Biomedical Engineering Reference
In-Depth Information
Nanoimmunotoxicity
Immunosuppresion:
•
Increased susceptibility to
•
Infection
•
Tumor growth
•
Suppression of maturation
and proliferation of immune
cells
Immunostimulation
Immunostimulation:
Immunosuppression
•
Increased incidence of
•
Autoimmunity
•
Allergy
•
Increased inflammatory response
FIGURE 20.3
Schematic overview of nanoimmunotoxicology. Immune dysfunction resulting from expo-
sure to nanomaterials or particles may take the form of specific stimulation of any components of the immune
system leading to allergy, autoimminuty disorder, and so on. It might also take the form of immunosuppres-
sion leading to more infectious pathologies and tumor growth.
structure of CNTs can be imagined as the cylindrical roll-up of one or more graphene sheets held
together with each carbon atom bonded to three neighboring carbon atoms forming only sp
2
hybrid-
ization in a honeycomb arrangement [5]. Owing to its high aspect ratio (length/diameter), these
CNTs represent a nearly one-dimensional structure. Since sp
2
hybridization is stronger than the
sp
3
hybridization found in diamonds, CNTs have a unique strength. From an atomic point of view,
a nanotube can be divided into two parts, that is, the side wall and the end cap. The end caps can
be considered as hemispherical fullerenes, curved in 2D and the side wall contains less distorted
carbon atoms and is curved in 1D.
Depending on the method of synthesis, CNTs have lengths that vary from some hundred nano-
meters to several millimeters, but their diameters depend on their class: (a) SWCNTs are 0.4-3 nm
in diameter and (b) MWCNTs are 2-500 nm in diameter. SWCNTs are formed when only one
graphene sheet is rolled in a tubular fashion. The MWCNTs also consist of several cylinders of
graphitic shells with a layer spacing of 0.3-0.4 nm, ideally closed at each end by half a fullerene
[6]. CNTs can be classified as carbon nanohorns (CNHs), nanobuds, and nanotorus, depending
upon their shape [7]. The CNTs are commercially manufactured using heavy metal as catalysts and
substrates that include silica (SiO
2
). The CNTs have low mass density, high electrical and magnetic
properties, high thermal conductivity, and good mechanical properties. Hence, exposure to carbon
NPs may be accidental, occupational, and also on biomedical grounds for diagnosis and therapeu-
tics. In addition to the potential for occupational exposure with increasing production of carbon
NPs, environmental exposures to low concentrations of MWCNTs but not SWCNTs, have been
reported [8]. The presence of MWCNTs in the environment may be due to combustion emissions,
as they have been found in the effluents from natural gas combustion.
The applications of carbon NPs are listed as follows:
1. CNTs in controlled and targeted drug delivery
2. CNTs as a nonviral gene delivery system
3. CNTs in diagnostics and imaging
4. Cancer therapy
5. Vaccine delivery
