Zero-Powered, Non-Invasive, Long-Term Sweat Sampling By Biomimetic Osmotic Principles

Sweat is an important biofluid as it contains biomarkers similar to the ones found in blood. However, collecting information from sweat poses a challenge as most of the available sweat sensing devices are either invasive or work only under active perspiration. These devices may not function under low-sweating conditions and can lower the incentive to continuously monitor one’s health under normal conditions. We present and discuss a new flexible, wearable design prototype that can contribute towards non-invasive sweat withdrawal under low-sweating or resting conditions. The prototype utilizes the simultaneous action of osmosis for fluid pumping, capillary wicking for transport, and evaporation for liquid disposal. The prototype is comprised of silicone, a polyacrylamide hydrogel, and a paper microfluidic conduit. The hydrogel is equilibrated with glucose solution to build up the desired osmotic strength. The multicomponent hydrogel patch facilitated artificial perspiration and biomarker collection for ~ 10 hours under benchtop settings. The patch was also validated on-skin for sweat lactate estimation under different physiological conditions. The prototype showed visual variations in sweat lactate between alternating periods of rest and exercise, where exercise corresponded to a higher sweat lactate concentration. The measured sweat lactate concentration also remained consistently higher than the blood lactate concentration under all conditions, indicating that the source of lactate is mainly from the sweat glands of muscles. We are presently developing a continuous sweat lactate sensing platform on our paper-based device by including electrochemical sensors. We also intend to extend similar principles for long- and short-term extraction of interstitial fluid (ISF) pumping by microneedles. Implementation of such new principles for sweat fluid harvesting and management via a wearable prototype can deliver an improved version of conventional sweat sampling methods and contribute towards the advancement of next generation wearables.