Double-crosslinked reduced graphene oxide-based hydrogel actuator system with fast electro-responsive deformation and enhanced mechanical properties

Recently, soft actuators made of electroactive materials that show fast environmental response, large deformation, and can mimic multifunctional actuation of living creatures have attracted considerable attention for a variety of applications including wearable electronics, microrobotic devices, and intelligent artificial muscles. In this study, we designed an electro-responsive hydrogel actuator system with high stretchability, good self-recovery, and fast electro-responsive actuation. We prepared a hydrogel with double network structure consisting of partially reduced graphene oxide (CRGO) with carboxylic groups, poly (acrylic acid) (PA), and Fe3+ ions. The partially reduced CRGO shows excellent dispersibility and stability in an aqueous solution. The CRGO-embedded PA/CRGO/Fe hydrogels synthesized by varying the content of CRGO, FeCl3·6H2O, and crosslinker exhibited more than 75% gel fraction and a relatively high equilibrium water content (EWC) of 80.0–95.0%. Particularly, PA/CRGO/Fe hydrogels with a dual crosslinked network structure showed high stretchability of more than 1,200% and excellent self-healing properties. The electro-responsive actuation of PA/CRGO/Fe hydrogel can be precisely controlled by varying the content of CRGO, electric field strength, and concentration of the electrolyte solution. By controlling these influencing factors, PA/CRGO/Fe hydrogels exhibited rapid bending actuation of more than 100° within 1 min under an electric field. In vitro cytotoxicity results showed a relatively high cell viability of more than 97%, indicating that the prepared PA/CRGO/Fe hydrogels had no significant cytotoxicity. Therefore, these PA/CRGO/Fe hydrogels could be a promising material for electro-responsive soft robot applications.