This stretchy biofuel cell powers wearables from your sweat

For years, wearables have had something of a power conundrum. Without a bulky and annoying rechargeable battery, there's no way to supply components with the energy they need to operate.

Multiple research teams across the globe are tackling this problem - trying to figure out how to harvest energy from the body's motion or its surroundings. But to date, these haven't succeeded in producing enough power, or they aren't stretchy and flexible enough to conform to the human body.

But now engineers at the University of California San Diego claim to have made a breakthrough. They've developed a biofuel cell that can extract enough energy from the body's sweat to power electronics like LEDs and Bluetooth radios.

How it works

Using a combination of chemistry, advanced materials and electronic interfaces, their fuel cell delivers ten times more power per surface area than any existing wearable biofuel cell.

Here's how it works. Using lithography, the team built up a stretchy electronic foundation out of gold, then screen printed three-dimensional carbon nanotube-based cathode and anode arrays on top. Finally, they filled the cell with an enzyme that oxidises the lactic acid found in human sweat to generate a current.

The challenge came in increasing the cell's energy density. "We needed to figure out the best combination of materials to use and in what ratio to use them," said Amay Bandodkar, one of the first authors on a paper describing the technology, published in Energy & Environmental Science

In tests, the team hooked up the cell to a custom made circuit board and had a team of volunteers cycle on a stationary bike. They were able to power a blue LED for about four minutes.

The team says that it's hoping to improve that lifespan by figuring out a way to store the energy produced and then release it gradually. They'd also like to replace the silver oxide used in the cathode, which degrades over time, with something more stable.