Biomedical Engineering Reference
In-Depth Information
surface protein receptors. FAK leads to reduction in cell proliferation and adhesion. SWCNTs disturb
the distribution of FAK in a human cell line (HEK293) along with a decrease in cell adhesion [20].
SWCNTs can indirectly cause toxicity by altering the composition of the culture media by reacting
with them, hence reducing the availability of medium components to the cells. For example, when
A549 cells were grown on media containing SWCNTs, significant cytotoxicity was observed [28].
Guinea pig alveolar macrophages, on exposure with SWCNTs and MWCNTs, are reported to
demonstrate cytotoxicity in many cases. High concentration of pristine and oxidized MWCNTs
have been shown to generate loss of viability of the human Jurkat T cells and human peripheral
blood lymphocytes. A comparative study of the toxicity of pristine and oxidized MWCNT in human
Jurkat T leukemia cells has shown that the latter were more toxic [32].
On the other hand, highly purified CNTs have reported to have low or no toxicity. In a report,
purified SWCNTs were taken up slowly by human macrophage cells, which showed low toxicity
[33] and CNTs found across the cell membrane of rat macrophages (NR8383) showed no cytotoxic-
ity [34].
20.15 DERMAL TOXICITY
Skin is at a high potential for both occupational and environmental exposure to any kind of air-
borne NPs. If CNTs get to penetrate the stratum corneum cells and become stuck into the feasible
epidermal cell layers of the skin, they may enter the keratinocytes directly or trigger the production
of proinflammatory cytokines or initiate other consequence. Moreover, once the NPs are housed
inside the avascular epidermis, they are difficult to be removed by phagocytosis. Studies on skin
irritation by CNTs are extremely limited at this time. One recent study illustrated that the length of
CNT modulates inflammation response.
Currently, not much evidence is available on whether nanomaterials can actually be absorbed
across the skin's stratum corneum and can accumulate in dermal tissues. When some products
containing SWCNTs and MWCNTs were tested for dermal toxicity and eye irritability using rabbits
and skin sensitization using guinea pigs, none of the SWCNTs and MWCNTs was found to cause
toxic skin sensitization effects. Only one of the products containing MWCNTs caused slight eye
irritation [35]. In separate studies, SWCNTs that contain iron as an impurity showed dermal toxic-
ity on murine epidermal cells (JB6 P+), EpiDerm FT engineered skin cells, and immunocompetent
hairless SKH-1 mice [36].
The large surface area of the skin and small size of NPs make it complicated to determine the
location of CNTs in the skin and within the systemic circulation. If they are systemically absorbed,
CNTs would be distributed right through the entire body or may be deposited in major organs, hence
making their detection and quantization even more difficult. Furthermore, CNTs are not absorbed
by the skin in a similar fashion as that of chemical absorption. This may be because of the fact
that they vary widely in their shape, size, and physiochemical properties, which could affect their
dermal toxic potential and their ability to penetrate across the skin. Standardization becomes even
more challenging for surface-modified CNTs. MWCNTs infiltrate through the stratum corneum,
concentrate, and trigger an irritation response in dermal cells [37]. In some cases, proteomics stud-
ies were also conducted to determine the effect of MWCNTs on human epidermal keratinocytes. As
compared to control cells, the CNT-treated cells show much variation in the expression of several
proteins, which infer information about cell cycle inhibition, deregulation of intermediate filament
expression, altered vesicular trafficking, as well as membrane protein downregulation [38].
20.16 GENOTOXICITY
Genotoxicity can be described as the lethal effect of NPs on a cell's genetic material. The first alarm
regarding genotoxicity of nanomaterials was raised by the Royal Society and Royal Academy of
Engineering in 2004. CNTs have the affinity as well as ability to interact with DNA, thus interpreting
