Accelerated Life Cycle Testing and Modeling of UHMWPE Bearings in Knee Prostheses

超高相对分子质量聚乙烯(UHMWPE)作为关节假体的轴承材料，其磨损是影响置换关节长期存活的主要问题。为了抵消这种磨损，已开发出使聚合物交联的方法。这种新型的高交联度材料旨在提高抗粘着磨损的能力，在最近的髋关节模拟器测试中，它们几乎表现出零磨损，在这些测试中，聚合物轴承受到振荡滑动接触条件的影响。这项研究将解决新引入的制造工艺和灭菌技术对UHMWPE膝关节假体轴承长期耐用性的影响。膝关节的载荷条件与髋关节有很大的不同；它们主要是振荡滚动/滑动接触，接触疲劳可能是膝关节轴承失效的一种比滑动磨损更重要的模式，如在髋关节假体中。这项工作将应用新的加速测试技术，目前正在开发这种技术来研究在空气中伽马辐照后观察到的传统UHMWPE的变化，以评估这些新开发的交联材料中随时间变化的化学和机械性能。将在几周内对轴承材料进行加速老化，以模拟以前在使用5至10年或更长时间的关节假体轴承中记录的长期变化。将对轴承在循环滚动/滑动接触下的化学氧化过程和应力分布进行数值模拟，以预测材料变化的临床影响。使用膝部模拟器和滚动/滑动接触试验机进行的循环磨损和接触疲劳测试将测试未老化和老化轴承材料的性能。应力分析和测试条件之间的关联将确保对关节假体中复杂的几何形状和应力状态进行准确建模。从患者那里获得的大量已建立的关节轴承档案将用于确认正在为预测能力而建模的临床磨损机制。*

9908096KennedyWear of ultra-high molecular weight polyethylene (UHMWPE) used as the bearing material in joint prostheses is a major problem in the long-term survival of replacement joints. To counteract this wear, methods of crosslinking the polymer have been developed. The new highly crosslinked materials are designed to have improved resistance to adhesive wear and they have shown nearly zero wear in recent hip simulator tests, in which the polymer bearings are subjected to oscillatory sliding contact conditions. This research will address the effects of newly introduced fabrication processes and sterilization techniques on long-term durability of UHMWPE knee joint prosthesis bearings. The loading conditions in the knee are substantially different than in the hip; they are primarily oscillatory rolling/sliding contact and contact fatigue can be a more important mode of knee bearing failure than is sliding wear as in the hip prostheses. The work will apply novel accelerated testing techniques, which are now being developed to study the changes observed in conventional UHMWPE following gamma irradiation in air, to assess the time dependent chemical and mechanical property changes in these newly developed crosslinked materials. Accelerated aging of bearing material will be done to simulate, within a few weeks, the long-term changes that previously have been documented in joint prosthesis bearings in use for 5 to 10 years or more. Numerical modeling of both the chemical oxidation process and the stress distribution in the bearings under cyclic rolling / sliding contact will be carried out to allow prediction of clinical impacts of material changes. Cyclic wear and contact fatigue testing using a knee simulator and a rolling/sliding contact tester will test the performance of unaged and aged bearing material. Correlation between the stress analyses and the test conditions will ensure accurate modeling of the complex geometry and stress states in joint prostheses. A large, established archive of joint bearings explanted from patients will be used to confirm the clinical wear mechanisms that are being modeled for predictive capability.***