Chemistry Reference
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Preparation of folate-conjugated starch nanoparticles
The lower toxicity and high effect of drug are very important for clinic therapy. So,
more and more attention has been paid to the targeted drug delivery system. Folate
receptor (FR) has been reported to be vastly overexpressed in most human tumors but
seldom ex-pressed on normal tissues, so the folate/FR mediated targeted drug delivery
system has been popularly re-searched. Folate, a vitamin with small molecular weight,
is stable, and not immunogenic and expensive compared to the monomolecular anti-
body. Folate displays extremely high affinity to its receptor, which enables them to
rapidly bind to the FR and become inter-nalized via an endocytic process. So, folate
is a valuable targeting molecular. For the purpose of sustaining release of drug, folate
was conjugated with drug carrier, such as lipids, polymers, protein, and nanoparticles,
and then the carriers conjugating with folate possess simultaneously the ability of tar-
geting and sustaining release.
As a natural biomaterial, starch is biocompatible, not immunogenic, stable in air,
and does not react with most drugs. The reducing of starch is rapid, and the production
of this reducing reaction is deoxidizing sugar, which could be digested easily. As a tra-
ditional fi lling agent, starch was lately found to have more properties through physical
or chemic denaturalization, thus it could be used diffusely in medicine fi eld as drug
carrier material. By far, there is no report about starch conjugating with folate and used
in targeted drug delivery system.
Novel pH-responsive starch-based nanoparticles
The new pH sensitive starch-based nanoparticles maybe useful for drug delivery and
diagnostic applications. Polymethacylic acid-graft-starch (PMAA-g-St) nanoparticles
with various molar ratio of starch to MAA were synthesized using a novel dispersion
polymerization method. The method enabled simultaneous grafting and nanoparticle
formation in a one-pot synthesis procedure. The grafting was confirmed using FTIR
and 1H NMR spectroscopy. The particles morphology was examined using TEM. The
particles size and surface charge of the nanoparticles as a function of pH in buffer were
determined by DLS and electrophoretic mobility measurements. The effect of formu-
lation and processing parameters such as cross-linker, surfactants, and total monomer
concentrations on the size and pH-sensitivity of the nanoparticles were studied using
DLS. The capability of nanoparticles for drug delivery was evaluated using math-
ylene blue as model drug. Drug loading and release from the nanoparticles was mea-
sured using UV-Vis spectroscopy. The PMAA-g-St nanoparticles with diameters in a
range of 120-600 nm were obtained. The particle size could be tailored by changing
the composition and process parameters. The PMAA-g-St nanoparticles were more
monodispersed compared to PMAA nanoparticles. The nanoparticles were relatively
spherical and had a porous surface morphology. The particles were able to effectively
load methylene blue, a cationic drug, and exhibited pH-dependent swelling and drug
release in a physiological pH range. The particle size and magnitude of phase transi-
tion were dependent on starch content and various processing parameters such as sur-
factant levels, cross-linker amount, and total monomer concentration. Depending on
the ratio of starch to MAA and cross-linking ratio the particles exhibited 1.5-10 fold
volume change when pH was increased from 4 to 7.4.
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