Constitutive Model for Polyethylenes in Joint Components

描述(申请人提供)：高交联型超高相对分子质量聚乙烯(UHMWPE)组件分别于1998年和2001年被引入临床用于全髋关节和全膝关节置换。交联剂提高了UHMWPE的耐磨性，但同时也降低了极限强度、延展性和抗裂性。由于无法预测体外和体内的疲劳和断裂行为，使用高度交联型UHMWPE的新设计的开发受到限制。在过去的3年里，我们的研究成功地旨在开发和验证基于聚合物物理的本构模型，以准确地预测UHMWPE构件在多轴和循环加载条件下的大变形力学行为。 这项研究的持续全球目标是通过更可靠的元器件数值建模，改善任何UHMWPE配方的超高相对分子质量聚乙烯(UHMWPE)接头元件的长期性能。我们下一阶段研究的假设是，可以建立一个基于物理的失效模型，该模型将定量地预测UHMWPE组件的严重静态和疲劳断裂。通过实现以下四个具体目标，我们建议扩展我们的基于物理的超高相对分子质量聚乙烯的本构模型，以包括静态和疲劳破坏：1.扩展传统的和高度交联的超高相对分子质量聚乙烯的本构模型，将静态破坏准则纳入单调单轴拉伸直到破坏的随机框架中。2.在本构模型中引入疲劳损伤失效准则。3.通过在单调和循环加载条件下进行缺口(三轴应力状态)试验(然后进行数值模拟)来验证在特定目标(1)和(2)中建立的破坏模型。 拟议研究与公共健康的相关性：有必要能够前瞻性地预测骨折倾向，作为使用这些新的、延展性较差的超高分子量聚乙烯的当前和新的全髋关节和全膝关节设计的失败模式。最近，已经有四份医疗器械报告称，在不到两年的时间里，交联型UHMWPE髋关节假体因骨折而失效。在我们自己的种植体回收集合中，我们有一个交联型UHMWPE髋关节假体，在8个月后因骨折而失败。MDR和我们自己的植入物回收经验支持高度交联的UHMWPE的机械故障，尽管是在检索到的病例的子集中，但仍然是临床相关的现象。

DESCRIPTION (provided by applicant): Highly cross linked ultra-high molecular weight polyethylene (UHMWPE) components were introduced into clinical use for total hip and for total knee replacements in 1998 and 2001, respectively. Cross linking improves the wear resistance of UHMWPE, but there is also a loss in ultimate strength, ductility, and resistance to fracture. Development of new designs that use highly cross linked UHMWPEs are limited by the inability to predict fatigue and fracture behavior in vitro and in vivo. Our research for the past 3 years has been successfully aimed at developing and validating a polymer physics-based constitutive model to accurately predict the large deformation mechanical behavior of UHMWPE components under multiaxial and cyclic loading conditions. The continuing global goal of this research is to improve the long-term performance of UHMWPE joint components, for any UHMWPE formulation, through significantly more reliable numerical modeling of components. The hypothesis of this next phase of our research is that a physics-based failure model can be established that will quantitatively predict gross static and fatigue fracture of UHMWPE components. We propose to extend our physics-based constitutive model for UHMWPE to include static and fatigue failure through achievement of the next four specific aims: 1. Extend the constitutive model for conventional and highly cross linked UHMWPEs to incorporate a static failure criterion within a stochastic framework for monotonic uniaxial tension up to failure. 2. Incorporate a fatigue damage failure criterion into the constitutive model. 3. Verify the failure model developed in specific aims (1) and (2) by conducting (and then numerically simulating) tests conducted on notched (triaxial-stress-state) tests under monotonic and cyclic loading conditions. Relevance of Proposed Research to Public Health: There is a need to be able to prospectively predict the propensity for fracture as a failure mode for current and new component total hip and total knee designs that make use of these new, less ductile, UHMWPEs. Recently, there have been four Medical Device Reports of cross linked UHMWPE hip components that failed due to fracture in less than two years. In our own implant retrieval collection, we have one cross linked UHMWPE hip component that failed due to fracture after 8 months. The MDR's and our own implant retrieval experience support that mechanical failure of highly cross linked UHMWPE, albeit in a subset of retrieved cases, is nonetheless a clinically relevant phenomenon.