While it might sound like a weapon of oceanic destruction in the hands of Aquaman’s arch enemies, the new “stingraybot” from a team at ETH Zurich (the Federal Institute of Technology of Switzerland) offers enormous promise for surgery, medical care, wildlife biology, robotics, and more, thanks to muscular membranes of microbubbles.
At a mere 4 cm (1.6 inches) in width, the stingraybot swims using the same wavelike motions of the wing-like pectoral fins of real stingrays. Even more remarkably, this tiny ichthyo-droid requires no cables or batteries for remote control or power, because ultrasound stimulation directs and flexes its micro-muscles.
“Undulatory locomotion was a real highlight for us,” says team lead Daniel Ahmed, Professor of Acoustic Robotics for Life Sciences and Healthcare, and co-lead author of the Nature paper “Ultrasound-driven programmable artificial muscles.” “It shows that we can use the microbubbles to achieve not only simple movements but also complex patterns, like in a living organism.”
Using a microstructure mould, the team created silicone membranes with minute pores a mere tenth of millimeter deep and across (approximately the width of a human hair). Once submerged, those micropores trap air as microbubbles. By wirelessly beaming ultrasound at the membranes, the researchers could precisely manipulate them almost instantaneously (within milliseconds) to produce curving or wave motions in specific directions.
The choice between curving and wave motions depends on the arrangement of the microbubbles. Arrays of equally-sized bubbles curve according to the amplitude of the ultrasound, whereas arrays of differently-sized bubbles will, at varying frequencies, undulate.
While rigid machines, vehicles, and robots made of unbending steel, plastic, and composite materials are ideal for most contemporary manufacturing, transport and combat needs, other tasks require far greater flexibility, such as that which animals possess. Animals (including humans) rely on squishy flesh to give suppleness of movement and the ability to squeeze into and through tight spaces without damaging themselves or their surroundings.
Therefore, one of the most valuable applications of these ultrasound microbubbles muscles is precise, gentle manipulation for surgeons and biologists, as with the miniature gripper arm that Ahmed’s team has already developed. Co-lead author Zhiyuan Zhang and colleagues used their gripper to capture a zebrafish larva without inflicting damage. “It was fascinating to see just how precisely yet gently the gripper functioned,” says Zhang, one of Ahmed’s former doctoral students. “The larva swam away afterwards unharmed.”
Using microbubbles of varying sizes, Ahmed’s team has also developed a tiny silicone surgical wheel-bot that they have successfully remote-navigated through the coiling labyrinth of a pig’s intestines. “The intestine is a particularly complex environment because it is narrow, curved, and irregular,” says co-lead author Zhan Shi. “It was, therefore, particularly impressive that our wheel robot was actually able to move in there.”
As well, the team at ETH Zurich has created ultrasound-activated medication-delivery patches that can stick to curved surfaces including varying tissues, and has successful tested precise dye-delivery in a tissue model. If these developments continue yielding benefits, Ahmed’s team hopes they’ll be able to use stingraybots – possibly swallowed inside dissolvable capsules – to deliver medication inside the gastrointestinal tract without the risks and expense of surgery.
Source: ETH Zurich
