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 80C 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.

Titanium surface modification by anodization has been shown to promote bone formation. However, interactions between anodized layers and bone cells depend upon the anodized layer surface composition and morphology. The present study evaluated the effect of anodized layer phosphorus content, crystallinity, surface porosity, and roughness on the MC3T3-E1 osteoblast response. Commercially pure titanium specimens were anodized in two mixed-acid electrolytes to final forming voltages of 108 V and 180 V. The oxide crystallinity, surface porosity, surface roughness, and elemental composition of each specimen type were determined by X-ray diffraction, scanning electron microscopy, atomic force microscopy, and energy dispersive spectroscopy analyses. Osteoblast-like MC3T3-E1 cell attachment, proliferation, differentiation, and mineralization were assessed using optical and fluorescence microscopy, total protein content, alkaline phosphatase activity, osteocalcin production, and alizarin red assays. Oxide crystallinity and surface roughness increased with anodization forming voltage in each electrolyte. Phosphorus (P) uptake increased with forming voltage in the phosphoric acid containing electrolyte. The total protein assay showed P-incorporated, low surface pore density oxides to exhibit initially delayed proliferation compared to non-P containing high surface pore density oxides. Alkaline phosphatase and osteocalcin assays showed trends of early differentiation and maturation for P-incorporated, low surface pore density oxides compared to non-P containing high surface pore density oxides. Highly crystalline anodized layers were shown to induce enhanced mineralization compared to non-anodized titanium specimens. Overall, the biochemical influence of P-incorporation into the oxide layers showed trends of earlier osteoblast differentiation and maturation. The combination of P-incorporation, an anatase phase oxide, a low surface pore density, and a high surface roughness showed the highest mineralization levels.

The present study focused on evaluation of anodized oxides prepared in four mixed acid electrolytes with and without phosphoric acid as a function of forming voltage. Specifically the oxide surface characteristics, the mechanical integrity, and the bioactive performance were evaluated for a range of forming voltages in each electrolyte. Surface analyses showed phosphorus incorporation into the oxide layer started at localized areas after a threshold forming voltage, but became more uniform at higher voltages. Oxide crystallinity and thickness were retarded by the phosphoric acid levels present in the anodization electrolytes. Surface roughness was shown to be electrolyte dependent as a function of forming voltage, and in general was shown to increase with increasing voltage. Samples anodized up to a forming voltage of 144V did not show any oxide failure through shear strength testing with only epoxy delamination for three of the electrolytes. At 180V, the oxide layers showed failure or partial failure at approximately 30–35MPa, which is stronger than many values previously reported for anodized coatings in the literature. Additionally, oxide films prepared in phosphoric acid containing electrolytes showed greater bioactivity through enhanced apatite formation. These anodized coatings exhibiting enhanced bioactivity show promise for promoting faster osseointegration while providing better implant stability due to the superior coating adhesion strengths.

UV light preirradiation of anodized titanium oxide layers has recently been shown to produce a photocatalytic effect that may reduce early bacterial attachment on titanium surfaces. Streptococcus species have been identified as primary early colonizers and contribute to early biofilm formation on dental implant surfaces. Anodized layers with primarily amorphous, primarily anatase, primarily rutile, and mixtures of anatase and rutile phase oxides were preirradiated with UVA or UVC light for 10 min. Nanoscale surface roughness and pre- and post-UV-irradiated wettability were measured for each anodization group. Sample groups were subjected to streptococcus sanguinis for a period of 24 h. Bacterial attachment and killing efficacy were measured and compared to the corresponding non-UV control groups. UVA treatments showed trends of at least a 20% reduction in bacterial attachment regardless of the crystallinity, or combination of oxide phases present. Anodized layers consisting of primarily anatase phase on the outermost surface were shown to have a killing efficacy of at least 50% after preirradiation with UVA light. Anodized layers containing disperse mixtures of anatase and rutile phases at the outermost surface showed at least a 50% killing efficacy after pre-irradiation with either UVA or UVC light. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2284-2294, 2018.