oa Proteins role on fretting corrosion of Co-Cr-Mo alloys dedicated to hip implants

250,000 total hip prostheses are implanted each year, in the USA (approximately 160,000 in France). It is worth noting that the locomotion for human is essential for common life. It is the reason why restoring gait by using hip or knee prosthesis if the natural joint fails is related to a huge health issues and scientific interests. This work aims at investigating the fretting corrosion resistance of Co-Cr-Mo alloy (low carbon content, i.e. under 0.2%) used as hip implant. Specifically one will pay attention on the effect of proteins on the wear of the metallic alloy against a material simulating the bone, i.e. PMMA (PolyMethylMetacrylate). Fretting corrosion means friction under small displacements, lower than 100 µm approximately, in a corrosive medium between two materials in contact. This friction mechanism has been isolated as the worst mechanism of degradations of hip implants [1]. The solution is based on human physiological liquid. However the chloride concentration has been chosen equal to 1 mol.L-1.. This concentration is higher than the one of the physiological liquid but the solution conditions are well used for promoting degradations of metal by fretting corrosion that they are focused in this study. In physiological conditions the metallic implant is at Open Circuit Potential. It is well demonstrated that experiments at applied potential, i.e. -400 mv/SCE (Standard Calomel Electrode) are very close from the resultsat OCP [2]. The wear volume has been measured by 3D profilometry (Bruker nanoscopeTM, ex. Veeco NT 9100). The main goal of this work is: showing the influence of proteins in order to know if there is any influence, for this specific alloy, under fretting corrosion degradations. The results, Figure 1, showed that the concentration of proteins has a huge effect on the Co-Cr-Mo alloy from 0 by 10 to 20 g.L-1. The wear volume is decreasing gradually and with a factor 4 from 0 to 20 g.L-1 of albumin. One might conclude that protein has a protective effect on the metallic wear. This one is a big concern due to metallic allergy from patients. The Figure 2 is showing two wear track area of Co-Cr-Mo alloy with and without albumin. The one without albumin is close the one without albumin obtained with 316L SS sample during fretting corrosion. The usual 'W' wear shape is highlighted without albumin in solution. With albumin the wear track area is different. The 'W' wear shape is discontinuous and some grooves in the direction of fretting are present. These images are in accordance with the fact that the wear volume of Co-Cr-Mo is lower than the one without albumin. On the image b), from the Figure 2, it is worth noting that localized corrosion is triggered outside the wear track area. Additional investigations showed that the wear volume of 316L SS is higher than the one of Co-Cr-Mo alloy under this condition.