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Queen Mary University of LondonQueen Mary University of London
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School of Engineering and Materials Science
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PhD Thesis: Development and characterisation of a hydroxyapatite reinforced poly(ethylmethacrylate) bone cement

Author: HARPER (nee Sanham) Elizabeth

Year: 1996

Supervisor(s): John Behiri, Bill Bonfield

The majority of prostheses are fixed in place using poly(methylmethacrylate) (PMMA) bone cement, acting as a filler between the implant and bone. Although PMMA is widely used, it does not possess the ideal mechanical and biological characteristics required. The bone cement developed in this investigation was polymerised from poly(ethylmethacrylate) (PEMA) mixed with n-butylemthacrylate monomer. The resulting cement possesses a higher ductility than PMMA cement, providing a suitable matrix for the incorporation of hydroxyapatite (HA) particles. This approach allows the potential for enhanced bioactivity and control of mechanical properties.
The optimised HA content and chemical composition were obtained by mechanical tests, molecular weight, density and residual monomer measurements. The polymerisation reaction was monitored from the exotherm and FT-Raman spectroscopy. Cyclic stressing of the experimental PEMA cement showed that at the higher stress levels used, median fatigue lives were longer for PMMA cement. The difference was however, not statistically significant at the lower stress levels due to the large scatter of data for the PMMA. A reduction in cycles to failure was obtained with the addition of untreated HA particles; this effect was enhanced by the introduction of a silane coupling agent. The tensile strengths of the experimental PEMA cements after storage in water and Ringer's solution were not significantly altered, whereas the fatigue resistance was considerably reduced. Finally, a preliminary in vivo study showed that the presence of HA, whether untreated or silanated, within the PEMA cement introduced the possibility of an accelerated rate of bone growth at the bone-cement interface. Therefore, the HA reinforced PEMA cement was shown to offer a promising alternative to existing PMMA bone cements.