Biomedical Engineering Reference
In-Depth Information
O
O
HO
OH
N
HOOC
COOH
2
+
H
O
O
H
N
HOOC
COOH
OH
N
OO
H
O
OH
Fig. 3
Molecular structure of hydrogelator used for microfabrication of supramolecular hydro-
gel microspheres
and thiol groups [
19
]. The hydrogel that was formed from the components is light
sensitive and decomposes upon irradiation as a result of the photo-labile moiety
being cleaved. In this experiment, a green fluorescent protein (GFP) was used as
a model protein and hence it can be seen that the GFP was released from hydro-
gel and migrated into the solution. The use of such hydrogels could be extended
for the delivery of bioactive molecules due to its unique properties. In order to
fabricate hydrogel with greater sensitivity, Chen and coworkers developed a novel
strategy to fabricate supramolecular hydrogel microspheres with diameters of 15
to 105
ΚΌ
m using a microfluidic device from the hydrogelator shown in Fig.
3
[
20
].
The hydrogelator as shown in the figure is synthesized using 1,2,4,5-benzene tet-
racarboxylic acid and 4-hydroxy pyridine. High temperatures are used to form the
droplets and allowed to cool to promote the self-assembly of the hydrogelator. The
encapsulation ability of the hydrogel microspheres allows unstable or toxic bio-
molecules to be transported safely. With each microsphere fabricated uniformly,
there exists the possibility to improve drug-loading and release kinetics.
2.2 Ionic and Associative Interactions
The formation of hydrogels through ionic interactions is possible when ionic liquids
are in the presence of gelators. The presence of polymer chains with positive and
negative charges at the end results in the attraction of opposite charges, thus leading
to the gelation of the ionic liquids to form ionic-liquid supramolecular gels. These
gels have attractive properties that include high mechanical strength and stimuli-
responsive capabilities. With these enhanced properties, hydrogels formed through
electrostatic interactions have found roles in applications in various areas such
as microfluidics, drug delivery and artificial organ fabrication [
21
-
23
]. Interesting
work done on such hydrogels include the development of fluoride-responsive fluo-
rescent hydrogel which was embedded with CdTe quantum dots (QDs) by Zhou and
coworkers [
24
]. The hydrogel, namely DC5700-QDs, was prepared by electrostatic
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