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Details of Grant 

EPSRC Reference: GR/M59518/01
Principal Investigator: Fisher, Professor J
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Department: Mechanical Engineering
Organisation: University of Leeds
Scheme: ROPA
Starts: 01 October 1999 Ends: 31 December 2001 Value (£): 136,052
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Summary on Grant Application Form
Total joint replacements are one of the most successful applications of biomaterials in the short to medium term. However in the longer term (beyond 15 years) they fail by an interactive mechanical and biological process - wear debris unduced osteolysis - which leads to loosening and the need for a revision operation. With one percent of the population benefiting from joint replacements, the number of revision operations performed each year is increasing, at an ever increasing cost to the NHS. Although the materials used in bearings for joint replacement such as polyethylene are compatible in their bulk form, when functioning at articulating interfaces, they produce wear particles which are highly biologically reactive, stimulating macrophages to release cytokines such as TNFa which lead to osteolysis. Our recent research has identified a critical size range 200 to 7000 nm which produces elevated levels of biological activity. Our own, and other studies, have shown that the majority of polyethylene particles lie within this size range. Current research (as exemplified by our collaborative industrial work cited) is aimed at reducing the polyethylene wear and hence the number of reactive wear particles. In the hip, alternative bearing materials have been developed such as metal on metal, but they also produce wear particles and these have been found to elevate ion levels and cause tissue necrosis. Alumina/alumina ceramic materials have also been used and although they have been cited to produce low wear, in a recent explant study we have shown several cases of severe wear with inter granular fracture leading to wear particles in the biologically active size range. Historically bearing materials have been designed to reduce wear volumes even though prostheses per se do not generally wear out. In order to extend the lifetime of the prosthesis to 20 years and beyond, it is necessary to address the functional biocompatibility of the debris in the design of the bearing materials. Our recent understanding of the critical size dependency of the osteolytic potential of debris opens up an alternative approach, which is to design articulating interfaces with low wear in which all the particles produced are substantially less than 100 nm in size and chemically inactive. Carbon carbon composites in which physical properties approaching those of carmics and are chemically inert with good wear resistance, offer an attractive option that has not previously been studied for this application. The physical properties of novel carbon carbon composites can be engineered for bearing surfaces for artificial joints to give good wear resistance and to produce wear debris that is substantially less than 100 nm in size. These particles will be highly compatible, chemically inert and will not cause local osteolysis or tissue necrosis.
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