Anodic oxidation of a Co–Ni–Cr–Mo alloy and its inhibitory effect on platelet activation

In this study, surface treatment of a Co–Ni–Cr–Mo alloy (MP35N) was attempted to attain biocompatibility using an anodic oxidation technique. To determine the optimal condition of the anodic oxidation treatment for stent applications, anodic polarization of the alloy was first conducted. After anodic oxidation, the surface topology and wettability were examined, and the composition and chemical states of the surface oxide were characterized. For biocompatibility, stent surfaces must have both cell adhesion and antithrombogenic properties. Therefore, the anodically oxidized surface was assessed with an endothelial cell attachment test and an in vitro platelet adhesion test. The results indicated that the topography, wettability, and composition of the surface oxide film on the alloy were changed by anodic oxidation at a voltage near the passive and transpassive region. The surface roughness and wettability increased after anodic oxidation. The major content of the oxide layer after anodic oxidation was Cr containing a small amount of Mo, and Ni and Co were almost eliminated from the layer. Platelet activation of the alloy decreased significantly after anodic oxidation at an optimal potential, whereas the cytocompatibility remained constant. Therefore, the anodic oxidation is an effective process for treating this alloy for stent applications.