2.4 the heat, with no radiation, to increase


Since the stimulus of light can be imposed immediately and delivered in certain quantities
with high accuracy, are extremely advantageous for light-sensitive hydrogels. In addition, the
instantaneous delivery capacity potentially occupies the sol-gel stimulant, light-sensitive
polymers. Applicable for the development of optical switches, display units and ophthalmic
drug delivery systems.26 Light responsive polymers may be UV or visible light sensitive;
however, visible light-sensitive polymers and hydrogels can be easily supplied, cleaned, and
easily manipulated, which are safer, cheaper, and easier to handle. Bis (4-dimethylamino)

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phenyl methyl leucocyanurine, a leuco derivative molecule, incorporated in a polymer
network, is a UV light sensitive hydrogel. Triphenylmethane leucoides The derivatives are
normally neutral, but are broken down into ion pairs under ultraviolet radiation to produce
triphenyl methyl cations. At a constant temperature, the hydrogels swell intermittently in
response to UV radiation, but shrink when the UV light is removed. 27 Swelling is caused by
the increase of the osmotic pressure in the gel due to the emergence of cyanide ions formed
by UV irradiation. A radiation sensitive chromophore, e.g. The trisodium salt of copper
chlorophyllin, poly (N-isopropylacrylamide) hydrogels, visible light-sensitive hydrogels can
be prepared. When light is applied, the hydrogel absorbs the chromophoric light and then
diffuses locally into the heat, with no radiation, to increase the “local” temperature of the
hydrogel. This temperature increase changes the swelling behavior. Hydrogel. With the
addition of another functional group, for example, an ionizable polyacrylic acid group, the
light-sensitive hydrogel can also be pH sensitive and activated with visible light (i.e. causing
shrinkage) and with increased pH (i.e. causing swelling). Although the action of the light
stimulus is instantaneous, the reaction of the hydrogels in action is slow because the light
energy must first be converted to thermal energy. 28


In this review, it has been possible to show a small part of the literature in this growing
research field. Most of the research in this area has focused on “Thermo Responsive
polymers” and “pH Responsive Polymers” but there is other areas such as “Biomolecule
Responsive Polymers” are growing rapidly.

Stimuli responsive polymers have a huge importance for several areas especially biomedical
applications such as tissue engineering, drug delivery, molecular imprinting etc. In the
upcoming years, developments in this area can gain acceleration and these novel
developments can impact in a number of areas including microfluidic devices, biomimetic
sensors, catalysis, surface modifications, membrane seperation technologies and renewable
energy applications.825