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The general requirements for joint replacement devices emphasizes the importance of device material biocompatibility, with no inflammatory or toxic response to wear beyond a tolerable level, the appropriate mechanical properties for the desired application, and lastly economically viable manufacturing and processing methods. Implicit in these requirements is the importance of understanding wear and failure mechanisms of implanted devices. However, compared to orthopedic total joint replacement (TJR) devices, functional wear failure mechanisms for temporomandibular joint (TMJ) TJR implants have not been clearly defined. Our research group has started initial translational investigations involving the analysis of failed retrieved TMJ TJR devices alloy microstructure compared to control, never implanted, TMJ TJR devices utilizing established orthopedic TJR device retrieval tribocorrosion evaluation protocols. This and future studies will guide future material choices and functional design improvements for TMJ TJR devices. Orthopedic TJR implant schemes may also be improved by understanding the degradation mechanism of TMJ TJR implants, as the materials employed in both TJR devices are similar.

Cobalt chromium molybdenum alloy (CoCrMo) is widely employed in the orthopedic device industry due to a combination of properties that include low wear, high mechanical strength, and high corrosion resistance. However, when used as the bearing component of total hip implants, this material can be susceptible to wear and corrosion, which can be triggered or exacerbated by factors such as changing pH, biological fluids and cell interactions, particle release, and friction. The physiological fluid, which is composed of electrolytes, proteins, and other organic species, plays a critical role in the tribological behavior of CoCrMo alloy. The aim of this work is to generate a proteinaceous layer electrochemically and carry out nanoscale mechanical and surface evaluation of CoCrMo to understand the feasibility of a pre-treatment on this material. The treatments consisted of electrolytes, with different protein concentrations, and pre-selected transpassive potentials at ?0.6, ?0.7 and ?0.8 V and a passive potential of-0.4 V. These observations will help in determining the electrolyte concentration and potential combination that would yield the most protective film layer. The results demonstrated that all the positive transpassive potentials and electrolyte combinations led to surface degradation processes causing more material removal as seen by the formation of localized corrosion at carbide and grain boundaries. Only the negative potential of-0.4 V, used by itself as a pretreatment and in combination with an electrolyte with 30 g/ L of bovine calf serum (BCS), demonstrated more homogeneous oxide layer and proteinaceous layer distribution respectively. Keywords Cobalt chromium molybdenum Á Tribological behavior Á Transpassive potentials Á Coefficients of friction Á Electrochemical and mechanical degradation Á Third-body particle wear & Danieli C. Rodrigues

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