A Stretchable Strain-Insensitive Temperature Sensor Based on Free-Standing Elastomeric Composite Fibers for On-Body Monitoring of Skin Temperature

Abstract

To realize the potential applications of stretchable sensors in the field of wearable health monitoring, it is essential to develop a stable sensing device with robust electrical and mechanical properties in the present of varying external conditions. Herein, we demonstrate a stretchable temperature sensor with the elimination of strain-induced interference via geometric engineering of the free-standing stretchable fibers (FSSFs) of reduced graphene oxide/ polyurethane composite. The FSSFs were formed in serpentine structures and enabled the implementation of a strain-insensitive stretchable temperature sensor. On the basis of the controlled reduction time of graphene oxide, we can modulate the response and thermal index of the device. These results are attributed to the variation in the density of oxygen-containing functional groups in the FSSFs, which affect the hopping charge transport and thermal generation of excess carriers. The FSSF temperature sensor yields increased responsivity (0.8%/°C), stretchability (90%), sensing resolution (0.1 °C), and stability in response to applied stretching (±0.37 °C for strains ranging from 0 to 50%). When the sensor is sewn onto a stretchable bandage and attached to the human body, it can detect the temperature changes of the human skin during different body motions in a continuous and stable manner.

Stretchable and Temperature‐Sensitive Polymer Optical Fibers for Wearable Health Monitoring

“…The sensor was reproducible with the cycling temperature changes, indicating reliable and stable performances in repeated measurements. The response and recovery time of the sensor were about 4.5 and 12.5 s, respectively, calculated with an exponential fitting model (Figure f) . To test the long‐term stability, the UCNPs‐SPOFs sensor was kept at a constant temperature of 30 °C and the emission spectra were recorded for 4 days ( Figure a).…”

“…To meet the requirements of these applications, wearable sensors are required to be flexible, stretchable, and biocompatible so that they can stretch, bend, and twist like skin in long‐term wearing. As such, there has been considerable effort in developing various stretchable materials and structures to achieve a range of wearable devices for monitoring temperature, strain, pressure, and so on.…”

Controlling Long‐Distance Photoactuation with Protein Additives

“…The resistance of the PTL/rGO hybrid coatings shows a negative temperature coefficient behavior (Figure S9, Supporting Information), which indicated that conductivity modulation of the rGO nanosheets with temperature changes is a dominant mechanism rather than conductivity modulation induced by the thermal expansion of the protein matrix. [ 49 ] The high‐conductivity rGO nanosheets enclosed by the hygroscopic protein aggregation network provide a sensitive platform to sense a series of stimuli, typically including moisture and related human breathing monitoring (Figures S10 and S11, Supporting Information), and strain/pressure and related Morse code information transmission (Figure S12, Supporting Information). Unlike pristine rGO, generally having poor biocompatibility, [ 50 ] the protein component endowed the PTL/rGO hybrid coating with good biocompatibility, so that the adhesion and proliferation of HMEC‐1 endothelial cells, a commonly used cell line, on the hybrid coating were much better than those on the pristine rGO film (Figure 3e).…”

Fabrication and Patterning Methods of Flexible Sensors Using Carbon Nanomaterials on Polymers

“…They can be sewn into regular fabrics to measure the temperature in different parts of the body or attached to a bandage (Figure h). Through geometric engineering, it is possible to minimize the interference of strain on the temperature response …”

“…Flexible sensors are especially suited for novel applications in healthcare, which are represented by noninvasive, measurement and real‐time monitoring of biophysical and biochemical signals from the human body, such as wrist pulse monitoring, strain measurement, humidity measurement, vibration detection, touch and pressure measurement, electrochemical detection, body temperature measurement, and many others. Table shows the flexible sensors, materials used, their performance, and applications.…”