Non-toxic, edible batteries could one day power ingestible devices for diagnosing and treating disease. The batteries are made with melanin pigments naturally found in the skin, hair, and eyes.
To minimize the potential harm of future ingestible devices, the Carnegie Mellon University team chose melanins, which absorb ultraviolet light to quench free radicals and protect us from damage. They also happen to bind and unbind metallic ions.
Although the capacity of a melanin battery is low relative to lithium-ion, it would be high enough to power an ingestible drug-delivery or sensing device. For example, the battery could be used for devices that sense gut microbiome changes and respond with a release of medicine, or for delivering bursts of a vaccine over several hours before degrading.