A Noninvasive Wearable Device for Real-Time Monitoring of Secretion Sweat Pressure by Digital Display

Abstract

Sweat-based wearable devices have attracted increasing attention by providing abundant physiological information and continuous measurement through noninvasive healthcare monitoring. Sweat pressure generated via sweat glands to the skin surface associated with osmotic effects may help to elucidate such parameters as physiological conditions and psychological factors. This study introduces a wearable device for measuring secretion sweat pressure through noninvasive, continuous monitoring. Secretion pressure is detected by a microfluidic chip that shows the resistance variance from a paired electrode pattern and transfers digital signals to a smartphone for real-time display. A human study demonstrates this measurement with different exercise activities, showing the pressure ranges from 1.3 to 2.5 kPa. This device is user-friendly and applicable to exercise training and personal health care. The convenience and easy-to-wear characteristics of this device may establish a foundation for future research investigating sweat physiology and personal health care.

Keywords: Biomedical Engineering; Electronic Engineering; Electronic Materials; Sensor.

Graphical abstract

Figure 1

Schematics of the Wearable Secretion Pressure Device for Human Sweat Monitoring (A) The wearable device is located on the forehead area for sweat detection and fastened by a headband. (B) Photographic image of the easy-to-carry system and the replaceable microfluidic chip. The scale bar represents 10 mm for the insert. (C) 3D rendered image of the wearable device that measures the sweating pressure by microfluidic chip and sends the data to a smartphone via Bluetooth. (D) Circuit and basic operation diagram showing the signal transduction, processing and wireless transmission from the sensor to user interface. (E) Schematic diagram of the microfluidic chip, from the bottom layer in contact with the skin interface to the top layer.

Figure 2

Characterization of the Pressure Sensing Microfluidic Chips (A) The schematic of secretion pressure measurement of the microfluidic chip. (B) Response of the pressure value in the microchannel location. (C) Shows the simplified circuit diagram in microfluidic chip. (D) Flow monitoring for different numbers of electrode pairs. The scale bar represents 5 mm for the insert. (E) Illustrates the pressure monitoring system through flow positioned with longitudinally partnered electrode pairs. (F) The plot showing the resistance value measured through each electrode pair. (G) Different applied signal through G impedance variance with different input applied. (H) Impedance stability with bipolar signal applied.

Figure 3

Characterization of the Secretion Pressure Sensing System (A) Representative responses of three different ionic concentrations in flow detection. (B) Resistance variance in different electrode pairs in varied pH value artificial sweat. (C) Plot showing the resistance gradient trend depends on the thermal condition.

Figure 4

In Situ Measurements of Pressure Sensing Wearable Device During Different Exercise Processes Measured pressures from three different conditions (jogging, badminton and spinning bike). The thermal condition, resistance value and the adapted pressure result are shown in the real-time display.

Figure 5

Status and the Detection Results of in Situ Trials The images present the different exercise situations with (A) (jogging), (B) (badminton), and (C) (spinning bike). (D) shows the plot of average sweat pressure values during different exercises. (E) presents the maximum value of the secretion pressure in different exercises. (F) Infrared imaging of the jogging trail. (G) Close-up infrared image of the before and after exercise process on the forehead area.