Carbon Nanotubes in Acrylic Bone Cement - Biologically Responsive Biomaterials for Tissue Engineering - page 191

8.4 Biocompatibility of CNTs

The Royal Society and the Royal Academy of Engineering, UK, published a report
discussing the associated ethical, health and safety, and social implications of nano-
technology [ 92 ]. With an increased interest in the application of nanotechnology,
the UK Government later published its own report (“ Characterising the potential
risks posed by engineered nanoparticles ”, November 2005) and follow-up studies
(“ Firs t quarterly update on the Voluntary Reporting Scheme for engineered nano-
scale materials ”, December 2006). The full report addressed many issues concern-
ing the potential use of nanotechnology and CNT. Concerns have been raised that
the properties that promote the use of nanoparticles in certain applications may also
have health implications, such as their high aspect ratios, surface reactivity and their
ability to cross cell membranes [ 24, 42, 92 ]. The report highlighted that the main
risks associated with CNTs stem from their high surface area to which a target organ
may be exposed, in addition to the chemical reactivity of the surface, the physical
dimensions of the nanoparticles and their solubility. Speculation surrounding the
use of CNTs has equated their effect on health to that of asbestos (due to their simi-
lar size and shape). CNTs are therefore suspected as being potentially carcinogenic,
and additionally, may cause inflammation or functional changes to proteins due to
their large surface area. However, it has been argued that no new risks to health have
been introduced as a result of the increasing use of nanoparticles as part of compos-
ite materials, and that most concerns derive from the possibility of detached or
“free” nanoparticles and nanotubes from the matrix [ 92 ]. It is believed that, if air-
borne, the likelihood of CNTs existing as individual fibres is improbable as electro-
static forces cause the CNTs to agglomerate which reduces their ability to be inhaled
into the deeper areas of the lungs. However, when investigating the inhalation of
stable non-purified SWCNT aerosols in mice, Shvedova et al. [ 84 ] reported that the
chain of pathological events was realised through an early inflammatory response
and oxidative stress culminating in the development of multifocal granulomatous
pneumonia and interstitial fibrosis (Fig. 8.10 ).
Smart et al. [ 88 ] reviewed the often conflicting findings pertaining to the cyto-
toxicity and biocompatibility of CNT. They concluded that, as-received (i.e.
untreated, or unfunctionalised) CNT exhibited some degree of toxicity (observed
both in vitro and in vivo) with detrimental effects associated with the presence of
transition metal ions, used as catalysts in the CNT production. Smart et al. [ 88 ]
also reported that functionalised CNTs have yet to demonstrate toxicity effects. It
was highlighted that the tendency for CNT to aggregate may have impacted the
reported results, although quantification of this fact has yet to be investigated. With
research into the use of CNTs, and nanotechnology ever increasing, the uncertainty
regarding toxicity has been brought to public attention. As a result, it has been
recommended that further research is necessary regarding the biological impacts of
nanoparticles and nanotubes, including their exposure pathways within the body,
and that methodologies for in situ monitoring should also be developed [ 92 ] .
Recent studies have addressed the issue of CNT uptake by different cell types.