The role of mechanically activated area on tribocorrosion of CoCrMo

Co-Cr-Mo alloys are among the most used alloys for orthopedic implants because of their excellent corrosion resistance, mechanical properties, biocompatibility. Although there is extensive literature on corrosion properties of Co-Cr-Mo alloys, fewer articles are focused on the synergistic effect of corrosion and wear in a simulated physiological solution. It is generally assumed that the current density measured during wear conditions for passive materials comes from the active area. However, there are no clear data supporting this statement. The current article correlates electrochemical measurements with the active area generated during sliding wear tests. Open circuit potential and current measurements, potentiodynamic scans, electrochemical impedance spectroscopy were carried out on samples under static and sliding wear conditions. These measurements showed the importance of the active area, where the current coming from the surface not being abraded is negligible. Finally, by combining the sliding wear and electrochemical tests, the synergistic effect of wear and corrosion was characterized for this alloy, documenting the metal carbide's detachment from the cobalt alloy matrix, which leads to a significant increase of total wear volume. © 2013 The Minerals, Metals & Materials Society and ASM International.Peer Reviewe

Metal ion interpretation in resurfacing versus conventional hip arthroplasty and in whole blood versus serum. How should we interpret metal ion data

Contains fulltext : 96098.pdf (publisher's version ) (Closed access)Metal ions generated from joint replacements are a cause for concern. There is no consensus on the best surrogate measure of metal ion exposure, and both serum and whole blood measurements are used in clinical practice. This study provides a guideline for interpretation of metal ion analysis in clinical practice. In a prospective trial comparing hip resurfacing (HR) with a conventional metal-on-metal (MoM) total hip arthroplasty (THA) cobalt and chromium levels were determined for whole blood and serum in 343 paired samples at regular intervals up to 24 months postoperatively. Cobalt whole blood and serum levels increased significantly after both procedures. Cobalt concentrations were significantly higher for the HR group compared to the THA group, at 3, 6 and 12 months, for whole blood and serum. At 24 months cobalt levels decreased and differences between HR and THA were no longer significant. In contrast, chromium whole blood levels remained significantly higher for HR until 24 months. Whole blood and serum levels could not be used interchangeably. The mean differences for cobalt and chromium between blood and serum values were +0.13 microg/L and -0.91 microg/L respectively. Regression analysis provided a formula for conversion from serum to blood of 0.34+[0.88*Co serum] for cobalt and 0.14 + [0.58*Cr serum] for chromium, with an acceptable prediction error below +/-1.0 microg/L. Cobalt and chromium levels were significantly higher for HR versus THA, especially during the run-in phase of one year. Overall, the metal ion levels were well below 5 microg/L. We cannot recommend the use of whole blood over serum measurements or vice versa. The provided conversion formula between whole blood and serum in combination with the presented practical guidelines may be useful for clinical practice