One cause of the excellent hard‐tissue compatibility of Ti and Ti alloys compared with other metals is their ability to form calcium phosphate in biological environments. This is confirmed by many studies, although the formation mechanism has not been completely elucidated. In this study, to elucidate the initial formation kinetics of calcium phosphate on Ti in the human body, Ti was immersed in a simulated body fluid, Hanks' solution, for 100–106 s, followed by precise characterization using XPS. Ti specimens immersed in diluted Hanks' solutions were also characterized. The results reveal that phosphate ions are preferentially adsorbed and are incorporated onto the Ti surface in 100–102 s. This reaction is slow, and the apparent thickness of the surface layer is almost constant as 5.2 nm until 102 s. However, both calcium and phosphate ions are then rapidly incorporated, and calcium phosphate is formed after 103 s. The amounts of both calcium and phosphate increase with the logarithm of time because calcium and phosphate ions react directly with the Ti surface until 105 s. Other elements contained in Hanks' solution are not incorporated, calcium phosphate being formed preferentially. The incorporation of calcium is faster than that of phosphate, and the [Ca]/[P] ratio increases with the logarithm of time after 103 s. However, the chemical state of surface oxide film itself on Ti does not changed by immersion in Hanks' solution. The formation kinetics of calcium phosphate on Ti in a simulated body fluid are clearly revealed by this study.

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 0–28 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.

For the elucidation of the mechanism of calcium phosphate formation on commercially pure titanium (CP Ti) in the human body, rutile TiO 2 single crystal plates with (001), (110), and (111) facets, namely, TiO 2 (001), TiO 2 (110), and TiO 2 (111), and polycrystalline plates (TiO 2 (poly)) were immersed in a simulated body fluid, Hanks' solution (Hanks), for 10 0 −10 5 s, and the adsorption of calcium and phosphate ions was precisely characterized employing X-ray photoelectron spectroscopy (XPS). Previously published CP Ti data were used for comparison. Prior to immersion in Hanks, oxygen content was more than twice as high as that of titanium due to the existence of hydroxyl groups and water on the oxides. After immersion in Hanks, the composition and chemical state of the TiO 2 substrates remained unchanged. Among the electrolytes contained in Hanks, only calcium and phosphate ions were adsorbed by and incorporated onto TiO 2 surfaces. Adsorption of calcium ions onto rutile did not exhibit any systematic increase of calcium with immersion time except TiO 2 (poly). Adsorption of phosphate ions was initially constant, followed by an increase with the logarithm of immersion time. The adsorption rate of phosphate ions decreased in the following order: TiO 2 (001), TiO 2 (poly), TiO 2 (111), CP Ti, and TiO 2 (110). The coordination number and band gap of each crystal facet of rutile is important for the adsorption and incorporation of phosphate ions. Regular calcium phosphate formation on CP Ti is possibly enabled by the surface oxide film, which consists chiefly of amorphous TiO 2 . However, calcium phosphate formation kinetics on CP Ti differed from those on the TiO 2 crystalline phase. These findings may further the understanding of CP Ti hard tissue compatibility.