Investigation of cell-accelerated corrosion (CAC) on the CoCrMo alloy with segregation banding: Hip implant applications.

Metal alloy microstructure plays a crucial role in corrosion associated with total hip replacement (THR). THR is a prominent strategy that uses metal implants such as cobalt-chromium-molybdenum (CoCrMo) alloys due to their advantageous biological and mechanical properties. Despite all benefits, these implants undergo corrosion and wear processes in-vivo in a synergistic manner called tribocorrosion. Also, the implant retrieval findings reported that fretting corrosion occurred in-vivo, evidenced by the damage patterns that appeared on the THR junction interfaces. There is no scientific data on the studies reporting the fretting corrosion patterns of CoCrMo microstructures in the presence of specific biological treatments to date. In the current study, Flat-on-flat fretting corrosion set-up was customized and used to study the tribocorrosion patterns of fretting corrosion to understand the role of alloy microstructure. Alloy microstructural differences were created with the implant stock metal's longitudinal and transverse cutting orientations. As a result, the transverse created the non-banded, homogenous microstructure, whereas the longitudinal cut resulted in the banded, non-homogenous microstructure on the surface of the alloy (in this manuscript, the terms homogenous and banded were used). The induced currents were monitored using a three-electrode system. Three different types of electrolytes were utilized to study the fretting corrosion patterns with both homogeneous and banded microstructures: 1. Control media 2. Spent media (the macrophage cell cultured media) 3. Challenged media (media collected after the macrophage was treated with CoCrMo particles). From the electrochemical results, in the potentiostat conditions, the banded group exhibited a higher induced current in both challenged and spent electrolyte environments than in control due to the synergistic activity of CoCrMo particles and macrophage demonstrating more corrosion loss. Additionally, both Bode and Nyquist plots reported a clear difference between the banded and homogeneous microstructure, especially with challenged electrolytes becoming more corrosion-resistant post-fretting than pre-fretting results. The banded microstructure showed a unique shape of the fretting loop, which may be due to tribochemical reactions. Therefore, from the electrochemical, mechanical, and surface analysis data results, the transverse/homogenous/non-banded alloy microstructure groups show a higher resistance to fretting-corrosion damage.