Dharmastiti R, Barton D C, Fisher J, Edidin A, Kurtz S
School of Mechanical Engineering, Leeds University, Leeds, LS2 9JT, UK.
Biomed Mater Eng. 2001;11(3):241-56.
Unidirectional wear tests of UHMWPE against smooth counterfaces show that molecular chains at the surface of virgin material become oriented parallel to the sliding direction giving low wear rate. It is postulated that under more abrasive conditions and predominantly unidirectional motion as in knee prostheses, it may proof beneficial to provide molecular orientation of the bulk material. Therefore strips of UHMWPE were oriented by die drawing at elevated temperature and the resulting anisotropic material subjected to tensile tests, small punch tests and also unidirectional wear tests both parallel and perpendicular to the draw direction. The tensile tests showed that, in the parallel direction, the oriented UHMWPE became stiffer and less ductile compared to the virgin UHMWPE. In the perpendicular direction, there were reductions in yield stress, 5% proof stress and energy to failure compared to the virgin material. The small punch test showed that the oriented UHMWPE exhibited apparent hardening when tested in both parallel and perpendicular directions but the mechanical behaviour in the perpendicular direction was comparable to the virgin UHMWPE. The wear tests demonstrated that the oriented UHMWPE did not show any significant improvement of wear resistance for sliding against either isotropically rough or scratched counterfaces. There was no clear dependency between the mechanical properties and wear factors of the oriented UHMWPE.
超高分子量聚乙烯（UHMWPE）与光滑配对表面的单向磨损试验表明，原始材料表面的分子链会沿滑动方向取向，从而使磨损率较低。据推测，在更具磨蚀性的条件下以及在膝关节假体中常见的主要单向运动情况下，使块状材料具有分子取向可能是有益的。因此，通过在高温下模压拉伸使UHMWPE条带取向，并对所得的各向异性材料进行拉伸试验、小冲孔试验以及与拉伸方向平行和垂直的单向磨损试验。拉伸试验表明，与原始UHMWPE相比，在平行方向上，取向的UHMWPE变得更硬且延展性更低。在垂直方向上，与原始材料相比，屈服应力、5% 比例极限应力和断裂能均有所降低。小冲孔试验表明，取向的UHMWPE在平行和垂直方向上进行测试时均表现出明显的硬化现象，但垂直方向的力学行为与原始UHMWPE相当。磨损试验表明，取向的UHMWPE在与各向同性粗糙或有划痕的配对表面滑动时，耐磨性没有任何显著改善。取向的UHMWPE的力学性能与磨损因素之间没有明显的相关性。
