Remember that elementary school science project where you built a battery by sticking a couple pieces of wire into a lemon? Well, that same idea is now being used to develop ingestible electronic devices powered by stomach acid. That could eliminate the need for bulky, potentially hazardous batteries and bring us one step closer to more sophisticated drug delivery systems and internal sensors for things like temperature, heart rate, and breathing.
Researchers at MIT and Brigham and Women's Hospital took inspiration from the famous lemon battery, building a small sensor with zinc and copper electrodes on the outside. After being swallowed—by pigs, in this case—the two electrodes combined with stomach acid, producing enough electricity to power a temperature sensor. It also powered a wireless transmitter, which broadcast the temperature data every 12 seconds, for an average of six days as the device passed through the pigs' bodies. (As it reached the lower intestine, where there's less acid, power production dropped, but was still enough to be useful.)
"I think it really opens up different possibilities for ways of powering long-term resident systems in the body," says Giovanni Traverso, one of the lead authors of the study. The prototype evolved out of research into time-release drug applications. Using electronics lets you do all kinds of interesting things, Traverso says. But as with drones and electric cars, batteries remain a sticking point. They're a potential safety hazard, and add bulk to a device which, after all, has to be swallowed.
So the team set out to see whether they could produce energy from the body itself. Previous experiments had shown it was possible, but had only been effective for a short time. To get a better sense of what could work, they had their pigs swallow a battery-powered device that measured how much electricity could be produced in the stomach and intestines. Then they tailored their prototype to those numbers. It's a capsule about 40 millimeters long and 12 millimeters in diameter, but they believe they can shrink it to about one-third that size.
Traverso explains that getting electronics inside the body can have all kinds of useful applications. Measuring core temperature, for example, has more advantages than measuring peripheral temperature; future devices could remain in the body for weeks, diligently broadcasting measurements to the outside world. It also opens up new avenues for drug delivery: The researchers showed the device could release drugs encapsulated in a golden film. That could make for more precise and responsive treatment.
Of course, that's just in pigs, for now. Traverso says it will be three to five years before the work might shift to human subjects. The most important step is demonstrating long-term safety, though the experimented-upon pigs showed no ill effects. If all goes as planned, it might not be that long before you have a capsule in your stomach, sending your vital signs to your smart phone, which you can then tweak with the appropriate drugs. Think of it as the future of Fitbit.