Spectroellipsometric, AFM and XPS probing of stainless steel surfaces subjected to biological influences

Surface modification of austenitic stainless steel 316L due to incubation in growing cell cultures and cell culture media as control has been studied. The following treatments were applied: mouse fibrosarcoma cells L929 during 3 and 7 days, polymorphonuclear neutrophils 3 and 7 days and human osteosarcoma cells SAOS-2 in during 7 and 14 days. Cells were enzymatically removed in all cases. The modified surfaces were probed in comparison with untreated ones by means of spectroscopic ellipsometry (SE), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). XPS shows the appearance of the peak of bonded nitrogen at 400.5 eV characteristic for adsorbed proteins on the surface for each type of cells and for the cell-free medium. Migration of Ni in the adsorbed layer is observed in all cases for samples after the cell cultures. The protein layer thickness is ellipsometrically determined to be within 2.5-6.0 nm for all treated samples with parameterization of its optical constants in Cauchy approach. The study showed that for such biological treatments of the stainless steel the protein adsorption is the dominating process in the first two weeks, which could play a role in the process of corrosion by complex forming properties with metal ions.