title: Wear mechanisms in metal-on-metal bearings: the importance of tribochemical reaction layers.
abstract: Metal-on-metal (MoM) bearings are at the forefront in hip resurfacing arthroplasty. Because of their good wear characteristics and design flexibility, MoM bearings are gaining wider acceptance with market share reaching nearly 10% worldwide. However, concerns remain regarding potential detrimental effects of metal particulates and ion release. Growing evidence is emerging that the local cell response is related to the amount of debris generated by these bearing couples. Thus, an urgent clinical need exists to delineate the mechanisms of debris generation to further reduce wear and its adverse effects. In this study, we investigated the microstructural and chemical composition of the tribochemical reaction layers forming at the contacting surfaces of metallic bearings during sliding motion. Using X-ray photoelectron spectroscopy and transmission electron microscopy with coupled energy dispersive X-ray and electron energy loss spectroscopy, we found that the tribolayers are nanocrystalline in structure, and that they incorporate organic material stemming from the synovial fluid. This process, which has been termed "mechanical mixing," changes the bearing surface of the uppermost 50 to 200 nm from pure metallic to an organic composite material. It hinders direct metal contact (thus preventing adhesion) and limits wear. This novel finding of a mechanically mixed zone of nanocrystalline metal and organic constituents provides the basis for understanding particle release and may help in identifying new strategies to reduce MoM wear.
authors.affiliation: Department of Orthopedic Surgery, Rush University Medical Center, 1653 West Congress Parkway, Chicago, Illinois 60612, USA. markus_a_wimmer@rush.edu
authors.forename: Markus A
authors.initials: MA
authors.lastname: Wimmer
authors.forename: Alfons
authors.initials: A
authors.lastname: Fischer
authors.forename: Robin
authors.initials: R
authors.lastname: Büscher
authors.forename: Robin
authors.initials: R
authors.lastname: Pourzal
authors.forename: Christoph
authors.initials: C
authors.lastname: Sprecher
authors.forename: Roland
authors.initials: R
authors.lastname: Hauert
authors.forename: Joshua J
authors.initials: JJ
authors.lastname: Jacobs
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip / Q000295:instrumentation* / Q000379:methods; D001672:Biocompatible Materials / Q000737:chemistry; D005260:Female; D006622:Hip Prosthesis; D006801:Humans; D008297:Male; D053768:Metal Nanoparticles / Q000737:chemistry; D008670:Metals / Q000737:chemistry*; D046529:Microscopy, Electron, Transmission / Q000379:methods; D008875:Middle Aged; D011474:Prosthesis Design; D011475:Prosthesis Failure; D012086:Reoperation; D013057:Spectrum Analysis / Q000379:methods; D013314:Stress, Mechanical; D013499:Surface Properties; D013582:Synovial Fluid / Q000737:chemistry
chemical_list: D001672:Biocompatible Materials; D008670:Metals