The origami robot unfolded from an ingestible capsule in a stomach model to remove a lodged button battery.
Image credit: Melanie Gonick/MIT
Every year, more than 3,500 people in the United States swallow button batteries, which are commonly used to power toys, games, watches, hearing aids, among numerous other products.
While the batteries pass through the body in most cases, in other cases, they can become lodged in the esophagus or stomach.
When this happens, an electrical current can form around the battery. This produces an alkaline chemical called hydroxide, which burns the tissue.
However, researchers from the Massachusetts Institute of Technology (MIT), the University of Sheffield in the United Kingdom, and the Tokyo Institute of Technology in Japan, suggest their ingestible "origami robot" could offer an alternative treatment option.
The researchers, including Daniela Rus of MIT's Department of Electrical Engineering and Computer Science, are not new to the world of origami robots.
Last year, the team reported on their creation of an origami robot, revealing how the robot folds itself up and "crawls" away once batteries are attached to it.
Now, the researchers have created a newer version of the device, which they say boasts a significantly different design.
New robot made of biocompatible material
Both the earlier and the updated device consist of a material that shrinks in response to heat, and on either side is another material consisting of a number of slits. This outer material regulates how the robot will fold when the heat-sensitive material contracts.
Additionally, both devices incorporate a "stick-slip" motion. This is the process by which the robot propels itself in the body, allowing the device to attach to a surface through friction but free itself when the body flexes.
Unlike the earlier device, the updated version is made from a biocompatible material: a form of dried pig intestine used for sausage casings. The heat-sensitive material is made from Biolefin - a biodegradable shrink wrap.
Because of the new material, however, the team had to make some other changes to the device.
In order for the stick-slip motion to work, the robot must be stiff enough - a requirement that the new, biocompatible material fails to fulfill by itself. As such, the team reduced the number of slits on the device, so that when it folds, the stiffness of the material increases.
However, the researchers note that in order to move through the body, the device does not rely solely on the stick-slip process, due to the presence of stomach fluids.
"In our calculation, 20 percent of forward motion is by propelling water - thrust - and 80 percent is by stick-slip motion," says Shuhei Miyashita, who was at MIT's Computer Science and Artificial Intelligence Laboratory when the research was conducted.
"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."
Robot effectively removed button battery from stomach model
Furthermore, the new robot emerged as a rectangular device, consisting of perpendicular, accordion-like folds and pinched corners.
The accordion-like folds allow the device to be compressed enough so that it fits inside a capsule, while the pinched corners allow the device to grip onto surfaces.
The motion of the device - which is primarily rotational - is controlled by magnetic fields on the outside of the body, which send information to a permanent magnet situated in one of the robot's folds.
This magnet is also responsible for picking up the button battery inside the body.
The video below further explains how the origami robot works:
The researchers tested their new origami robot using a model of an open cross-section of the stomach and esophagus, which simulated the mechanical properties of a pig's stomach.
In order to mimic the presence of stomach acids, the team used a combination of water and lemon juice.
They then simulated the swallowing of a button battery. On mimicking the subsequent ingestion of the origami robot, they found the device was able to unfold itself from the capsule, crawl across the wall of the stomach and remove the battery.
The team believes the device could also heal wounds caused by ingestion of button batteries.
"It's really exciting to see our small origami robots doing something with potential important applications to healthcare.
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."
While further testing is clearly required, the researchers believe they may well be on the way to a novel treatment for button battery ingestion.
"Shuhei bought a piece of ham, and he put the battery on the ham," notes Rus. "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."