Characterization of the surface oxide film of nickel-free austenitic stainless steel located in simulated body environments

The surface oxide film on the nickel-free austenitic stainless steel located in various environments was characterized to estimate the reconstruction of the film in the human body. The specimens were polished, autoclaved, immersed in Hanks' solution, immersed in Eagle's minimum essential medium containing fetal bovine serum, and incubated with cultured cells. X-ray photoelectron spectroscopy was performed to determine the composition of the surface oxide film and substrate and thickness of the film. The depth profiles of elements in the surface region were also characterized using Auger electron spectroscopy in combination with argon-ion-sputtering. The surface oxide film on the nickel-free austenitic stainless steel, Fe-24.0Cr-1.1Mo-5.1N (at%), polished mechanically in deionized water consists of oxidic species of iron, chromium, and molybdenum, thickness of the surface oxide was about 4 nm and contained a large amount of OH^-. Large amount of carbon, nitrogen, oxygen, and sulfur originating from amino acids and proteins were detected after immersion in the MEM + FBS and incubation with L929. Sulfur existed as sulfite or sulfide. Nitrogen as alloy component was enriched in the substrate just under the film. Calcium phosphate was formed on the film after immersion in the Hanks and MEM + FBS and incubation with L929.