The re-passivation kinetics and composition of the passive film of CoCrMo alloys in simulated body fluids have been investigated, with key emphasis being to assess the effect that proteins have on these features. The kinetics were analyzed using potentiostatic polarization, applying a second order exponential decay to the current transients obtained, which consists of two phases: coverage and thickening. Repassivation occurred quickest in a phosphate environment with presence of bovine serum albumin (BSA) hindering the process as it inhibits access of the oxidant. By using X-ray photoelectron spectroscopy (XPS) the composition of the re-passivated layer was studied. As expected, the film is mainly composed of chromium (III) oxide with small amounts of cobalt (II) oxide and molybdenum oxides (IV-VI). When exposed to BSA the percentage of molybdenum in the passive film decreases. This is shown to be due to the protein having a high affinity for the element causing it to be lost to solution when the metal was exposed to corrosion.
Throughout the last century, orthopedic surgery has helped to improve the quality of life for millions of people around the world by restoring mobility and reliving pain . Prosthetic joint replacement is one of the most successful and common treatments for people suffering from arthritis/rheumatism, due to great advancements in joint replacement technology over recent years in terms of investment, research and clinical trials . For the majority of patients this occurs on the weight-bearing joints which are the knee and hip. According to statistics approximately 400,000 hip replacements are performed annually in the USA, with operations being carried out on people under 60 rising dramatically in the last decade alone .
Since the 1990’s metal-on-metal (MoM) hip joints saw a drastic increase in use as the much used metal-on-polymer (MoP) was proven to generate polyethylene wear particles which cause osteolysis i.e. destruction of bone tissue [1,3,4]. CoCrMo hip implants were chosen due to possessing excellent corrosion resistance and a postulated higher longevity which bodes well for the greater need of younger people requiring an implant . Some MoM devices have lasted up to 25 years in-vivo with a wear rate even lower than that in a MoP device . These have become extremely contentious in recent years due to clinical problems arising due to adverse effects, release of debris and metal ions from the device have meant that instances of CoCrMo for hip implantation has dropped to almost zero . The metal ions that are released can enter the bloodstream where they are absorbed by erythrocytes allowing them to enter cells, remain in localized tissues or be transported throughout the body which can lead to genotoxicity and immunological effects .