We've seen numerous ingestible medical devices dreamt up over the years, includingcamera pills, and capsules designed to listen out for your heartbeat and breathing rate. But if use of such smart capsules is to become widespread, then we need to be totally sure that they're not going to cause harm. With that goal in mind, a team of researchers has developed a tiny battery that's entirely non-toxic, providing just enough power for tiny sensing or diagnostic devices to get their jobs done.

We've seen numerous ingestible medical devices dreamt up over the years, includingcamera pills, and capsules designed to listen out for your heartbeat and breathing rate. But if use of such smart capsules is to become widespread, then we need to be totally sure that they're not going to cause harm. With that goal in mind, a team of researchers has developed a tiny battery that's entirely non-toxic, providing just enough power for tiny sensing or diagnostic devices to get their jobs done.

According to the team, which is headed by Carnegie Mellon University's Christopher Bettinger, the batteries currently used in ingestible medical devices aren't entirely safe. Being of an "off-the-shelf" nature, such batteries often contain toxic materials that, if trapped inside the body, could cause harm to the patient.

To tackle the issue, the researchers built an all new battery that makes use of materials that either occur naturally in the body, or that are entirely harmless to it. They used melanin pigments, found in the skin, hair and eyes, as a key component of the battery.

Melanin has a protective function in the body, absorbing UV light and protecting against free radicals. It's also able to bind and unbind with metallic ions, making it a perfect candidate battery material.

The design of the battery is somewhat changeable, in that the researchers plan to adjust it to fit the requirements of a particular application – for example, timed drug delivery. Broadly speaking, it makes use of melanin as either the anode or cathode of the battery (it works equally well as either), with a second substance, such as the mineral manganese oxide or the benign metal magnesium, forming the second terminal. The aqueous fluid in the GI tract comprises the electrolyte.

The whole thing is supported structurally by PLGA, and encapsulated in gelatin. The design allows the battery to maintain structure and function as it moves through the body, but should some unforeseen circumstance stop it from exiting the patient's system after its work is done (usually some 20 hours), it will degrade harmlessly.

The researchers claim that while the capacity of the battery is very low when compared to lithium-ion designs, it would still provide enough power for small sensing or drug-delivery devices. While the exact numbers vary depending on configuration, the team says that it's possible for a battery using 600 milligrams of melanin as a cathode to power a 5-milliwatt device for 18 hours.

The team is currently looking for industry partners to help bring the melanin-based battery to market. In the meantime, it's also working on making edible batteries using other biomaterials, such as pectin – a compound found in plants.

The work was presented this week at the National Meeting and Exposition of the American Chemical Society (ACS).