Micromechanical aspects of fatigue failure in conventional and carbon nanotube-reinforced acrylic bone cement


Sinnett-Jones, Polly (2007) Micromechanical aspects of fatigue failure in conventional and carbon nanotube-reinforced acrylic bone cement. University of Southampton, School of Engineering Sciences, Doctoral Thesis , 263pp.

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Description/Abstract

Bone cement is required for the majority of implant procedures. The mechanical integrity of
cemented implants may be compromised by fatigue failure of the bone cement, mainly due to
internal defects or debonding at the implant interfaces; improvements in the mechanical
properties of bone cement may therefore be valuable if the implant lifetime of cemented
arthroplasties are to be increased and revision rates decreased.
The present study investigated the use of synchrotron X-ray microtomography for the
observation of internal defects and failure processes that occur during fatigue loading. Initial
assessments of fatigue damage processes in in-vitro fatigue test specimens demonstrated the
uncertain nature of locating fatigue cracks and other defects, identifying the need for a
synthesis of high resolution tomographic imaging with complementary prior damage
monitoring methods. This was achieved via a novel amalgamation of acoustic emission,
ultrasound and/or microfocus computed tomography scans prior to testing. Location of
cracks/defects prior to high resolution tomographic imaging increased the probability of
capturing crack initiation, furthering the underlying understanding of crack formation and
propagation. Experiments performed at the European Synchrotron Research Facility have
shown that the microstructural features of a commercial bone cement are readily imaged
using microtomography of short exposure times. Furthermore, interactions (for example crack
deflection and ligament formation) have been clearly identified between failure processes and
both the cement defect population and internal microstructure. Early stages of crack initiation
have also been captured: a new mechanism of crack initiation is proposed where porosity and
local BaSO4 distribution are seen to act together to cause resultant crack initiation in the
cement matrix rather than directly from pore surfaces.
An opportunity for cement enhancement has been identified in the use of carbon nanotubes
(CNTs); improved mechanical and physical properties of acrylic bone cement reinforced with
CNTs are reported in the literature, although current methods utilised for CNT dispersion in
polymers do not immediately lend themselves to surgical deployment. Adding CNTs to bone
cement may further provide bio-active and sensing capabilities, beyond the conventional
fixation and load-bearing rôle. The present study confirms that CNT-reinforcement (using
shear mixing techniques) enhances the fatigue performance of a PMMA matrix and additional
acoustic emission parameter based analyses confirm that the presence of CNTs alters the
associated failure mechanisms. An insight into the potential capabilities of CNT reinforced
cements, using relatively simple preparation techniques suitable for surgical deployment, is
provided. These results suggest that enhanced fatigue performance may be achieved by means
of CNT reinforcement of the matrix leading to crack shielding mechanisms such as crack
bridging. Biologically, the presence of CNTs may reduce local thermal necrosis in the tissue
surrounding the cemented construct through a reduction of the peak exothermic
polymerisation temperature.

Item Type: Thesis (Doctoral)
Subjects: R Medicine > RD Surgery
T Technology > TA Engineering (General). Civil engineering (General)
Divisions: University Structure - Pre August 2011 > School of Engineering Sciences > Engineering Materials & Surface Engineering
ePrint ID: 64769
Date Deposited: 15 Jan 2009
Last Modified: 27 Mar 2014 18:46
URI: http://eprints.soton.ac.uk/id/eprint/64769

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