MIT engineers have recently developed an ingestible smart pill that expands in the stomach to track temperature for up to a month. The pill swells to the size of a squishy ping pong ball upon entering the stomach, and can easily be removed from the stomach if the patient drinks a calcium solution that triggers the ball to shrink. The data obtained from this sensor allowed the researchers to accurately track activity patterns for up to 30 days in an animal study recently published in Nature Communications.
This new pill is comprised of two different hydrogels, or mixtures of polymers and water that are similar in consistency to Jell-O. Use of these two unique compounds allow the pill to quickly expand in the stomach, while maintaining its shape at the same time.
This hydrogel structure allows the pill to be last longer and be more biocompatible than traditional ingestible sensors. Many of these other ingestible sensors only reside in the stomach for several days, whereas this hydrogel pill allows the sensor to remain in the stomach for as long as a month. The hydrogel components are also much safer for the gastrointestinal tract that sensors containing hard plastic or metal.
“The dream is to have a Jell-O-like smart pill, that once swallowed stays in the stomach and monitors the patient’s health for a long time such as a month,” explained Xuanhe Zhao, an associate professor of mechanical engineering at MIT.
The pill can potentially deliver a variety of sensors to monitor the stomach for conditions such as pH level, or vitals indicative of bacterial or viral presence. The utility of this hydrogel pill comes from its ability to stay in the stomach for such a long period of time, and it has the ability to be used with many sensors outside of the temperature sensing one used in the study.
To test their product, the researchers embedded commercial temperature sensors into several of the pills and fed them to pigs. The pig is an animal whose digestive system is considered to be very similar to the human’s for testing purposes. The team then retrieved the sensors from the pigs’ stool and tracked the sensors’ temperature recordings over time. They found that within the hydrogel pill, the sensor accurately tracked the daily activity patterns for up to 30 days.
In developing this pill, the researchers decided to use an inner material known as sodium polyacrylate, a compound involved with rapid absorption on liquid. The team knew that a pill composed of only this compound would not hold shape in the stomach, so they created a hydrogel protective layer to encapsulate these absorbent particles.
“You would have to crack through many crystalline domains to break this membrane,” said study author Shaoting Lin. “That’s what makes this hydrogel extremely robust, and at the same time, soft.”
To test their pill, the researchers put the pill in several solutions resembling gastric conditions and found that the pill inflated to 100 times its original size in 15 minutes. Zhao describes the inflated pill to have a consistency like Jell-O, but with impressive strength. This toughness held up in tests where the inflated pill was squeezed at forces greater than it would experience in the stomach, and it did not burst.
“The stomach applies thousands to millions of cycles of load to grind food down,” said Lin. “And we found that even when we make a small cut in the membrane, and then stretch and squeeze it thousands of times, the cut does not grow larger. Our design is very robust.”
This research was conducted by Zhao and senior collaborator Giovanni Traverso, who will be joining MIT faculty this year. In addition to Lin, other lead authors include Xinyue Liu and Christoph Steiger, and the study was funded by the National Science Foundation, NIH, and the Bill and Melinda Gates Foundation.
Inflatable pill that swells in the stomach could monitor cancer
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