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.

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. Researchers have dubbed them “stingraybots.”

The artificial muscles were created using a casting mold with a defined microstructure. The silicone membrane produced in this mold 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 exposed to sound waves, these microbubbles 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.

Long-term prospects for these devices include deployment in the gastrointestinal tract, possibly to release medication with absolute precision or support minimally invasive procedures. 

The researchers also produced a small, wheel-like silicone structure, featuring microbubbles of different sizes, which can also be driven using ultrasound.

In experiments with a porcine intestine, the researchers demonstrated their ability to navigate through intestinal convolutions by sequentially stimulating microbubbles of different sizes.

Researchers have also already considered how a stingraybot could be transported into the stomach: they propose rolling the robot up and placing it in a specially developed capsule that could be swallowed before dissolving in the patient’s stomach.

The researchers also developed medical patches that, through ultrasound activation, are capable of adhering to curved structures. These patches can be specifically tailored to different tissue types and release medication in precise locations, such as to treat scars or tumors. 

In lab experiments, the team has already successfully delivered dye to a specific location in a tissue model.