Biomedical Engineering Reference
In-Depth Information
between Q[8] and chitosan due to the absence of diethylamino group. The gel
also showed cross-linked network structure with many cavities, shown by images
obtained using scanning electron microscopy. The drug release property of the
hydrogel across different pH was also studied. Results showed that drug release
is significantly slower in gels with a lower pH, compared to those at a higher pH.
This implies that the rate of release of selected protein can be varied based on dif-
ferent pH media. Possible explanations for the slower release include the higher
concentration of ammonium cations, which boosts the electrostatic interactions
and enhances the structure. Hence this demonstrates that the Q[8]/EBCS gel is
a possible pH-sensitive drug carrier. In another work, Appel and coworkers used
cucurbit[8]uril (CB[8]) as host molecules to form reversible cross-links of multi-
valent copolymers with high binding constants leading to formation of a supramo-
lecular hydrogel [
35
]. Two types of polymers involved were viologen (MV) and
2-naphthoxy (Np) derivatives. The supramolecular hydrogels were then prepared,
by first adding equal amounts of the two polymers, after which CB[8] was added.
An interesting point to note is that the colourless clear solution turns bright red
upon the addition of CB[8], with simultaneous formation of hydrogel observed.
The high association of functional polymer was due to the presence of CB[8], that
holds onto the two polymers in its cavity, thus forming a network in the gel. The
work then moved on to characterise the gel that was formed in terms of its rheo-
logical properties. The hydrogel pore size was controlled by the amount of CB[8]
that was added into the solution. As more CB[8] was added, the gel was observed
to have smaller pores in scanning electron microscopy images. Higher concentra-
tions of CB[8] in gels appear to form a hydrogel that is a darker shade of red.
This unique gel thus could have industrial applications that need such controlled
viscosity or smart hydrogels. Using the same concept, self-assembled hydrogels
with extremely high water content and tunable mechanical properties were pre-
pared from cellulose derivatives [
36
]. These hydrogels are easily processed and
the simplicity of their preparation, their availability from inexpensive renewable
resources, and the tunability of their mechanical properties are distinguishing for
important biomedical applications. The protein release characteristics were inves-
tigated to determine the effect of both the protein molecular weight and polymer
loadings of the hydrogels on the protein release rate. Extremely sustained release
of bovine serum albumin is observed over the course of 160 days from supramo-
lecular hydrogels containing only 1.5 wt% polymeric constituents. CD is used as
another popular host molecule. In a recent report, Hou and coworkers copolymer-
ised modified gelatin with PLA-PEG-PLA under UV light illumination, which
was later added to
ʱ
-CDs in order to obtain a new biodegradable gel (Fig.
4
) [
37
].
The gel was observed to have good elasticity and appears opaque in water, in con-
trast to being transparent in DMSO. This new hydrogel was then characterised
using techniques like thermal gravimetry analysis in order determine interactions
between the host and guest molecules. It was found that the gel has a two-step
thermal degradation process, the first being the decomposition of
ʱ
-CDs, and the
second step being the decomposition of the guest polymer. The increased decom-
position temperature suggests that the structure of the hydrogel is stabilized by the
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