Printed Wearable Sweat Rate Sensor for Continuous <i>In Situ</i> Perspiration Measurement

Sweat rate measures key physiological states such as hydration levels and heat tolerance. Incorporating wearable technology with sweat rate sensors allows individuals to conveniently monitor their health, optimize workouts, and enhance occupational safety. However, challenges persist in such integration techniques, including intricate manufacturing, non-linear responses to changes in sweat rates, and errors from the intermediate measurement of the distance sweat travels in the sensor. To address these issues, we present a comprehensive wearable platform that includes a fully printed, flexible sensor patch, readout electronics, and a mobile app for continuous, real-time monitoring of sweat rate. Utilizing direct 3D printing and scalable microfluidic fabrication, we produced a sensor patch measuring 700 <i>mm</i> ² and weighing 380 <i>mg</i>. The microfluidic channels are 850 <i>μm</i> wide, and 164 <i>μm</i> thick with serpentine electrodes measure sweat rate using capacitance. Our custom readout electronics capture these changes in capacitance to accurately measure sweat rate, achieving a sensitivity of 0.01 <i>μLmin</i> ^-1. We validated the sensor's performance against analytical models, simulations, and on-body trials with commercial sensors. This cost-effective, flexible, and fully integrated sweat-sensing solution has significant potential in precision health.