38
responsible for reactive oxygen species (ROS). Free radicals can affect biosystems
in various ways: DNA damage, oxidation of lipids, and inflammation. It has been
observed that toxicity is size dependent as mentioned by many authors. Several
toxicological studies have proved that nanoparticles smaller than 100 nm have more
detrimental effects on respiratory system than larger particles (Ferreira et al. 2013).
For titanium dioxide nanoparticles, it has been shown that 20–30 nm particles are
considerably more toxic when it comes to respiratory health than their microparticle
counterpart (>100 nm) (Vogel 2012). It has been also shown that the collection of
nanoparticle on the different regions of respiratory path has been determined by the
size of nanoparticles. While inhaled nanoparticles smaller than 100 nm are accumulated almost in all parts, particles smaller than 10 nm and particles in the range of
10–20 nm get deposited in tracheobronchial and alveolar region, respectively (Price
et al. 2009). Also, larger particles might be safe at relatively higher doses, whereas
smaller ones can be dangerous even at moderate levels (Bouallegui et al. 2017).
There are exceptional cases in which it is hard to associate toxicity with particle
dimensions. For example, it was observed that relatively large particles have toxicity due to their chemical properties rather than particles size. A research carried out
on zebrafish using silver and gold nanoparticles has demonstrated that the behavior
of silver nanoparticle was size dependent while it was not true for gold nanoparticles (Bar-Ilan et al. 2009). The size of nanoparticles is decisive in both their penetration into systems and their accumulation in organs such as liver and spleen. Larger
particles were reported to lead to vascular occlusion as compared to relatively
smaller particles (Fröhlich 2016).
Recently, there have been raised some concerns about whether carbon nanotubes
might be hazardous due to their physical similarities with asbestos fibers.
Experimental studies confirmed that some nanotubes showed asbestos-like effects.
One particular concern is the potential cancer-causing risks from inhaled particles
similar to those that were posed by asbestos fibers. Asbestosis is a chronic lung
disease in which there is scar-like tissue formed in the lungs (pulmonary fibrosis).
This fibrosis decreases the elasticity of the lungs, making breathing more difficult.
Shortness of breath is the most common symptom (Poland et al. 2008; National,
Health, Lung, and Blood Institute).
As mentioned above, nanotubes have many applications due to their physical,
electrical, chemical, and biological attributes. However, there have been many crucial questions to be solved. Because nanotubes contain more or less impurities like
metal catalyst, their biological responses may not be such desired or expected.
Additionally, structural variations have also great impacts on their functionalities.
Thus, precise control over nanotubes processes is particularly vital to be applied on
biological systems. Because foreign substances, in this case nanotubes, are attacked
by sentinel cells, there should be a way to cheat these cells by camouflage of familiar coatings. This issue also makes it quite difficult to deliver intended dose of drug
to the targeted region. Besides this undesired effect, there are also numerous studies
pointing out that nanotubes have toxicological effects (Poland et al. 2008). A study
carried out on mouse by Takagi et al. showed that intraperitoneal injection of multiwalled nanotubes resulted in mesothelioma, a kind of cancer occurring in
S. Tekmen and S. Öksüz
responsible for reactive oxygen species (ROS). Free radicals can affect biosystems
in various ways: DNA damage, oxidation of lipids, and inflammation. It has been
observed that toxicity is size dependent as mentioned by many authors. Several
toxicological studies have proved that nanoparticles smaller than 100 nm have more
detrimental effects on respiratory system than larger particles (Ferreira et al. 2013).
For titanium dioxide nanoparticles, it has been shown that 20–30 nm particles are
considerably more toxic when it comes to respiratory health than their microparticle
counterpart (>100 nm) (Vogel 2012). It has been also shown that the collection of
nanoparticle on the different regions of respiratory path has been determined by the
size of nanoparticles. While inhaled nanoparticles smaller than 100 nm are accumulated almost in all parts, particles smaller than 10 nm and particles in the range of
10–20 nm get deposited in tracheobronchial and alveolar region, respectively (Price
et al. 2009). Also, larger particles might be safe at relatively higher doses, whereas
smaller ones can be dangerous even at moderate levels (Bouallegui et al. 2017).
There are exceptional cases in which it is hard to associate toxicity with particle
dimensions. For example, it was observed that relatively large particles have toxicity due to their chemical properties rather than particles size. A research carried out
on zebrafish using silver and gold nanoparticles has demonstrated that the behavior
of silver nanoparticle was size dependent while it was not true for gold nanoparticles (Bar-Ilan et al. 2009). The size of nanoparticles is decisive in both their penetration into systems and their accumulation in organs such as liver and spleen. Larger
particles were reported to lead to vascular occlusion as compared to relatively
smaller particles (Fröhlich 2016).
Recently, there have been raised some concerns about whether carbon nanotubes
might be hazardous due to their physical similarities with asbestos fibers.
Experimental studies confirmed that some nanotubes showed asbestos-like effects.
One particular concern is the potential cancer-causing risks from inhaled particles
similar to those that were posed by asbestos fibers. Asbestosis is a chronic lung
disease in which there is scar-like tissue formed in the lungs (pulmonary fibrosis).
This fibrosis decreases the elasticity of the lungs, making breathing more difficult.
Shortness of breath is the most common symptom (Poland et al. 2008; National,
Health, Lung, and Blood Institute).
As mentioned above, nanotubes have many applications due to their physical,
electrical, chemical, and biological attributes. However, there have been many crucial questions to be solved. Because nanotubes contain more or less impurities like
metal catalyst, their biological responses may not be such desired or expected.
Additionally, structural variations have also great impacts on their functionalities.
Thus, precise control over nanotubes processes is particularly vital to be applied on
biological systems. Because foreign substances, in this case nanotubes, are attacked
by sentinel cells, there should be a way to cheat these cells by camouflage of familiar coatings. This issue also makes it quite difficult to deliver intended dose of drug
to the targeted region. Besides this undesired effect, there are also numerous studies
pointing out that nanotubes have toxicological effects (Poland et al. 2008). A study
carried out on mouse by Takagi et al. showed that intraperitoneal injection of multiwalled nanotubes resulted in mesothelioma, a kind of cancer occurring in
S. Tekmen and S. Öksüz