Swelling Characterization of Anionic Acrylic Acid Hydrogel in an External Electric Field

Apolymer gel is a cross-linked polymer which undergoes a reversible volume and/or sol-gel phase transition in response to physiological (temperature, pH and presence of ion in organism fluids) or other external (electric field, light) stimuli. In structurally soft gels, the motion of polymer network and the diffusion of ions easily take place by an external stimulus. A typical function of gel containing ionic groups is to swell under the influence of an electric field, making it useful for wide biomedical applications. In this study, poly(acrylic acid) (PAA) hydrogel network was prepared by free radical polymerization whose average molecular weight between crosslinkes was calculated as 18500 g/mol and its homogeneity assessment evaluated by comparing 30 samples swelling ratios after 48 h soaking in distilled deionized water. The swelling behaviour of PAA under an electric field application was also investigated as a function of cross-linking agent and electric field intensity variation. It is seen that equilibrium swelling ratio of PAA gel increases from 16 (no electric field) to 30 (by application of 300 V/m electric field), however this variation is dependent on the sample location relative to electrodes. The normalized swelling ratio of sample changes by 4.8 to 0.9 relative to its distance from positive electrode. Increasing the concentration of cross-linking agent (EGDMA) from 0.14 to 0.71 molar percent of monomer resulted in 45% decrease of gel volume fraction. It is proven that applying an external electric field can make an improvement in the time-response of the hydrogel expansion phase and swelling behaviour.