Biomedical Engineering Reference
In-Depth Information
6.2.2 Polymer-grafted Chitosan
Apart from some functional groups, polymers were also incorporated into chitosan as
grafted chains to modulate the hydrophilic and hydrophobic equilibrium of hydrogel, to
obtain different drug release profiles according to the practical requirements, to tailor the
degradation behavior, or to create an
in situ
gelation drug vehicle.
6.2.2.1 Chitosan-g-Pluronic
Pluronic is a temperature-sensitive triblock copolymer of poly(ethylene oxide)/poly
(propylene oxide)/poly(ethylene oxide) (PEO-PPO-PEO), consisting of more than 30 dif-
ferent nonionic surface-active agents, with ethylene oxide/propylene oxide weight ratios
varying from 1:9 to 8:2. Pluronic series were liquid at room temperature or below and were
found to form a gel at different elevated temperatures. Chung et al. [35] coupled chitosan
and monocarboxy Pluronic using 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC)
and
N
-hydroxysuccinimide (NHS) as coupling agents (
cf
. Figure 6.4). In this way, chitosan
became soluble in physiological conditions and turned into a thermosensitive hydrogel
used for DDSs with a sol-gel transition at body temperature. The most important fact was
O
O
O
OH
+
HO
PEO
65
PPO
100
PEO
65
Pluronic
40
(F127)
Succinic anhydride
DMAP, TEA
dioxane
RT, 24 hr
COOH
PEO
65
PPO
100
PEO
65
HO
Monocarboxy pluronic (F127)
CH
3
OH
CH
3
OH
O
O
O
O
EDC/NHS
RT, 24 hr
OH
OH
t
CH
3
H
C
O
CH
3
CH
2
OH
CH
2
OH
O
O
O
O
OH
OH
H
H
HH
OCCH
3
PEO
66
OC
PPO
100
PEO
65
OH
Figure 6.4
Schematic representation of the procedure for preparation of chitosan-Pluronic. (From Chung, H. J. et al. 2005.
Macromol Symp
224: 275-286. With permission.)
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