(343e) A Wearable Patch for Sweat Lactate Analysis

Sweat lactate is an essential biomarker for monitoring anaerobic metabolism, oxidative stress levels, muscle health, and tissue hypoxia in individuals. Its concentration depends on the duration and the intensity of the physiological state (rest or exercise) that the body experiences. Most of the current sweat sensing devices measure sweat lactate for a short duration (~ minutes) and are incapable of delivering comprehensive data on lactate metabolism in the body. We address these issues with our non-invasive, zero-electric powered wearable sweat sampling patch¹, that can measure sweat lactate levels under rest, during medium intensity exercise, and post-exercising conditions upon directly interfacing with the skin. Our patch simultaneously uses osmosis, capillary wicking, and evaporation to deliver long-term sweat collection and lactate monitoring. Osmotic action is achieved through a hydrogel with a higher solute content than sweat, while wicking and evaporation occur in paper microfluidic channel. We use a glucose hydrogel, PBS hydrogel, and a silicone disk as the major pumping sources in the patch and test them under different physiological conditions. On body trials show that all three pumping materials can register lactate on paper for 2 hours. The glucose hydrogel withdraws sweat lactate majorly via osmosis during rest and post-exercise trials. Sampling of lactate via osmosis reduces upon exercising due to inflow of active sweat in the paper channel. The PBS hydrogel and silicone disk patches show traces of lactate on paper as an outcome of the natural sweat release by the body. We also measured blood lactate levels and found no correlation between blood and sweat lactate levels under all physiological conditions. Hence, sweat appears to be a more informative medium than blood for lactate. Overall, such simple, non-invasive patches for measuring sweat lactate levels can generate a wide variety of information about human health and contribute towards the advancement of next generation wearable health monitoring devices.

References:

1. Saha, T., Fang, J., Mukherjee, S., Dickey, M.D., and Velev, O.D. (2021) Wearable Osmotic-Capillary Patch for Prolonged Sweat Harvesting and Sensing. ACS Appl. Mater. Interfaces, 13 (7), 8071–8081.