The future of ingestible sensors could be a hybrid of silicon-based circuits and biodegradable materials, with batteries made of nutrients and run on gastric juices.
At least, that’s the vision of Christopher Bettinger, an assistant professor of materials science and biomedical engineering at Carnegie Mellon University. His group is working on edible electronics and ways to power them. Ingestible sensors could provide a gut check for early signs of bacterial infection, look for symptoms of gastrointestinal disorders like Crohn’s disease, monitor drug intake, and even study the microbiome in the human body.
I think a lot of people power these devices with external RF handwaves, but the body is a pretty good Faraday cage”
Some ingestible sensors, such as clear pills containing cameras to examine the gastrointestinal tract up close, already exist, but they run the risk of getting stuck and requiring surgical removal. Researchers are working on devices made from biocompatible materials such as gelatin and indigo. Bettinger thinks the trick is to make logic circuits out of silicon, taking advantage of the technology’s complexity but encapsulating them in, say, a biodegradable hydrogel that can be squeezed through narrow openings . Other components, such as antennas and batteries, will be made of organic and other biosafe materials.
“If you really want to use these in a clinical setting, we think silicon is very good,” said Bettinger, who wrote an opinion piece about the next-generation device in the latest issue of Trends in Biotechnology.
One of the main issues is how to power the sensor. “I think a lot of people power these devices with handwaves via external RF,” he said, “but the body is a really good Faraday cage” that would prevent RF energy from reaching the sensor. His team built a battery with a cathode made of melanin (the pigment that colors hair and skin) and an anode made of manganese oxide, a mineral that plays a role in nerve function. The battery has an open design, so when it hits the stomach, the gastrointestinal fluids act as electrolytes and transmit electricity, much like the emergency lights that come on when a lifejacket falls into seawater. In lab tests, it delivered 5 milliwatts of power for up to 20 hours.
Various minerals, such as manganese, magnesium, and copper, are considered essential nutrients used in the manufacture of electronics in amounts below the FDA’s “recommended daily intake,” which should help convince The agency believes in their safety, Bettinger said. “We thought we could go to the FDA and say, ‘This is a battery compound that’s made of a substance that’s already in our body and water,'” he explained. Even silicon, if it interacts with the body, turns into silicic acid, which has certain health benefits.
As for melanin, Bettinger says, “There’s already more melanin in a serving of squid ink pasta than there is in our batteries.”
The vision of edible electronics may not be so far away. Proteus Digital Health, based in Redwood Shores, Calif., has made an absorbable sensor that sends data to a patch that sticks to the skin. Earlier this month, they and Otsuka Pharmaceutical of Tokyo, Japan, submitted their first combination application for the drug and a smart pill to the FDA. It then hopes to sell an Abilify pill, a drug for mental disorders, that has Proteus sensors embedded in it to monitor drug uptake.