Biomedical Engineering Reference
In-Depth Information
After the absorption, the amount of NPs can reach the blood circulation,
and if enough of an amount is present, then this can induce a therapeutic or
a toxic effect [9]. The amount of NPs absorbed is variable and depends on the
size and the surface chemistry of NPs. Several studies show that between
2% and 3% of NPs orally exposed are absorbed by the GIT tissue [6]. For
researchers who want to increase the intestinal absorption, they need to
understand and optimize the linkage between surface chemistry of the NPs
and the M cells [9]. In general, the efficiency of the uptake for NPs is ≤100 nm
in size and is approximately 15- to 250-fold higher compared with a larger
size [11]. In addition, from the same region, the PP tissue has 200-fold higher
uptakes than non-PP tissue from the same region.
9.2.2 Inhalation
As described by the International Commission on Radiological Protection
(ICRP) in its document, the commission measured the distribution probabil-
ity of particles related to their size [16]. The ICRP study showed that NPs
with a diameter of <10 μm have a greater probability of penetrating beyond
the head airways. Particles <100 nm in aerodynamic diameter have a signifi-
cant probability of reaching the alveolar region of the lungs. In fact, there
is at least a 50% probability that particles <4 μm in aerodynamic diameter
will reach this region [17]. Regarding the smaller diameter sizes of particles,
another factor called inertia is secondary to Brownian diffusion in deter-
mining deposition, leading to particles penetrating deep into the lungs and
diffusing to a large lung surface area presented in the alveolar region [17].
According to the ICRP, at 1 nm diameter, almost everything will be depos-
ited onto the head and tracheobronchial region of the lung, which means
that almost nothing will reach the alveolar region because the negligible
mass significantly reduces the velocity of the NPs.
For NPs to deposit into the inner wall of the lungs, the particles may induce
two types of toxicities (i.e., a local toxicity or a systemic toxicity), depend-
ing on their intrinsic properties. In addition to the deposition site, differ-
ent factors will influence clinical observations. For instance, the deposition
site will depend on the size and concentration of NPs, the durability of NPs
(i.e., insoluble aqueous), and the stability of NPs (stable NPs will have higher
durability and defense immune system in the lung area). The last important
factor focuses on mucociliary clearance (acting in the upper airways) and
the macrophages' immune system (acting in the lower airways and alveolar
region), which tries to actively remove the deposition of NPs [16].
The local toxicities may cause inflammation, oxidative stress, tissue
damage, and disease. Many of the biological mechanisms observed in the
literature involved particle-related lung diseases (e.g., oxidative stress,
inflammation, production of cytokines, chemokines, and cell growth fac-
tors) [18]. Much of our understanding about the key factors that influence
the biological reactivity and toxicity of airborne particulate matter has come
