Abstract
Diamond-like carbon coatings may decrease implant wear, therefore, they are helping to reduce aseptic loosening and increase service life of total knee arthroplasties (TKAs). This two-part study addresses the development of such coatings for ultrahigh molecular weight polyethylene (UHMWPE) tibial inlays as well as cobalt-chromium-molybdenum (CoCr) and titanium (Ti64) alloy femoral components. While the deposition of a pure (a-C:H) and tungsten-doped hydrogen-containing amorphous carbon coating (a-C:H:W) as well as the detailed characterization of mechanical and adhesion properties were the subject of Part I, the tribological behavior is studied in Part II. Pin-on-disk tests are performed under artificial synovial fluid lubrication. Numerical elastohydrodynamic lubrication modeling is used to show the representability of contact conditions for TKAs and to assess the influence of coatings on lubrication conditions. The wear behavior is characterized by means of light and laser scanning microscopy, Raman spectroscopy, scanning electron microscopy and particle analyses. Although the coating leads to an increase in friction due to the considerably higher roughness, especially the UHMWPE wear is significantly reduced up to a factor of 49% (CoCr) and 77% (Ti64). Thereby, the coating shows continuous wear and no sudden failure or spallation of larger wear particles. This demonstrated the great potential of amorphous carbon coatings for knee replacements.
Highlights
The endoprosthetic replacement of the knee joint aims at restoring its functionality, which has been reduced due to gonarthrosis and rheumatoid arthritis, enabling patients to enjoy a mobile and pain-free life [1]
The particle size of the ultrahigh molecular weight polyethylene (UHMWPE):H|Ti64:W pairing was similar to that of the reference groups and did not change from Interval 3 to Interval 7 too. These results indicated that the coated groups did not suffer from any delamination, which would result in an increased wear from Interval 3 to Interval 7 with particles of several micrometers in size
The particle sizes and morphologies of the studied pairings might demand for further investigations, for instance in a multidirectional test-setup, to determine whether cross shearing would lead to delamination and/or the release of bigger particles. This contribution evaluated the potential of amorphous carbon coatings for improving the tribological behavior of total knee arthroplasties (TKAs)
Summary
The endoprosthetic replacement of the knee joint aims at restoring its functionality, which has been reduced due to gonarthrosis and rheumatoid arthritis, enabling patients to enjoy a mobile and pain-free life [1] The numbers of this surgical treatment continue to grow, and the implantation of total knee arthroplasties (TKAs) is becoming relevant for increasingly younger patients [2,3]. Diamond-like carbon (DLC) coatings can be considered attractive due to their advantageous ratio of hardness-to-elasticity and the ability to form wear-protecting transfer layers [27,28] These excellent and tunable mechanical properties [29] can be complemented by medically relevant properties [30], such as chemical resistance, antibacterial behavior and good biocompatibility [31,32]
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