Environmental Engineering Reference
In-Depth Information
Anticancer drugs targeting to tumors can also be triggered by hyperthermia. This
method has significant advantages in clinical applications because of its ease of
implementation and reduction of side effects of chemotherapy. For such types of
targeting, drugs are loaded into the thermosensitive polymer matrix with a low
critical solution temperature (LCST) between 37 and 42
C to release drug site
specifically upon local heating [
61
]. However, because the LCST of most thermore-
sponsive materials is below 37
C, PMs with such materials would precipitate once
injected into the human body with a normal body temperature of 37
C and thus lose
their thermal targeting function. Locally lowering or increasing the temperature
sometimes becomes difficult, because local application can only activate the
micelles that are situated closely underneath the skin but not those that are deeply
distributed as in the bloodstream. This obstacle can be overcome by the incorpo-
ration of metal or metal oxide nanoparticles such as gold and
-Fe
2
O
3
, which can be
activated by irradiation by infrared light or by exposure to an alternating magnetic
field, respectively [
62
,
63
].
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16.5 Engineered Amphiphilic Bio-Polysaccharides
Polysaccharides are polymers of monosaccharides (sugars). They are found in
abundance and are inexpensive and available in a variety of structures exhibiting
a variety of properties [
64
]. They can be easily modified chemically and biochem-
ically. Further, they are nontoxic and in addition biodegradable, which suggests
their use in targeted drug delivery systems.
Usually, natural polysaccharides are used in the food industry and in developing
pharmaceutical dosage forms. They are commonly used as binder, thickener,
suspending agents, and matrix forming materials and regarded as safe for human
consumption. Therefore, in recent years, much emphasis is being given to the
polysaccharide biomaterials and their structural modifications via chemical path-
way with the aim to have better materials for designing novel drug delivery
systems. Some of the potential bio-polysaccharides and their design as micellar
carriers have been discussed below:
(a) Gellan Gum. Gellan gum is an anionic, bacterial (
Sphingomonas clodea
)
exopolysaccharide, and consists of repeating tetrasaccharide units of
β
-
D
-
glucose,
-
L
-rhamnose residues [
65
]. There are two
chemical forms of gellan gum (1) native or natural form, which has high acyl
contents, and (2) low or deacetylated form (Gelrite
®
). The native form con-
tains two acyl substituents, namely, acetate and glycerate, both of which are
located on the same glucose residue.
The synthesis of C
18
-
g
-gellan copolysaccharide was described as follows.
Initially, 20 ml of thionyl chloride was added to 5 % (w/v) solution of sorbitan
monooleate in chloroform and refluxed for 2 h without heat for chlorination. A
semisolid, blackish brown mass of chlorinated sorbitan monooleate was
β
-
D
-glucuronic acid, and
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