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Fabrication and evaluation of SixNy coatings for total joint replacements
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, Applied Materials Sciences.
Fraunhofer, Institute for Mechanics of Material.
Fraunhofer, Institute for Mechanics of Material.
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2012 (English)In: Journal of materials science. Materials in medicine, ISSN 0957-4530, E-ISSN 1573-4838, Vol. 23, no 8, 1879-1889 p.Article in journal (Refereed) Published
Abstract [en]

Wear particles from the bearing surfaces of joint implants are one of the main limiting factors for total implant longevity. Si3N4 is a potential wear resistant alternative for total joint replacements. In this study, SixNy-coatings were deposited on cobalt chromium-discs and Si-wafers by a physical vapour deposition process. The tribological properties, as well as surface appearance, chemical composition, phase composition, structure and hardness of these coatings were analysed. The coatings were found to be amorphous or nanocrystalline, with a hardness and coefficient of friction against Si3N4 similar to that found for bulk Si3N4. The low wear rate of the coatings indicates that they have a potential as bearing surfaces of joint replacements. The adhesion to the substrates remains to be improved.

Place, publisher, year, edition, pages
2012. Vol. 23, no 8, 1879-1889 p.
National Category
Materials Engineering Inorganic Chemistry
Research subject
Chemistry with specialization in Inorganic Chemistry; Engineering Science with specialization in Materials Science
Identifiers
URN: urn:nbn:se:uu:diva-156798DOI: 10.1007/s10856-012-4625-3ISI: 000306586900005OAI: oai:DiVA.org:uu-156798DiVA: diva2:433348
Available from: 2011-08-09 Created: 2011-08-09 Last updated: 2017-12-08Bibliographically approved
In thesis
1. Friction and Wear Mechanisms of Ceramic Surfaces: With Applications to Micro Motors and Hip Joint Replacements
Open this publication in new window or tab >>Friction and Wear Mechanisms of Ceramic Surfaces: With Applications to Micro Motors and Hip Joint Replacements
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Surfaces exposed to wear always transform and typically a layer of new structure and composition is formed. This layer, often called tribofilm, changes the friction and wear properties. Tribofilms formed on ceramic surfaces may consist of products from chemical reactions between the materials in contact and the environment or consist of compacted wear debris.

In this thesis, focus has been to understand the friction and wear mechanisms of ceramic surfaces, as well as acquiring knowledge about the properties of the new surfaces created during wear. Ultimately, this understanding can be used to develop ceramic systems offering high or low friction, while the material loss in both cases should be minimised. Such ceramics could improve numerous tribological systems and applications, out of which ultrasonic motors, low-friction ceramic coatings and hip joint replacements have been treated in this thesis. Friction and wear tests, and subsequently various surface analyses have been essential for the knowledge about the friction, wear and tribofilm formation.

 For ultrasonic motors of the studied type, the highest driving force is achieved when the friction is high between the alumina components in the friction drive system. The highest friction was here accomplished with a thick tribofilm on the surfaces. The formation of such tribofilms was favoured by dry conditions, and using an initially rough surface, which increased the initial generation of wear debris.

In a detailed investigation of the importance of microtopography on tribofilm formation and friction behaviour, a low-friction, PVD coating of TaC/a-C was studied. This coating showed a very low, stable friction. High sensitivity to the microtopography was demonstrated, smooth coating exhibited a faster build-up of a dense tribofilm of fine ground material on the counter steel surface and subsequently a faster running in and friction decrease. 

The life span for total hip joint replacements can be prolonged by minimising the wear particles that cause inflammation and subsequent implant loosening. In this work coatings of amorphous/nanocrystalline silicon nitride have shown low wear rate, and hence produce a minimum of wear particles. Furthermore, these particles that are expected to resorb in vivo. This system therefore has potential to reduce problems with inflammation and osteolysis connected to wear particles.    

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2011. 65 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 841
Keyword
Tribology, Friction, Wear, Ceramic, Tribofilm, Alumina, Silicon nitride, Ultrasonic Motors, Hip Joint Replacement, PVD coating
National Category
Materials Engineering
Research subject
Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-156801 (URN)978-91-554-8123-0 (ISBN)
Public defence
2011-09-23, Häggsalen, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2011-09-02 Created: 2011-08-09 Last updated: 2011-11-03Bibliographically approved
2. Silicon nitride for total hip replacements
Open this publication in new window or tab >>Silicon nitride for total hip replacements
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

For more than 50 years total hip replacements have been a common and successful procedure to increase patient mobility and quality of life. The 10-year implant survival rate is 97.8%. However, for longer implantation times there are limitations linked to the negative biological response to wear and corrosion products from the currently used biomaterials.

In this thesis silicon nitride (SiNx) coatings were evaluated for use in total hip replacements, on the articulating bearing surface and modular taper connections. Homogeneous, dense SiNx coatings were deposited using reactive high power impulse magnetron sputtering (HiPIMS) up to a thickness of 8 µm. The N/Si atomic ratios ranged from 0.3 to 1.1 and the coatings showed a low surface roughness. The wear rate of a SiNx coated cobalt chromium molybdenum alloy (CoCrMo) was similar to that of bulk Si3N4, and less than one 46th of uncoated CoCrMo, an alloy that is commonly used in joint replacements. Wear debris generated from SiNx coatings was round in shape, with a mean size of 40 nm, and ranged between 10 and 500 nm. Model particles, similar in size and shape as the wear debris, were soluble in simulated body fluid. The dissolution rate was higher than the expected rate of debris generation. Along with the size of the debris, which is not in the critical range for macrophage activation, this dissolution may limit negative biological reactions. The SiNx coatings also dissolved in simulated body fluid. The coating with the highest N/Si ratio exhibited the lowest dissolution rate, of 0.2 to 0.4 nm/day, while CoCrMo under the same condition dissolved at a rate of 0.7 to 1.2 nm/day. SiNx-coated CoCrMo exhibited a reduced release of Co, Cr and Mo ions into the solution by two orders of magnitude, compared to uncoated CoCrMo. Si3N4 evaluated under micro-displacement in a corrosive environment, replicating the modular taper, showed a lower corrosion current compared to common biomedical alloys. SiNx coatings may also act beneficially to reduce issues associated with this type of contact.

SiNx coatings have shown several properties in a laboratory environment that are hypothesised to increase the longevity of joint replacements. The promising results encourage further evaluation closer to the clinical application of total hip replacements, in particular in the articulating bearing surface and in modular tapers.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. 53 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1242
Keyword
SiNx, Si3N4, coatings, CoCr, Ti, alloy, tribology, wear, corrosion, dissolution, debris, hip, arthroplasty
National Category
Materials Engineering Medical Materials
Research subject
Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-247800 (URN)978-91-554-9211-3 (ISBN)
Public defence
2015-05-22, Häggsalen, Ångströmslaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:30 (English)
Opponent
Supervisors
Funder
Swedish Foundation for Strategic Research EU, FP7, Seventh Framework Programme, 310477
Available from: 2015-04-29 Created: 2015-03-24 Last updated: 2015-07-07

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Olofsson, JohannaPettersson, MariaLarsson, KarinGrandfield, KathrynPersson, CeciliaJacobson, StaffanEngqvist, Håkan

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