Carbon Nanotubes in Acrylic Bone Cement - Biologically Responsive Biomaterials for Tissue Engineering - page 187

active responses such as secretion of small “isolation” proteins to isolate the cells
attached to the SWCNT from the rest of the cell mass, a response that offers
potential for medical chemistry and disease therapy. Synthetic bone scaffolds is
an area where the biocompatibility of materials used, such as polymers or peptide
fibres, is still an issue where possible rejection by the body is feasible. CNTs offer
mechanical advantages over the polymers or peptide fibres currently used in bone
scaffolds. Zhao et al. [ 100 ] investigated the use of chemically functionalised
SWCNT as a scaffold material for the growth of artificial bone and they identified
the potential for the self-assembly of hydroxyapatite on the SWCNT surface.
They suggested that this was possibly due to the presence of negatively charged
functional groups on the SWCNT that attracted the calcium cations present in the
hydroxyapatite [ 100 ]. The group also proposed that it is the high tensile strength,
high degree of flexibility and low density of CNTs that make these materials ideal
for the production of bone. The diameters of SWCNT used in the study by Zhao
et al. [ 100 ] are of similar order and magnitude to the triple-helix collagen fibres
within bone, and as such can act as scaffolds for the nucleation and growth of
hydroxyapatite.
The potential for CNT to be used within biomaterials and biomedical applica-
tions is by no means endless; however while many more applications could be
discussed, the following papers offer further information on the use of nanotech-
nology for biomedical applications [ 8, 87, 96 ] . Investigations concerning the
cytotoxic response of CNT-containing materials have reported encouraging results
confirming their potential use in orthopaedic applications [ 88 ] . However, many
questions remain unanswered and as yet, the understanding of the toxicity and
biocompatibility of CNT-reinforced materials is not fully established. More recent
studies completed by Marrs et al. [ 56 ] have shown that the addition of MWCNT
to PMMA bone cement may significantly improve the mechanical and fatigue
properties, with an optimal loading of 2 wt.% MWCNT [ 55 ]. Marrs et al. achieved
a high level of homogeneous dispersion by high-speed shear mixing and vacuum
hot-pressing. However, these methods are of limited use in TJR applications—
both studies used non-clinically relevant methods to incorporate the MWCNTs
into the cement. Marrs et al. dispersed the nanotubes through molten PMMA
using stainless steel counterrotating rotors in a mixing chamber at 220 °C. The
molten PMMA was then collected and allowed to cool under ambient conditions
until solid, thus ensuring maximum dispersion of the MWCNTs in the cement
matrix and a reduction in the incidence of entanglements. Following full polymeri-
sation, the cement was crushed into pellets and then hot-pressed under vacuum
into thin sheets [ 56 ]. Additionally, non-standardised test methods were used for
specimen preparation.
Ormsby et al. [ 67 ] overcame the limitations of these studies by Marrs et al., by
incorporating MWCNT (either unfunctionalised, or carboxyl functionalised) into
PMMA bone cement via three clinically relevant techniques. Ormsby et al. [ 67 ]
added the MWCNT to the liquid monomer phase via either magnetic stirring, or
ultrasonic dispersion, or to the polymer powder phase via turbo blending. They
reported that the addition of MWCNTs (0.1 wt.%) could significantly improve the