Abstract
The body naturally and continuously secretes sweat for thermoregulation during sedentary and routine activities at rates that can reflect underlying health conditions, including nerve damage, autonomic and metabolic disorders, and chronic stress. However, low secretion rates and evaporation pose challenges for collecting resting thermoregulatory sweat for non-invasive analysis of body physiology. Here we present wearable patches for continuous sweat monitoring at rest, using microfluidics to combat evaporation and enable selective monitoring of secretion rate. We integrate hydrophilic fillers for rapid sweat uptake into the sensing channel, reducing required sweat accumulation time towards real-time measurement. Along with sweat rate sensors, we integrate electrochemical sensors for pH, Cl−, and levodopa monitoring. We demonstrate patch functionality for dynamic sweat analysis related to routine activities, stress events, hypoglycemia-induced sweating, and Parkinson’s disease. By enabling sweat analysis compatible with sedentary, routine, and daily activities, these patches enable continuous, autonomous monitoring of body physiology at rest.
Highlights
The body naturally and continuously secretes sweat for thermoregulation during sedentary and routine activities at rates that can reflect underlying health conditions, including nerve damage, autonomic and metabolic disorders, and chronic stress
At-rest thermoregulatory sweat is secreted at much lower rates than during exercise—as low as a few nL min−1 cm−2 compared to higher exercise rates of 100’s of nL min−1 cm−2—making it challenging to collect and analyze[1]
Resting sweat is uniquely poised to give insight into these conditions by ensuring that endogenous sweating rates associated with stress, injury, or illness are not overwhelmed or confounded by the vastly higher rates associated with exercise or other external sweat triggers
Summary
The body naturally and continuously secretes sweat for thermoregulation during sedentary and routine activities at rates that can reflect underlying health conditions, including nerve damage, autonomic and metabolic disorders, and chronic stress. Accessing resting sweat remains an outstanding challenge, as low secretion rates and rapid evaporation limit the amount of biofluid volume available to be collected in a sensor for analysis For this reason, most wearable sweat sensors have focused on exercise, thermal, or chemically stimulated sweat produced at rates of 10’s or 100’s of nL min−1 cm−2 or higher[10,11,12,13,14,15,16,17,18,19,20,21,22,23]. Along with the electrical sensor for sweat rate monitoring, we integrate electrochemical sensors for pH, Cl−, and levodopa detection inside the microchannel for continuous analysis of resting sweat rate and compositions These analytes are chosen to demonstrate the patch’s capabilities for ion and enzymatic sensing, and further because of the potential significance of these markers for indicating physiological state. It can advance sweat investigations beyond what current wearable sweat sensors can provide by promoting a fundamental understanding of at-rest sweat secretion and its relation to diverse health conditions
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