Flexible aerosol-jet-printed sweat rate sensors with SEBS-based microfluidic channels for enhanced accuracy and bending stability

Flexible sweat sensors offer a promising avenue for non-invasive and continuous monitoring of sweat loss, providing useful information about human physiological status. However, existing sweat analysis methods face challenges related to body-device interfacing, measurement accuracy, reliability, and fabrication constraints. In this study, we present a flexible wearable sensor for sweat rate monitoring, fabricated by integrating flexible aerosol-jet printed (AJP) silver electrodes with a soft microfluidic channel. The device operates in an electroquasistatic, field-coupled regime with electrodes insulated from the electrolyte. The layout of a serpentine channel alternately crossing two parallel electrodes produces discrete admittance increments as sweat progressively fills the channel, and the step magnitude varies with electrolyte concentration due to differences in conductivity. The sensor’s linearity in measuring flow rate is found to be directly correlated with the material’s hydrophobicity, with the Flexdym-based device exhibiting the highest response consistency (R2 ≈ 0.98). Under mechanical bending tests designed to simulate skin flexion, the Flexdym sensor demonstrated exceptional signal stability, whereas sensors fabricated from other materials (such as PDMS) showed significant deviation due to channel deformation.