Nav: Home

Ingestible robot operates in simulated stomach

May 12, 2016

In experiments involving a simulation of the human esophagus and stomach, researchers at MIT, the University of Sheffield, and the Tokyo Institute of Technology have demonstrated a tiny origami robot that can unfold itself from a swallowed capsule and, steered by external magnetic fields, crawl across the stomach wall to remove a swallowed button battery or patch a wound.

The new work, which the researchers are presenting this week at the International Conference on Robotics and Automation, builds on a long sequence of papers on origami robots from the research group of Daniela Rus, the Andrew and Erna Viterbi Professor in MIT's Department of Electrical Engineering and Computer Science.

"It's really exciting to see our small origami robots doing something with potential important applications to health care," says Rus, who also directs MIT's Computer Science and Artificial Intelligence Laboratory (CSAIL). "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."

Joining Rus on the paper are first author Shuhei Miyashita, who was a postdoc at CSAIL when the work was done and is now a lecturer in electronics at the University of York, in England; Steven Guitron, a graduate student in mechanical engineering; Shuguang Li, a CSAIL postdoc; Kazuhiro Yoshida of Tokyo Institute of Technology, who was visiting MIT on sabbatical when the work was done; and Dana Damian of the University of Sheffield, in England.

Although the new robot is a successor to one reported at the same conference last year, the design of its body is significantly different. 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 -- and like several other origami robots from the Rus group -- 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.

Material difference

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," says Guitron. "With the original Mylar design, it was much stiffer than the new design, which is based on a biocompatible material."

To compensate for the biocompatible material's relative malleability, the researchers had to come up with a design that required fewer slits. At the same time, the robot's folds increase its stiffness along certain axes.

But because the stomach is filled with fluids, the robot doesn't rely entirely on stick-slip motion. "In our calculation, 20 percent of forward motion is by propelling water -- thrust -- and 80 percent is by stick-slip motion," says 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. Through a design process that Guitron describes as "mostly trial and error," the researchers arrived at 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. The forces applied to the robot are principally rotational. A quick rotation will make it spin in place, but a slower rotation will cause it to pivot around one of its fixed feet. In the researchers' experiments, the robot uses the same magnet to pick up the button battery.

Porcine precedents

The researchers tested about a dozen different possibilities for the structural material before settling on the 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," Li says. The shrinking layer is a biodegradable shrink wrap called Biolefin.

To design their synthetic stomach, the researchers bought a pig stomach and tested its mechanical properties. Their model is an open cross-section of the stomach and esophagus, molded from a silicone rubber with the same mechanical profile. A mixture of water and lemon juice simulates the acidic fluids in the stomach.

Every year, 3,500 swallowed button batteries are reported in the U.S. alone. Frequently, the batteries are digested normally, but if they come into prolonged contact with the tissue of the esophagus or stomach, they can cause an electric current that produces hydroxide, which burns the tissue. Miyashita employed a clever strategy to convince Rus that the removal of swallowed button batteries and the treatment of consequent wounds was a compelling application of their origami robot.

"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."
Additional background

ARCHIVE: Centimeter-long origami robot

ARCHIVE: New way to make batteries safer

ARCHIVE: Origami robot folds itself up, crawls away Bake your own robot

Massachusetts Institute of Technology

Related Esophagus Articles:

Oxford University Press to publish Diseases of the Esophagus
Oxford University Press and the International Society for Diseases of the Esophagus (ISDE) are pleased to announce their new partnership to publish Diseases of the Esophagus, ISDE's monthly scientific journal.
Blood pressure medication paves the way for approaches to managing Barrett's syndrome
New ways of using mechanisms behind certain blood pressure medications may in the future spare some patient groups both discomfort and lifelong concern over cancer of the esophagus.
New detection method paves the way for 100 percent detection of esophageal cancer
Recognizing early stages of esophageal cancer is difficult because it can easily be missed.
Piping hot drinks may lead to cancer of the esophagus
Drinking piping hot coffee, tea and the caffeine-infused beverage yerba mate probably causes cancer, the World Health Organization announced.
Surprising mechanism of acid reflux damage identified by UTSW/Dallas VA researchers
The 'acid' in 'acid reflux' may not be the direct cause of damage to the esophagus as previously suspected, according to researchers at UT Southwestern Medical Center and Dallas VA Medical Center.
Fred Hutch researcher receives grant for esophageal cancer screening study
Dr. William Grady, a clinical researcher and cancer geneticist at Fred Hutch, has been awarded a $180,000 grant from the DeGregorio Family Foundation for Gastric and Esophageal Cancer Research and the Price Family Foundation for a two-year project to develop a better way to identify people at highest risk for esophageal adenocarcinoma, the most common cancer of the esophagus.
Closer to a treatment for the 'asthma of the esophagus'
Scientists from Brazilian institutions and the Yale University School of Medicine have elucidated the chemical process behind a mysterious gastrointestinal disease that is becoming more frequent every day: the eosinophilic esophagitis (EoE), also known as the 'asthma of the esophagus'.
New treatment for common digestive condition Barrett's esophagus
New research from the University of Warwick and University Hospitals Coventry and Warwickshire NHS Trust could transform treatments and diagnosis for a common digestive condition which affects thousands of patients.
New minimally invasive test identifies patients for Barrett's esophagus screening
A new minimally invasive cell sampling device coupled with assessment of trefoil factor 3 expression can be used to identify patients with reflux symptoms who warrant endoscopy to diagnose Barrett's esophagus, according to a study published by Rebecca Fitzgerald and colleagues from the MRC Cancer Unit, UK, in this week's PLOS Medicine.
First step: From human cells to tissue-engineered esophagus
In a first step toward future human therapies, researchers at The Saban Research Institute of Children's Hospital Los Angeles have shown that esophageal tissue can be grown in vivo from both human and mouse cells.

Related Esophagus Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Climate Crisis
There's no greater threat to humanity than climate change. What can we do to stop the worst consequences? This hour, TED speakers explore how we can save our planet and whether we can do it in time. Guests include climate activist Greta Thunberg, chemical engineer Jennifer Wilcox, research scientist Sean Davis, food innovator Bruce Friedrich, and psychologist Per Espen Stoknes.
Now Playing: Science for the People

#527 Honey I CRISPR'd the Kids
This week we're coming to you from Awesome Con in Washington, D.C. There, host Bethany Brookshire led a panel of three amazing guests to talk about the promise and perils of CRISPR, and what happens now that CRISPR babies have (maybe?) been born. Featuring science writer Tina Saey, molecular biologist Anne Simon, and bioethicist Alan Regenberg. A Nobel Prize winner argues banning CRISPR babies won’t work Geneticists push for a 5-year global ban on gene-edited babies A CRISPR spin-off causes unintended typos in DNA News of the first gene-edited babies ignited a firestorm The researcher who created CRISPR twins defends...