Surface characteristics and cell-adhesion performance of titanium treated with direct-current gas plasma comprising nitrogen and oxygen

In this study, we attempted to form titanium oxynitride (TiOxNy) layers on titanium (Ti) surfaces using direct-current (DC) plasmas generated from gas mixture comprising hydrogen, nitrogen, and oxygen. Additionally, the effect of gas mixture ratio on the surface characteristics and cell-adhesion performance was investigated. Scanning probe microscopy (SPM) images showed that the plasma-treated surfaces were slightly rougher than untreated Ti surfaces, owing to the formation of new layers. Chemical state analysis using X-ray photoelectron spectroscopy (XPS) revealed that the layers were comprised TiOxNy, titanium nitride (TiN), and titanium dioxide (TiO2); the concentrations of TiOxNy and TiN decreased and that of TiO2 increased with an increase in the amount of oxygen in the gas. An increase in the amount of oxygen gas did not affect the layer thickness, which was approximately 25 nm. Furthermore, no differences in cell morphology and cell-adhesion performance were found between the specimens treated with various plasma gases. This is probably because the treatment insufficiently improved the hydrophilicity. Layers composed of TiOxNy, TiN, and TiO2 were formed using the DC plasma treatment; however, the layers did not improve the cell-adhesion at an initial stage after the seeding.