Electrochemical characterization of intelligent hydrogel materials with double-responsive behavior for in vitro release of DNA

Interest in stimuli-responsive polymers is steadily increasing especially in the fields of controlled and self-regulated gene delivery. The insertion of appropriate genes into the cells that will repair or replace, is an essential step in gene therapy. Also termed ‘environmental-sensitive’ or ‘smart’, stimuli-responsive polymers experience rapid and reversible changes in their microstructure from a hydrophilic to a hydrophobic state triggered by small changes in the environment, at level of pH, temperature, as well as light, magnetic and electric fields. In this work, we investigate the electrochemical properties of a highly hydrophilic hydrogel based on supramolecular polymers derived from methacrylation of branched polyethyleneimine (PEI-MA). We use electrochemical impedance spectroscopy (EIS) to study the charge transfer at the interface electrode/hydrogel for different applied voltages and buffer solution pH, and we analyze the hydrogel behavior in terms of equivalent circuit models. Results show that the PEI-MA hydrogels respond to both pH and electric fields to an extent that is related to their degree of methacrylation. In addition, we show that DNA can be released in a controlled manner from the hydrogel under the effect of an applied potential, thus demonstrating the possibility of in vitro gene delivery applications for these intelligent hydrogels.