Electrochemical and Corrosion Studies on CoCrMo Biomedical Alloy under Artificial Inflammatory Condition
Akhavan Farshchi, Yasaman
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CoCrMo biomedical alloys have been used for dental and othopaedics prostheses for more than six decades. A good biocompatibility, high corrosion resistance, wear resistance and excellent mechanical properties characterize this alloy. The key feature of CoCrMo alloy is that it forms an oxide layer on its surface, mainly composed of Cr 2 O 3 with minor contribution of Co and Mo oxide. The physical-chemical properties of the passive film not only control the material’s corrosion behavior, but also control the interaction of implanted materials with the biological system and tissues and therefore play an essential role in material’s biocompatibility. Although, this alloy is protected by the surface oxide layer, when implanted into the body, CoCrMo implants may degrade from corrosion, mechanically assisted corrosion, or combination of corrosion and wear. The human body is not an environment that one would consider hospitable for an implanted metal alloys due to the presence of various salts and various organic and biological species. In addition, inflammatory cells produce a wide range of special chemicals, such as superoxide and their by-products including H 2 O 2 to attack foreign bodies and invading bacteria. Production of these reactive species has an effect on the corrosion of biomaterials and may lead to the degradation of the materials. Also, the pH value near the implant drops to 5.3 to 5.6 due to severe pathological changes in surrounding tissues from the surgical procedure or the presence of implant itself. All these parameters can alter the stability of the passive layer and may accelerate the corrosion process of CoCrMo implants within the body. These degradation mechanisms shorten the lifetime of the implants and therefore limit the patient’s quality of life. The degradation of the implants also leads to the release of toxic ions and wear particles into the body that can have an adverse effect on the body’s tissues. Examinations of retrievals CoCrMo prosthesis have shown that the biocorrosion of this alloy is a serious clinical concern. The Co and Cr release from this alloy may be biologically active and potentially toxic or even carcinogenic. The aim of this work was to investigate how inflammatory condition changes the electrochemical properties of CoCrMo alloy. The electrochemical properties of CoCrMo alloy under normal and simulated inflammatory conditions were analyzed by different electrochemical techniques. Normal and inflammatory conditions were simulated using PBS at pH7 and 150mM H 2 O 2 + PBS at pH5, respectively. Change in pH and H 2 O 2 concentration was monitored over the 24 h incubation period. In addition, the metal ion release subjected to different simulated body fluid was determined by inductively coupled plasma mass spectroscopy. An Increase in corrosion susceptibility was observed under inflammatory conditions. Electrochemical impedance spectroscopy showed a decrease in polarization resistance and in constant phase element under inflammatory condition compared to normal condition. The results also revealed that the inflammatory condition increase dissolution of metals into the test electrolyte. The results of this study may provide insight on some of the potential clinical complications associated with CoCrMo biomedical alloys used in orthopaedics.