Putting batteries in a kidsafe coat of armor

"To date, there has been no innovation to address this issue with small batteries," says Jeff Karp, PhD, BWH Division of Biomedical Engineering in the Department of Medicine, Harvard Medical School, Harvard Stem Cell Institute. "To address this challenge we sought to develop something that would render the battery inert, specifically when it was outside of a device."

Each year, roughly 5 billion "button" batteries are produced across the world. These small, disc-shaped batteries power everything from children's toys, hearing aids and laser pointers to remote controls and musical greeting cards. While recent legislation requires battery compartments in children's toys to be secured with screws, many items commonly used by adults contain these batteries in easily accessible formats and their packaging provides no protection. With the proliferation of such gadgets, and the demand for ever-powerful batteries to power them, the problem of accidental ingestion is increasing. In 2013, there were more than 3,000 reported cases of accidental battery ingestion -- the majority in children under age 6.

"Ingested disc batteries require emergent removal from the esophagus," says co-first study author Giovanni Traverso, MB, BCh, PhD, a gastroenterologist at Massachusetts General Hospital and a researcher at MIT. "The swallowing of these batteries is a gastrointestinal emergency given that tissue damage starts as soon as the battery is in contact with the tissue, generating an electric current and leading to a chemical burn."

Karp and his colleagues became aware of this issue in 2010, and decided to apply their collective expertise toward developing a novel solution. "This seemed like a tractable problem that we could make significant headway on in a short period of time, just based on our expertise in materials and devices," says Karp.

Karp, together with first author Bryan Laulicht, PhD, a postdoctoral fellow in Karp's lab, noticed that when a battery sits within a device, there is gentle pressure applied to it, yet when it is outside the device, such force does not exist.

"We set out to create a specialized coating that could switch from an insulator to a conductor when subjected to pressure," said Co-author Robert Langer, Institute Professor from the Harvard-MIT Division of Health Sciences and Technology.

The scientists discovered this unique substance in an unlikely place -- touch screens. Using an off-the-shelf material known as a quantum tunneling composite, they identified a nanoparticle-based coating that, when subjected to pressure, allows an electrical current to pass through. In contrast, it allows no current to run in the absence of such pressure.

They used this material to coat one side of the batteries -- covering the "minus" ends or the anodes. To determine the coating's effectiveness, they teamed up with Traverso, exposing coated and uncoated batteries to gut tissue both in a laboratory dish and in living animals. In all cases, the coated batteries caused no damage while the uncoated batteries, as expected, caused significant damage.

In addition to reducing injuries, this innovation is also likely to be quite cost-effective. "The ultimate cost will depend on the exact composition of the material that is used, but for our current formulation, we're talking cents, not dollars," says Laulicht, first author of the paper.

Now, Karp and his colleagues are working to determine the best route toward manufacturing and scaling up to a sufficiently large number of batteries, and then working with battery manufacturers to get the coated batteries into the hands of consumers.