ETH Zurich - Zurich, Switzerland: Novel artificial muscles move with sound

Researchers at ETH Zurich have developed artificial muscles that contain microbubbles and can be controlled with ultrasound. In the future, these muscles could be deployed in technical and medical settings as gripper arms, tissue patches, targeted drug delivery, or robots.

It might look like a simple material experiment at first glance, as a brief ultrasound stimulation induces a thin strip of silicone to start bending and arching. But that's just the beginning. A team led by Daniel Ahmed, Professor of Acoustic Robotics for Life Sciences and Healthcare, has developed a new class of artificial muscles: flexible membranes that respond to ultrasound with the help of thousands of microbubbles.

The researchers created the artificial muscles using a casting mould with a defined microstructure. The silicone membrane produced in this mould has tiny pores on its underside, each around 100 micrometres in depth and diameter – around the width of a human hair. When the researchers submerge the membrane in water, tiny microbubbles become trapped in these pores.

When subjected to sound waves, these microbubbles begin to oscillate and produce a directed flow that moves the muscle. The size, shape and positioning of these microbubbles can be precisely controlled, which makes it possible to produce movements ranging from uniform curving to wave-like patterns. The muscles respond within milliseconds and can be controlled wirelessly.

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