The Fundamentals of Fretting Crevice Corrosion of Metallic Biomaterials for Orthopedic Implants

Metallic medical devices have been widely used in clinical applications, especially for joint arthroplasty or joint replacement surgery. Fretting corrosion, one of the most common forms of mechanically-assisted corrosion (MAC), has become a major concern associated with orthopedic medical devices. Crevice corrosion, a second mechanism of corrosion related to metallic medical devices, is a second factor of corrosion for many circumstances in medical devices that is an additional factor in the overall corrosion performance of these implants. It is a form of localized corrosion of metal surfaces present within the gap or crevice between two adjoining interfaces. The relationship and interplay between fretting and crevice corrosion is poorly understood and the observed damage seen in retrievals, which includes pitting, selective dissolution, intergranular and interphase corrosion has not been adequately duplicated in in vitro tests of mechanically assisted crevice corrosion.CoCrMo alloy, T-i6Al-4V alloy and stainless steel are the principal alloys in use today in orthopedics and are the focus of corrosion related studies. In addition, alternative materials, including ceramic materials with trusted biocompatibility, are also playing an increasingly-important role in medical device implantation. Here, we performed a series of studies intended to explore the fundamentals of fretting crevice corrosion of metallic biomaterials for orthopedic implants. We first studied CoCrMo alloy fretting corrosion debris generation and distribution using a range of characterization techniques and a custom-made fretting corrosion testing system. These several analytical surface techniques include SEM/EDS, AFM, and XPS. They were used to determine what debris was generated and to where it was distributed. Also, solution chemistry measurement (using ICP-MS) after testing was included to determine which ions and in what proportion remained in the solution. Next, a tribocorrosion model, which linked fretting mechanics, current and potential, was developed to predict currents and potential shifts resulting from fretting corrosion based on tribocorrosion theory. The model was tested against controlled fretting corrosion test conditions for its ability to predict the current-time and potential-time response. This model established a strong connection between mechanical and electrochemical aspects to demonstrate that potential and current affect each other during tribocorrosion and both are affected by other electrochemical factors (electrode area, impedance, contact mechanics, etc.) In the next step, fretting-initiated crevice corrosion in stainless steel alloys was observed and described, where fretting disruption of the surface initiated a self-sustained crevice corrosion reaction that continued even in the absence of additional fretting. The result was to comprehensively investigate fretting initiated-crevice corrosion (FICC) mechanism of stainless steel and to explore the factors, including potential and fretting duration that leads to this process. Lastly, device testing using the MTS servo-hydraulic test frame was performed to measure fretting corrosion performance of Si3N4 heads/Ti-6Al-4V modular tapers for total hip replacements in vitro and compared their behavior to standard CoCrMo heads/Ti-6Al-4V modular tapers tested under identical conditions. It was shown that using a Si3N4 ceramic head on metal trunnion significantly reduced the fretting corrosion reactions present