0815ctt sweaty tattoo lo res

[Image above] Could sweat provide the power for a new type of biobattery? Credit: Breno Peck; Flickr CC BY-NC-SA 2.0

Tattoos are everywhere.

According to a poll conducted a couple of years ago, 21 percent of American adults have at least one tattoo, with stats rising above 30 percent in young-ish adults (30 percent of 25–29-year-olds, and a whopping 38 percent of 30–39-year-olds). Check out this nifty infographic for some more tattoo stats.

I have to imagine that those numbers are even higher today—I personally know very few peers who don’t have any tattoos whatsoever. But despite the rise in numbers, tattoos are nothing new. In fact, the art is really old—thousands of years old.

Thanks to immunology, we now know that the science of tattoos is surprisingly simple—a needle injects ink under the skin (into the dermis, which lies beneath the outer epidermal layer), and the immune system reacts by sending white blood cells to take care of the damage. The ink particles are too big to be engulfed by the cells, so the ink stays there. Like forever.

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Credit: Deanna Wardin; Flickr CC BY-NC-ND 2.0

Conversely, the tattoos of science are an equally fascinating topic. Lots of scientists have immortalized their life’s work in ink form (like that DNA-, molecule-, and astonomy-laden number over there to the right). Science writer Carl Zimmer has compiled a large number of these on his Discover blog, in an online Science Tattoo Emporium. His fascination also inspired a printed book on the topic, Science Ink. (It’s sitting on my own coffee table at home, and I highly recommend it!)

But what if a tattoo could do more than look pretty, tell a story, or represent something worth representing?

Jessica has previously reported about the potential of stretchy pants to power devices of the future. And I’ve reported on organ-affixed devices that can harvest energy from the body’s natural rhythms. In fact, batteries are an all-around popular topic at the ACerS headquarters. 

And now, new research presented at the recent 248th National Meeting & Exposition of the American Chemical Society in San Francisco, Calif., shows that it’s possible to combine sensors embedded in tattoos (albeit temporary ones) with power generators.

These simple and cheap biobatteries make use of bodily fluids to gain their power. And this time, urine is not in, but—perhaps equally undesirable—sweat is.

Watch this video to learn more about this sweat new tech.

Credit: American Chemical Society; YouTube

The biobattery runs on lactate, a substance found in sweat that is a by-product of glycolysis. When in heavy use, such as during intense exercise, muscle cells activate glycolysis to extract energy from glucose molecules, creating lactate, or lactic acid—responsible for the burn in “feel the burn.”

A research team from the University of California San Diego came up with a little lactate sensor that they could print on temporary tattoo paper. Prior to this development, the only way to measure lactate was with a blood test, a invasive and inconvenient process amidst exercise.

“The sensor contained an enzyme that strips electrons from lactate, generating a weak electrical current,” according to an American Chemical Society press release. “Batteries produce energy by passing current, in the form of electrons, from an anode to a cathode. In this case, the anode contained the enzyme that removes electrons from lactate, and the cathode contained a molecule that accepts the electrons.”

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Credit: Joe Wang; ACS

But in the researchers’ tests so far, less-fit individuals produced far more power than regular exercisers, probably because glycolysis set in sooner when these out-of-shape individuals became fatigued rather early on, generating more power overall.

“The current produced is not that high, but we are working on enhancing it so that eventually we could power some small electronic devices,” postdoctoral researcher Wenzhao Jia says. “Right now, we can get a maximum of 70 μW per cm2 [of skin], but our electrodes are only 2 by 3 mm in size and generate about 4 μW—a bit small to generate enough power to run a watch, for example, which requires at least 10 μW. 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.”

Eventually, the little skin stickers could provide enough energy to power a host of wearables, and hopefully someday, supply your smartphone with a little extra juice to get through each sweat session.

The research is published in Angewandte Chemie and is titled “Epidermal biofuel cells: Energy harvesting from human perspiration” (DOI: 10.1002/ange.201302922).