Supramolecular Soft Biomaterials for Biomedical Applications - In-Situ Gelling Polymers: For Biomedical Applications - page 113

Fig. 6 a Switching gel-sol-gel transition in PAA (20 wt%) + Fe(III) (0.02 mol/L)- citrate
(0.04 mol/L) aqueous system at pH 4.0 and room temperature. b Schematic illustration of the
gel-sol transition in the PAA + Fe(III)-citrate aqueous system switched by photoreduction and
oxidation. c Left : PAA + Fe(III) gel 3 days after preparation. Center : the gel irradiated for
12 min at the center part. Right : the same gel after exposure to oxygen for 5 days. Reproduced
from Ref. [ 39 ]
reversible gel-sol state transition, with pH showing considerable effect on both
BA-Ag + and Ba-Au 3 + systems. The rheological behavior indicated that irradiation
helps to increase the strength of the gels. Moreover, photo-reduction was found
to be a more simple and environment friendly method in comparison with using a
reducing agent such as NaBH 4 . The systems studied here provide a general strat-
egy for incorporating AuNP or AgNPs, thereby opening up the possibility of cre-
ating effective chemo-sensing platforms, catalytic and anti-bacterial functional
materials by exploiting the interesting properties of metal NPs and hydrogels.
2.5 Low Molecular Weight Hydrogels
Given the constraints of covalent bonds found in traditional polymer gels, low
molecular weight hydrogels are increasingly sought as alternative replacements.
These gels are made of small constituent molecules that self-assemble in water
to form nanofibers that have the ability to entrap water and subsequently form
a 3D network. Low molecular weight hydrogels have been attractive mate-
rials due to their biocompatibility and responsiveness to external stimuli such
as temperature, pH, and mechanical force, as well as the simplicity of the gel
preparation. In addition, these gels serve as biomaterials for biomedical applica-
tions as they undergo gel-sol phase transitions, which allow for the release of