DLC coated CoCrMo femural parts for knee prostheses and biomimetic micro-pattering with femto-second laser techniqueThursday (09.05.2019) 11:50 - 12:10 Part of:
CoCrMo-alloys form a thin oxide film, primarily of Cr2O3 with small amounts of Co3O4 and MoOx with a reported thickness of about 2 nm. The thin oxide film improves the biocompatibility. However, the oxide film is locally damages due to tribological or tribo-chemical impacts, i.e. the harsh conditions in a load carrying artificial knee joint. Both tribological pairs of these artificial joints, the CoCrMo (metallic femur and the ultrahigh molecular weight polyethylene (UHMWPE) inlay show wear in clinical observations. Wear particles and metallic ions generated from the worn surfaces of CoCrMo and UHMWPE can pose a severe threat to human tissues and organism. In some cases, it leads to Inflammation and failure of implants. It is known, that metallic corrosion and wear products exist as protein bone complexes which had the ability to induce bone resorption in vitro. Such negative and toxic impacts of metallic ions and particles on tissue are called metallosis.
Different wear resistant and bio-inert or antibacterial (i.e. Ag-doped) DLC-coating (DLC: Diamond-Like Carbon) types are investigated over decades as surface toping on loaded implants. DLC with tailored nanostructure on CoCrMo femoral part prevents metallosis due to wear on CoCrMo alloys. The present contribution discuss results from tests with DLC coated femoral parts. The tests last 5 million cycles in a knee joint simulator according to the standard ISO/DIS 14243. In our previous studies, Raman spectroscopy confirmed a similar structure of hydrogenated DLC coatings before and after tests.
Such optimised DLC toping remain almost unworn and structural similar due to the wear tests. However, different coatings thickness effects different material loss from the UHMW-PE inlays. The reason may be, heat generation in the tribological micro-contacts on UHMW-PE inlays, if DLC coating thickness increases. In order to improve the heat transfer, we suggest a laser treatment and generating biomimetic surface structures. The femtosecond laser Pharos 15-1000-PP of the company Light Conversion, Lithuania is a single-unit integrated laser system combining mJ pulse energies and high average power. For laser micro-pattering, the coated surface was treated with pulse duration was 220 fs, repetition rate of 220 Hz and laser beam radius 11.5 µm in focus. Two different biomimetic surface structures were generated.