Studies have shown ultraviolet-A (UVA) irradiation of crystalline titanium oxides leads to the production of reactive oxygen species (ROS) via a photocatalytic process. The ROS exhibit antimicrobial properties that may be of benefit in preventing bacterial attachment to implant devices. Recent studies have suggested a potential benefit of mixed anatase and rutile oxides and dopants on the photocatalytic properties of titanium oxides. The goal of this work was to compare the photocatalytic activity of different anodized commercially pure titanium grade 4 (CPTi4) surfaces. CPTi4 specimens were anodized in three mixed-acid electrolytes to create crystalline oxide surfaces that were either primarily anatase, primarily rutile, or a combination of anatase and rutile. Additionally, the primarily anatase and combination oxides incorporated some phosphorous from the phosphoric acid component in the electrolyte. The photocatalytic activity of the anodized specimens was measured using both methylene blue (MB) degradation assay and comparing the attachment of S. aureus under irradiation with UVA light of differing intensities (1 mW/cm2, 8 mW/cm2, and 23 mW/cm2). Primarily rutile oxides exhibited significantly higher levels of MB degradation after exposure to 1 mW/cm2 UVA lights. Primarily rutile specimens also had the largest reduction in bacterial attachment followed by the mixed phase specimens and the primarily anatase specimens at 1 mW/cm2 UVA lights. Phosphorous-doped, mixed phase oxides exhibited an accelerated MB degradation response during exposure to 8 mW/cm2 and 23 mW/cm2 UVA lights. All anodized and unanodized CPTi4 groups revealed similar S. aureus attachment at the two higher UVA intensities. Although MB degradation assay and the bacteria attachment assay both confirmed photocatalytic activity of the oxides formed in this study, the results of the MB degradation assay did not accurately predict the oxides performance against S. aureus.

Titanium has been the material of interest in biological implant applications due to its unique mechanical properties and biocompatibility. Their design is now growing rapidly due to the advent of additive manufacturing technology that enables the fabrication of complex and patient-customized parts. Titanium dioxides (TiO 2 ) coatings with different phases (e.g., anatase, rutile) and morphologies have shown to be effective in enhancing osteointegration and antibacterial behavior. This enhanced antibacterial behavior stems from the photocatalytic activity generated from crystalline TiO 2 coatings. Anatase has commonly been shown to be a more photocatalytic oxide phase compared to rutile despite its larger band gap. However, more recent studies have suggested that a synergistic effect leading to increased photocatalytic activity may be produced with a combination of oxides containing both anatase and rutile phases. Here, we demonstrate the selective and localized formation of TiO 2 nanostructures on additive and wrought titanium parts with anatase, rutile, and mixed phases by a laser-induced transformation approach. Compared to conventional coating processes, this technique produces desired TiO 2 phases simply by controlled laser irradiation of titanium parts in an oxygen environment, where needed. The effects of processing conditions such as laser power, scanning speed, laser pulse duration, frequency, and gas flow on the selective transformation were studied. The morphological and structural evolutions were investigated using various characterization techniques. This method is specifically of significant interest in creating phase-selective TiO 2 surfaces on titanium-based bioimplants, including those fabricated by additive manufacturing technologies.

Titanium dioxide (TiO2) has been a key material in a wide range of applications such as catalysis, energy harvesting, and antibacterial surfaces. Typically, different TiO2 phases are first synthesized and then coated onto the test parts. Here, the authors demonstrate a direct method for the formation of TiO2 nanostructures and patterns with rutile, anatase, and mixed phases by a controlled laser-assisted surface modification approach on additive manufacturing titanium parts. A tunable nanosecond fiber laser coupled to a galvo scanner was employed to regulate the laser material for a controlled and localized transformation process in an oxygen environment. The influence of processing conditions such as scanning speed, laser power, laser pulse duration, frequency, and gas flow rate on the selective formation of rutile, anatase, and mixed phases was studied. The structural evolutions and morphology have been investigated using different characterization techniques, including scanning electron microscopy and Raman spectroscopy methods. The main advantage of this laser-assisted process is its ability to create selective TiO2 phases on complex titanium parts such as implants.

Titanium alloys provide excellent corrosion resistance and favorable mechanical properties well suited for a variety of biomaterial applications. The native oxide surface on titanium alloys has been shown to be less than ideal and surface modification is often needed. Previously, an optimized anodization process was shown to form a porous phosphorus‐enhanced anatase oxide layer on commercially pure Ti grade 4. The anodized layer was shown to improve osseointegration and to reduce bacteria attachment when photocatalytically activated with UVA preillumination. The primary objective of the present study was to create a similar phosphorus‐enhanced anatase oxide layer on series of titanium alloys including commercially pure Ti grade 4, Ti‐6Al‐7Nb, Ti‐6Al‐4V ELI, alpha + beta Ti‐15Mo, beta Ti‐15Mo, and Ti‐35Nb‐7Zr‐5Ta. Phosphorus‐enhanced anatase oxide layers were formed on each titanium substrate. Anatase formation was shown to generally increase with oxide thickness, except on substrate alloys containing niobium. Phosphorus uptake was shown to be dependent on the titanium alloy chemistry or microstructure. Anodized layers formed on beta‐structured titanium alloys revealed the lowest phosphorus uptake and the most nanosized surface porosity. A methylene blue degradation assay showed anodized layers on commercially pure Ti and both Ti‐15Mo alloys to exhibit the highest levels of photocatalytic activity. Given the range of mechanical properties available with the commercially pure Ti and Ti‐15Mo alloys, the results of this study indicate the benefits of phosphorus‐enhanced anatase oxide coatings may be applicable to a wide variety of biomaterial applications.