Wear of Conventional UHMWPE Articulating Against Additively Manufactured Ti-6Al-4V and Co-Cr-Mo

Abstract

Preclinical wear testing of joint implants has primarily focussed on the wear properties of Ultra-High Molecular Weight Polyethylene (UHMWPE) articulating on wrought/cast metals. Advancements in additive manufacturing (AM) technologies, such as laser-based powder bed fusion (LPBF), have led to the increasing use of this manufacturing method in metal articulating joint components. There is, however, still uncertainty regarding the wear properties of UHMWPE against AM metals. This study employed LPBF Co-Cr-Mo and Ti-6Al-4V pins in articulation against UHMWPE to assess the wear of the latter. A multidirectional pin-on-plate wear testing machine was used to simulate in vivo knee joint conditions over 5 × 106 cycles. Wear testing was conductedwith ASTM F732 as guideline. The LPBF Ti-6Al-4V pins underwent a thermal oxidation heat treatment to improve the material's wear properties. The state of the thermal oxide layer was investigated after wear testing by sectioning the pins and measuring the thickness of the oxide layer. Wear testing showed that UHMWPE against Co-Cr-Mo had better wear properties compared to UHMWPE on Ti-6Al-4V. The wear properties of UHMWPE against Co-Cr-Mo and UHMWPE on Ti-6Al-4V were within ASTM F732 requirements and comparable to those reported in the literature. The thermal oxide layer on the LPBF Ti-6Al-4V pins showed signs of delamination after 5 × 106 cycles. A small oxygen diffusion zone of 1–2 μm was argued to be the reason for the delamination.