Thesis submitted 23-03-2012.pdf - University of Limpopo ...

3.4.3 The fate of nanoparticles after administration into the body
The distribution of nanoparticles and their loads throughout the body
depends on numerous physicochemical factors: size of particles, toxicity,
surface charge, capacity for protein adsorption, surface hydrophobicity,
drug loading and release kinetics, stability, degeneration of carrier system,
hydration behavior, electrophoretic mobility, porosity, specific
characteristics, density, crystallinity, contact angle, and molecular
weight. 245 Nevertheless, the fate and consequently the possible toxicity of
magnetic nanoparticles also depends strongly on the dose and
administration route.
After particles are injected into the blood sream,they are conditioned or
coated by elements like plasma proteins and glycoproteins available in the
circulatory system. This process is called opsonization. The process
makes the nanoparticles recognizable by the major defense system of the
body like the macrophages (mainly kupffer cells in the liver) and other
macrophages remove these opsonized particles. Particles having
hydrophobic surface are more efficiently coated, but those having
hydrophilic surface resist coating and are therefore cleared more slowly
from the body. The macrophages take the particles to the endosomes and
lysosomes where they are degraded, so that the drug the particle is
carrying is released and diffused to the circulatory system. The particles
are later excreted from the body or processed further by the body for other
possible metabolic activities.
Where uptake of particles by macrophages may be a hinderance in drug
delivery to target area, the particles may be disguised, so that they are not
recognized by the kupffer cells and therefore escape capture by the cells.
The nanoparticles may be disguised partly by making them hydrophilic
(depending on the type of treatment) and by stabilizing them using
absorbed polymers which did not allow recognition of liposome by
macrophages and thus prevent opsonization. 255
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