A 3D-transient elastohydrodymanic lubrication hip implant model to compare ultra high molecular weight polyethylene with more compliant polycarbonate polyurethane acetabular cups

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Ford, A., Hua, Z., Ferguson, S.J., Pruitt, L.A. and Gao, L. ORCID: 0000-0002-3738-3573, 2021. A 3D-transient elastohydrodymanic lubrication hip implant model to compare ultra high molecular weight polyethylene with more compliant polycarbonate polyurethane acetabular cups. Journal of the Mechanical Behavior of Biomedical Materials, 119: 104472. ISSN 1751-6161

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Official URL: https://doi.org/10.1016/j.jmbbm.2021.104472

Abstract

Wear remains a significant challenge in the design of orthopedic implants such as total hip replacements. Early elastohydrodynamic lubrication modeling has predicted thicker lubrication films and, consequently, improved friction and wear performance in compliant polycarbonate polyurethane (PCU) bearing materials compared to stiffer materials like ultra-high molecular weight polyethylene (UHMWPE). However, experimental wear studies showed mixed results compared to the model predictions. The mismatch between model and experimental results may lie in the simplifying assumptions of the early models such as: steady state, one dimensional rotation and loading, and high viscosities. This study applies a 3D-transient elastohydrodymanic model based Email address: leiming.gao@ntu.ac.uk (Leiming Gao) on an ISO standard gait cycle to better understand the interaction between material stiffness and film thickness in total hip arthroplasty material couples. Similar to previous, simplified models, we show that the average and central film thickness of PCU (∼ 0.4 µm) is higher than that of UHMWPE (∼ 0.2 µm). However, in the 3D-transient model, the film thickness distribution was largely asymmetric and the minimum film thickness occurred outside of the central axis. Consequently, although the overall film thickness of PCU was higher than that of UHMWPE, the minimum film thickness of PCU was lower than that of UHMPWE for the majority of the gait cycle. The minimum film thickness of PCU also had a larger range throughout the gait cycle. Both materials were found be be operating between boundary and mixed lubrication regimes. This 3D-transient model reveals a more nu-anced interaction between bearing material stiffness and film thickness that supports the mixed results found in experimental wear studies of PCU hip implant designs.

Item Type:

Journal article

Publication Title:

Journal of the Mechanical Behavior of Biomedical Materials

Creators:

Ford, A., Hua, Z., Ferguson, S.J., Pruitt, L.A. and Gao, L.

Publisher:

Elsevier

Date:

July 2021

Volume:

119