Electrochemical studies on the influence of proteins on the corrosion of implant alloys.

The effect of proteins on corrosion rates of 316L stainless steel, commercially pure titanium and titanium 6-aluminium 4-vanadium was studied in the static and fretting modes. The static mode was studied using cylindrical specimens as per ASTM F-746, and static fracture fixation plates. The fretting mode was studied using a two-hole plate fretting machine which caused a cyclic rocking motion between the plate and the screws, as per ASTM F-897. Electrochemical techniques of polarization resistance and Tafel slope measurements were used to study effects of proteins on the anodic and cathodic corrosion reactions. It was found that proteins increased the corrosion rate of the stainless steel and C.P. titanium cylindrical specimens, but did not have an effect on the Ti-6AI-4V cylinders. In the fretting mode proteins decreased the corrosion rate of the stainless steel plates, but did not have an appreciable effect on either of the titanium alloys. The presence of proteins appeared to cause an increase in the anodic Tafel constant and a decrease in the cathodic Tafel constant of stainless steel specimens. Significant differences in the shapes of the cathodic Tafel slopes were also seen with cylinders with different surface conditions, and static versus fretting plates.