cell culture responses for each of the organic-acid-based anodized oxides. Moreover, two of the oxides showed good cytocompatibility and early osteogenic differentiation compared to non-anodized titanium controls. Thus, the organic acid anodization processes developed in this study show promise to enhance future titanium implant clinical outcomes.