US researchers have tested a new smart pill that quickly inflates in the stomach like a pufferfish, and could one day carry tiny sensors to track cancers, ulcers and other signs of disease.

The Massachusetts Institute of Technology (MIT) engineers said the jelly-like capsule swelled to the size of a ping pong ball within an hour of ingesting, and stayed in the gut for up to 30 days.

This means the pill was small enough to ingest by mouth and enter through the oesophagus, but once inflated, it didn’t pass through the gastrointestinal tract too early.

When fitted with temperature sensors, the device was also capable of remotely tracking activity in the stomach during animal studies.

The new device swells to more than twice its size within a few minutes in water. Photo: Xinyue Liu

Ingestible technology is a fast-emerging area in the medical engineering field, and scientists have already used edible sensors to monitor bugs in the gut, and harvest energy from stomach acid.

In the future, the new device could transport other sensors down the gastrointestinal tract to monitor pH levels, bacteria or signs of viruses, the MIT researchers said.

Tiny cameras could also be embedded so that doctors can track the progress of tumours or ulcers in the stomach.

The clever design was inspired by the pufferfish, or blowfish, which rapidly takes in water to balloon out to a tough spiky ball when trying to deter predators.

Mimicking this fast-acting defence mechanism, the device uses a super-absorbent and soft hydrogel material, also used in nappies and other commercial products, to rapidly soak up liquid and inflate to up to 100 times its original size.

The researchers said that existing hydrogel devices are made from hard plastics or metals that are too stiff for the stomach, or exit the body within only a few days.

“Currently, when people try to design these highly swellable gels, they usually use diffusion, letting water gradually diffuse into the hydrogel network,” mechanical engineer and researcher Xinyue Liu said.

“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.”

The researchers also developed a second hydrogel layer so the device would remain intact when exposed to the stomach’s high acid levels.

This “anti-fatigue” feature was also borrowed from the pufferfish’s natural reaction when startled, the researchers said.

“You would have to crack through many crystalline domains to break this membrane,” researcher Shaoting Lin said.

“That’s what makes this hydrogel extremely robust, and at the same time, soft.”

If the patient needs to remove the device, they need only to drink a bio-compatible salt solution to shrink the device to its original size so that it can pass out of the body.

The edible device swells to a large soft sphere in the gut and can deflate to a floppy membrane on demand. Photo: Xinyue Liu, Shaoting Lin

The researchers acknowledged that the device has only been tested in lab and animal (pig) studies, and more studies are needed to see if it works in humans.

But engineers remain optimistic.

“Ingestible electronics is an emerging area to monitor important physiological conditions and biomarkers,” Arizona State University engineering professor Hanqing Jiang, who was not involved in the study, said.

“Conventional ingestible electronics are made of non-bio-friendly materials … It also represents a new application of tough hydrogels that the group has been devoted to for years.”

The MIT researchers published their results in Nature Communications on Wednesday.