Monitoring Body Fluids in Textiles: Combining Impedance and Thermal Principles in a Printed, Wearable, and Washable Sensor

Abstract

This work explores the feasibility of coupling two different techniques, the impedance and the transient plane source (TPS) principle, to quantify the moisture content and its compositional parameters simultaneously. The sensor is realized directly on textiles with the use of printing and coating technology. Impedance measurements use the fluid's electrical properties, while the TPS measurements are based on the thermal effusivity of the liquid. Impedance and TPS measurements show equal competency in measuring the fluid volume with a lowest measurable quantity of 0.5 μL, enabling ultralow volume passive measurements for sweat analysis. Both sensor principles were tested by monitoring the drying of a wet cloth and the measurements show perfect repeatability and accuracy. Nevertheless, when the biofluid property changes, the TPS sensor does not reflect this information on its readings, whereas, on the other hand, impedance can provide information on compositional changes. However, since the volume of the fluid changes simultaneously, one cannot differentiate between a volume change and a compositional change from impedance measurements alone. Therefore, we show in this work that we can apply impedance to measure the compositional properties; meanwhile, the TPS measurements accurately carry out volume measurements irrespective of the interferences from its compositional variations. To prove this, both of these techniques are applied for the quantification and composition monitoring of sweat, showing the capability to measure moisture content and compositional parameters simultaneously. TPS measurements can also be an indicator of the local temperature of the medium confined by the sensor, and it does not influence the fluid parameters. Compiling both impedance and thermal sensors in a single platform triggers smart wearable prospects of metering the liquid volume and simultaneously analyzing other compositional changes and body temperature. Finally, the repeatability and stability of the sensor readings and the washability of the device are tested. This device could be a potential sensing tool in real-life applications, such as wound monitoring and sweat analysis, and could be a promising addition toward future smart wearable sensors.

Textile-Based Sensors for Biosignal Detection and Monitoring

“…Besides colorimetric sensors which are often applied in sweat analysis [131][132][133][134][135], there are also other types of sensors based on measuring the electrical properties of specifically functionalized conductive fibers, yarns or textile fabrics, which are changed upon contact of the functionalized sensor with a defined molecule, etc. [136][137][138][139][140].…”

Recent Advances in Multidimensional (1D, 2D, and 3D) Composite Sensors Derived from MXene: Synthesis, Structure, Application, and Perspective

“…On the present overall view, the key issue focuses on how to realize ideal sensors compatible with high sensitivity, wide detection range, ultralow response time, ultralow detection limitation, superb linearity, and cyclic stability. [ 51–60 ]…”

“…On the present overall view, the key issue focuses on how to realize ideal sensors compatible with high sensitivity, wide detection range, ultralow response time, ultralow detection limitation, superb linearity, and cyclic stability. [51][52][53][54][55][56][57][58][59][60] What is noteworthy is that conductive materials interacting with other substances have been considered as an extremely efficient strategy to realize high sensing performance, being able to give out fast response reacting to outer tiny changes. Currently, aiming to endow sensors superb sensitivity and wide sensing range, flexible substrates for sensors commonly choose polydimethylsiloxane (PDMS), hydrogenated styrene-butadiene block copolymer (SEBS), and silicone rubber and other high elastic polymer materials.…”

Influence of design and material characteristics on 3D printed flow-cells for heat transfer-based analytical devices

“…The wire is heated periodically with an alternating current and thereby minimises parasitic heat loss that was inherent to previous thermal-resistance biosensors. An alternative option to minimise sample volumes of thermal analysis includes the use of transient plane source technology to measure the thermal conductivity of materials [ 15 ], which has been integrated into wearable sensors to measure the moisture content [ 16 ]. Furthermore, it is possible to replace thermocouples with thermistors, which exhibit higher sensitivity in specific temperature ranges and can be miniaturised [ 17 ].…”