Ross W. Ormsby

Fatigue and biocompatibility properties of a poly (methyl methacrylate) bone cement with multi-walled carbon nanotubes

Composites of multi-walled carbon nanotubes (MWCNT) of varied functionality (unfunctionalised and carboxyl and amine functionalised) with polymethyl methacrylate (PMMA) were prepared for use as a bone cement. The MWCNT loadings ranged from 0.1 to 1.0 wt.%. The fatigue properties of these MWCNT-PMMA bone cements were characterised at MWCNT loading levels of 0.1 and 0.25 wt.% with the type and wt.% loading of MWCNT used having a strong influence on the number of cycles to failure. The morphology and degree of dispersion of the MWCNT in the PMMA matrix at different length scales were examined using field emission scanning electron microscopy. Improvements in the fatigue properties were attributed to the MWCNT arresting/retarding crack propagation through the cement through a bridging effect and hindering crack propagation. MWCNT agglomerates were evident within the cement microstructure and the degree of agglomeration was dependent on the level of loading and functionality of the MWCNT. The biocompatibility of the MWCNT-PMMA cements at MWCNT loading levels upto 1.0 wt.% was determined by means of established biological cell culture assays using MG-63 cells. Cell attachment after 4h was determined using the crystal violet staining assay. Cell viability was determined over 7 days in vitro using the standard colorimetric MTT assay. Confocal scanning laser microscopy and SEM analysis was also used to assess cell morphology on the various substrates.

Incorporation of multiwalled carbon nanotubes to acrylic based bone cements: Effects on mechanical and thermal properties

Polymethyl methacrylate (PMMA) bone cement-multiwalled carbon nanotube (MWCNT) nanocomposites with a weight loading of 0.1% were prepared using 3 different methods of MWCNT incorporation. The mechanical and thermal properties of the resultant nanocomposite cements were characterised in accordance with the international standard for acrylic resin cements. The mechanical properties of the resultant nanocomposite cements were influenced by the type of MWCNT and method of incorporation used. The exothermic polymerisation reaction for the PMMA bone cement was significantly reduced when thermally conductive functionalised MWCNTs were added. This reduction in exotherm translated in a decrease in thermal necrosis index value of the respective nanocomposite cements, which potentially could reduce the hyperthermia experienced in vivo. The morphology and degree of dispersion of the MWCNTs in the PMMA matrix at different scales were analysed using scanning electron microscopy. Improvements in mechanical properties were attributed to the MWCNTs arresting/retarding crack propagation through the cement by providing a bridging effect into the wake of the crack, normal to the direction of crack growth. MWCNT agglomerations were evident within the cement microstructure, the degree of these agglomerations was dependent on the method used to incorporate the MWCNTs into the cement.

Carboxyl functionalised MWCNT/polymethyl methacrylate bone cement for orthopaedic applications:

The incorporation of carboxyl functionalised multi-walled carbon nanotube (MWCNT-COOH) into a leading proprietary grade orthopaedic bone cement (Simplex P™) at 0.1 wt% has been investigated. Resultant static and fatigue mechanical properties, in addition to thermal and polymerisation properties, have been determined. Significant improvements (p ≤ 0.001) in bending strength (42%), bending modulus (55%) and fracture toughness (22%) were demonstrated. Fatigue properties were improved (p ≤ 0.001), with mean number of cycles to failure and fatigue performance index being increased by 64% and 52%, respectively. Thermal necrosis index values at ≥44℃ and ≥55℃ were significantly reduced (p ≤ 0.001) (28% and 27%) versus the control. Furthermore, the onset of polymerisation increased by 58% (p < 0.001), as did the duration of the polymerisation reaction (52%). Peak energy during polymerisation increased by 672% (p < 0.001). Peak area of polymerisation increased by 116% (p < 0.001) indicating that the incorporation of MWCNT-COOH reduced the rate of polymerisation significantly. A non-significant reduction (8%) in percentage monomer conversion was also recorded. Raman spectroscopy clearly showed that the addition of MWCNT-COOH increased the ratio between normalised intensities of the G-Band and D-Band (IG/ID), and also increased the theoretical compressive strain (−1.72%) exerted on the MWCNT-COOH by the Simplex P™ cement matrix. Therefore, demonstrating a level of chemical interactivity between the MWCNT-COOH and the Simplex P™ bone cement exists and consequently a more effective mechanism for successful transfer of mechanical load. The extent of homogenous dispersion of the MWCNT-COOH throughout the bone cement was determined using Raman mapping.

MWCNT Used in Orthopaedic Bone Cements

This chapter discusses the use of carbon nanotube (CNT) based nanocomposites for biomedical applications, particularly in the area of orthopaedic bone cement used in joint replacement surgery. The chapter initially introduces total joint replacements and poly methyl methacrylate (PMMA) bone cement. The associated issues and drawbacks with the use of these PMMA bone cements in terms of mechanical and thermal properties are then discussed in detail. The application of various MWCNT types (in terms of chemical functionality) at various weight loadings in augmenting some of the issues described is then presented. The next section of this chapter discusses the biological response to the various nanocomposite bone cements with MWCNT. The chapter concludes by discussing issues of CNT interaction with the body, and outlines the current trends in tagging and tracking the movement of MWCNT.

Carbon Nanotubes in Acrylic Bone Cement

The number of primary hip replacements continues to increase each year and, even with the reported decrease in the proportion of cemented implantations performed, poly methylmethacrylate (PMMA) bone cement is still required for the majority of procedures. At present, with longer life expectancy and younger patient populations requiring total joint replacements (TJRs), an increase in cemented revisions seems inevitable. Aseptic loosening is continually cited as being the most common indication for revision. It is well established that for cemented implants a number of factors contribute to aseptic loosening, of which fatigue damage of the cement mantle has been observed in vivo. Fibre-reinforced materials with a high degree of fibre–matrix interaction have been shown to increase the fracture resistance of many polymer matrices: for example, CF-reinforced bone cement exhibits reduced fatigue crack propagation rates due to mechanisms such as crack bridging, telescopic failure and fibre pull-out due to interface failure. Furthermore, it has been reported that fibre-reinforcement of PMMA bone cement leads to increased viscosity and reduced polymerisation temperatures. Superior mechanical performance has been shown through the inclusion of MWCNT (carbon nanotubes) due to their high aspect ratios and enhanced mechanical properties (cf. carbon fibres). The use of CNT in cemented TJRs may also offer additional biological benefits such as biosensing, controlled drug release and stimulation of bone regrowth. CNTs, due to the presence of van der Waals forces, exhibit a tendency to aggregate into large bundles that could be potentially detrimental to service life of the bone cement. Enhanced fatigue performance has previously been cited for PMMA bone cement with a high degree of MWCNT dispersion; however the mixing techniques utilised were not clinically applicable, highlighting the potential value of developing a clinically transferable CNT-reinforced PMMA bone cement.