Effect of proteins and pH on fretting corrosion and metal ion release.

The objectives of this study were to determine the effect of proteins and protein charge on the corrosion of stainless steel. As Zwitter ions, proteins have a positive charge in solutions acidic to their isoelectric point (pI) and a negative charge in solutions basic to the pI. Fretting corrosion rates of stainless-steel plates and screws as determined by weight loss and metal ion release were studied in saline and protein solutions with the pH adjusted to 3, 5, and 8. Alterations in pH did not affect the corrosion rate in saline solutions. However, alterations of the pH in albumin solutions did affect the corrosion rate. In protein solutions acidic to the isoelectric point the presence of the positively charged albumin did not alter the corrosion rates as compared to that in saline. However, the presence of negatively charged proteins in solutions basic to their isoelectric points decreased the amount of corrosion. Thus, the effect of proteins on fretting corrosion is dependent on the charge on the protein. When the release of nickel was compared to the release of chromium, it was shown that the release was in proportion to the composition of the alloy when fretting corrosion took place in saline. The nickel/chromium ratio in the albumin and gamma globulin solutions was increased relative to that predicted indicating preferential release of nickel in protein solutions.