A skin patch that measures the wearer’s sweat to show how their body is responding to exercise has been developed by scientists at Northwestern University.
Designed for one-use only it analyses key biomarkers to help an athlete decide if any adjustments, such as drinking more water or replenishing electrolytes, need to be made.
“The intimate skin interface created by this wearable, skin-like microfluidic system enables new measurement capabilities not possible with the kinds of absorbent pads and sponges currently used in sweat collection,” said John A. Rogers, who led the multi-institution research team.
“Sweat is a rich, chemical broth containing a number of important chemical compounds with physiological health information. By expanding our previously developed ‘epidermal’ electronics platform to include a complex network of microfluidic channels and storage reservoirs, we now can perform biochemical analysis of this important biofluid.”
“The sweat analysis platform we developed will allow people to monitor their health on the spot without the need for a blood sampling and with integrated electronics that do not require a battery but still enable wireless connection to a smartphone,” said collaborator Yonggang Huang.
The device was tested on two different groups of athletes: one cycling indoors in a fitness centre under controlled conditions and the other participating in the El Tour de Tucson, a long-distance cycle race in arid and complex conditions. The researchers placed the device on the arms and backs of the athletes to capture sweat.
During exercise sweat enters four different small, circular compartments within the patch, which monitor pH and concentrations of glucose, chloride and lactate. These compartments then change colour according to the results.
When a smartphone is brought into proximity with the device (see video below), the wireless electronics trigger an app that captures a photo of the device and analyses the image to yield data on the biomarker concentrations.
“We chose these four biomarkers because they provide a characteristic profile that’s relevant for health status determination,” said Rogers, director of Northwestern’s Center for Bio-Integrated Electronics. “The device also can determine sweat rate and loss, and it can store samples for subsequent laboratory analysis, if necessary.”
In the group that cycled indoors, the researchers compared the new device’s biomarker readouts to conventional laboratory analysis of the same sweat and found the two sets of results agreed with each other.
With the long-distance cyclists, the researchers tested the durability of the device in the complex and unpredictable conditions of the desert. They found the devices to be robust: They stayed adhered to the athletes’ skin, did not leak and provided the quality information the researchers sought.
The sweat analysis device features a number of innovations:
- The device can capture, store and analyse sweat in situ in real time
- The device can quantitatively determine biomarker levels using colorimetric analysis
- A power source is not required to display the results; instead, a smartphone camera and app are used to read the biomarker change
Details of the versatile platform for sweat analysis were published on November 23 as the cover story by the journal Science Translational Medicine.