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.