Environmental Engineering Reference
In-Depth Information
obtained. Later, a homogenous dispersion of gellan polysaccharide (3 %, w/v)
was prepared in dimethyl formamide (DMF) and the temperature of the
dispersion was maintained at 10
C. To this, same amount of sodium hydride
was added. After this, a dispersion of chlorinated sorbitan monooleate in DMF
(0.02 %, w/v) was also added. Thereafter, the resultant mixture was stirred for
1 h at room temperature and the total reaction mixture was transferred into
50 ml of distilled water. Subsequently, the copolysaccharide layer was isolated
and adjusted to pH 7.0. The copolysaccharide was purified in ethanol, filtered
off, and air-dried.
The dispersion of the copolymer led to the formation of nanomicellar carrier
(371-750 nm), which was capable of holding
95 % budesonide and
exhibited a longer dissolution profile in simulated nasal fluid (pH 5.5) [
66
].
(b) Dextran. Dextrans are a class of polysaccharides with a linear polymer back-
bone with mainly 1,6-
>
-
D
-glucopyranosidic linkages. They are obtained from
bacterial cultures of
Leuconostoc mesenteroides
NRRL B-512 [
67
]. Dextrans
are colloidal, hydrophilic, and water-soluble substances, inert in biological
system, and do not affect cell viability.
Francis and his coworkers reported this method for the synthesis of amphi-
philic polysaccharides [
68
]. In order to impart dextran (DEX) an amphiphilic
character, a small number of hydrophobic cetyl groups were linked to its
backbone. The hydrophobic groups were attached to the polysaccharide
hydrophilic backbone via a short PEO linker, yielding DEX grafted with
PEO
10
-C
16
(DEX-
g
-PEO
10
-C
16
); the digit next to PEO refers to the number
of ethylene oxide groups in PEO, and the digit next to the carbon refers to the
number of carbons in the alkyl chains. In aqueous solution, DEX-C
16
form
micelles that can entrap up to 8.5 % w/w of Cyclosporine A, incorporated
within the hydrophobic core of the micelle by a dialysis process. Micelles with
average hydrodynamic diameters of ~11-14 nm are formed in aqueous solu-
tions of DEX-C
16
.
(c) Chitosan. Chitosan is a high molecular weight, polycationic polysaccharide
derived from naturally occurring chitin by alkaline N-deacetylation [
69
].
Chitosan, a natural aminopolysaccharide, is a pharmaceutical excipient for
drug delivery because it has favorable biological properties, such as biocom-
patibility, biodegradability, positive charge, nontoxicity, and bioadhesivity.
However, in spite of many reported successes, the major drawback of chitosan
is its poor solubility at physiological pH, whereas it is soluble only in acidic
environments with pH values lower than 6.0; this limits its application in the
pharmaceutical field.
N
-Trimethyl chitosan chloride (TMC), a partially quaternized chitosan
derivative, is soluble in the entire pH range. However, TMC is a hydrophilic
polymer which lacks any hydrophobic segments, so that it does not form
micelles for solubilization in aqueous media. Therefore, hydrophobically
modified TMC were constructed by chemically conjugating the hydrophobic
segments to the hydrophilic TMC backbone.
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