Researchers 3-D printed tiny soft robots using a hydrogel that scientists can steer with an electric field. ↓↓More info and references below↓↓

Electroactive hydrogels—networks of water-loving polymers—swell and contract when electric fields alter the ion concentration in the solution surrounding them. By precisely controlling the dimensions of hydrogel structures, researchers could control how the hydrogels move and change shape within an electric field. A team from Rutgers University and Korea University did just that by 3-D printing hydrogel robots to perform complex functions such as walking and picking up objects. They hope that faster, more sophisticated hydrogel structures could one day serve as artificial muscles, stimulated by electrical impulses in the human body.

DARPA video on hydrogel biosensors