Carbon Nanotubes in Acrylic Bone Cement - Biologically Responsive Biomaterials for Tissue Engineering - page 189

>44 °C and >55 °C. These were purposefully chosen as the temperature threshold
for impaired bone regeneration has been reported to be in the range of 44-47 °C [ 23,
59 ]. The incorporation of MWCNT to PMMA bone cement may reduce the inci-
dence of polymerisation-induced hot spots resulting in thermal necrosis of the sur-
rounding tissue adjacent to the cement mantle, which is believed to be observed
radiographically [ 53 ]. Reducing the occurrence of such tissue damage may improve
the mechanical integrity of the bone cement-bone interface, thereby promoting
implant longevity.
Ormsby et al. [ 68 ] also recorded that the incorporation of MWCNTs assisted
in the dissipation of the heat produced during the exothermic polymerisation reac-
tion of PMMA bone cement. The addition of carboxyl functionalised MWCNT to
the liquid monomer using magnetic stirring was successful in reducing the TNI
values at >44 °C and >55 °C to levels below one. It is proposed that the MWCNT
acted as a heat sink within the PMMA bone cement and therefore contributed to
dissipation of the heat produced during the polymerisation reaction by increasing
the thermal conductivity of the cement. Bonnet et al. [ 10 ] reported a 55 % increase
in thermal conductivity of PMMA on addition of 7 vol.% of SWCNTs [ 10 ] . It is
hypothesised that the reductions reported here are largely due to the heteroge-
neous nature of the MWCNTs within the PMMA cement, which significantly
reduces the mechanical properties of the cement. The thermal properties of the
MWCNT-PMMA bone cement composites can be discussed in terms of the suc-
cessful dispersion of MWCNT within the cement microstructure. As for electri-
cally or thermally conductive MWCNT composites, the MWCNTs must form a
percolated network of overlapping or touching CNT to allow for the transport of
electrons, phonons and heat energy [ 56 ]. Therefore, the cement with the poorest
mechanical properties, i.e. cement that has been magnetically stirred, demon-
strated the optimal thermal properties. This is due to poor dispersion of MWCNT
and subsequent agglomerations. Conversely, the MWCNT-PMMA composite
cement that provided the greatest improvements in mechanical properties (ultra-
sonic dispersion), attributed to the successful dispersion of MWCNT, actually
increased the polymerisation exotherm.
Ormsby et al. [ 68 ] also investigated the influence of adding MWCNT of vary-
ing chemical functionalities at different loadings (0.1, 0.25, 0.5, 1.0 wt.%) to
PMMA bone cement as a means of improving MWCNT dispersion and mechani-
cal properties. Dunne et al. [ 22 ] characterised the rheological and handling prop-
erties of the same composite cements. The MWCNTs were either unfunctionalised
or amine (NH 2 ) or carboxyl (COOH) functionalised. Adding MWCNT at loadings
£0.25 wt.% improved the mechanical properties of the resultant nanocomposite
cement. Adding carboxyl and amine functionalised MWCNT enhanced the dis-
persion of the MWCNT within the cement matrix and, as a result, increased the
interaction between the carbon nanotubes and the cement, thereby improving the
mechanical integrity of the resultant nanocomposite cement. Adding MWCNT at
higher loadings (³0.5 %wt.) provided a negative effect on the mechanical perfor-
mance of the MWCNT-PMMA cement. This was attributed to poor dispersion of