Some implantable medical devices such as pacemakers run on batteries containing toxic components that are isolated from contact with the body. But for low-power, repeat applications such as drug-delivery devices that are meant to be swallowed, non-toxic and degradable batteries are desirable.

To minimize the potential harm of ingestible devices, Christopher Bettinger, Carnegie Mellon University, Pittsburgh, PA, USA, and colleagues decided to turn to melanins and other naturally occurring compounds such as pectin, which is used as a gelling agent. In our skin, hair, and eyes, melanins absorb UV light to quench free radicals and protect us from damage. They also happen to bind and unbind metal ions. “We thought, this is basically a battery,” Bettinger says.

Building on this idea, the researchers experimented with battery designs that use melanin pigments, various electrode materials such as manganese oxide and sodium titanium phosphate, and cations such as copper and iron that the body uses for normal functioning.

The team could power a 5 mW device for up to 18 hours using 600 mg of active melanin as a cathode. Although the capacity of a melanin battery is relatively low, it would be high enough to power an ingestible drug-delivery or sensing device. The researchers envision using the battery for sensing gut microbiome changes and responding with a release of medicine, or for delivering bursts of a vaccine over several hours before degrading.

• Presented at the 252nd American Chemical Society (ACS) National Meeting & Exposition in Philadelphia, PA, USA