A new multiphase polymeric material for cushion-bearing orthopedic implants

描述（由申请人提供）：全关节置换假体的使用寿命受到三个因素的限制：聚乙烯组件的氧化降解、磨损和机械失效。近年来，耐磨性和抗氧化性的问题已经得到解决。辐射交联显著提高了聚乙烯对颗粒磨损的抵抗力。研究表明，加入抗氧化剂可以对抗聚乙烯的氧化降解。然而，聚乙烯组件的机械损坏和开裂问题尚未得到充分解决。此外，已知交联会降低聚乙烯的机械性能，这已经受到限制，从其临床历史中可以明显看出，其中观察到髌骨部件的灾难性失效、胫骨部件分层和对线不良髋臼部件的边缘开裂。这种机械故障的发生率可以通过使用设计方法来限制，该设计方法可以减少施加在部件上的应力。然而，它们通常导致患者的运动范围减小。由于弹性体具有高度柔顺性，因此基于弹性体的缓冲轴承可以防止脆性断裂。此外，它们与非常低的摩擦相关，因为它们可以在显微镜下变形以诱导与滑液相关的流体膜润滑。这使得材料不需要具有耐磨性，因为关节置换物的两个关节面不会相互接触。然而，当与第三体颗粒（如骨屑和骨水泥）相关的粗糙体嵌入其表面并产生磨损条件时，这种策略就会失败。本研究的主要目的是研究一种基于聚乙烯和超低密度聚乙烯（本质上是一种弹性体）共混物的新型关节面材料。后者预期具有生物相容性，因为其组成与聚乙烯相似。这种共混物的交联可以使其耐磨，而抗氧化剂的掺入将使其抗氧化。与纯聚乙烯相比，这种混合多相材料具有在弹性体的某些体积分数下激活流体膜润滑或弹性流体动力润滑的潜力，纯聚乙烯具有与混合边界润滑相关的更高摩擦。无论它可以激活的润滑机制如何，这类轴承材料都具有高度柔顺性和耐脆性断裂的潜力。具体目标是：（1）在聚乙烯-超低密度聚乙烯轴承材料中引入抗氧化性。(2)研究了超低密度聚乙烯含量对聚乙烯-超低密度聚乙烯轴瓦材料摩擦磨损性能和力学性能的影响。该提案有可能指导各种关节的长效部件的制造，包括半月板、椎间盘、关节盂、髋关节和膝关节部件，所有这些部件都有可能耐磨损、氧化和断裂。更持久的关节置换将大大有利于患有骨关节炎的老年人，他们需要这些植入物来提高活动能力。

DESCRIPTION (provided by applicant): The lifetime of total joint replacement prostheses has been limited by three factors: oxidative degradation, wear and mechanical failure of its polyethylene components. In recent years, the problem of wear and oxidation resistance has been addressed. Radiation crosslinking substantially increases the resistance of polyethylene to particulate wear. Studies have shown that incorporation of antioxidants can combat oxidative degradation of polyethylene. However, the issue of mechanical damage and cracking of polyethylene components has not been adequately addressed. Also, crosslinking is known to decrease the mechanical properties of polyethylene, which is already limited, evident from its clinical history in which catastrophic failure of patellar components, delamination in tibial components and rim-cracking in mal-aligned acetabular components have been observed. The incidence of such mechanical failure can be limited by using a design approach, which can decrease applied stress on components. However, they often lead to a decrease in range of motion for the patient. Cushion bearings based on elastomers can prevent brittle fracture since elastomers are highly compliant. Also, they are associated with very low friction since they can deform microscopically to induce fluid film lubrication associated with synovial fluid. This makes it unnecessary for the material to be wear resistant since the two articulating surfaces of the joint replacements do not make contact with each other. However, this strategy fails when asperities associated with third body particles such as bone chips and cement get embedded on their surfaces and create conditions of abrasive wear. The primary objective of this research is to investigate a new bearing material based on a blend of polyethylene and an ultra-low density polyethylene, which is essentially an elastomer. The latter is expected to be biocompatible since it is compositionally similar to polyethylene. Crosslinking of this blend can render it wear resistant while incorporation of an antioxidant would render it oxidation resistant. This hybrid multiphase material has the potential to activate fluid film lubrication or elastohydrodynamic lubrication at certain volume fractions of elastomer compared to pure polyethylene, which has higher friction associated with mixed boundary lubrication. Regardless of the mechanism of lubrication that it can activate, this class of bearing materials has the potential to be highly compliant and resistant to brittle fracture. The specific aims of the proposal are: (1) To induce oxidation resistance in polyethylene-ultra low density polyethylene bearing materials. (2) To determine the effect of ultra- low density polyethylene content in altering the friction, wear and mechanical properties of polyethylene-ultra- low density polyethylene bearing material. This proposal has the potential to guide in the fabrication of long lasting components for a variety of joints, including meniscus, disc, glenoid, hip and knee components, all of which have the potential to be resistant to wear, oxidation and fracture. Longer lasting joint replacements would greatly benefit the elderly afflicted with osteoarthritis who require these implants for mobility.