Fretting corrosion with proteins: the role of organic coating about the synergistic mechanisms

International audienceEvery year, one in every 30 Americans has a hip prosthesis implanted, i.e. 250,000 every year implants in the US market. Health issues with regard to patient mobility, which in turn reflects an aging population, are of increasing concern, but we also see a trend toward younger and younger patients. Younger, first time recipients of hip prostheses are of concern, because of the high probability that they will be recipients of multiple prostheses replacements over their lifetimes, since some implants have approximate lifetimes of 15 years. The femoral stem, for example, should be made of 316L/316LN stainless steel, in order to optimize lifetime. Fretting corrosion, friction under small displacements, between stainless steel and bone, for instance, occurs during human gait, due to repeated loadings and un-loadings,. Some experimental investigations of fretting corrosion have been reported. As is well known, metallic alloys and especially stainless steels are covered with a passive film that inhibits corrosion and hence degradation when implanted within the body. This passive layer of few nanometers in thickness at ambient temperature is the key of our reactive metals-based civilization according to some authors. This work is dedicated to predicting the passive layer thicknesses of stainless steel under fretting corrosion conditions, with specific emphasis on the role of proteins. The analysis is based on the Point Defect Model (PDM, micro scale) and an update of the model on the friction process (micro macro scale) to yield the Fretting Model (FM). A genetic algorithm was used to optimize the fretting model on the experimental data, in order to derive values for important model parameters. The major results are, as expected from experimental results, albumin inhibits corrosive degradation of the steel; an incubation time is necessary for degradation of the passive film; under fretting corrosion and in the presence of a high concentration of chloride ion, passivity of the steel is also inhibited. These factors are identified as those that determine the ultimate lifetime of the prosthesis