Constitutive Model for Polyethylenes in Joint Components

描述(来自申请人的逐字记录)：关节磨损 超高分子质量聚乙烯(UHMWPE)接头表面 替代物仍然被认为是一个重要的临床问题。 限制了全部关节置换的寿命。事实证明， 超高相对分子质量聚乙烯的循环大应变行为影响损伤机理 髋关节和膝关节假体；然而，仍然缺乏定量的 关于改变变形状态如何影响 常规UHMWPE或高度交联型UHMWPE的机械响应 UHMWPE最近进入临床用于全髋关节置换术和 正在考虑用于全膝关节置换术。有必要 超高相对分子质量聚乙烯数值分析对损伤和磨损的更好预测 组件。然而，要做到这一点，UHMWPE的本构模型可以解释 多轴和循环行为必须首先开发、验证和 实施。我们的全球假设是，一种基于物理的本能 理论将更准确地描述大变形力学行为 超高相对分子质量聚乙烯结构在多轴和循环加载条件下的性能 当前使用的材质模型。建议：(1)建立三种超高相对分子质量聚乙烯模型 材料(在氮气和伽马辐射中灭菌的原始伽马辐射 交联型)使用基于物理的聚合物本构理论 将结果与当前的材料模型(各向同性塑性)进行比较；(2) 确定哪种本构理论为每种UHMWPE提供最佳模型 材料通过确定哪种理论最能预测实验结果；以及 (3)将最佳本构理论应用于髋关节假体有限元分析。 预测随时间变化的多轴应力应变的单元模型 各州。下一步将利用本研究开发的工具来 从体外髋关节和膝关节预测磨损、表面损伤(和大体损伤) 模拟器研究，并最终从活体使用。我们的目标是改善 UHMWPE接头组件的长期性能，与UHMWPE无关 配方，通过显著改进的组件数值建模 在植入之前。

DESCRIPTION (Verbatim from the Applicant): Wear damage to the articulating surfaces of ultra high molecular weight polyethylene (UHMWPE) joint replacements continues to be recognized as a significant clinical problem limiting the longevity of total joint replacements. It has been shown that the cyclic large strain mechanical behavior of UHMWPE affects the damage mechanisms of hip and knee components; however, there is still a lack of quantitative understanding regarding how changing the state of deformation affects the mechanical response of either conventional UHMWPE, or the highly cross-linked UHMWPEs recently introduced into clinical use for total hip arthroplasty and under consideration for use in total knee arthroplasty. There is a need for better predictions of damage and wear from numerical analyses of UHMWPE components. However, to do so, a constitutive model for UHMWPE that accounts for multiaxial and cyclic behavior must first be developed, validated and implemented. Our global hypothesis is that a physically based constitutive theory will more accurately describe the large deformation mechanical behavior of UHMWPE structures under multiaxial and cyclic loading conditions than the material models in current use. It is proposed to: (1) model three UHMWPE materials (virgin, gamma radiation sterilized in nitrogen and gamma radiation cross-linked) using physically-based constitutive theories for polymers and compare the results to the current material model (isotropic plasticity); (2) determine which constitutive theory provides the best model for each UHMWPE material by determining which theory best predicts experimental results; and (3) implement the best constitutive theory into hip and knee implant finite element models to predict the time-dependent multiaxial stress and strain states. The next step will be to utilize the developed tools from this study to predict wear, surface damage (and gross damage) from in vitro hip and knee simulator studies, and ultimately, from in vivo use. The goal is to improve the long-term performance of UHMWPE joint components, regardless of UHMWPE formulation, through significantly improved numerical modeling of components prior to implantation.