In vitro corrosion study by EIS of a nickel-free stainless steel for orthopaedic applications

The electrochemical impedance spectroscopy (EIS) technique was used for the study of the electrochemical behaviour of Ni-free austenitic stainless steel for orthopaedic applications. Experiments were carried out using four different test solutions: (i) phosphate-buffered saline (PBS), (ii) minimum essential medium (MEM), (iii) MEM + 10% fetal calf serum (FCS), (iv) MEM + 10% fetal calf serum + L929 fibroblast cell line (Cell). Bode-phase spectra showed the presence of two maxima and were fitted with an equivalent circuit characterized by two parallel combinations (Resistance, Constant Phase Element). The (R1, CPE1) branch was assigned to the inner compact passive film and the (R2, CPE2) branch to the external porous film. The resistance of the inner film R1, here directly related to the material's uniform corrosion resistance, raised with the immersion time and increased in the following order: PBS