Department of Mechanical Engineering, 6141 Etcheverry Hall, Mail Code 1740, University of California Berkeley, Berkeley, CA 94720-1740, USA.
School of Mechatronics Engineering and Automation, Shanghai University, 266 Jufengyuan Rd, Baoshan, Shanghai, China.
J Mech Behav Biomed Mater. 2021 Jul;119:104472. doi: 10.1016/j.jmbbm.2021.104472. Epub 2021 Mar 20.
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 in hip replacement designs with compliant polycarbonate polyurethane (PCU) bearing materials compared to stiffer materials like ultra-high molecular weight polyethylene (UHMWPE). The predicted thicker lubrication films suggest improved friction and wear performance. However, when compared to the model predictions, experimental wear studies showed mixed results. The mismatch between the model and experimental results may lie in the simplifying assumptions of the early models such as: steady state conditions, one dimensional rotation and loading, and high viscosities. This study applies a 3D-transient elastohydrodynamic model based 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 (∼0.4μm) is higher than that of UHMWPE (∼0.2μm). However, in the 3D-transient model, the film thickness distribution was largely asymmetric and the minimum film thickness occurred outside of the central axis. Although the overall film thickness of PCU was higher than UHMWPE, the minimum film thickness of PCU was lower than 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 to be operating between boundary and mixed lubrication regimes. This 3D-transient model reveals a more nuanced interaction between bearing material stiffness and film thickness that supports the mixed results found in experimental wear studies of PCU hip implant designs.
在全髋关节置换等骨科植入物的设计中，磨损仍然是一个重大挑战。早期的弹性流体动力润滑模型预测，与超高分子量聚乙烯（UHMWPE）等更硬的材料相比，具有弹性聚碳酸酯聚氨酯（PCU）承载材料的髋关节置换设计具有更厚的润滑膜。预测的更厚的润滑膜表明摩擦和磨损性能得到改善。然而，与模型预测相比，实验磨损研究结果喜忧参半。模型与实验结果之间的不匹配可能在于早期模型的简化假设，例如：稳态条件、一维旋转和加载以及高粘度。本研究应用基于 ISO 步态周期的 3D 瞬态弹性流体动力模型，以更好地理解全髋关节置换材料对中材料刚度和膜厚之间的相互作用。与之前的简化模型类似，我们表明 PCU 的平均和中心膜厚（约 0.4μm）高于 UHMWPE（约 0.2μm）。然而，在 3D 瞬态模型中，膜厚分布很大程度上是不对称的，最小膜厚出现在中心轴之外。尽管 PCU 的整体膜厚高于 UHMWPE，但在大多数步态周期中，PCU 的最小膜厚低于 UHMPWE。PCU 的最小膜厚在整个步态周期中的范围也更大。两种材料都被发现处于边界润滑和混合润滑之间。该 3D 瞬态模型揭示了承载材料刚度和膜厚之间更细微的相互作用，这支持了 PCU 髋关节植入物设计的实验磨损研究中发现的混合结果。
