Tribocorrosion Performance and Cytotoxicity of Additive Manufactured CoCrMo: A Benchmark Against Wrought CoCrMo

Abstract

Additive Manufacturing (AM) has increasingly gained attention as a tool for the fabrication of complex biomedical components, due to the flexibility of the technique for accounting to the patient individuality. Additive manufacturing techniques, like laser beam melting, often result in highly anisotropic microstructures that greatly differ from those obtained in conventionally manufactured alloys. This study evaluates the potential of AM manufactured CoCrMo for body implants as an alternative to the wrought CoCrMo, especially considering tribocorrosion performance in buffered fluid. Its biocompatibility is also assessed via in-vitro cytotoxicity assays. The results show that both materials have a comparable tribocorrosion performance, independently of the manufacturing process, despite their radically different initial microstructure. This results from the microstructural convergence arising from the plastic deformation imparted by sliding motion. While the initially elongated grains of the AM CoCrMo tend to grain refinement, the microstructure of the wrought CoCrMo undergoes grain coarsening, resulting in a similar final grain size detected after the tribocorrosion experiments. The addition of albumin to the phosphate buffer testing fluid, simulating body fluid applications, reduces the grain refinement, particularly under constant 0.21 V, due to lower shear stresses caused by the lower coefficient of friction. Therefore, the initial dissimilarity found in the untested microstructure between the materials does not affect the wear rate nor lead to an increased metal release. As the cytotoxicity is neither impaired by the manufacturing process, the use of AM CoCrMo could be recommended on those biomedical applications requiring wear resistance in body fluid environment.