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Surface properties like charge and coating, morphology, small size, reactivity,
specific surface area, solubility, structure, aspect ratio, production of reactive species, chemical composition and photochemistry are some of the physicochemical
properties of nanomaterials. These properties have important effects on toxicity of
nanomaterials (Yadav et al. 2014).
Let us try to figure out what happens as size of material decreases. First of all, it
is crystal clear that dimensions, at least one dimension, should be shrunk to
nanoscale range in order to talk about nanoscale. One of the major roles of particle
size and surface area emerges in interactions between nanomaterials and surroundings (e. g., other particles, biological system, and solution). Because specific surface
area is defined as surface square meters per gram of material, it is evident that the
surface area dramatically increases and results in a more reactive surface determining the way of response of the system. Since the size and surface area are very crucial for interaction, especially in biological system, they should be strictly controlled.
For example, a number of studies support the hypothesis that alveolar macrophages
are less efficient at engulfing nanoparticles than micron-sized particles (Pratten and
Lloyd 1986).
However, it has not been elucidated the relation between shape, aspect ratio and
nanomaterial behavior, and studies have shown that these factors have significant
effects on nanomaterials toxicity, endocytosis mechanism (uptake of material by
cell membrane via either pinocytosis or phagocytosis), and various and complicated
chemical interactions. It will be informative to give some behaviors of nanomaterial
as determined by the above-mentioned parameters. It has been observed that spherical nanoparticles are easier to be accepted by cell than nanorods and nanofibers
(Champion and Mitragotri 2006). For example, uptake of gold nanorods is slower
than spherical gold particles (Chithrani et al. 2006). It has also been illustrated that
cytotoxicity of nanomaterial is also shape dependent. Hsiao and Huang showed that
rod-shaped ZnO particles were more toxic than spherical ZnO nanoparticles in the
research in which effects of physicochemical properties on human liver epithelium
cell were investigated (Hsiao and Huang 2011). In another experiment, rod-shaped
silver nanorods and gold nanorods were manufactured by electron beam physical
vapor deposition, and their cytotoxicity on human skin fibroblasts was determined.
The findings demonstrated the maximum toxicity in fibroblast cells for both rodshaped silver nanorods and gold nanorods (Favi et al. 2015). Another factor playing
a role in the behavior of nanoparticles is the aspect ratio defined as the ratio of surface area to the volume. It is evident that aspect ratio increases as the size of particle
decreases. It has been shown that materials with higher aspect ratio are more likely
to be toxic (Shvedova et al. 2005).
The next factor affecting the behavior of nanomaterials is their surface charge.
Surface charge, charge per unit area, has significant effects on process, product
quality, and performance. In applications related to imaging and drug delivery, surface charge is one of key factors determining the performance of nanocarriers.
Surface charge is also responsible for biocompatibility and uptake (Fröhlich 2012).
Additionally, it has a significant effect on the clearance of nanoparticles from the
immune system (Teodoro et al. 2011). Materials can be positively charged,
S. Tekmen and S. Öksüz
Surface properties like charge and coating, morphology, small size, reactivity,
specific surface area, solubility, structure, aspect ratio, production of reactive species, chemical composition and photochemistry are some of the physicochemical
properties of nanomaterials. These properties have important effects on toxicity of
nanomaterials (Yadav et al. 2014).
Let us try to figure out what happens as size of material decreases. First of all, it
is crystal clear that dimensions, at least one dimension, should be shrunk to
nanoscale range in order to talk about nanoscale. One of the major roles of particle
size and surface area emerges in interactions between nanomaterials and surroundings (e. g., other particles, biological system, and solution). Because specific surface
area is defined as surface square meters per gram of material, it is evident that the
surface area dramatically increases and results in a more reactive surface determining the way of response of the system. Since the size and surface area are very crucial for interaction, especially in biological system, they should be strictly controlled.
For example, a number of studies support the hypothesis that alveolar macrophages
are less efficient at engulfing nanoparticles than micron-sized particles (Pratten and
Lloyd 1986).
However, it has not been elucidated the relation between shape, aspect ratio and
nanomaterial behavior, and studies have shown that these factors have significant
effects on nanomaterials toxicity, endocytosis mechanism (uptake of material by
cell membrane via either pinocytosis or phagocytosis), and various and complicated
chemical interactions. It will be informative to give some behaviors of nanomaterial
as determined by the above-mentioned parameters. It has been observed that spherical nanoparticles are easier to be accepted by cell than nanorods and nanofibers
(Champion and Mitragotri 2006). For example, uptake of gold nanorods is slower
than spherical gold particles (Chithrani et al. 2006). It has also been illustrated that
cytotoxicity of nanomaterial is also shape dependent. Hsiao and Huang showed that
rod-shaped ZnO particles were more toxic than spherical ZnO nanoparticles in the
research in which effects of physicochemical properties on human liver epithelium
cell were investigated (Hsiao and Huang 2011). In another experiment, rod-shaped
silver nanorods and gold nanorods were manufactured by electron beam physical
vapor deposition, and their cytotoxicity on human skin fibroblasts was determined.
The findings demonstrated the maximum toxicity in fibroblast cells for both rodshaped silver nanorods and gold nanorods (Favi et al. 2015). Another factor playing
a role in the behavior of nanoparticles is the aspect ratio defined as the ratio of surface area to the volume. It is evident that aspect ratio increases as the size of particle
decreases. It has been shown that materials with higher aspect ratio are more likely
to be toxic (Shvedova et al. 2005).
The next factor affecting the behavior of nanomaterials is their surface charge.
Surface charge, charge per unit area, has significant effects on process, product
quality, and performance. In applications related to imaging and drug delivery, surface charge is one of key factors determining the performance of nanocarriers.
Surface charge is also responsible for biocompatibility and uptake (Fröhlich 2012).
Additionally, it has a significant effect on the clearance of nanoparticles from the
immune system (Teodoro et al. 2011). Materials can be positively charged,
S. Tekmen and S. Öksüz