Constitutive Model for Polyethylenes in Joint Components

描述（来自申请人的逐字描述）：关节面磨损损坏 超高分子量聚乙烯（UHMWPE）接头表面 置换仍然被认为是重要的临床问题 限制了全关节置换的寿命。已显示 UHMWPE的循环大应变力学行为影响其损伤机制 髋关节和膝关节组件;然而，仍然缺乏定量 了解变形状态的变化如何影响 传统UHMWPE或高度交联UHMWPE的机械响应 最近引入临床用于全髋关节置换术的骨水泥， 正在考虑用于全膝关节置换术。有必要 通过UHMWPE的数值分析更好地预测损坏和磨损 件.然而，要做到这一点，UHMWPE的本构模型， 对于多轴和循环行为，必须首先开发，验证和 切实贯彻我们的总体假设是， 理论将更准确地描述大变形力学行为 UHMWPE结构在多轴和循环载荷条件下的 目前使用的材料模型。建议：（1）模型3 UHMWPE 材料（原始材料、在氮气和伽马辐射中进行伽马辐射灭菌的材料 交联的）聚合物的基于物理的本构理论， 将结果与当前材料模型（各向同性塑性）进行比较;（2） 确定哪种本构理论可为每种UHMWPE提供最佳模型 通过确定哪种理论最好地预测实验结果来确定材料;以及 (3)将最佳本构理论应用于髋关节和膝关节植入物的有限元分析 预测时变多轴应力应变的单元模型 states.下一步将是利用本研究开发的工具， 预测体外髋关节和膝关节的磨损、表面损伤（和大体损伤） 模拟器研究，并最终从体内使用。目标是改善 UHMWPE关节部件的长期性能，不考虑UHMWPE 通过显著改进部件的数值建模， 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.