Biomedical Engineering Reference
In-Depth Information
necrosis and apoptosis. For example, cationic surface charges for most nanoparticles correlate to
higher cellular uptakes and greater cytotoxicities in nonphagocytic cells. Cationic nanoparticles
appear to cause plasma-membrane disruptions to a great extent and anionic nanoparticles, apop-
tosis (Frohlich 2012).
3.5.8 s
urface
c
oatINgs
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epeNdeNt
N
aNotoxIcIty
As the particle surface is in direct contact with body cells and biological media, these plays a very
critical role in inducing toxicity. Materials, such as surfactants, in reactions with nanoparticles can
change its physicochemical properties, react chemically (Oberdörster et al. 2005; Yin et al. 2005;
Gupta and Gupta 2005), and affect their cytotoxicity. Surface coatings can render noxious particles,
nontoxic, and less toxic particles, highly toxic. The presence of oxygen, ozone (Risom et al. 2005),
oxygen radicals (Sayes et al. 2004), and transition metals (Donaldson and Stone 2003) on nanopar-
ticle surfaces lead to the creation ROS and the induction of inflammation. For example, the specific
cytotoxicity of silica is strongly associated with the occurrence of surface radicals and ROS (Hoet
et al. 2004) (Table 3.15). Diesel exhaust particles in interactions with ozone can cause increased
inflammation in the lungs of rats compared to diesel particles alone (Risom et al. 2005). Spherical
gold nanoparticles with various surface coatings are not toxic to human cells, despite the fact that
they are internalized (Goodman et al. 2004; Connor et al. 2005). CdSe quantum dots can be ren-
dered nontoxic when appropriately coated (Derfus et al. 2004).
3.6 NANOPARTICLES TOXICITY COMPARISON STUDIES
Several studies have investigated the toxicity of nanoparticles by comparing their toxic effects as
related to their physicochemical properties (Warheit et al. 2004; Lam et al. 2004; Soto et al. 2005;
Muller et al. 2005; Braydich-Stolle et al. 2005; Hussain et al. 2009). These studies concluded that
CNTs are extremely toxic and produce more damage to the lungs than carbon black or silica (Muller
et al. 2005). Certain varieties of CNT aggregates, and some carbon blacks, were shown to be as cyto-
toxic as asbestos (Soto et al. 2005). Silver nanoparticle aggregates were found to be more toxic than
asbestos, while TiO
2
, aluminum, iron oxide, and zirconium oxide were found to be less toxic (Soto
et al. 2005). Table 3.16 shows different types of nanomaterials, their sizes, and relative cytotoxicity
indices (RCI) on macrophage cells (Soto et al. 2005). Table 3.17 shows the possible mechanisms and
pathways by which nanotoxicity can take place for different types of cationic nanoparticles.
3.7 CONCLUSION
Considering several studies on the applications of nanotechnology versus the limited amount of
studies related to the toxicities associated with their physicochemical properties, it is evident that
there is a serious risk posed by it, attributed to the associated toxicities and due to the widespread
commercialization of this novel technology. This demands for an urgent intervention of the regu-
latory bodies toward the identification of these risks and methods to mitigate and control them,
thereby making this promising technology of the modern era free from any threats to human use.
Immediate attention is envisaged to establish legislative mechanisms in regards to the application
of nanotechnology to govern its safe use for mankind, thereby bridging the existing gaps between
enormous commercial interests and the community's expectations for regulatory safeguards and
protections.
Exhaustive studies are needed for the characterization of critical nanoparticles aimed at chang-
ing and controlling various physicochemical properties, such as size, shape, concentration, crystal-
line structure, and surface chemistry, and their impact on toxicities in humans. Apart from the focus
on LD50 determinations, research should be aimed at determining the ED 50 (dose required to pro-
duce a therapeutic response in 50% of the population) to ascertain the effective therapeutic dose of
