(379h) Osmotic-Capillary Principles for Microfluidic Pumping and Fluid Management for Sweat Sensing Devices

Sweat is an essential biofluid for monitoring individuals’ health as it contains several key biomarkers. However, sampling sweat for analysis is still challenging as most of the commercially available sweat sensing devices are either invasive in nature or work only during active perspiration. These devices may not function under low-sweating conditions and may be incapable of sensing in sweat from sedentary subjects. We demonstrate a new principle for the design of flexible and wearable patches, which are capable of extracting sweat under both resting and actively perspiring conditions using osmotic pressure difference for pumping, and evaporation for liquid disposal.¹ The patch is composed of silicone, hosting polyacrylamide hydrogel patch, and paper microfluidic conduit with a site of evaporation at the end (evaporation pad). The hydrogel is equilibrated with glycerin, glucose, or NaCl solution to build up the desired osmotic strength to extract fluid from the skin.² We investigate the performance of the patch using a model biomarker (dye) solution. In-vitro testing with gelatin-based model skin platform revealed that both glucose and glycerin-infused gels facilitate high analyte accumulation on the evaporation pad, with glucose as osmolyte having the highest driving pressure. The cumulative dye collection also depends on the dimensions of the paper channel, hydrogel area and paper pore size. Human trials show the potential to extract sweat and analyze it for lactate under both resting and non-resting conditions within a period of two hours. We used lactate as a concept demonstrator, as sweat appears to be more informative medium for lactate quantification than blood. The ability to measure lactate enables monitoring metabolism and oxidative stress levels in athletes and military personnel. Our group is currently investigating how this sweat sampling concept can be integrated in continuously operating wearable devices using enzymatic electrochemical sensors³, and with microneedle patches for long-term interstitial fluid (ISF) sampling.

References:

1. Shay, T., Saha, T., Dickey, M.D., and Velev, O.D. (2020) Principles of long-term fluids handling in paper-based wearables with capillary–evaporative transport. Biomicrofluidics, 14 (3), 034112.

2. 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.

3. Yokus, M.A., Saha, T., Fang, J., Dickey, M.D., Velev, O.D., and Daniele, M.A. (2019) Towards Wearable Electrochemical Lactate Sensing using Osmotic-Capillary Microfluidic Pumping. 2019 IEEE SENSORS, 2019-Octob, 1–4.