Environmental Engineering Reference
In-Depth Information
Fig. 16.4 Structure of methoxy poly (ethylene glycol) grafted chitosan copolymer [
73
]
CSOS (2.0 g) is dissolved in 50 ml distilled water. SA (1.75 g) and EDC (10 mol/
mol SA) are dissolved in 40 ml ethanol. CSOS solution is heated up to 80
C under
vigorous stirring accompanied by dropwise addition of SA solution. The
by-products were removed using the ultrafiltration by Millipore Labscale TFF
system (MWCO 10,000) after 5 h. The size of CSOS-SA micelles is about
30 nm. The saturated solubility of 10-hydroxycamptothecin was 1.01
ʼ
g/ml in
distilled water under 37
C, and it is enhanced markedly to be 18.92
ʼ
g/ml due to
encapsulation of the micelles.
The hydrophilic polysaccharides can be used as hydrophilic carrier in the design
of nano-polysaccharide micelles. The polysaccharides which lacks sufficient hydra-
tion/water solubility and do not qualify for the use as hydrophilic part former of
micellar structure, they can be modified chemically via etherification reaction to
make them useful. Polymeric micelles are unstable at elevated temperature, at
concentrations below their CMC, and to changes in solvent composition. Given
the need for well-defined robust nanostructures for applications as vessels for
targeted delivery vehicles, there has been significant interest in the stabilization
of these micelles. The shell cross-linked nanostructures have been demonstrated to
have great potential as encapsulation and delivery agents due to their higher core
mobility and more rigid form compared with core cross-linked particles.
Covalent crosslinking is a common method for the generation of stable, hydro-
philic shell-crosslinked micelles. In case, the water soluble is the hydrophilic shell,
then by controlling the concentration of gelation metal ions, shell-crosslinked
micelles can easily be obtained without the need of toxic, chemical reagents and
solvents. This approach is ecofriendly and as the micelles are designed for targeted
delivery, hence, there are no additional chances of remaining toxic reagents/
solvents.
Further, galactose, mannose residues are also installed into PEG backbone of the
micellar structure as ligand for drug targeting. Because, natural polysaccharides
already contain sugar moieties there is no need to add such type of ligands in the
micelles where polysaccharides have been used as hydrophilic corona.
Etherification involves the reaction of an alcohol (here a saccharide alcohol)
with an alkylating agent in the presence of a base. Normally, a strong base will be
used to deprotonate the alcohol to give the alkoxide. The hydroxyl groups of
polysaccharides can be chemically modified via etherification reaction by using
either dry method or wet method.
