Ultrastretchable, Antifreezing, and High-Performance Strain Sensor Based on a Muscle-Inspired Anisotropic Conductive Hydrogel for Human Motion Monitoring and Wireless Transmission

Abstract

Integrating structural anisotropy, excellent mechanical properties, and superior sensing capability into conductive hydrogels is of great importance to wearable flexible electronics yet challenging. Herein, inspired from the aligned structure of human muscle, we proposed a facile and universal method to construct an anisotropic hydrogel composed of polyacrylamide and sodium alginate by pre-stretching in a confined geometry and subsequent ionic cross-linking. The designed hydrogels showed extraordinary mechanical performances, such as ultrahigh stretchability, a comparable modulus to that of human tissues, and good toughness, ascribed to their anisotropically aligned polymer networks. Additionally, the hydrogel possessed anisotropic conductivity due to the anisotropy in ion transport channels. The hydrogel along the vertical direction was further cut and assembled into a flexible strain sensor, exhibiting a low detection limit (0.1%), wide strain range (1585%), rapid response (123 ms), distinct resilience, good stability, and repeatability, thereby being capable of monitoring and discriminating different human movements. In addition, the relatively high ionic conductivity and superior sensitivity enabled the anisotropic hydrogel sensor to be used for wireless human–machine interaction. More interestingly, the Ca2+-cross-linking strategy also endowed the hydrogel sensor with antifreezing ability, further broadening their working temperature. This work is expected to speed up the development of hydrogel sensors in the emerging wearable soft electronics.

Electron Conductive and Transparent Hydrogels for Recording Brain Neural Signals and Neuromodulation

“…Figure S16, Supporting Information, shows the comparison of HPM-1 with other transparent hydrogels for bioelectronics in the literature on conductivity and stretchability. [47][48][49][50][52][53][54][55] The HPM-1 exhibits superior performances in terms of conductivity and stretchability. To qualitatively demonstrate the conductive property, an HPM-1 sheet and column were used as conductors to link a power source and a LED.…”

“…The comparison of the HPM-1 sensor with other reported hydrogel strain sensors in terms of maximal strain and GF has been shown in Figure 3h. [42][43][44][45][46][47][48][49][50]54,55] The HPM-1 sensor exhibits a larger GF and broader strain range than these strain sensors. The excellent mechanical performance and conductivity enable the HPM-1 to be used as a wearable strain sensor for recording physiological signals.…”

Anisotropic and super-strong conductive hydrogels enabled by mechanical stretching combined with the Hofmeister effect

“…The Morse code can represent 26 English letters in different combinations of dots and dashes. 53 As shown in Fig. 7g–i, when the multifunctional sensor was attached to the index finger for evaluation, the dots and short lines can be represented by fast bending fingers and longer bending fingers.…”

High-Sensitivity Wearable Sensor Based On a MXene Nanochannel Self-Adhesive Hydrogel

“…1−3 At present, wearable sensors have the capability to sense different human physical and chemical signals, such as heart rate, 4 body temperature, 5,6 blood glucose, 7,8 and diverse motions of the human body. 9,10 The modern flexible sensors are mainly based on double network hydrogels 11,12 with various conductive materials (ionic, 13,14 polymers, 15,16 carbon fibers, 17,18 black carbon, 19,20 graphene, 21,22 carbon nanotubes, 23,24 and MXene 25 ) dispersed therein. However, in practice, these flexible sensors often possess some shortcomings, for example, low sensitivity, poor long-term reliability, loss of adhesion to skin, and low cold resistance.…”