Aerosol Jet and 3D Printed Impedance-Based Wearable Sensors for Local Sweating Rate Monitoring

Sweat rate is a crucial indicator for assessing human hydration status, electrolyte balance, and metabolic health. Real-time and continuous monitoring of sweating rate is of great significance for physiological state evaluation. This study developed a fully printed microfluidic sweat sensing patch. The sensing component integrates micron-resolution aerosol inkjet printing and 3D printing technologies, using the sequence of printing the electrodes and then printing the channels. This approach ensures electrode integrity and good interfacial contact while achieving complex spiral channel structure. For signal acquisition and transmission, an impedance detection module and a Bluetooth module are integrated via Flexible Printed Circuit Board (FPCB) technology, enabling real-time detection and wireless data transmission. When sweat enters the channel and contacts the electrodes, a high-precision impedance chip measures changes in circuit admittance in real time, dynamically tracking and quantifying sweat accumulation to further calculate the sweat rate. The device was tested and validated on the human body surface under different exercise modes, demonstrating its capability for sensitive and continuous monitoring of sweat rate. We also used a pulse monitoring device, combined with heart rate data, to study the relationship between sweat flow and exercise intensity. The fully printed technology employed in this study provides a novel, low-cost, and easily customizable integrated solution for wearable sweat sensing.