Coefficient of friction (COF) tests were conducted on 28-mm and 36-mm-diameter hip joint prostheses for four different material combinations, with or without the presence of Ultra High Molecular Weight Polyethylene (UHMWPE) particles using a novel pendulum hip simulator. The effects of three micro dimpled arrays on femoral head against a polyethylene and a metallic cup were also investigated. Clearance played a vital role in the COF of ceramic on polyethylene and ceramic on ceramic artificial hip joints. Micro dimpled metallic femoral heads yielded higher COF against a polyethylene cup; however, with metal on metal prostheses the dimpled arrays significantly reduced the COF. In situ images revealed evidence that the dimple arrays enhanced film formation, which was the main mechanism that contributed to reduced friction.

Department of Computer Science University of Saskatchewan 176 Thorvaldson Building 110 Science Place Saskatoon SK Canada S7N 5C9

Department of Mechanical Engineering Faculty of Engineering University of Malaya 50603 Kuala Lumpur Malaysia

Department of Mechanical Engineering University of Arkansas Fayetteville AR 72701 USA; Faculty of Mechanical Engineering Brno University of Technology Technicka 2896 2 616 69 Brno Czech Republic

Faculty of Mechanical Engineering Brno University of Technology Technicka 2896 2 616 69 Brno Czech Republic; CEITEC Central European Institute of Technology Brno University of Technology Technicka 3058 10 616 00 Brno Czech Republic

Faculty of Science and Technology Anglia Ruskin University Chelmsford Essex CM1 1SQ UK

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Analysis of Chemisorbed Tribo-Film for Ceramic-on-Ceramic Hip Joint Prostheses by Raman Spectroscopy