Stretchable and Thermally Responsive Semi‐Interpenetrating Nanocomposite Hydrogel for Wearable Strain Sensors and Thermal Switch

Abstract

Wearable electronics based on stimuli-responsive hydrogels are promising in various applications such as soft robots, artificial skin, and health monitoring. Herein, a novel wearable and strain/thermal dual sensor is developed utilizing a nanocomposite hydrogel, which is prepared by incorporating allyl mercaptan (ALM) functionalized Au nanoparticles (Au@ALM) into poly(N-isopropylacrylamide-co-hydroxyethylmethacrylate)/poly(Nisopropylacrylamide) (P(NIPAM-co-HEMA)/PNIPAM) semi-interpenetrating hydrogel network. PNIPAM acts as the thermally responsive component. Semi-interpenetrating network and Au nanoparticles are introduced to enhance the mechanical properties of the hydrogel. Au nanoparticles also work as the electrically conductive component. Strain sensor and thermoreceptor are realized by using the mechanical stretchability and strainor temperature-dependent conductivity. The strain sensor exhibited excellent stability and repeatability in the strain range of 0-150%. Remarkably, the thermal sensor made of this hydrogel can monitor the ambient temperature from 0 to 70 °C. Therefore, an intelligent thermal switch is designed that can effectively protect electronic components by disconnecting high-temperature circuits. The nanocomposite hydrogel holds great potential in smart devices and flexible sensors.

Stretchable Semi-Interpenetrating Carboxymethyl Guar Gum-Based Composite Hydrogel for Moisture-Proof Wearable Strain Sensor

“…Compared with the CMGG/PAM hydrogel, the CMGG 1.5 / PAM-Au@PDA 5 hydrogel exhibited superior mechanical properties (strength: 1.00 MPa; Young's modulus: 199 kPa, and toughness: 2.89 MJ m −3 ) owing to the increased hydrogen bond interactions and π−π stacking in the CMGG 1.5 /PAM-Au@PDA 5 hydrogel. 53 However, compared with CMGG 1.5 / PAM-Au@PDA 3 hydrogel, the Young's modulus of CMGG 1.5 / PAM-Au@PDA 5 hydrogel decreased with the increase of Au@ PDA content, which is due to the density imbalance of hydrogen bonds between dopamine on AuNPs and PAM in the polymer network. 54 That is, the hydrogen bond interaction between PAM and excessive dopamine is insufficient, leading to the reduction of the density of the physical cross-linking network formed.…”

“…The tensile characteristics of hydrogels with various Au@PDA contents were also investigated as shown in Figure c,d. Compared with the CMGG/PAM hydrogel, the CMGG 1.5 /PAM-Au@PDA 5 hydrogel exhibited superior mechanical properties (strength: 1.00 MPa; Young’s modulus: 199 kPa, and toughness: 2.89 MJ m –3 ) owing to the increased hydrogen bond interactions and π–π stacking in the CMGG 1.5 /PAM-Au@PDA 5 hydrogel . However, compared with CMGG 1.5 /PAM-Au@PDA 3 hydrogel, the Young’s modulus of CMGG 1.5 /PAM-Au@PDA 5 hydrogel decreased with the increase of Au@PDA content, which is due to the density imbalance of hydrogen bonds between dopamine on AuNPs and PAM in the polymer network .…”

Recent advances in flexible and soft gel-based pressure sensors

“…It can be combined with peptides, proteins and other drugs, as well as grafted with natural polymers, to produce the desired properties for specific applications. Cai et al prepared a freezeresistant hydrogel by treating PVA and PEG functionalized with chitin nanocrystals in a dimethyl sulfoxide (DMSO) and water solvent through a freezing-thawing process [120] . The prepared hydrogel had high stretchability (435%) and mechanical strength (2.0 MPa).…”

“…(C) Schematic illustrating the fabrication process and composition of a PVA/PEG-g-ChNC conductive organohydrogel. Reproduced with permission [120] . Copyright 2022, Elsevier.…”

Transparent stretchable hydrogel sensors: materials, design and applications

“…Transparent hydrogel sensors are divided into wearable strain sensors, 52 pressure sensors, 53 temperature sensors, 54 humidity sensors 55 and gas sensors, 56 according to different applications (Fig. 1).…”