Muratoglu O K, Bragdon C R, O'Connor D O, Jasty M, Harris W H, Gul R, McGarry F
Massachusetts General Hospital, Orthopaedic Biomechanics Laboratory, Boston 02114, USA.
Biomaterials. 1999 Aug;20(16):1463-70. doi: 10.1016/s0142-9612(99)00039-3.
Crosslinking has been shown to improve the wear resistance of ultra-high molecular weight polyethylene in both in vitro and clinical in vivo studies. The molecular mechanisms and material properties that are responsible for this marked improvement in wear resistance are still not well understood. In fact, following crosslinking a number of mechanical properties of UHMWPE are decreased including toughness, modulus, ultimate tensile strength, yield strength, and hardness. In general, these changes would be expected to constitute a precursor for lower wear resistance, presenting a paradox in that wear resistance increases with crosslinking. In order to understand better and to analyze this paradoxical behaviour of crosslinked UHMWPE, we investigated the wear behavior of (i) radiation-crosslinked GUR 1050 resin, (ii) peroxide-crosslinked GUR 1050 resin and (iii) peroxide-crosslinked Himont 1900 resin using a bi-directional pin-on-disk (POD) machine. Wear behavior was analyzed as a function of crystallinity, ultimate tensile strength (UTS), yield strength (YS), and molecular weight between crosslinks (Mc). The crosslink density increased with increasing radiation dose level and initial peroxide content. The UTS, YS, and crystallinity decreased with increasing crosslink density. While these variations followed the same trend, the absolute changes as a function of crosslink density were different for the three types of crosslinked UHMWPE studied. There was no unified correlation for the wear behavior of the three types of crosslinked UHMWPE with the crystallinity, UTS and YS. However, the POD wear rate showed the identical linear dependence on Mc with all three types of crosslinked UHMWPEs studied. Therefore, we have strong evidence to propose that Mc or crosslink density is a fundamental material property that governs the lubricated adhesive and abrasive wear mechanisms of crosslinked UHMWPEs, overriding the possible effects of other material properties such as UTS, YS and crystallinity on the wear behavior.
在体外和临床体内研究中均已表明，交联可提高超高分子量聚乙烯的耐磨性。然而，导致耐磨性显著提高的分子机制和材料特性仍未得到充分理解。事实上，交联后超高分子量聚乙烯的一些机械性能会下降，包括韧性、模量、极限拉伸强度、屈服强度和硬度。一般来说，这些变化预计会导致耐磨性降低，这就产生了一个悖论，即耐磨性会随着交联而增加。为了更好地理解和分析交联超高分子量聚乙烯的这种矛盾行为，我们使用双向销盘（POD）试验机研究了（i）辐射交联的GUR 1050树脂、（ii）过氧化物交联的GUR 1050树脂和（iii）过氧化物交联的Himont 1900树脂的磨损行为。磨损行为作为结晶度、极限拉伸强度（UTS）、屈服强度（YS）和交联点间分子量（Mc）的函数进行分析。交联密度随着辐射剂量水平和初始过氧化物含量的增加而增加。UTS、YS和结晶度随着交联密度的增加而降低。虽然这些变化遵循相同的趋势，但对于所研究的三种交联超高分子量聚乙烯类型，作为交联密度函数的绝对变化是不同的。三种交联超高分子量聚乙烯的磨损行为与结晶度、UTS和YS之间没有统一的相关性。然而，POD磨损率对所研究的所有三种交联超高分子量聚乙烯的Mc均表现出相同的线性依赖性。因此，我们有充分的证据表明，Mc或交联密度是一种基本的材料特性，它控制着交联超高分子量聚乙烯的润滑粘着和磨料磨损机制，超越了其他材料特性（如UTS、YS和结晶度）对磨损行为可能产生的影响。
