Sputtered carbon coatings have been reported to have excellent tribological properties (low friction coefficient and wear rate) and therefore have the potential to be used as hard, solid lubricant, wear resistant coatings. During a research program aimed at reducing the wear of UHMWPE hip joint prostheses by coating the metal femoral head, a new type of carbon coating was developed which now has the trade name Graphit-iC~(TM). This coating gave exceptional friction and wear results in simple laboratory tests against coated and uncoated metal counterfaces, but not against UHMWPE as originally intended. Research was redirected towards the production of Graphit-iC coated metal-on-metal THR, and simple configuration laboratory tests predicted a prosthetic lifetime in excess of 50 years. CoCrMo prostheses were subsequently coated and performed well in pendulum tests conducted at the University of Leeds. Further tests on a physiological hip simulator gave mixed results with coating failure detected on some pairs, whilst one pair showed no detectable wear after considerable testing. Further testing is required to fully establish the cause of the failures. Recent work has studied characteristics of the Graphit-iC coating under a wider range of deposition parameters with a view to producing increased toughness for softer substrates, or graded coatings which reach steady state friction values more quickly, or provide different surface characteristics to bulk characteristics. Biocompatibility tests indicate that the Graphit-iC coating may be a suitable surface for hip joint, and other, implants used within the body.
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