The future of ingestible sensors could be a cross between silicon-based circuitry and biodegradable materials, with batteries made of nutrients and running on stomach juices.
That, at least, is the vision of Christopher Bettinger, 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 on bacterial infection, look for symptoms of gastrointestinal disorders such as Crohn’s Disease, monitor uptake of medications, and even study the microbiome living inside people.
Some ingestible sensors, such as a clear pill containing a camera to examine the GI tracts up close, already exist, but they carry a risk of getting stuck and requiring surgery to remove. And researchers are working on devices made from biocompatible materials such as gelatin and indigo. Bettinger thinks the trick is to make the logic circuits out of silicon, taking advantage of the sophistication of that technology, but to encapsulate them in, say, a biodegradable hydrogel that can squeeze through tight openings. The other parts, such as antennas and batteries, would be made from organic and other bio-safe materials.
“If you really want to use these in a clinical setting, we think silicon is pretty good,” says Bettinger, who authored a review article on next-generation devices in the latest issue of Trends in Biotechnology.
One of the main issues is how to supply the sensors with power. “I think a lot of people hand-wave powering these devices through external RF,” he says, “but bodies are a pretty good Faraday cage,” which would prevent radio frequency energy from reaching the sensors. His team has built a battery with a cathode made of melanin—the pigment that colors hair and skin—and an anode made of manganese oxide, a form of a mineral that plays a role in nerve function. The battery has an open design, so that when it hits the stomach, gastrointestinal fluids act as the electrolyte and transport current, much the way the emergency lights of life vests light up when they’re dropped in ocean water. In lab tests, it provided 5 milliwatts of power for up to 20 hours.
Various minerals, such as manganese, magnesium, and copper are considered essential nutrients, and could be used to build electronics in amounts smaller than the U.S. Food and Drug Administration “Recommended Daily Allowance”, which should help convince that agency of their safety, Bettinger says. “We think we can go to FDA and say, ‘here’s a battery compound of things that are already in our bodies, plus water,’” he explains. Even silicon, if it interacts with the body, can turn into silicic acid, which has some health benefits.
As for the melanin, Bettinger says, “there’s already more melanin in a serving of squid-ink pasta than will be in our batteries.”
The vision of edible electronics may not be far in the future. Proteus Digital Health, of Redwood Shores, Calif., already makes an ingestible sensor that sends data to a patch worn on the skin. Earlier this month they and Otsuka Pharmaceutical, of Tokyo, Japan, filed an application with the FDA for the first combination of a drug with a smart pill. Then hope to sell a pill of Abilify, a drug for mental disorders, with the Proteus sensor embedded within it to monitor drug uptake.