AsianScientist (May 18, 2016) – Researchers from Japan, the US and the UK have developed a tiny origami robot ‘microsurgeon’ that can be steered by magnets to crawl across the stomach wall, removing a swallowed button battery or patch a wound. To get it into the stomach, patients swallow a capsule from which the robot unfolds itself.
The work will be presented at the Institute of Electrical and Electronics Engineers’s International Conference on Robotics and Automation, currently ongoing in Stockholm, Sweden from 16-21 May.
Every year, 3,500 swallowed button batteries are reported in the US alone. The batteries are usually digested normally, but if they come into prolonged contact with esophagus or stomach tissue, they can cause burns, particularly in small children.
Post-doctoral researcher Dr. Shuhei Miyashita from Tokyo Tech employed a clever strategy to convince lead scientist Professor Daniela Rus from MIT that the removal of swallowed button batteries—and treatment of consequent burn wounds—was a compelling application of their origami robot.
“Shuhei bought a piece of ham, and he put the battery on the ham,” Rus said. “Within half an hour, the battery was fully submerged in the ham. So that made me realize that, yes, this is important. If you have a battery in your body, you really want it out as soon as possible.”
Although the new robot is a successor to one reported at the same conference last year, the design of its body is significantly different.
However, like its predecessor, it can propel itself using what’s called a ‘stick-slip’ motion, in which its appendages stick to a surface through friction when it executes a move, but slip free again when its body flexes to change its weight distribution.
Also like its predecessor, the new robot consists of two layers of structural material sandwiching a material that shrinks when heated. A pattern of slits in the outer layers determines how the robot will fold when the middle layer contracts.
The robot’s envisioned use also dictated a host of structural modifications.
“Stick-slip only works when, one, the robot is small enough and, two, the robot is stiff enough,” said Mr. Steven Guitron, a graduate student in mechanical engineering at MIT. “With the original Mylar design, it was much stiffer than the new design, which is based on a biocompatible material.”
But because the stomach is filled with fluids, the robot doesn’t rely entirely on stick-slip motion.
“In our calculations, 20 percent of forward motion is by propelling water—thrust—and 80 percent is by stick-slip motion,” said study first author Miyashita. “In this regard, we actively introduced and applied the concept and characteristics of the fin to the body design, which you can see in the relatively flat design.”
It also had to be possible to compress the robot enough that it could fit inside a capsule for swallowing. Similarly, when the capsule dissolved, the forces acting on the robot had to be strong enough to cause it to fully unfold. The researchers eventually decided on a rectangular robot with accordion folds perpendicular to its long axis and pinched corners that act as points of traction.
In the center of one of the forward accordion folds is a permanent magnet that responds to changing magnetic fields outside the body, which control the robot’s motion.
To test their device, the researchers devised experiments involving a simulation of the human esophagus and stomach. Their model is an open cross-section of the stomach and esophagus molded from a silicone rubber with the same mechanical profile as a pig stomach. A mixture of water and lemon juice simulated the stomach’s acidic fluids.
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Source: Massachusetts Institute of Technology.
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