Electrospinner: Electrospun Nanofbers-based wearable sensor: easy control of temperature management, health monitoring accompanies you!

Background

Flexible sensing devices have attracted extensive attention due to their high sensitivity, wide detection range, fast response and perfect fit to human skin. Most of the reported flexible sensors are prepared on polymer substrates, which hinder the breathability of the skin and cause discomfort when wearing. However, the practical application of textile-based sensors is also limited due to their inherent defects of hydrophilicity, high thickness and low elastic modulus. Nanofibers made by a simple electrospinning process have good wear resistance and comfort, ultra-thin, breathable, hydrophobic, high porosity and good surface functions, which can effectively replace the substrate of wearable sensors. Due to their ultra-thin and porous nature, they inevitably lead to poor thermal insulation ability, which weakens the comfort of wearing in cold conditions. Therefore, it is of great significance to develop wearable sensors with personal thermal management functions and human health monitoring functions.

Recently, Li Yang from Shandong University, Wang Peng from Jinan University and Professor Meng Chuizhou from Hebei University of Technology collaborated to publish a research result entitled "Natural Human Skin‑Inspired Wearable and Breathable Nanofiber‑based Sensors with Excellent Thermal Management Functionality" in Advanced Fiber Materials. This achievement uses electrospun nanofibers with good air permeability as the substrate and ion-rich porous gel as the electrolyte to obtain a flexible sensor with dual functions of pressure sensing and human body thermal management.

The main point of this paper

Inspired by natural human skin, this work developed a wearable, breathable nanofiber-based sensor that not only has thermal management functions of passive insulation and active Joule heating effect, but also has good sensing performance. The sensor consists of a carbon nanotube (CNT)/thermoplastic polyurethane (TPU) nanofiber electrode layer, a microporous ionic aerogel electrolyte intermediate layer, and a microstructured Ag/TPU nanofiber electrode layer, and exhibits excellent sensing performance with a sensitivity of 24.62 kPa-1, a response time of 50 ms, and a detection range of 120 kPa. Due to the overall porous structure and hydrophobicity of TPU, the sensor exhibits excellent breathability (62 mm/s) and waterproof properties (contact angle of 151.2°). In addition, the sensor is composed of CNT (upper layer) with high solar absorptivity (70%), aerogel (middle layer) with low thermal conductivity (0.063 W/(m·K)) for heat insulation, and Ag (bottom layer) with high infrared reflectivity (85%) facing the skin, showing good passive thermal insulation performance. Therefore, the surface temperature of the sensor is 16.8 ℃ higher than that of commercial cotton cloth. By applying current to the bottom resistor Ag electrode, the surface temperature of the sensor can be quickly increased by 58.8 ℃ within 2 minutes even in an extremely cold environment. It can be heated as needed and is expected to be used for health monitoring and hyperthermia.

Figure 1 shows the sandwich structure of the sensor, namely the upper structured CNT/TPU nanofiber electrode layer, the middle porous ion gel electrolyte layer, and the lower Ag/TPU nanofiber electrode layer. The flexibility of the nanofibers and porous electrolytes enables the sensing unit and array to bend and twist, laying the foundation for good adhesion of the sensor to the skin and high-precision signal monitoring.

The CNT electrode with high radiation absorption rate, the Ag/TPU nanofiber electrode with high infrared reflectivity, and the ion gel film with low thermal conductivity give the sensor thermal management function, as shown in Figure 2. The test results show that the thermal conductivity of the ion gel is as low as 0.032W/(m·K), which is close to the thermal conductivity of air, and can effectively prevent heat loss; the high solar absorption rate and low atmospheric window thermal emissivity have good radiation heating performance and can heat the sensor in cold weather; the Ag/TPU nanofiber electrode has a high infrared reflectivity (85%), which can effectively prevent heat loss caused by human radiation heat exchange.

In the cold winter, the Ag/TPU nanofiber electrode in the sensor has a good Joule heating effect and can be used as a heat source for the wearer to provide an appropriate temperature for normal physiological activities of the human body (Figure 3).

Thanks to the microstructure and supercapacitor sensing mechanism of the sensor, the sensor exhibits excellent sensing performance and can detect human limb movement and two-dimensional pressure distribution, as shown in Figure 4.

Electrospinning Nanofibers Article Source:

https://doi.org/10.1007/s42765-024-00464-y