The wearable device incorporates a bubble-trapping region in its microfluidic system. (Credit: Tokyo University of Science)

A new wearable sensor continuously monitors sweat lactate during exercise. The device incorporates a bubble-trapping region in its microfluidic system. The proposed technology can facilitate athlete training management and health monitoring.

The proposed wearable device consists of a relatively simple layered structure ― a conventional lactate oxidase sensor attached via double-sided tape to a microfluidic system made of a silicone polymer. When the person wearing the device begins to perspire, the sweat enters the microfluidic channels via four inlets and flows toward a reservoir near which the electrodes are located. Old sweat exits the system through an outlet as new sweat enters, and a small wireless transmitter reports the measured lactate levels.

The key innovation in the proposed design was the use of a larger-than-usual sweat reservoir. The researchers tested their sensor in a series of laboratory experiments. They verified that the bubble-trapping region worked as intended by injecting bubbles into the device while measuring lactate levels in artificial sweat.

In addition, the measurements were not affected by the sweat flow rate, and the response of the sensor remained stable for approximately two hours. Lastly, the researchers tested the device on a male volunteer who exercised on a stationary bike for almost an hour. The sensor showed a lactate concentration correlation ranging from 1 to 50 mM as well as a correlation between sweat and blood lactate levels.