MIT scientists have designed an ingestible pill that swells into a soft, squishy ball, big enough to stay in the stomach and monitor ulcers, cancers, or other conditions for up to a month. The inflatable pill is embedded with a sensor that continuously tracks the stomach’s temperature for up to 30 days, researchers said.
If the pill needs to be removed from the stomach, a patient can drink a solution of calcium that triggers the pill to quickly shrink to its original size and pass safely out of the body.
The new pill is made from two types of hydrogels — mixtures of polymers and water that resemble the consistency of jelly. The combination enables the pill to quickly swell in the stomach while remaining impervious to the stomach’s churning acidic environment.
The hydrogel-based design is softer, more biocompatible, and longer-lasting than current ingestible sensors, which either can only remain in the stomach for a few days, or are made from hard plastics or metals that are orders of magnitude stiffer than the gastrointestinal tract.
“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,” said Xuanhe Zhao, associate professor at Massachusetts Institute of Technology (MIT) in the US.
The design for the new inflatable pill is inspired by the defense mechanisms of the pufferfish, or blowfish. Normally a slow-moving species, the pufferfish will quickly inflate when threatened, like a spiky balloon. It does so by sucking in a large amount of water, fast.
“Currently, when people try to design these highly swellable gels, they usually use diffusion, letting water gradually diffuse into the hydrogel network,” Shaoting Lin, one of the lead authors of the study published in the journal Nature Communications.
“But to swell to the size of a ping-pong ball takes hours, or even days. It’s longer than the emptying time of the stomach,” said Lin.
The researchers instead looked for ways to design a hydrogel pill that could inflate much more quickly, at a rate comparable to that of a startled pufferfish. The design they ultimately landed on resembles a small, Jell-O-like capsule, made from two hydrogel materials.
The inner material contains sodium polyacrylate — superabsorbent particles that are used in commercial products such as diapers for their ability to rapidly soak up liquid and inflate.
A second, protective hydrogel layer encapsulates the fast-swelling particles, preventing the sodium polyacrylate from breaking apart and pass out of the stomach as individual beads.
Researchers then embedded small, commercial temperature sensors into several pills, and fed the pills to pigs, which have stomachs and gastrointestinal tracts very similar to humans.
The team later retrieved the temperature sensors from the pigs’ stool and plotted the sensors’ temperature measurements over time. They found that the sensor was able to accurately track the animals’ daily activity patterns up to 30 days.