Anodized titanium with calcium and phosphorus surface enhancements for dental and orthopedic implant applications

•Hydrothermal treatments optimized calcium-phosphate ratios on anodized titanium.•Hydrothermal soaked anodized revealed superior adhesion compared to hydroxyapatite.•Anodization and hydrothermal soak combinations increased apatite formation.•Hydrothermal soaking enhanced osteoblast mineralization on anodized titanium. Titanium anodization in mixed-acid electrolytes containing phosphoric acid has been shown to result in phosphorus (P)-doped amorphous or crystalline titanium oxide layers. Recently, aqueous hydrothermal soak treatments have been shown to further enhance the bioactivity of titanium and titanium oxide through the addition of calcium (Ca) to the specimen surfaces. For the present study, a combination of mixed-acid electrolyte anodization and subsequent calcium nitrate tetrahydrate (Ca(NO3)2) hydrothermal treatments were used to create optimized titanium specimens with favorable Ca/P surface ratios. Commercially pure titanium specimens were anodized in two mixed-acid electrolytes to final forming voltages of 72 V, 108 V, or 180 V. Three specimens per group were subsequently soaked for 72 h at 80°C in 1.2 M Ca(NO3)2 solution. Energy dispersive spectroscopy revealed the Ca(NO3)2-soaked specimens anodized to 108 V in each electrolyte exhibited favorable surface Ca/P ratios averaging of 2.27 and 1.67. Bioactivity testing revealed increased apatite formation on 108 V Ca(NO3)2-soaked specimens compared to their un-soaked counterparts. Pre-osteoblast cell culture studies showed similar cellular proliferation and differentiation but increased mineralization on Ca(NO3)2-soaked specimens. This two-step combination of anodization and subsequent Ca(NO3)2 hydrothermal treatments shows great promise for future biomaterials applications.