Biomedical Engineering Reference
In-Depth Information
study also shows promising applications of semiconductor NMs for efficient
delivery and efficacy of vaccines for diseases that currently have no cure.
In a separate study, semiconductor QDs conjugated to tumor-targeting anti-
human epidermal growth factor receptor 2 (HER-2) mAb forming QD-mAb
have been used to locate tumors using high-speed confocal microscopy.
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After
injection of QD-mAb conjugates, distinct steps were identified as the particles
traveled from the injection site to the tumor site. The blood-borne QD-mAb
conjugates extravasated into the tumor, bound to HER-2 on cell membranes,
entered the tumor cells, and migrated to the perinuclear region. The images
collected provide evidence for the analysis of the delivery processes of NPs in
vivo as well as valuable information on NP-based mAb-conjugated therapeu-
tics. This is very important in the development of QDs and other semiconductor
NPs for anticancer therapeutic efficacy.
5.9.7 Dendrimers
Early studies on dendrimer-based drug delivery systems focused on encapsu-
lating drugs but it was difficult to control the release of drugs. New develop-
ments in polymer and dendrimer chemistry provided a new class of molecules,
dendronized polymers which are linear polymers that bear dendrons at each
repeat unit. Dendronized polymers provide drug delivery advantages because
of their enhanced circulation time. The drugs can also be conjugated with the
drug to the dendrimers through a degradable link that can be used to control
the release of the drug. A study using dox that was conjugated to a biodegrad-
able dendrimer with optimized blood circulation time was achieved through the
meticulous design of size and molecular architecture.
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The dox-dendrimer
drug loading was controlled through multiple attachment sites and its solubility
was controlled through PEGylation; the drug release was controlled through
the use of pH-sensitive hydrazone dendrimer linkages. In vitro studies using
colon carcinoma cells showed that the dox-dendrimers were more than 10 times
less toxic than free dox. I.v. administration to tumor-bearing mice showed that
the tumor uptake of dox-dendrimers was ninefold higher than i.v.-free dox and
caused complete tumor regression with 100% survival of the mice after 60 days.
5.10 THE BLOOD BRAIN BARRIER (BBB)
The molecular level interaction of NMs with cells and tissues provides a distinct
advantage over other substances. NMs have been recognized to pass across the
BBB.
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The BBB consists of a tightly packed layer of endothelial cells sur-
rounding the brain that prevents high-MW molecules from passing through.
The ability of NMs to pass through the BBB is an important advantage for
drug delivery systems for effective treatments. However, the efficacy of NPs
toward the treatment of neurological disorders, like brain tumor, stroke, and
Alzheimer's disease, have been largely constrained in spite of the advances and
