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Power from sweat

Brigitte OsterathAugust 15, 2014

At a meeting of the American Chemical Society, scientists presented a "biobattery" that measures how hard you exercise. Along the way, the tattoo patch produces electric current that could some day run a smart phone.

https://p.dw.com/p/1CumR
Jogger in Bonn Photo: DW/ Jaime Campoamor
Image: DW/J. Campoamor

Imagine you are jogging along and at the same time producing the power you need for your mp3 player - simply by sweating. This is what researchers at the University of California, San Diego have in mind when they talk about their "tattoo biobattery".

"We can harvest energy directly from the body in a non-invasive manner," lead scientist Joseph Wang said. "This is the first example of a bio-fuel cell that harvests from body fluids like sweat."

What your sweat can tell you

Originally, the researchers set out to develop something less sci-fi: a sensor to measure lactate in sweat continuously. Lactate is formed from glucose in the body. During hard exercise, the lactose level in tissue begins to rise, as it is formed faster than it can be removed.

bio-battery tattoo Photo: Joe Wang, ACS (American Chemical Society)
The sensor patch looks like a stick-on tattooImage: Joe Wang, ACS

That's why "lactate is a very important indicator of how you are doing during exercise," said Wenzhao Jia of the University of California, San Diego.

If the body produces too much lactate during workout, you might be asking too much of it.

Up to now, a doctor needs to draw blood from an athlete to measure the level of lactate in the body.

But the molecule is also found in sweat on the skin.

Wenzhao Jia's new sensor measures lactate in sweat produced during physical activity.

"So it can tell you […] to stop your intense workout," Jia said, adding that it would give a more comprehensive overview of your fitness level than modern devices could provide.

glucose meter
A glucose meter also uses enzymes to measure a molecule (glucose) in body fluid (blood)

Proteins at work

The sensor works in a similar way to a glucose analyzer for diabetics.

It contains an enzyme, a protein, which turns lactate into pyruvate, another molecule in the human metabolism.

During this process, two electrons are released. Electrons mean electric current. So if more lactate is present in the sweat, more electric current is generated. A device measures the current and translates it back into lactate levels.

"We fabricated this sensor on tattoo paper and it can be easily transferred to the human skin just like temporary tattoos," Jia said.

A skin-based power station

But it doesn't stop at measuring lactate.

According to the researchers, the current generated during lactate conversion could also power small electronic devices like heart rate monitors or even smart phones.

The sensors generate a maximum power of about 70 microWatts per square centimeter. As the sensors are very small, they will only provide 4 microWatts in total.

"To run something like a watch, you need more than 10 microWatts," Jia admits. " The current produced is not that high, but we are working on enhancing it."

She says they are working together with a start-up firm to turn the research into a device ready for the market.

Couchpotato
Less fit people produce more lactate when they get round to working out.Image: Fotolia/runzelkorn

Couch potatoes make more energy

Not all people will generate the same amount of power when wearing the bio-battery, the researchers explained at a press conference at a meeting of the American Chemical Society in San Francisco.

How much power someone generates depends on the lactate levels he or she produces - and that amount depends on his or her level of fitness.

"Usually, for a fit person the lactate level is lower compared to less fit persons," Jia said.

In their experiment, people who exercised less than once a week produced more power than those who were moderately fit, and much more than enthusiasts who worked out more than three times per week. The researchers say that this is probably because the less-fit people became fatigued sooner, causing glycolysis to kick in earlier, forming more lactate.

So very fit people would have to sweat much more while jogging to generate the same amount of power for their mp3 player than couch potatoes. The latter, though, will probably not go for a jog at all.