Self-Healing Robot Muscles Are Stronger, Faster and More Flexible Than People—and They Only Cost 10 Cents to Make

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One of the robotic actuators lifts a raspberry. Keplinger Research Group/Science/AAAS

Updated | Scientists have created nimble robotic muscles as strong as an elephant and as bendy as an octopus. These soft but powerful new artificial muscles can sense their own movements and self-heal from electrical damage. What's more, they cost only 10 cents to make.

The team of researchers from the University of Colorado Boulder was inspired by organic muscles to develop the soft "actuators." The technology could streamline bulky metal androids and enable them to mimic human movements, according to papers published in Science and Science Robotics.

The team filled elastic pouches with vegetable oil and hydrogel electrodes. When electricity is applied, the oil around the electrodes spasms. This pulls on the electrodes, making the whole artificial muscle contract and release in milliseconds. These movements can beat the speed of human muscle reactions.

By tailoring the shape of the pouches, researchers created a wide range of actuators with unique movements. Doughnut-shaped actuators, for example, helped a robotic gripper pick up a raspberry. These particular muscles survived more than a million contraction cycles.

The team calls the flexible muscles "Hydraulically-amplified Self-healing Electrostatic" actuators, or HASEL actuators.

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The Peano HASEL actuator is nimble enough to lift an egg. Kellaris et al/Sci Robot

"We draw our inspiration from the astonishing capabilities of biological muscle," said Christoph Keplinger, senior author of both papers and assistant professor at the University of Colorado Boulder, in a statement.

Keplinger added, "Just like biological muscle, HASEL actuators can reproduce the adaptability of an octopus arm, the speed of a hummingbird and the strength of an elephant."

Doctoral student and lead author of the Science paper Eric Acome said in a statement: "The ability to create electrically powered soft actuators that lift a gallon of water at several times per second is something we haven't seen before."

Liquid Over Solid

Using a layer of insulating liquid also allows the muscles to heal from electrical damage. This gives them an advantage over other "soft robotic" actuators that have a solid insulating layer.

Solid layers can stop working because of electrical damage. Liquid insulation is more resilient and recovers instantly after electrical damage.

Just like human muscles, the actuators can sense environmental input. The electrical components create a kind of capacitor that stores potential energy according to the stretch of the actuator. This can be measured to figure out the strain of the muscle.

Low-Cost Robotics

One device—the Peano-HASEL actuator—comprises three polymer pouches made from the same material as bags for potato chips. This material is cheap, as well as flexible.

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The Peano-HASEL actuator is made from the same material as potato chip bags. Kellaris et al/Sci Robot

"We can make these devices for around 10 cents, even now," said Nicholas Kellaris, a doctoral student at the University of Colorado Boulder and lead author of the Science Robotics study. "The materials are low-cost, scalable and compatible with current industrial manufacturing techniques."

Power-Hungry Muscles

While the super-strength muscles can be stronger, faster and more flexible than our own, they are not perfect. At present, the powerful muscles are held back by their thirst for electricity.

Acome explains: "The high voltage required for operation is a challenge for moving forward. However, we are already working on solving that problem and have designed devices in the lab that operate with a fifth of the voltage used in this paper."

This is not the first time soft robotics has produced remarkably flexible actuators. Last year, a team from Harvard University and the Massachusetts Institute of Technology created origami-inspired robotic muscles six times stronger than mammalian muscle.

Moving forward, the Colorado team aims to develop their portfolio of robots for a wider range of applications.

This article has been updated to include more information about the artificial muscles.