Constitutive Model for Polyethylenes in Joint Components

描述（由申请人提供）：高交联超高分子量聚乙烯（UHMWPE）组件分别于1998年和2001年引入全髋关节和全膝关节置换术的临床应用。交联提高了UHMWPE的耐磨性，但也会损失极限强度、延展性和抗断裂性。由于无法预测体外和体内的疲劳和断裂行为，使用高度交联的HDPE的新设计的开发受到限制。我们在过去3年的研究已成功地旨在开发和验证基于聚合物物理学的本构模型，以准确预测UHMWPE部件在多轴和循环载荷条件下的大变形力学行为。 本研究的持续全球目标是通过对组件进行更可靠的数值建模，改善任何UHMWPE配方的UHMWPE关节组件的长期性能。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，该模型将定量预测UHMWPE部件的总体静态和疲劳断裂。我们建议通过实现以下四个具体目标，扩展我们基于物理的UHMWPE本构模型，以包括静态和疲劳失效：1.扩展传统的和高度交联的CIPPE的本构模型，将静态失效准则内的一个随机框架内的单调单轴拉伸失败。2.在本构模型中引入疲劳损伤失效准则。3.通过在单调和循环载荷条件下进行缺口（三轴应力状态）试验（然后进行数值模拟），验证特定目标（1）和（2）中开发的失效模型。 拟议研究与公共卫生的相关性：需要能够前瞻性地预测使用这些新的、韧性较低的髋臼杯的当前和新部件全髋关节和全膝关节设计的失效模式的骨折倾向。最近，在不到两年的时间内，有四份交联UHMWPE髋关节部件因断裂而失效的医疗器械报告。在我们自己的植入物回收收集中，我们有一个交联UHMWPE髋关节部件在8个月后因断裂而失效。MDR和我们自己的植入物回收经验支持高度交联UHMWPE的机械失效，尽管是在一部分回收病例中，但仍是一种临床相关现象。

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.