The “ionoprinting” technique, as the team has dubbed it, uses a copper electrode to inject positively-charged copper ions into a hydrogel material (a highly absorbent polymer material that is nearly 99.9 percent water). The copper ions bond with negatively charged ions n the hydrogel’s polymer network, creating a more robust and mechanically stiffer structure.
Applying an electrical current then causes the hydrogel to flex. Although electrical fields have been used to actuate hydrogel materials before, this is the first time that electromechanically active electrodes have been used to drive the motion. Also, this is the first time that the binding of ions has been used to create a more rigid hydrogel network in this way.