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copper (Cu) and stainless steel 316 L are widely used for biomedical applications, such as intrauterine devices and orthopedic/dental implants. Amino acids are abundantly present in biological environments. We investigated the influence of select amino acids on the corrosion of Cu under naturally aerated and deaerated conditions using a phosphate-free buffer. Amino acids increased the corrosion of Cu under both aeration conditions at pH 7.4. Cu release was also significantly (up to 18-fold) increased in the presence of amino acids, investigated at pH 7.4 and 37 °C for 24 h under naturally aerated conditions. Speciation modelling predicted a generally increased solubility of Cu in the presence of amino acids at pH 7.4. 316 L, investigated for metal release under similar conditions for comparison, released about 1,000-fold lower amounts of metals than did Cu and remained passive with no change in surface oxide composition or thickness. However, amino acids also increased the chromium release (up to 52-fold), significantly for lysine, and the iron release for cysteine, while nickel and molybdenum release remained unaffected. This was not predicted by solution speciation modelling. The surface analysis confirmed the adsorption of amino acids on 316 L and, to a lower extent, Cu coupons. [ABSTRACT FROM AUTHOR]

The kinetics of oxygen reduction have been studied electrochemically on the Ni-Cr-Mo(W) Alloy C-22 in 5 M NaCl at 70°C using potentiostatic and voltammetric techniques and electrochemical impedance spectroscopy. Oxygen reduction was observed to occur at low potentials on defective oxide films containing a high concentration of anion vacancies and appeared to proceed by a combination of 2-electron and 4-electron transfer processes. At more positive potentials a passive film comprising a CrIII-dominated barrier layer at the alloy/oxide interface and a Mo/W enriched outer layer at the oxide/solution interface was formed, and oxygen reduction was completely suppressed. Oxygen reduction could be revived after transpassive degradation of the oxide film at more positive potentials, and appeared to be catalyzed on the MoVI/WVI surface film. [ABSTRACT FROM AUTHOR]