Skin Patch Mines Sweat for Performance-Enhancing Data

The device measures electrolytes and hydration and could someday replace blood samples at the doctor's office.

Epifluidic system that includes multiple colorimetric assays for analyzing sweat composition and sweat rate in a time-sequential manner | Jungil Choi, Northwestern University
Epifluidic system that includes multiple colorimetric assays for analyzing sweat composition and sweat rate in a time-sequential manner | Jungil Choi, Northwestern University

Next time you're finishing a workout, don't just towel off that sweat. Turns out there's a lot of good data in there.

Researchers with Northwestern University have announced details on a disposable sweat analysis device that can track electrolytes, hydration, and other biometric information from simple perspiration. The first iterations of the device are aimed at helping athletes stay hydrated, but future applications of the system could eventually help medical patients or even replace those finger pricks and blood draws that make doctor visits so much fun.

The Northwestern team is currently collaborating with partners including Gatorade, the Seattle Mariners, and the US Air Force, among others, to bring the wearable sweat analytics system to market.

The device, which requires no batteries or electronics, is basically a thin piece of silicone material that adheres to the skin like a Band Aid, said Northwestern professor John A. Rogers, whose lab has been developing the technology for several years.

“On the bottom of the device we have small inlet openings that allow sweat emerging from the surface of the skin to enter a collection of very tiny channels and small scale reservoirs,” Rogers told Seeker.

Epifluidic device measures sweat rate during swimming | Jonathan T. Reeder, Northwestern University

From there, the device collects and measures the captured perspiration using a collection of food colors and chemical reagents, which in turn trigger visual cues on the surface of the device. When the sweat levels hit certain thresholds, the chemical agents change the color of the fluids.

“The device is carefully calibrated so that, even though you're only measuring a small patch of skin, the device automatically converts that number into a full-body sweat loss number,” Rogers said. “So you can essentially track how much sweat loss you experience at any given time during an exercise or athletic event.”

In addition to displaying the basic amount of sweat loss, the system also generates color-coded readings triggered by specific biomarkers in the fluid.

“These other inlets that transport sweat into little circular reservoirs that contain the chemical reagents,” Rogers said. “They change color in relation to the proportion of a given biomarker — glucose, lactate, electrolyte concentration, and PH balance.”

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Wearers can simply look at the displayed information, which corresponds to etchings and color indicators on the surface of the patch. For example, if your electrolyte levels are dropping too low, you might see a red coloration appear in a particular marker. If you've got a smart phone handy, you can mine even more data from your sweat.

“You can just eyeball it and tell if you've lost a lost of electrolytes, or not so much,” Rogers said. “If you want to get more quantitative, snap a picture with your smart phone. Software algorithms analyze the images and color, extract qualitative information, then convert that into text explanations.”

Details on the device were published February 16 in the journal Science Advances. The paper was co-authored with scientists at the Gatorade Sports Science Institute, which has been developing the technology along with the Northwestern lab.

“As you can imagine, Gatorade is rather interested in sweat,” Rogers said. “The academic aspects that's kind of my main job, but we're also interested in broader deployment.”

The researchers have also delivered a batch of the devices to the Seattle Mariners, who plan to use them to track player hydration during this year's spring training. Active duty airmen at the Wright-Patterson Air Force Base in Dayton, Ohio are also using the devices.

Rogers said that future applications of the device could extend into all sorts of areas.

“There are a lot of obvious and interesting applications in sports and fitness, but you know sweat is an interesting biofluid,” he said. “There is a lot of chemistry happening all the time. If we can establish regular correlations, than sweat becomes the new biofluid for clinical grade analysis.”

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Rogers said that the research team is already looking into specific medical applications.

“We have some efforts around kidney health, for example,” he said. “We can measure creatinine concentrations. Chloride turns out to be a biomarker for system fibrosis. For stroke patients, we can measure asymmetries from the right and left side of the body.”

The researchers also hope to bring the device directly to the consumer market, giving amateur athletes an opportunity to monitor their workouts via sweat output.

Rogers said the team is learning new things about sweat with every round of studies.

“Yeah, it's interesting,” he said. “It appears that once sweat glands activate, they work at a very constant rate. The amount of sweat coming out is in a very fixed and controlled way, we can quantify that for the first time.”

He added, “It's a space where there is going to be a lot of really interesting discoveries in the next few years.