Scientists have developed a temporary tattoo with a built-in, sweat-powered biobattery that could one day be used to charge your phone while you are out for a run.

The biobattery works using lactate, a key chemical found in sweat that can be used to monitor exercise performance.

This means that the more the wearer sweats, the more energy is going to be produced, creating the interesting scenario where less physically fit people are able to produce more power.

The technology is one of the first examples of skin-based power sources, and could pave the way for a host of technologies powered by devices attached to the skin.

The biobattery works by using an enzyme to extract the electrons in the sweat’s lactate and move them to the battery. At present, the amount of energy produced is very small, but the researchers are confident that they will be able to develop this to enable small electronic devices to be charged.

“The current produced is not that high, but we are working on enhancing it so that eventually we could power some small electronic devices,” said Dr Wenzhao Jia, a postdoctoral researcher at the University of California San Diego.

“Right now, we can get a maximum of 70 microWatts per cm², but our electrodes are only 2 by 3 millimeters in size and generate about 4 microWatts — a bit small to generate enough power to run a watch, for example, which requires at least 10 microWatts.

“So besides working to get higher power, we also need to leverage electronics to store the generated current and make it sufficient for these requirements.”

The device has also been developed as a lactate monitor, which will be a valuable tool for both doctors and athletes. Previously lactate has been monitored using a series of blood tests, so this monitor is likely to prove simpler and less invasive.

The biobattery’s reliance on sweat means that the amount of power produced can vary significantly depending on the person wearing it.

The researchers tested the initial biobattery on 15 exercise bike-riding volunteers, and found that not only did those who were least fit produce the most energy, but the most regularly active participants produced the least energy.

This could affect the potential success of the technology, as such variation in performance could make it difficult to market.

However, this is one of the first examples of skin-based batteries, and the technology is likely to be developed much further.

“These represent the first examples of epidermal electrochemical biosensing and biofuel cells that could potentially be used for a wide range of future applications,” said Dr Joseph Wang, professor of nanoengineering at University of California San Diego.

From here we could see the development of an array of wearable technologies and gadgets siphoning power through our skin, perhaps even one day powering whole computers, medical augmentations and more.

Inline image courtesy of Dr Joseph Wang.