Sun. Feb 5th, 2023
A small, digestible voltaic cell that is powered by the acidic fluids in the stomach.
Enlarge / A small, digestible voltaic cell that is powered by the acidic fluids in the stomach.

Move over, wearables. Soon, ingestibles that run on the power of a grumbling gut may be the go-to health-tracking devices.

New wireless gadgets can deliver drugs and continuously measure temperature while simultaneously harvesting energy from churning, acidic intestinal fluids, researchers report this week in Nature Biomedical Technology. Prototypes have successfully made their way through the intestines of pigs and the design needs to be adapted for human use. But the findings suggest that next-generation recordable devices will be able to safely harvest energy for a slew of health tracking and monitoring purposes — possibly even for longer periods of time.

Consumables have already proven useful for video recording and health monitoring. They measure things like respiration, temperature, pH, drug release, heart rate, and pressure. But most swallowable gadgets still require an old-fashioned battery, which can cause life-threatening burns and injuries to living tissue.

To get around that problem, MIT researchers and colleagues turned to the “lemon battery” for inspiration. In the classic science class demonstration, a zinc element, such as a galvanized nail, and a copper penny act as electrodes when inserted into a lemon. The citric acid of the lemon creates a small current between them.

By trading citric acid for gut acid, the researchers created their own tiny Zn-Cu cells using low-cost, commercially available, biocompatible materials. The first device was for continuous, wireless temperature monitoring. It consisted of a microcontroller with a radio frequency transmitter and a temperature sensor (among other things) and an “energy harvesting boost converter integrated circuit”, which “took energy directly from the Zn-Cu cell at low voltage (0.1–0. 2 V) and amplified it on a higher voltage temporary storage capacitor (2.2-3.3 V) for use by the circuits.

In early ingestion experiments with pigs, the researchers found that the energy harvest from the device decreased as it reached the intestines. So basically the integrated circuit allowed the device to keep working even if the power varied.

When assembled, the device was a bullet-shaped capsule approximately 40mm by 12mm in diameter. When three pigs ate from it, it continuously measures the temperature and sends the information every 12 seconds to a base station two meters away. The devices averaged 0.23 microwatt mm2 of the electrode area during their journeys through pig intestines, which averaged about six days.

Then the researchers created another version of their drug delivery device. This one was box-shaped and small, only 2 by 1 by 1.5 mm – a fraction of a dime. The small box may contain drugs, which are released when a gold membrane lid dissolves upon an electrochemical trigger.

The researchers warn that more work will be needed to miniaturize the technology for humans. In addition, they have to adapt it specifically for the human stomach system. But overall, they’re hopeful that the new devices are the start of a next generation of ingestibles.

In a statement, John Rogers, a professor of materials science and engineering at Northwestern University who was not involved in the study, said the study “reports an exciting and remarkably broad collection of advances in ‘recordable’ electronics — from bioresorbable power supplies to energy-efficient electronics, advanced sensors/actuators and wireless communication systems… These types of systems have great potential to address important clinical needs.”

Nature Biomedical Technology2017. DOI: 10.1038/s41551-016-0022 (About DOIs).

By akfire1

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