Baker D A, Bellare A, Pruitt L
Department of Mechanical Engineering, University of California, Berkeley, California 94720.
J Biomed Mater Res A. 2003 Jul 1;66(1):146-54. doi: 10.1002/jbm.a.10606.
Crosslinked ultrahigh molecular weight polyethylene (UHMWPE) has been recently approved by the Food and Drug Administration for use in orthopedic implants. The majority of commercially available UHMWPE orthopedic components are crosslinked using e-beam or gamma radiation. The level of crosslinking is controlled with radiation dose and free radicals are eliminated through heat treatments to prevent long-term degradation associated with chain scission or oxidation mechanisms. Laboratory studies have demonstrated a substantial improvement in the wear resistance of crosslinked UHMWPE. However, a concern about the resistance to fatigue damage remains in the clinical community, especially for tibial components that sustain high cyclic contact stresses. The objective of this study was to investigate both the initiation and propagation aspects of fatigue cracks in radiation crosslinked medical-grade UHMWPE. This work evaluated three levels of radiation, which induced three crosslink densities, on the fatigue crack propagation and total fatigue life behavior. Both as-received UHMWPE, as well as those that underwent an identical thermal history as the crosslinked UHMWPE were used as controls. Fractured crack propagation specimens were examined using scanning electron microscopy to elucidate fatigue fracture mechanisms. The results of this work indicated that a low crosslink density may optimize the fatigue resistance from both a crack initiation and propagation standpoint.
交联超高分子量聚乙烯（UHMWPE）最近已获美国食品药品监督管理局批准用于骨科植入物。大多数市售的UHMWPE骨科部件是通过电子束或伽马辐射进行交联的。交联程度由辐射剂量控制，自由基通过热处理消除，以防止与链断裂或氧化机制相关的长期降解。实验室研究表明，交联UHMWPE的耐磨性有显著提高。然而，临床界仍对其抗疲劳损伤能力存在担忧，特别是对于承受高循环接触应力的胫骨部件。本研究的目的是调查辐射交联医用级UHMWPE疲劳裂纹的萌生和扩展情况。这项工作评估了三种辐射水平，它们诱导了三种交联密度，研究其对疲劳裂纹扩展和总疲劳寿命行为的影响。未交联的UHMWPE以及与交联UHMWPE经历相同热历程的材料均用作对照。使用扫描电子显微镜检查断裂的裂纹扩展试样，以阐明疲劳断裂机制。这项工作的结果表明，从裂纹萌生和扩展的角度来看，低交联密度可能会优化抗疲劳性能。
