Non-toxic battery could be safely ingested

A NEW type of battery made with melanin, a naturally occurring, non-toxic pigment found in hair, skin and eyes, could be used in safe, ingestible medical devices, according to its developers.

Conventional batteries are made from metals that are dangerous to the body. In implantable medical devices like a pacemaker, the battery is sealed and is never in contact with the body. However, for other short-lived or low-power devices, such as ingestible medical cameras or smart drug delivery devices that could sense and deliver drugs when needed, this is more difficult, and can pose a risk to patients. Christopher Bettinger, a professor of materials science and biomedical engineering at Carnegie Mellon University, and his team say that such non-toxic, degradable batteries made from components found within the body anyway, would be useful.

Bettinger and the team investigated the use of melanin, which as well as absorbing UV light in skin, also has a role in binding and releasing metallic cations, in much the same way as a battery electrode. They used melanin pigments in a thin film either on the positive or negative electrodes, which are made of stacked biodegradable polymers. The complementary electrode is made from an ingestible mineral, such as manganese oxide, while they use an aqueous electrolyte.

“The exact numbers depend on the configuration, but as an example, we can power a 5 mW device for up to 18 hours using 600 mg of active melanin material as a cathode,” said researcher Hang-Ah Park.

While this may sound like a low capacity, the battery is plenty powerful enough to power an ingestible drug delivery or sensing device, for example to release medicine in response to a change in gut microbiome or to deliver a vaccine in stages. The batteries are also more powerful than other techniques to power ingestible devices, such as energy-harvesting techniques or glucose oxidase fuel cells, which have an output in the microwatts range, three orders of magnitude less. The prototype battery is 3D printed from poly(lactic-co-glycolic acid (PLGA), a biodegradable polymer.

Bettinger says that the next step will be to develop casing materials which will allow the battery to be safely delivered to the acidic environment in the stomach.

The research was presented on 23 August at the 252nd National Meeting & Exposition of the American Chemical Society (ACS), held this year in Philadelphia.