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Wear performance of a new biocompatible silicon nitride for biomedical applications
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.ORCID iD: 0000-0001-9529-650X
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering.ORCID iD: 0000-0002-7356-3002
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Ceramics are used in bearings of joint implants due to their high wear resistance and biocompatibility. Silicon nitride (Si3N4) is a biomaterial with bacteriostatic properties, high wear resistance, it shows slow dissolution in aqueous environments and contains mainly biocompatible ions. In this work sintering additives SrO, MgO and SiO2 were used in order to gain improvement in biocompatibility, over the commonly used Al2O3 and Y2O3. This substitution may however have a substantial effect on the wear properties of the material, and the aim of the study was to evaluate these properties in a relevant setting. Si3N4 was sintered by spark plasma sintering in the shape of discs for later grinding and polishing. The wear resistance was evaluated by multidirectional pin-on-disc wear tests against ultra-high molecular weight polyethylene pins. Tests were performed in bovine serum solution at 37 °C for 2 million cycles. The surface roughness of the materials was measured by an optical surface profiler, phase composition by X-ray diffraction, surface morphology by scanning electron microscopy, and the pH of the wear lubricant was measured at intervals of half a million cycles. The surface roughness of the ceramic discs and UHMWPE pins was in accordance with the biomedical standard, and the XRD measurements and SEM images showed the presence of α- and β-phase silicon nitride. The multidirectional wear tests showed a low wear factor and a comparable coefficient of friction to previous work, showing promise for application in joint implants. No difference between the material groups could be found in terms of UHMWPE pin wear. However, the dissolution of the materials over time may be a concern for biotribological applications.

Keywords [en]
silicon nitride; spark plasma sintering; wear; joint replacements
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Materials Science
Identifiers
URN: urn:nbn:se:uu:diva-405317OAI: oai:DiVA.org:uu-405317DiVA, id: diva2:1397176
Projects
European Union, grant number FP7-NMP-2012-310477 (Life Long Joints project)EBW+ Project Erasmus Mundus Programme, Action 2 – STRAND 1, Lot 9 (Latin America), Brazil, Grant number 2014-0982Available from: 2020-02-27 Created: 2020-02-27 Last updated: 2020-03-13
In thesis
1. Functional properties of silicon nitride based materials for joint applications
Open this publication in new window or tab >>Functional properties of silicon nitride based materials for joint applications
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Total hip and total knee replacements are generally successful procedures for patients suffering with pain due to bone fracture or diseases affecting the joints. However, the materials that are commonly used still have limitations. In particular, corrosion products and wear debris may give rise to negative body reactions.

In this thesis, silicon nitride based materials were investigated for use in joint implants, namely as a coating for e.g. femoral heads and the metallic modular taper junction in hip implants, as well as a bulk bioceramic for joint applications. One of the main advantages of these materials is the potential to dissolve slowly in aqueous solutions, releasing only biocompatible ions.

To understand the mechanical and wear properties of these materials, thin film coatings were deposited using magnetron-based techniques onto Si wafers and a CoCrMo alloy, the latter frequently used in biomedical implants. Coatings up to 8.8 µm thick were deposited on 2D flat discs as well as full 3D implant heads, following a CrN interlayer for improved adhesion. The chemical composition, microstructure, surface roughness, adhesion, wear resistance, and dissolution properties of the coatings were evaluated as a function of substrate rotation, bias voltage, target power as well as the addition of different elements.

Results show that it is possible to produce coatings with mechanical properties and a wear performance similar to bulk ceramics and other ceramic coatings already evaluated in vivo. It was evident that a high coating density is needed, to avoid premature failure in an in vivo environment. The coating density, and stability over time in solution, was found to increase when a higher target power and process heating were used.

New bulk silicon nitride materials containing only biocompatible additives, were evaluated for potential use in joint applications by wear tests for the first time, showing very low wear rates of the counter material.

Silicon nitride coatings and bulk materials tested in this work showed promising results for further investigation and a basis for future application in joint bearings.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2020. p. 60
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1912
Keywords
Silicon nitride, Coatings, Wear, Joint replacements, HiPIMS
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-406223 (URN)978-91-513-0891-3 (ISBN)
Public defence
2020-04-23, Å4001, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2020-04-01 Created: 2020-03-05 Last updated: 2020-04-01

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