Details

Autor(en) / Beteiligte

• Watters, E P. J

Titel

Wear properties of artificial hip joint materials (BL)

Ort / Verlag

ProQuest Dissertations & Theses

Erscheinungsjahr

2000

Quelle

ProQuest Dissertations & Theses A&I

Beschreibungen/Notizen

• The wear properties of the standard hip replacement materials, ultra-high molecular weight polyethylene (UHMWPE) and high-nitrogen stainless steel were studied on a custom wear tester. The environment of the tests were varied to investigate some of the wear factors thought to increase the wearing of the artificial hip joint in vivo.Test runs were carried out with hard micron-scale debris introduced into the test chamber from a gas cylinder. There was an increase in the wear rate for the debris tests compared to the control tests. This is significant, as no debris was visible on the macroscopic scale, or apparent on the electron microscope. The samples showed wear features and debris similar to that seen in vivo and in simulators and test rigs in the field. Observation of submicron scale texture on the surface of the polymer component was linked to submicron scale debris and wear features observed on the stainless steel component. Such submicron debris is shown to be caused by the inherent granular structure of UHMWPE. Machining is linked to the exacerbation of the problem by loosening the grains forming the structure of the UHMWPE. The size distribution of micron and submicron particles produced on the rig closely matched retrieved debris.Some experiments with lubricants added sodium azide, a bactericide. These tests showed a retention of the surface machining marks inside the wear area of the polymer sample, indicative of cushion form lubrication, suggesting the surface of the polymer was having its elastic modulus reduced by the azide.A solution of cholesteryl palmitate in ethanol was used as a lubricant. This is a liquid crystal. Liquid crystal lubricated solutions showed significantly reduced wear compared to control tests. Microscopy showed the presence of a protective layer on the polymer surface. The surface under this layer showed plastic flow but low wear, indicative of fluid lubrication. Nematic liquid crystal solutions are known to produce a lubricating shear plane above the surface of materials, the surface layer is probably a remnant of this. Surface films were also observed on the stainless steel component.