For those who hate needle pricks, a team of researchers at the University of California, Berkeley, are designing wearable skin sensors that can sense what is present in one’s sweat.
They anticipate that in the near future, tracking perspiration could avoid the need for more invasive procedures such as blood draws, and offer real-time updates on health issues such as fatigue or dehydration.
In a paper published recently in Science Advances, the researchers explain a new sensor design that can be quickly manufactured using a “roll-to-roll” processing method that prints the sensors onto a sheet of plastic similar to words on a newspaper.
They used the sensors to track the sweat rate, and the metabolites and electrolytes in sweat, from volunteers who were exercising and others who were going through chemically induced perspiration.
The goal of the project is not just to make the sensors but start to do many subject studies and see what sweat tells us—I always say ‘decoding’ sweat composition. For that we need sensors that are reliable, reproducible, and that we can fabricate to scale so that we can put multiple sensors in different spots of the body and put them on many subjects.
Ali Javey, Paper’s Senior Author and Professor of Electrical Engineering and Computer Science, UC Berkeley
Javey also serves as a faculty scientist at Lawrence Berkeley National Laboratory.
The new sensors have a spiraling microscopic tube (or microfluidic) that absorbs sweat from the skin. By monitoring how quickly the sweat moves through the microfluidic, the sensors can reveal how much a person is sweating, or their sweat rate.
The microfluidic is also equipped with chemical sensors that can sense concentrations of electrolytes like sodium and potassium, and metabolites such as glucose.
Javey and his team partnered with scientists at the VTT Technical Research Center of Finland to create a way for rapid manufacture of the sensor patches in a roll-to-roll processing method akin to screen-printing.
“Roll-to-roll processing enables high-volume production of disposable patches at low cost,” Jussi Hiltunen of VTT said. “Academic groups gain significant benefit from roll-to-roll technology when the number of test devices is not limiting the research. Additionally, up-scaled fabrication demonstrates the potential to apply the sweat-sensing concept in practical applications.”
To better comprehend what sweat can reveal about the real-time health of the human body, the team first positioned the sweat sensors on various spots on volunteers’ bodies—including the underarm, forearm, forehead, and upper back—and measured their sweat rates and the potassium and sodium levels in their sweat while they rode on an exercise bike.
They learned that local sweat rate could specify the body’s total liquid loss during exercise, meaning that monitoring sweat rate might be a way to give athletes a heads up when they may be exercising too hard.
Traditionally what people have done is they would collect sweat from the body for a certain amount of time and then analyze it. So you couldn’t really see the dynamic changes very well with good resolution. Using these wearable devices we can now continuously collect data from different parts of the body, for example, to understand how the local sweat loss can estimate whole-body fluid loss.
Hnin Yin Yin Nyein, Study Lead Author and Graduate Student in Materials Science and Engineering, UC Berkeley
They also used the sensors to compare blood glucose levels and sweat glucose levels in healthy and diabetic patients, discovering that a single sweat glucose measurement cannot essentially specify a person’s blood glucose level.
There’s been a lot of hope that non-invasive sweat tests could replace blood-based measurements for diagnosing and monitoring diabetes, but we’ve shown that there isn’t a simple, universal correlation between sweat and blood glucose levels. This is important for the community to know, so that going forward we focus on investigating individualized or multi-parameter correlations.
Mallika Bariya, Study Lead Author and Graduate Student in Materials Science and Engineering, UC Berkeley
The paper’s co-authors include Liisa Kivimaki, Sanna Uusitalo, Elina Jansson, Tuomas Happonen, and Christina Liedert of the VTT Technical Research Center of Finland; and Tiffany Sun Liaw, Christine Heera Ahn, John A. Hangasky, Jianqi Zhao, Yuanjing Lin, Minghan Chao, Yingbo Zhao, and Li-Chia Tai of UC Berkeley.
The NSF Nanomanufacturing Systems for Mobile Computing and Mobile Energy Technologies (NASCENT), the Berkeley Sensor and Actuator Center (BSAC), and the Bakar Fellowship supported this research.
Ali Javey describes an earlier version of his lab’s wearable sweat sensor in this video from 2016. (Video credit: UC Berkeley video by Roxanne Makasdjian and Stephen McNally)