Biomedical Engineering Reference
In-Depth Information
inluence the toxicological proile of the samples. Accordingly, the tubular
structure of CNTs provides a large and reactive surface area,
8,9
which might
render CNTs accountable for the observed cytotoxicity and thus unsuitable
for biomedical applications. An inverse correlation between toxicity of CNTs
and extent of their functionalisation has been suggested
10
; in other words,
the higher the functionalisation at the tips and sidewalls of CNTs, the lower
is their inluence on cell viability. As support of such evidence, it has also
emerged that several alarming data were mainly due to studies performed
only on pristine, non-functionalised CNTs. For example, Sayes and Ausman
studied the effect of some water-dispersible SWCNTs on human ibroblasts
(HDF).
11
It was found that cytotoxicity of compounds decreased signiicantly
with the increased degree of functionalisation on the surface.
1
The effect
of functionalised, water-soluble CNTs on cell viability was also analysed by
Pantarotto
et al.
during the study of translocation of bioactive peptides across
the cell membrane.
12
3T6 and 3T3 ibroblasts were exposed to 1-10
μ
M
concentration of luorescent SWCNTs. It was noticed that below 5
μ
M almost
90% of the cell population remained alive, suggesting a non-toxic behaviour
of functionalised nanotubes (
f
-CNTs). Alternatively, HeLa cells, incubated
for several hours with about 1 mg/mL of CNTs mixed with plasmid DNA in
different charge ratios, did not demonstrate signs of apoptosis.
13
In addition,
f
-CNTs complexed to different types of nucleic acids, including plasmid DNA,
RNA and oligodeoxynucleotides CpG sequences were not toxic for cells such
as breast cancer cells (MCF7) or splenocytes.
14-16
This was conirmed by
other groups that investigated the effects of both
f
-SWCNTs and
f
-MWCNTs in
different cell subtypes.
17,18
In parallel investigations, SWCNTs were evaluated in terms of their ability
to activate mouse spleen cells.
19
Since different cell types (monocytic leukemia
THP-1 and spleen cells) and incubation times were employed, it was dificult
to compare the obtained results. It was only possible to conirm that SWCNTs
induced an immune response, although the stimulating activity resulted to be
lower than that of microbial systems.
In an
in vivo
study, SWCNTs were investigated to verify their inluence on
the immune system through the activation
of complement.
20
For this purpose,
SWCNTs in concentrations between 0.62 and 2.5 mg were tested in rabbit
red blood cells. They displayed a dose-dependent potency in complement
activation comparable to that of the positive control, the potent activator
Zymosan. In particular, it seemed that such activation followed the classical
pathway, but with high selectivity, as conirmed by the direct binding of
CNTs to the main complement subunit C1q. On the contrary, chemical
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