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Effect of γ-irradiation sterilization in nitrogen on oxidation of hip-simulated UHMWPE cups
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
Corrosion- and Metals Research Institute, Stockholm.
Corrosion- and Metals Research Institute, Stockholm.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

A hip simulator study with roughened heads revealed unexpected high wear rates for the γ-irradiated UHMWPE cups (sterilization performed in nitrogen) and also higher fluid absorbtion than that of the non-sterilized cups. Infrared spectroscopy and high-resolution scanning of samples stained with HCl and SO2 showed that the outer parts of cross-sections of the sterilized cups were oxidized after the wear testing. The non-sterilized cups showed essentially no polymer oxidation with only minor surface oxidation due to roughened head. The higher wear rate and the more extensive fluid absorption of the sterilized cups is thus attributed to oxidation of the polymer; the latter presumably being facilitated by the presence of long-living radicals generated during γ-irradiation sterilization.

Keyword [en]
UHMWPE; gamma irriadiation; sterilization; oxidation
National Category
Medical Laboratory and Measurements Technologies
Identifiers
URN: urn:nbn:se:kth:diva-14278OAI: oai:DiVA.org:kth-14278DiVA: diva2:331996
Note
QC 20100729Available from: 2010-07-29 Created: 2010-07-29 Last updated: 2010-07-29Bibliographically 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
Opponent
Supervisors
Note
QC 20100716Available from: 2007-11-07 Created: 2007-11-07 Last updated: 2010-11-19Bibliographically approved

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