Tiny, ingestible electronic devices are proving to be a better substitute for drug delivery or invasive procedures like colonoscopies, but powering them can be a challenge. Safe-to-swallow batteries are being developed, but now researchers at MIT have designed a way for these electronics to be powered by acids in the stomach, making for a cheaper and safer alternative to other power sources.
The senior authors of the new study, Giovanni Traverso and Robert Langer, have previously developed a drug delivery system that unfolds like a star in the stomach to release medicine slowly over a few weeks, and a pill-sized sensor that monitors a patient's heart beat and breathing from the inside. Devices like the latter need to get power from somewhere, but regular batteries tend to wear out over time, and can contain chemicals that you wouldn't want leaking into the body.
"We need to come up with ways to power these ingestible systems for a long time," says Traverso. "We see the GI tract as providing a really unique opportunity to house new systems for drug delivery and sensing, and fundamental to these systems is how they are powered."
Considering most batteries use acid to run anyway, why not take advantage of the acidic environment of the stomach? A common science class experiment demonstrates the idea using a lemon: sticking a piece of zinc and a piece of copper into a lemon, the citric acid can act as an electrolyte and carry the current between the two metals, like electrodes. The power generated can be enough to run an LED.
The researchers scaled that principle down by attaching their own zinc and copper electrodes to the outside of a small, ingestible device containing a temperature sensor and a 900 MHz transmitter. Like in the lemon, the stomach acid can carry the electric current from the zinc to the copper and power the device, which, when tested in pigs, was able to take temperature readings and then send that data wirelessly, every 12 seconds, to a receiver up to 2 m (6.6 ft) away.
"A big challenge in implantable medical devices involves managing energy generation, conversion, storage, and utilization," says Anantha Chandrakasan, senior author of the study. "This work allows us to envision new medical devices where the body itself contributes to energy generation enabling a fully self-sustaining system."
The team tracked the device's journey through the pigs' digestive tract, and found the journey took about six days on average. After it leaves the stomach and enters the small intestine, the lower acidity reduces its effectiveness to about 1 percent of its peak performance, but harvested over a longer period of time, that could still be enough power to transmit data less frequently than at 12 second intervals.
In its current form, the ingestible system is about 40 mm long by 12 mm wide (1.5 x 0.5 in) and uses the power generated to release drugs that are wrapped in a thin layer of gold. The researchers say that by customizing the circuitry, they should be able to shrink it to about a third of that size, and equip it with other sensors and devices to monitor a range of vital signs and treat various diseases and conditions.
"You could have a self-powered pill that would monitor your vital signs from inside for a couple of weeks, and you don't even have to think about it," says Philip Nadeau, lead author of the study. "It just sits there making measurements and transmitting them to your phone."
The research was published in the journal Nature Biomedical Engineering.