Effect of the Residual Porosity of CoCrMo Bearing Parts Produced by Additive Manufacturing on Wear of Polyethylene

Abstract

Additive manufacturing (AM) has proven to be a flexible technique to create complex designs layer-by-layer. Among others, this versatility has disabled the production of advanced total joint replacements. The high degree of customization offered by AM provides countless opportunities to empower the fabrication accuracy of complex biomaterial constructs to tailor patient-specific implants according to their morphology and pathology. In addition, AM offers interesting microarchitecture control of surfaces, which influences biotribological performances. Porosity is an inherent defect of AM-based metallic material and has been shown to affect mechanical performances such as tensile stress. Thus, in the context of bearing surfaces of artificial joints, this article aims to understand the physical behavior of AM-created cavities on the wear performance of polyethylene in a synovial-like environment with a multidirectional pin-on-disc machine at 37 °C.The article provides quantitative ultra-high molecular weight polyethylene wear results against AM-based cobalt-based alloy parts with a gradient of cavities. The results demonstrate a strong correlation between mass loss of UHMWPE and the total surface porosity defects in the metallic counterparts. Reducing the surface porosity of AM parts is therefore beneficial for improving the wear resistance of UHMWPE.This work not only underlines the negative effect of metallic surface cavities in the wear resistance of UHMWPE but also gives some understanding of the physical behavior of metallic cavities produced by AM. The AM-created cavities modify adhesion wear and abrasion wear mechanisms. Interestingly the pores also limit the abrasive effect of a third body particles by acting as debris collector.