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Hydrogels composed of poly (ethylene glycol) (PEG)/poly (N-isopropylacrylamide-co-acrylamido-2-methylpropyl sulphonic acid) exhibited electro-responsive behaviour. The swelling properties of hydrogels were influenced by the content of negatively charged ionic groups inside the network structure, cross-linking density, electric field intensity and electrolyte solution. The swelling ratio (SR) increased from 92.4 to 188.08, and normalized swelling ratio (NSR) increased from 2.88 to 3.62 depending on 2-acrylamido-2-methylpropane sulphonic acid (AMPS) concentration under electric field intensity 429 V/m. The swelling process of hydrogels in deionized water followed non-Fickian diffusion in the absence of electric field and Super Case II transport model in presence of electric field. The methylene blue (MB) was used as a model drug, and the influence of various factors like loading percent of MB, AMPS concentration in hydrogels, pH of the release medium and applied electric field was investigated on the release profiles of the MB. The release study showed that the interaction between hydrogels and MB, pH of the medium and electric field are the parameters that affect the releasing behaviour of methylene blue. The partition coefficient (K d ) of MB in hydrogels increased with increasing AMPS content in the hydrogels. The application of external electric field has increased the time response of swell and release of methylene blue through hydrogels.

The temperature sensitive copolymer of microsize hydrogels consist of N-isopropylacrylamide (NIPAM) and 2- acrylamido-2 methylpropanesulphonic acid (AMPS) have been synthesized by soap free emulsion polymerization method in the presence of polyethylene glycol (PEG) as macro initiator and N, N´-methylenebisacrylamide (NMBA) as crosslinker. In this work, Dynamic Light Scattering (DLS), Transmission Electron Microscope (TEM) and Atomic Force Microscope (AFM) technique were used for structural analysis of microgels. It was found that particle size observed by TEM and AFM were spherical with a diameter around 103.0 nm to 133.1 nm and 121.1 nm to 189.0 nm. While DLS measurement shows narrow particle size distribution with hydrodynamic diameter from 343.6nm to 528 nm at a temperature 25°C and 132.5nm to 414.4nm at temperature 50°C depending on the AMPS content in Microgels samples. The surface roughnesses of particles were observed to be increasing with increased AMPS content. Moreover, decrease in hydrodynamic diameter from 25°C to 50°C revealed the temperature sensitivityproperty of microgels.

Temperature sensitive hydrogels were prepared by free radical polymerization of N-isopropylacrylamide (NIPAM) and 2-acrylamido-2-methylpropanesulphonic acid (AMPSA) in presence of polyethylene glycol (PEG) as macroinitiator. The aim of the work reported here was to investigate temperature sensitive swelling and deswelling behaviors of the hydrogels in water in order to investigate the effect of various amounts of AMPSA. The result indicated that the incorporation of a hydrophilic ionizable comonomer (AMPSA) affects the temperature sensitivity, swelling/deswelling, morphology and network structure of the hydrogels. The volume fraction in the swollen state (V 2m ), the number average molecular weight between cross-links (M c ), the number of segments between the cross-linked point (N), polymer-solvent interaction parameter (χ), enthalpy (ΔH) and entropy (ΔS) were determined using the Flory-Rehner theory at equilibrium swelling. The negative values of ΔH and ΔS showed that the prepared hydrogels had lower critical solution temperature (LCST). The Flory-Rehner theory of swelling equilibrium was qualitatively satisfied with the experimental data of hydrogels at different temperature.