Biomedical Engineering Reference
In-Depth Information
OH
OH
O
O
R r
NaOH
HO
HO
NHR
NH
2
Figure 6.2
N
-alkylated chitosan prepared with alkyl bromide.
chitosan carrier. Another important reason for the thiolation of chitosan lies in the moti-
vation to increase the mechanical properties of the hydrogel and the introduction of
in situ
gelling features to the DDS. Hornof et al. [31] demonstrated that the elastic proper-
ties increased with increasing thiol group content. Krauland et al. showed that inter-
and/or intramolecular disulfide bonds can be formed in order to obtain an
in sit u
chitosan
hydrogel [32]. The release of a fluorescent dextran can be controlled by the degree of
this cross-linking process. Furthermore, as thiols are very active groups, they can easily
interact with either acrylates or vinyl sulfones. Several kinds of
in situ
chitosan-based
hydrogels for drug release can be prepared via Michael addition of the above functional
groups [33,34].
Thiolated chitosan is usually synthesized by coupling chitosan with
N
-acetyl-l-cysteine
via 1-ethy-3-(3-dimethylaminopropyl-carbodiimide) hydrochloride (EDAC.HCl) and
1-hydroxybenzotrizole (
cf
. Figure 6.3) [33].
O
OH
NHCCH
3
O
NAC
HO
O
O
OH
EDC, HOBt, pH 3~5
O
NH
2
OH
m
z
Chitosan
O
OH
NHCCH
3
NH
2
O
HO
HO
O
O
O
OH
O
O
NH
OH
OH
y
z
x
C
O
O
Chitosan-NAC
NHCCH
3
SH
Figure 6.3
Synthesis of thiol-containing chitosan.
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