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Effect of head surface roughness and sterilization on wear of UHMWPE acetabular cups
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
Laboratorio di Tecnologia Medica, Istituti Ortopedici Rizzoli, Bologna.
Centro di Studio Sulla Spettroscopia Raman, Dipartimento di Biochimica G. Moruzzi, Università di Bologna, Bologna.
Laboratorio di Tecnologia Medica, Istituti Ortopedici Rizzoli, Bologna.
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2009 (English)In: Journal of Biomedical Materials Research, ISSN 0021-9304, E-ISSN 1097-4636, Vol. 90, no 4, 1032-1042 p.Article in journal (Refereed) Published
Abstract [en]

The impact of femoral head surface roughness on wear of gamma-irradiation sterilized (3 MRad in nitrogen, crosslinked) and nonsterilized (not crosshnked) UHMWPE acetabular cups has been evaluated. Gravimetric wear testing was performed in a hip joint simulator for 2 x 10(6) cycles. CoCrMo heads were used with different surface roughness (R-a = 15 nm and R-a = 400 rim). The surface roughness after wear test was unchanged for the roughened heads, whereas the initially smooth heads showed a few scratches. The roughened heads increased the wear of the acetabular cups 2-fold. The gamma-irradiated cups tested against rough heads underwent the highest wear. The absorption of water was highest for the gamma-irradiated cups (0.0204% compared to 0.0031% after 85 days). Raman spectroscopy showed small but significant crystallinity changes in the wear zone, where the gamma-irradiated cups with the most extensive abrasion increased in crystallinity, whereas the nonsterilized cups underwent a crystallinity decrease.

Place, publisher, year, edition, pages
2009. Vol. 90, no 4, 1032-1042 p.
Keyword [en]
Crystallinity; Gamma-irradiation; Raman spectroscopy; Roughness; UHMWPE acetabular cups
National Category
Medical Laboratory and Measurements Technologies
Identifiers
URN: urn:nbn:se:kth:diva-14275DOI: 10.1002/jbm.a.32161ISI: 000268940100009Scopus ID: 2-s2.0-68249152033OAI: oai:DiVA.org:kth-14275DiVA: diva2:331992
Note
QC 20100729Available from: 2010-07-29 Created: 2010-07-29 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Computed Tomography of Acetabular Cup Wear and Effect of Surface Roughness on Wear and Oxidation of UHMWPE Hip Prostheses
Open this publication in new window or tab >>Computed Tomography of Acetabular Cup Wear and Effect of Surface Roughness on Wear and Oxidation of UHMWPE Hip Prostheses
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Aseptic loosening is the most common complication in total hip replacement (5- 10% at 10 years follow up). The magnitude of the problem is illustrated by the fact that about one million hip prostheses are implanted worldwide each year. Many parameters affect the longevity of the implant where aseptic loosening caused by wear debris and raised intraarticular pressure are the most common reasons for revisions. To monitor wear in vivo and also to predict the longevity of new materials for hip prostheses are therefore important issues.

The main aims of this thesis are to validate a new non-invasive method for assessment of in vivo wear of acetabular cups in 3 dimensions using computed tomography (CT), and to investigate the influence of counterface surface roughness and γ-irradiation sterilisation in wear testing of ultra high molecular weight polyethylene (UHMWPE) for hip prostheses. A new low friction coating, Micronite was also investigated using a multidirectional pin-on-disk machine.

The 3D-CT method was found to be easy to use and showed an accuracy and repeatability at a clinical relevant level for assessment of acetabular cup wear. The method should lend itself well to semi-automation. The Micronite coating showed potential for use in artificial joints due to its low friction and intact surface after wear testing compared to a stainless steel disk that showed wear tracks. However, the surface roughness of the stainless steel disks was increased by the coating. Therefore further investigations are needed. In the hip simulator study, it was found that a rougher counter surface increased the wear 2-fold. It was also found that sterilisation by γ-irradiation (in nitrogen) increased both fluid absorption and wear of the UHMWPE cups compared to the non-sterilised cups. A study with infrared spectroscopy and derivatisation techniques using NO, HCl, and SO2 showed that the increased wear and absorption were due to oxidation induced by γ-irradiation. The oxidation was found to be inhomogeneous with higher oxidation near the surfaces. The contribution of the roughened heads to the increased oxidation was only minor. Crystallinity changes upon wear testing of the sterilised cups were detected with Raman spectroscopy and differential scanning calorimetry. However, the changes were small and the influence on wear properties is therefore questionable.

Place, publisher, year, edition, pages
Stockholm: KTH, 2007. 70 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2007:69
Keyword
Hip prostheses, Computed Tomography, Surface roughness, UHMWPE, Wear, Coating, Gamma-irradiation, pin-on-disc, hip simulator
National Category
Medical Laboratory and Measurements Technologies
Identifiers
urn:nbn:se:kth:diva-4522 (URN)978-91-7178-786-6 (ISBN)
Public defence
2007-11-23, F3, F, Lindstedtsväg 26, Stockholm, 14:00
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Supervisors
Note
QC 20100716Available from: 2007-11-07 Created: 2007-11-07 Last updated: 2010-11-19Bibliographically approved

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