Perspiration Power: Scientists Turn Sweat Into Electrical Energy

A tattoo biosensor (enlarged above) detects lactate levels during exercise; a biobattery using the technology could power electronics (Photo: Joseph Wang)

A tattoo biosensor (enlarged above) detects lactate levels during exercise; a biobattery using the technology could power electronics (Joseph Wang)

By Richard Knox

It takes energy to work up a sweat. But now researchers have cleverly figured out how to turn sweat into energy.

Scientists have devised a small skin patch they call a “temporary tattoo” that can transform lactate — one of 800 or so chemicals in sweat — into electrical energy.

Not much energy, so far. Only about 4 microwatts, less than half of what it takes to power a digital watch. But the energy alchemists are confident they can scale up their sweat “biobattery” enough to play an iPod, power a GPS device, or warn a marathoner when it’s time to top up her electrolytes.

The researchers think their work could also have military and biomedical applications, if they can tweak the technology to squeeze more electricity out of sweat.

“Sweat has been largely neglected, not thought of as a worthwhile physiological fluid.”

– Researcher Josh Windmiller

“Right now we’re working on the biofuel cell so it can get higher power,” Wenzhao Jia, of the University of California San Diego, tells CommonHealth. She’s describing the skin-patch biobattery tomorrow at a meeting of the American Chemical Society in San Francisco.

One problem in experiments so far: People who are less fit produce more energy from their sweat than those who are moderately fit. The fittest subjects produce the least amount of power. The researchers are trying to figure out how to compensate for this.

“We want to integrate another electronic element such as a super-capacitor that can store the power,” Jia says. “Ultimately, we can connect a number of cells together to make the current higher.”

Jia says the sweat-powered battery grew out of an earlier effort to monitor levels of lactate, a metabolic byproduct when sugar (glucose) is broken down to produce energy — a process called glycolysis. (It’s the buildup of lactate, or lactic acid, that makes your muscles sore after strenuous exercise.)

“Lactate is a very important indicator of how you are doing during exercise,” Jia says. High-performance athletes monitor their lactate levels to evaluate their endurance capacity and their training program. It’s also an important marker of heart failure, shock or generalized infection.

But up to now, measuring lactate required drawing blood and analyzing it in a laboratory. Last year Jia and her UCSD colleagues reported a new way to measure lactate levels by analyzing sweat.

They devised a lactate sensor that could be printed onto a flexible plastic strip — the same process used in printing T-shirts. The strip can be worn like a bandage, collecting data that can be streamed to a mobile device –- and voila, continuous monitoring of lactate in sweat during exercise, something not possible before.

The new “biobattery” takes the approach a step farther, from collecting data through sweat to harvesting energy.

Josh Windmiller, one of the researchers, says the work shows that sweat deserves more respect.

“Sweat has gotten a bum reputation,” Windmiller said in a recent online interview. “It makes us uncomfortable, makes us smell…Sweat has been largely neglected, not thought of as a worthwhile physiological fluid.”

He’s founded a company called Electrozyme to develop wearable sweat monitors. It’s betting that fitness buffs will pay for a device — maybe someday a sweat-powered device — that gives them a minute-by-minute read-out of their metabolism.

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