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The band structures and band gap energies, E (g), of passive films formed on titanium (Ti) in simulated bioliquids, Hanks' solution (Hanks) and saline, were evaluated. Ti was polarized at 0, −0.1, and −0.2 V-Ag/AgCl, E (f), for 1 h. After polarization, the surfaces were characterized using X-ray photoelectron spectroscopy, and the photoelectrochemical responses were evaluated. The current change during photoirradiation was recorded as a photocurrent transient at each measuring potential, E (m), and by changing the wavelength of the incident light. Passive films consisted of a very thin TiO2 layer containing small amounts of Ti2O3 and TiO, hydroxyl groups, and water. During polarization in Hanks, calcium and phosphate ions were incorporated or formed calcium phosphate but not in saline. Calcium phosphate and hydroxyl groups influenced the band structure. E (g) was graded in Hanks but constant in saline, independent of E (f) and E (m). The passive film on Ti behaved as an n-type semiconductor containing two layers: an inner oxide layer with a large E (g) and an outer hydroxide layer with a small E (g). In Hanks, E (g) was 3.3–3.4 eV in the inner oxide layer and 2.9 eV in the outer hydroxide layer. In saline, E (g) was 3.3 eV in the inner layer and 2.7 eV in the outer layer. Calcium phosphate and hydroxyl groups influenced the band structure of the passive film. The E (g) of the outermost surface was smaller than that of TiO2 ceramics, which is probably one of the principles of the excellent biocompatibility of Ti among metals.

Titanium (Ti) is always covered by thin passive films. Thus, valence band (VB) spectra, obtained using X-ray photoelectron spectroscopy (XPS), are superpositions of the VB spectra of passive films and that of the metallic Ti substrate. In this study, to obtain the VB spectra only of passive films, angular resolution (for eliminating the substrate Ti contribution) and argon ion sputtering (for removing passive films) were used along with XPS. The passive film on Ti was determined to consist of a very thin TiO2layer with small amounts of Ti2O3, TiO, hydroxyl groups, and water with a thickness of 5.9 nm. The VB spectra of Ti were deconvoluted into four peak components: a peak at ~1 eV, attributed to the Ti metal substrate; a broad peak in the 3–10 eV range, mainly attributed to O 2p (~6 eV) and O 2p-Ti 3d hybridized states (~8 eV), owing to the π (non-bonding) and σ (bonding) orbitals in the passive oxide film; and a peak at ~13 eV, attributed to the 3σ orbital of O 2p as OH−or H2O. The VB region spectrum between approximately 3 and 14 eV from Ti is originating from the passive film on Ti. In particular, characterization of VB spectrum obtained with a takeoff angle of less than 24° is effective to obtain VB spectrum only from the passive film on Ti. The property as n-type semiconductor of the passive film on Ti is probably higher than that of rutile TiO2ceramics.

A customized micro-arc oxidation (MAO) treatment technique was developed to obtain antibacterial properties with no toxicity on Ti surfaces. A two-step MAO treatment was used to fabricate a specimen containing both Ag and Zn in its surface oxide layer, and the optimal incorporation conditions were determined. Surface characterization by EDS was performed followed by the antibacterial properties against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) and osteogenic cell compatibility evaluations. In addition, metal ion release tests were performed to evaluate the contents of Ag and Zn and the ion release behavior in order to simulate practical usage. MAO-treated specimens prepared using proper concentrations of Ag and Zn (0.5Ag-5Zn: 0.5 mM AgNO3 and 5.0 mM ZnCl, respectively) exhibited excellent antibacterial properties against E. coli and S. aureus and no toxicity to MC3T3-E1 in antibacterial and cytotoxic evaluations, respectively. The antibacterial property of 0.5Ag-5Zn against S. aureus was sustained even after two months of immersion in physiological saline, simulating the in vivo environment.

A customized micro arc oxidation (MAO) treatment technique was developed to obtain desirable antibacterial properties on titanium surfaces. The two-step MAO treatment was applied to fabricate a specimen containing both Ag and Zn in its surface oxide layer. Surface analyses and metal-ion release tests were performed to evaluate the presence of Ag and Zn and the ion release behavior for simulating practical usage, respectively. Additionally, the antibacterial properties of the specimens were also evaluated using gram-negative facultative anaerobic bacteria. The MAO-treated specimens containing both Ag and Zn showed excellent antibacterial properties against Escherichia coli, and the properties were sustained even after 28 days of immersion in physiological saline to simulate the living environment.

Recently, silver (Ag) and copper (Cu) have been incorporated into a titanium (Ti) surface to realize their antibacterial property. This study investigated both the durability of the antibacterial effect and the surface change of the Ag- and Cu-incorporated porous titanium dioxide (TiO2) layer. Ag- and Cu-incorporated TiO2 layers were formed by micro-arc oxidation (MAO) treatment using the electrolyte with Ag and Cu ions. Ag- and Cu-incorporated specimens were incubated in saline during a period of 0&ndash, 28 days. The changes in both the concentrations and chemical states of the Ag and Cu were characterized using X-ray photoelectron spectroscopy (XPS). The durability of the antibacterial effects against Escherichia coli (E. coli) were evaluated by the international organization for standardization (ISO) method. As a result, the Ag- and Cu-incorporated porous TiO2 layers were formed on a Ti surface by MAO. The chemical state of Ag changed from Ag2O to metallic Ag, whilst that of Cu did not change by incubation in saline for up to 28 days. Cu existed as a stable Cu2O compound in the TiO2 layer during the 28 days of incubation in saline. The concentrations of Ag and Cu were dramatically decreased by incubation for up to 7 days, and remained a slight amount until 28 days. The antibacterial effect of Ag-incorporated specimens diminished, and that of Cu was maintained even after incubation in saline. Our study suggests the importance of the time-transient effects of Ag and Cu on develop their antibacterial effects.

An electrochemical surface treatment was developed to visualize the corrosion-inducing inclusions of Zr in chloride environments. Pure Zr and Zr alloy (Zr–0.5O–0.5C) were evaluated in this study. The electrochemical surface treatment consisted of repeated galvanostatic anodic polarization and potentiostatic cathodic polarization. After the electrochemical surface treatment, only one brittle and non-conductive shell of Zr oxide was observed at the corrosion initiation site on the tested surface. The corrosion-inducing inclusions were found inside the corrosion pit under the optimum polarization conditions. At the corrosion initiation site on pure Zr, the area inside the corrosion pit contained larger amounts of O, C, and Si than the surrounding matrix. In the case of the Zr-0.5O–0.5C alloy, relatively larger inclusions were observed after the treatment. Extremely large amounts of Si, together with O and C, were present in the inclusions. The inclusions that induced localized corrosion on the pure Zr and Zr-0.5O–0.5C specimens were found to be precipitated, involving the specific aggregation of Si. The surface treatment developed in this study is expected to be utilized as a powerful tool to elucidate the localized corrosion mechanism of Zr in chloride environments.

Recently, biofilm formation caused by bacterial adhesion and colonization has been recognized as the major cause of failure in orthopedic and dental implant surgeries. In this study, a customized micro-arc oxidation (MAO) treatment technique was developed to obtain desirable antibacterial properties on Ti surfaces. The two-step MAO treatment was applied in the fabrication of specimens with Ag and with/without Zn in their surface oxide layer. In order to simulate practical usage, surface analyses and immersion tests were performed to evaluate the incorporation of Ag and Zn into the resulting oxide layer and ion release behavior, respectively. Additionally, the antibacterial properties of the specimens after long-term immersion in physiological saline were evaluated using Gram-negative facultative anaerobic bacteria. The MAO-treated specimens containing Ag and Zn exhibited excellent antibacterial properties against Escherichia coli, which were sustained even after 6 months of immersion in physiological saline to simulate practical usage. Moreover, the Ag ions released from the surface oxide indicate the antibacterial properties of the specimen in the early stage, while the release of the corrosion products of Zn demonstrates its antibacterial properties in the later stage.

To clarify the mechanism of localized corrosion on zirconium in chloride environments, corrosion tests of zirconium and its alloys were performed using conventional and micron-scale measurement systems with surface areas of 0.35 cm2 and less than 0.04 cm2, respectively. The pitting potential significantly dropped by more than 1 V when zirconium was alloyed with over 10 mol% of tin. Zr4Sn and Zr5Sn3 intermetallics hindered the formation of passive films on the substrate. Additionally, tin was found on the surface of a commercially pure zirconium. From the micron-scale measurement results, the inclusion with the highest concentration of tin (at least 0.44 mol%) in the tested area was selected as the preferential initiation site for pitting corrosion. Thus, tin played an important role in determining the corrosion resistance of zirconium in chloride environments.