Voltage-switchable artificial muscles actuating at near neutral pH

Novel artificial muscle materials were developed, which can be electrically actuated at near neutral pH environments by low applied potential (3 V or less). The artificial muscle material is based on a hydrogel that is composed of acrylamide and a carboxylic acid derivative, such as acrylic acid, and is doped with a polypyrrole/carbon black composite. The electroactuation response of the artificial muscle is optimized in terms of the constituents of the hydrogel precursor solution and the polymerization conditions. It is shown that the introduction of the dicarboxylic acid monomer maleic acid increases the osmotic pressure arising at the hydrogel/electrolyte interface, increasing the bending response of the material. Additionally, the increase of the polymerization temperature and the use of the crosslinking agent N,N′-methylenebisacrylamide, which promotes intermolecular interactions within the hydrogel network, result in the development of artificial muscles with increased and reproducible electroactuation.