Doctor of Philosophy
CoCrMo alloys, which have excellent corrosion and wear resistance, are widely used for implants in the human body. Even for the most corrosion-resistant alloys, interfacial reactions occur between the metal surface and the biological environment. It is important to investigate the mechanism of corrosion behavior of CoCrMo in protein-rich solutions. This research is focused on the metal release and corrosion behavior of CoCrMo in protein-rich solutions under different simulated conditions and for different manufacturing processes. Implants can sometimes be present in patients who need to undergo cancer radiotherapy. Therefore, the effect of gamma irradiation on the metal release from CoCrMo alloy was investigated. It found that the radiation slightly influenced the extent of metal release from CoCrMo. CoCrMo are used in wearing parts of implants, where they are exposed to friction and a protein-rich environment. Hence, the effect of sliding, protein aggregation and metal precipitation on metal release from CoCrMo were investigated. In this study, metal release under sliding condition was increased in the presence of albumin. However, protein aggregation and metal precipitation result in underestimation of the extent of metal release from CoCrMo in mixed protein solutions. Generally, 3D printers are used for manufacturing implants of various shapes. However, the print direction may affect the properties of CoCrMo. The influence of the manufacturing process on protein-induced corrosion for CoCrMo was minor. All these studies give a deep insight in the extent and mechanism of metal release from CoCrMo in protein-rich solutions, which helps to minimize the failure of implants.
Summary for Lay Audience
This thesis discusses the use of cobalt-chromium-molybdenum (CoCrMo) alloys in dental and orthopedic implants due to their excellent corrosion and wear resistance. While these metals are ideal for use in the body, the interfacial reactions that occur between the metal surface and the biological environment can lead to the failure of implants or adverse health effects such as brain damage. Thus, it is important to investigate the mechanisms of CoCrMo alloy's corrosion behavior in similar environments as the human body, which means protein-rich solutions.
Another study investigated the effect of gamma irradiation on the metal release from CoCrMo alloy and 316L stainless steel. We found that the relatively low total irradiation doses slightly influenced the extent of metal release from CoCrMo alloy.
It was also discussed how the alloy's excellent wear resistance makes it ideal for use in bearing and wearing parts of implants. However, it was found that the metal release from CoCrMo under sliding conditions increased in the presence of bovine serum albumin, which simulates a common protein in the human body. Further, it was found that protein aggregation and metal precipitation resulted in an underestimation of the extent of metal release from CoCrMo in mixed protein solutions, especially under sliding conditions. This means that the estimated safety of CoCrMo by similar tests can be too high.
Finally, 3D printers are widely used for the manufacturing of implants of various and customized shapes. However, the print direction may have an influence on the properties of CoCrMo alloys, such as corrosion resistance. This thesis found a relatively minor influence, however, it was greater in protein-rich and aggressive environments, such as diluted hydrochloric acid and depended on the surface condition of the alloy.
By investigating the mechanism of corrosion behavior of CoCrMo in protein-rich solutions, it can be better understood how these alloys behave in the body and the safety and effectiveness of the implants can be improved. These studies can help minimize the failure of implants, ultimately leading to better health outcomes for patients who receive these types of implants.
Wei, Zheng, "Metal Release of CoCrMo Alloy in Protein-Rich Solutions – Effect of Irradiation, Sliding and Manufacturing Process" (2023). Electronic Thesis and Dissertation Repository. 9208.
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