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

9908096超高分子量聚乙烯（UHMWPE）作为关节假体中的关节面材料，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，已经开发了交联聚合物的方法。 新型高交联材料的设计旨在提高耐粘着磨损性，并且在最近的髋关节模拟器测试中显示出几乎为零的磨损，其中聚合物关节面受到振荡滑动接触条件的影响。 本研究将阐述新引入的制造工艺和灭菌技术对UHMWPE膝关节假体关节面长期耐久性的影响。膝关节中的载荷条件与髋关节中的载荷条件有很大不同;它们主要是振荡滚动/滑动接触，并且接触疲劳可能是比髋关节假体中的滑动磨损更重要的膝关节轴承失效模式。这项工作将采用新型加速试验技术，目前正在开发这些技术，以研究在空气中伽马辐照后在传统UHMWPE中观察到的变化，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变化。 将在几周内对关节面材料进行加速老化，以模拟之前记录的使用5 - 10年或更长时间的关节假体关节面的长期变化。 将对循环滚动/滑动接触下的化学氧化过程和关节面应力分布进行数值建模，以预测材料变化的临床影响。 使用膝关节模拟器和滚动/滑动接触测试仪进行的循环磨损和接触疲劳测试将测试未老化和老化关节面材料的性能。 应力分析和测试条件之间的相关性将确保关节假体中复杂几何形状和应力状态的准确建模。 将使用从患者身上收集的大量已建立的关节面档案来确认正在建模的临床磨损机制，以实现预测能力。*

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.***