Biomedical Engineering Reference
In-Depth Information
NMs. Existing reports on the toxicological investigations of NMs imply that
e.g. size, shape, chemical composition, surface charge, solubility, their ability
to bind and affect biological sites as well as their metabolic fate and excretion
influence the toxicity of NPs. The toxicity of the most common NMs will be
discussed in this chapter.
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8.2.1 Carbon Nanotubes and Fullerenes
Carbon nanotubes (CNTs) are NMs made of the element carbon. CNTs are
composed of carbon units that tend to aggregate due to strong van der Waals
forces.
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They are characterized by their electrical and mechanical properties
especially their incredible tensile strength.
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CNTs are needle-like fibers in
appearance under TEM or SEM like asbestos. CNTs can come in the form of
single-walled nanotubes (SWNTs), multiwall nanotubes (MWNTs), or as fuller-
enes (C
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).
3,54,58,62,65,67-69
CNTs have found varied applications from biosen-
sors,
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regenerative medicine,
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cell growth,
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electronic devices,
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and electrocatalysis.
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The unique properties of this well-studied class of NMs
offers a full range of potential medical applications and more.
To harness the full potential of CNTs toxicological studies must go hand in
hand with the development for medical applications. A clear acceptable frame-
work for regulatory authorities and the public based on the toxicological and
pharmacological studies must be presented and used as a basis for developing
guidelines for the safe use of carbon nanotubes in medicine.
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A number of studies have focused on the potential toxicities of CNTs in
various biological systems. A study that introduced carbon nanotubes into the
abdominal cavity of mice showed long thin carbon nanotubes to be similar in
effect as long thin asbestos fibers and as such, exposure to carbon nanotubes may
lead to mesothelioma which is the cancer of the lining of the lungs that is caused
by exposure to asbestos.
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The similarities in shape and size between asbestos
and CNTs have led to speculations of possible potential risks that require thor-
ough and effective control as well as proper regulations under defined circum-
stances to evaluate the CNTs for safe handling and proper disposal.
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CNTs
have been shown to accumulate in cells of various types including macrophages
(
Figure 8.1
).
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One of the studies conducted on CNTs have shown that these can enter
human cells and accumulate in the cytoplasm leading to cell death.
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The stud-
ies conducted on rodents indicated that regardless of the synthesis process to
produce the CNTs and the types and amounts of metals they contained, the
CNTs resulted in inflammation, granulomas, fibrosis, and toxicological changes
in the lungs.
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Studies that involved equal weights of tested materials showed
that SWNTs were more toxic than the bulk material quartz.
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In contrast, ultra-
fine carbon black was shown to produce minimal lung damage compared with
CNTs (
Figures 8.2
).
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A pilot study that exposed the mesothelial lining of the
body cavity of mice to long MWNTs showed asbestos-like, length-dependent,
