XPS characterization of the surface oxide film of 316L stainless steel samples that were located in quasi-biological environments

The purpose of this study was to characterize the surface oxide films on 316L austenitic stainless steel located in various environments to estimate the reconstruction of the film in human body. Five kinds of specimens were prepared according to the following methods: polished in deionized water, autoclaved, immersed in Hanks' solution, immersed in cell culture medium, and incubated with cultured cells. X-ray photoelectron spectroscopy (XPS) was performed to estimate the compositions of the surface oxide film and substrate and the thickness of the film. Surface oxide film on 316L steel after polished in water consists of iron and chromium oxides containing small amount of nickel, molybdenum, and manganese oxides. The surface oxide contained a large amount of OH^-. Calcium phosphate was formed on/in the film after immersion in the Hanks' solution and medium and incubated with the cells. Sulfate is adsorbed by the surface oxide film and reduced to sulfite and/or sulfate in cell culture medium and with culturing cells. The results in this study suggest that nickel and manganese are depleted in the oxide film and the surface oxide changes into iron and chromium oxides containing a small amount of molybdenum oxide in human body.