Tribo-oxidation of a zirconium nitride multilayer coated knee explant in comparison with an in-vitro tested implant
Mechanical Properties of Metallic Materials and their Microstructural Origins
Final Report Abstract
Understanding the failure of artificial knee joint replacement is of enormous relevance in our growing and simultaneously aging society. Often, the underlying processes in the tribological contact within the human body are inadequately understood. One way to make the occurring processes within the body more visible is through in-vitro wear simulation in mechanical test apparatuses in the lab. The aim is to mimic the processes in the body as closely as possible, using “real” explants taken out from patients as a comparison. In the past, improvements of the longevity and performance of implants were achieved through variations in implant materials and various protective coatings. One such protective coating on a knee implant consists of a 7-layer structure with alternating CrN- and CrCN- layers and an outermost ZrN layer. This layer, known as the AS-layer, is applied to the CoCrMo implant base metal. In this study, an in-vitro tested sample was compared with an implant explanted after approx. 2 years. Special attention was given to the oxides formed on the ZrN layer, which had previously received little consideration. Previous practice involved characterizing the wear behavior of the implant system based on the softer countersurface (polyethylene (PE) articulating surface). The here studied explant was removed due to early aseptic loosening. Notably, colorations (grey/purple) were observed outside the articulating surface (contacting surface) compared to a polished, golden surface within the articulating areas. At that time, the exact cause of this appearance was not fully understood. By combining high-resolution characterization methods such as atom probe tomography (APT), (transmission) electron microscopy (TEM/SEM) and secondary ion mass spectrometry (ToF-SIMS), the formed oxides were examined in terms of their microstructure, chemical composition and thickness. An as-fabricated implant served as a reference sample. The results of these investigations revealed oxides on all surfaces with larger thicknesses than expected under ambient conditions. As a consequence, the exposure to the human body has an oxidizing effect on the implants. Further investigation suggests that oxidation in the human body does not lead to accelerated wear. In-vitro wear simulation tests were unable to fully reproduce the oxidation observed on the explanted sample, but most of the resulting oxides were similar. It was observed that the color of the ZrN layer was not a reliable measure of the oxide thickness. In addition, there were indications that ZrN oxidation might occur along dislocations – a mechanism which was observed in other systems exhibiting tribologically-induced oxidation. The insights gained in this work regarding the underlying mechanisms in the contact could be relevant for further coating development. Targeted adjustments to microstructures and material selection may ultimately improve the lifespan of artificial knee joint replacements.
Publications
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Poster: „Oxidation of a ZrN knee implant coating under tribological loading”, APT&M 2023, Leuven, Belgium, 17th – 21st of September 2023.
Rau, Julia; Eriksson, Gustav; Andersson, Martin & Thuvander, Mattias
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Poster: „Tribologically-induced oxidation of a zirconium nitride multilayer coated knee explant”, FEMS EUROMAT 2023, Frankfurt, Germany, 3rd – 7th of September 2023.
Rau, Julia; Eriksson, Gustav; Andersson, Martin & Thuvander, Mattias
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Oxidation of a Zirconium Nitride Multilayer Covered Knee Implant after Two Years in Clinical Use. Elsevier BV.
Rau, Julia; Eriksson, Gustav; Malmberg, Per; Puente, Reyna Ana Laura; Schwiesau, Jens; Andersson, Martin & Thuvander, Mattias
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Oxidation of a zirconium nitride multilayer-covered knee implant after two years in clinical use. Acta Biomaterialia, 190, 593-604.
Rau, Julia S.; Eriksson, Gustav; Malmberg, Per; Puente, Reyna Ana Laura; Schwiesau, Jens; Andersson, Martin & Thuvander, Mattias
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Raw Data to manuscript on “Oxidation of a Zirconium Nitride Multilayer Covered Knee Implant after Two Years in Clinical Use”
Rau, Julia; Eriksson, Gustav; Malmberg, Per; Puente, Reyna Ana Laura; Schwiesau, Jens; Andersson, Martin & Thuvander, Mattias
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Talk: “Oxidation of a ZrN multilayer coated knee implant within the human body”, 7th Young Tribological Researcher Symposium, Erlangen, 22nd – 23rd of July 2024.
Rau, Julia; Eriksson, Gustav; Malmberg, Per; Puente, Reyna Ana Laura; Schwiesau, Jens; Andersson, Martin & Thuvander, Mattias
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Talk: „Oxidation of a ZrN knee implant coating under in-vitro wear simulation“, Division Seminar, Varberg, 10th – 11th of June 2024.
Rau, Julia; Eriksson, Gustav; Malmberg, Per; Puente, Reyna Ana Laura; Schwiesau, Jens; Andersson, Martin & Thuvander, Mattias
