Self-Healing Actuators Mimic Muscles

New soft electrostatic actuators can contract and expand like actual muscles.

That’s a big deal for soft robotics, a field long plagued by problems with functionality. Most soft actuators developed so far have to trade off speed for strength or vice versa. Many are controlled by pressurized fluids or gas and must be tethered to a reservoir by valves and tubing, so they cannot be mobile.

One class of electrostatic devices, dielectric elastomer actuators, position stretchable electrodes on either side of a rubber membrane, which allows for rapid expansion and contraction when the electrodes are exposed to a voltage. These devices almost inevitably suffer from dielectric breakdown, making them unreliable and difficult to scale up.

Now, a team led by Christoph Keplinger, a professor of mechanical engineering at the Univ. of Colorado Boulder, has come up with a way to combine the performance potential of dielectric elastomer actuators with the versatility of pneumatic and hydraulic devices. They fill a stretchy silicone-based elastomer shell with a vegetable-based transformer oil and attach the shell to simple hydrogel electrodes. Then they apply a high voltage, which displaces the liquid, squeezing the shell and changing the actuator’s shape. Depending on the electrodes’ size and placement, the actuator can function in different ways, including lifting and grasping objects. The team dubbed the device hydraulically amplified self-healing electrostatic (HASEL) actuators.

The researchers demonstrated a donut-shaped HASEL actuator lifting a 1-kg load...