Embeddable sensors that can track a person's vitals could eventually be a boon for healthcare, but something equally small, portable, and safe is going to have to power those sensors. Researchers from the University of Illinois may have an answer: batteries that slowly decompose in the body. Using magnesium and either iron, tungsten, or molybdenum, the researchers were able to build a small battery that delivered a constant output for at least 24 hours. Operating voltage varies by element, ranging from approximately 0.45V to 0.75V, and by stacking cells in series, the researchers say that they were able to create a battery strong enough to power a conventional LED.

The work was detailed in a paper that was published last week in Advanced Materials. The time it takes for a battery to dissolve varies by temperature. Sitting in a salt-water solution at 98.6 degrees Fahrenheit, it took a four-cell battery 11 days to break apart; the temperature was then increased to 185 degrees, almost fully dissolving the battery after another eight days. That battery weighed about 3.5 grams, with cells measuring 3 cm by 1.3 cm and placed 4mm apart. The researchers say the materials are both biocompatible and benign to the environment.

"Implantable batteries require power efficient designs, to allow operation with batteries at sizes compatible with use in the body," the paper reads. "As with most battery technologies, size and total power capacity are tightly linked." The researchers have some ideas for how they can increase the battery's lifetime and make it smaller, such as by treating its surfaces. They're confident that it can be shrunk down to the proper size for use in humans eventually — though they don't suggest that they'll be performing any type of trial just yet.