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Temporary tattoos turn sweat to power in biobattery

Electrical currents generated from sweat could someday be a way to charge your phone while burning calories.

This temporary tattoo turns sweat into a more useful type of juice. Video screenshot by Eric Mack/CNET

One day soon, the juice that powers your phone or other portable devices could pour forth from your pores. Researchers at the University of California San Diego have created a biosensor in the form of a temporary tattoo that uses sweat to monitor exercise progress and produces a weak electrical current in the process.

The sensor detects and reacts with lactate in sweat, which is produced by the body through a process called glycolysis during exercise. Measuring the stuff can be helpful in athletic training, but up until now was a tedious process that required taking multiple blood samples during a workout. Measuring lactate through an external sweat sensor is obviously much more convenient, but the really cool part of this approach is the electrical current created as a byproduct.

Not wanting to lose those sweet sweat electrons, the research team developed a biobattery that could connect to the sweat sensor and be worn during a workout. Using the current design, which has electrodes only 2 by 3 millimeters in size, exercising volunteers were only able to generate about 4 microwatts, less than half of what would be required to power a watch.

"The current produced is not that high, but we are working on enhancing it so that eventually we could power some small electronic devices," says postdoctoral student Wenzhao Jia in a release on the ACS site.

But don't assume the harder you work, the faster your smartphone would charge. Among the 15 volunteers who wore the biobatteries and produced power while riding a stationary bike, those who were more physically fit tended to produce less power. This is likely because less fit folks become fatigued sooner, causing glycolysis to kick in, therefore forming more lactate in their sweat to be converted to power.

Even if sweat power is subject to the law of diminishing returns, it surely couldn't hurt to have an extra reason to work some up.

Check out a video about the research team's work below: