Corrosion and Fretting Corrosion Studies of Medical Grade CoCrMo Alloy in a Clinically Relevant Simulated Body Fluid Env
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CoCrMo alloys are successfully used in orthopedic implants such as hips and knee replacements. Their use is due to their good abrasion resistance and high corrosion resistance in the synovial fluid environment of human joints.[1–3] Synovial fluids are natural joint lubricants that enhance the formation of a thin surface protective film (1 to 4 nm) on CoCrMo alloys,[4–6] which contains largely oxides of chromium.[7–9] These protective oxides make these implants very biocompatible in the human body environment. Factors such as the type of alloy, the synovial fluid composition, implant–fluid interface potential, and implant exposure time influence the nature and kinetics of the passive film formed on active–passive metals.[10–12] For example, the work of Yan et al.[13] reported an enhanced lubrication effect of a synovial fluid containing amino acids used to model EMMANUEL K. OCRAN, Engineering Officer, Former Graduate Student, and OLANREWAJU A. OJO, Professor, are with the Department of Mechanical Engineering, University of Manitoba, Winnipeg, MB, Canada. Contact e-mail: [email protected] LEAH E. GUENTHER, Manager of Biomedical Engineering & Services, is with the Orthopaedic Innovation Center, Inc, Winnipeg, MB, Canada. JAN-M BRANDT Adjunct Professor, and URS WYSS, Professor, are with the Department of Mechanical Engineering, University of Manitoba, and also with the Orthopaedic Innovation Center, Inc, Winnipeg, MB, Canada. Manuscript submitted July 28, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS A
proteins. Valero et al.[14] showed that different alloys may exhibit different passive behaviors when exposed to the same type of solution. Therefore, the need for laboratory testing in a clinically relevant fluid environment is crucial. Fretting corrosion, a synergistic effect of wear and corrosion, has been identified as a major cause of early revision in modular hip implants.[15] The effects of micro-motion at the head/neck and neck/stem interface of modular prostheses can lead to the breakdown and depassivation of the protective passive film, and hence the release of metallic ions and particles from the substrate alloy into surrounding tissues.[3,16,17] The rate of intermittent passivation and depassivation due to mechanical interaction influences the contribution of corrosion and corrosion-related damage to the fretting corrosion synergy. Further, the nature of the protective passive film formed on a CoCrMo alloy in a synovial fluid environment affects the rate of film passivation and depassivation. Therefore, to properly understand the existing implants and effectively design future implants, there is a need to replicate the human body environment as closely as possible during in vitro testing. Various synthesized fluids are currently being used in experimental testing of orthopedic biomaterials. However, most of these synthesized fluids are less stable and more prone to protein degradation under high temperatures and friction during testing.[18] These degraded proteins can affect how the moving parts of an artificial joint
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