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Title: Characterisation of polyetheretherketone for use in total knee replacement
Author: Fong, Yin Ki Kiki
ISNI:       0000 0004 6347 7367
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 2017
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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 uid 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 identied, 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 suffciently effcient 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.
Supervisor: Browne, Martin Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available