And crawls through the stomach to remove swallowed battery buttons.
Researchers at MIT, the University of Sheffield, and the Tokyo Institute of Technology have collaborated to design a tiny origami that can unfold itself in the body from a swallowed capsule. The robot is steered by magnetic fields, and can crawl across the stomach to remove a swallowed button battery or patch up wounds.
"It's really exciting to see our small origami robots doing something with potential important applications to health care," Daniela Rus, who directs MIT's Computer Science and Artificial Intelligence Laboratory (CSAIL), said in a press release.
"For applications inside the body, we need a small, controllable, untethered robot system. It's really difficult to control and place a robot inside the body if the robot is attached to a tether."
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The researchers will be presenting their new work at the International Conference on Robotics and Automation in Sweden next week (May 16 - 21), and although the new robot builds on one which was reported at the same conference last year, the design of its body is significantly different.
Like its predecessor, the new robot has two layers of structural material sandwiching a material that shrinks when it’s heated. The outer layer consists of a pattern of slits that determines how the robot will fold when the middle layer shrinks.
The robot propels itself using “stick-slip” motion — its limbs stick to a surface through friction when the robot executes a move, but slip free again once the body flexes to change its weight distribution.
"Stick-slip only works when, one, the robot is small enough and, two, the robot is stiff enough," explains Steven Guitron, a graduate student in mechanical engineering. "With the original Mylar design, it was much stiffer than the new design, which is based on a biocompatible material."
In order to compensate for the biocompatible material’s flexibility, the researchers had to devise a new design that required fewer slits, but at the same time, the robot’s folds increase its stiffness along certain axes.
The researchers say they tested about a dozen different possibilities for this biocompatible material before settling on a type of dried pig intestine used in sausage casings.
"We spent a lot of time at Asian markets and the Chinatown market looking for materials," said Shuguang Li, a CSAIL postdoc. The intestines coat the shrinking layer which is a biodegradable shrink wrap called Biolefin.
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The researchers bought a pig stomach and tested its mechanical properties in order to design the synthetic stomach for the research. Then, they modeled their own cross-section of the stomach and esophagus from a silicone rubber with the same mechanical profile. A mixture of water and lemon juice simulates the acidic fluids in the stomach, according to the press release.
Through their research, the scientists were convinced that a compelling application of their origami robot is the removal of swallowed button batteries and the treatment of wounds.
First author of the paper, Shuhei Miyashita, convinced Rus of this application with a clever strategy, the researchers say.
"Shuhei bought a piece of ham, and he put the battery on the ham," Rus says. "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."
There are 3,500 reported cases of swallowed button batteries each year in the US alone, according to the press release. If the batteries come into prolonged contact with the esophagus or stomach tissue, they can cause an electric current that produces hydroxide, which then burns the tissue.
Soon enough, we may have a little origami robot to swim through the stomach and save the day.
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