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Characterisation of polyetheretherketone for use In total knee replacement

Characterisation of polyetheretherketone for use In total knee replacement
Characterisation of polyetheretherketone for use In total knee replacement
A polymer-based total knee replacement (TKR) system that utilises an injection moulded polyetheretherketone (PEEK) femoral component has been proposed. The current project was designed to characterise the material at the coupon level by acknowledging the issues related to the processing route as well as the in-service conditions of the proposed component. Surface characterisation (wide angle X-ray scattering (WAXS), nanoindentation, atomic force microscopy (AFM) and photographic image processing) showed that heterogeneity was introduced to the material as a result of differential cooling that occurred during injection moulding. The crystallinity level and the nanoindentation hardness were highest at the core of the sample and lowest at the surface. These were visible as variation in shading on the cross-section of the sample. Although these findings supported the presence of an amorphous surface layer, the lack of abrupt change in properties from surface to bulk meant that its thickness could only be estimated (318m to 545m) and could not be more accurately gauged. Nonetheless, the findings showed that the mechanical properties of the amorphous surface layer were lower than that of the bulk. While this could possibly be deleterious by promoting fluid ingress in-service, it could also potentially be beneficial as it might provide a crack-shielding effect to the proposed TKR femoral component. Mechanical characterisation showed that the static response of the material was rate sensitive at the coupon level, but not at the nano-scale. This could be related to the difference in global and local responses, but also attributed to the difference in the mode of testing. The design and the execution of a multi parameter fatigue test programme has successfully demonstrated how the effects of test parameters on the material could be studied in a strategic manner. Failure limits were identified, where samples failed (predominantly due to cyclic softening) as opposed to running out. The fatigue life of the material was shortened by (i) increasing the stress level, (ii) increasing the frequency, (iii) suppressing cooling, and (iv) using a sinusoidal waveform instead of a waveform taken from TKR knee contact force data from the OrthoLoad database. These suggest that testing at 5Hz using a sinusoidal waveform in an ambient environment would be a sufficiently efficient and robust test method for the proposed TKR femoral component, and the developed method may be used to identify appropriate characterisation methods for other novel implants.
University of Southampton
Fong, Yin, Ki Kiki
d780ad03-5886-453f-883c-c66392a059e1
Fong, Yin, Ki Kiki
d780ad03-5886-453f-883c-c66392a059e1
Browne, Martin
6578cc37-7bd6-43b9-ae5c-77ccb7726397

Fong, Yin, Ki Kiki (2017) Characterisation of polyetheretherketone for use In total knee replacement. University of Southampton, Doctoral Thesis, 359pp.

Record type: Thesis (Doctoral)

Abstract

A polymer-based total knee replacement (TKR) system that utilises an injection moulded polyetheretherketone (PEEK) femoral component has been proposed. The current project was designed to characterise the material at the coupon level by acknowledging the issues related to the processing route as well as the in-service conditions of the proposed component. Surface characterisation (wide angle X-ray scattering (WAXS), nanoindentation, atomic force microscopy (AFM) and photographic image processing) showed that heterogeneity was introduced to the material as a result of differential cooling that occurred during injection moulding. The crystallinity level and the nanoindentation hardness were highest at the core of the sample and lowest at the surface. These were visible as variation in shading on the cross-section of the sample. Although these findings supported the presence of an amorphous surface layer, the lack of abrupt change in properties from surface to bulk meant that its thickness could only be estimated (318m to 545m) and could not be more accurately gauged. Nonetheless, the findings showed that the mechanical properties of the amorphous surface layer were lower than that of the bulk. While this could possibly be deleterious by promoting fluid ingress in-service, it could also potentially be beneficial as it might provide a crack-shielding effect to the proposed TKR femoral component. Mechanical characterisation showed that the static response of the material was rate sensitive at the coupon level, but not at the nano-scale. This could be related to the difference in global and local responses, but also attributed to the difference in the mode of testing. The design and the execution of a multi parameter fatigue test programme has successfully demonstrated how the effects of test parameters on the material could be studied in a strategic manner. Failure limits were identified, where samples failed (predominantly due to cyclic softening) as opposed to running out. The fatigue life of the material was shortened by (i) increasing the stress level, (ii) increasing the frequency, (iii) suppressing cooling, and (iv) using a sinusoidal waveform instead of a waveform taken from TKR knee contact force data from the OrthoLoad database. These suggest that testing at 5Hz using a sinusoidal waveform in an ambient environment would be a sufficiently efficient and robust test method for the proposed TKR femoral component, and the developed method may be used to identify appropriate characterisation methods for other novel implants.

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Published date: March 2017

Identifiers

Local EPrints ID: 412400
URI: http://eprints.soton.ac.uk/id/eprint/412400
PURE UUID: b838328a-f356-414d-8cc6-67ab0b034416
ORCID for Martin Browne: ORCID iD orcid.org/0000-0001-5184-050X

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Date deposited: 17 Jul 2017 13:34
Last modified: 16 Mar 2024 05:23

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Contributors

Author: Yin, Ki Kiki Fong
Thesis advisor: Martin Browne ORCID iD

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