Wearable sweat sensing device determining sweat rate per gland.

Patient monitoring is an established method in healthcare, guarding the health status of patients by recording vital signs. The inclusion of sweat sensing in patient monitoring provides prominent opportunities since sweat contains physiologically and metabolically rich information about the patient. Sweat can be non-obtrusively obtained and could therefore enable continuous biomarker measurement. However, for several biomarkers, the concentration not only depends on a disorder but also on the sweat rate per gland and this is a major challenge for the clinical use of sweat sensing. In this work, we developed a sensing device framework, based on an innovative statistical analysis, capable of determining the average sweat rate per gland without a-priori knowledge of the number of glands. The statistical analysis can be adapted for various sweat rates and sweat gland densities. For a gland density of 0.1 glands$.\mathrm{mm}^{-2}$, a first prototype based on an open microfluidic structure has been fabricated. The prototype sweat collection device is fabricated by femtosecond laser machining of fused silica substrates, followed by a wet etching step. The prototype is tested by different flow rates of DI water that are supplied to it. The experiment shows that the design is capable of collecting and transporting low volumes of sweat as excreted by persons in a sedentary state.