A Wearable Microfluidic Sensing Patch for Dynamic Sweat Secretion Analysis

Abstract

Wearable sweat sensing is a rapidly rising research area driven by its promising potential in health, fitness, and diagnostic applications. Despite the growth in the field, major challenges in relation to sweat metrics remain to be addressed. These challenges include sweat rate monitoring for its complex relation with sweat compositions and sweat sampling for sweat dynamics studies. In this work, we present a flexible microfluidic sweat sensing patch that enhances real-time electrochemical sensing and sweat rate analysis via sweat sampling. The device contains a spiral-patterned microfluidic component that is embedded with ion-selective sensors and an electrical impedance-based sweat rate sensor on a flexible plastic substrate. The patch is enabled to autonomously perform sweat analysis by interfacing the sensing component with a printed circuit board that is capable of on-site signal conditioning, analysis, and transmission. Progressive sweat flow in the microfluidic device, governed by the pressure induced by the secreted sweat, enhances sweat sampling and electrochemical detection via a defined sweat collection chamber and a directed sweat route. The characteristic of the sweat rate sensor is validated through a theoretical simulation, and the precision and accuracy of the flow rate is verified with a commercial syringe pump and a Macroduct sweat collector. On-body simultaneous monitoring of ion (H, Na, K, Cl) concentration and sweat rate is also demonstrated for sensor functionality. This sweat sensing patch provides an integrated platform for a comprehensive sweat secretion analysis and facilitates physiological and clinical investigations by closely monitoring interrelated sweat parameters.

Multifunctional Skin‐Inspired Flexible Sensor Systems for Wearable Electronics

“…Various wearable platforms have been demonstrated, such as temporary tattoos, patches, or wrist‐bands . Among a variety of architectures for wearable sweat sensors, microfluidic‐based sweat systems are one of the most promising strategies owing to their shorter sweat sampling and filling times . Koh et al developed a stretchable microfluidic system with the capability to be intimately and robustly bonded to the skin surface ( Figure a–c) .…”

Advanced Wearable Microfluidic Sensors for Healthcare Monitoring

“…Electrochemical analysis methods are mainly categorized into amperometric sensors for metabolites (e.g., glucose and lactate) and potentiometric sensors for electrolytes (e.g., sodium and potassium ions), which enable the rapid, selective, precise, and label‐free detection of biofluids …”

“…Multiple electrolyte measurements can be implemented by incorporating more ISEs selectively for diverse electrolytes in microfluidic reservoirs. Hyein et al invented a wearable microfluidic patch for dynamic electrolyte monitoring, including Na + , K + , H + , and Cl − (Figure b) . Several groups demonstrated ion‐sensitive field‐effect transistors (ISFETs) based on the combination of FETs and ion‐sensitive membranes for electrolyte analysis of a liquid .…”

“…b) Illustration of microfluidic networks for sweat capture (left), and optical image of a sweat sensor attached to the skin surface (right). Reproduced with permission . Copyright 2018, American Chemical Society.…”

Application of Microfluidics in Wearable Devices

“…B) Optical images of microfluidic sweat patch and sweat compositions measurements. Reproduced with permission . Copyright 2018, American Chemical Society.…”