Bio-Inspired Instant Underwater Adhesive Hydrogel Sensors

Abstract

Underwater adhesion plays an essential role in soft electronics for the underwater interface. Although hydrogel-based electronics are of great interest, because of their versatility, water molecules prevent hydrogels from adhering to substrates, thus bottlenecking further applications. Herein, inspired by the barnacle proteins, MXene/PHMP hydrogels with strong repeatable underwater adhesion are developed through the random copolymerization of 2-phenoxyethyl acrylate, 2-methoxyethyl acrylate, and N-(2-hydroxyethyl) acrylamide with the presence of MXene nanosheets. The hydrogels are mechanically tough (elastic modulus of 32 kPa, fracture stress of 0.11 MPa), and 2-phenoxyethyl acrylate (PEA) with aromatic groups endows the hydrogel with nonswelling property and prevents water molecules from invading the adhesive interface, rendering the hydrogels an outstanding adhesive behavior toward various substrates (including glass, iron, polyethylene terephthalate (PET), porcine). Besides, dynamic physical interactions allow for instant and repeatable underwater adhesion. Furthermore, the MXene/PHMP hydrogels exhibit a high conductivity (0.016 S/m), fast responsiveness, and superior sensitivity as a strain sensor (gauge factor = 7.17 at 200%–500% strain) and pressure sensor (0.63 kPa–1 at 0–70 kPa). The underwater applications of bionic hydrogel-based sensors have been demonstrated, such as human motion, pressure sensing, and holding objects. It is anticipated that the instant and repeatable underwater adhesive hydrogel-based sensors extend the underwater applications of hydrogel electronics.

Bio-Inspired Homogeneous Conductive Hydrogel with Flexibility and Adhesiveness for Information Transmission and Sign Language Recognition

“…In summary, the hydrogel exhibited excellent sensitivity throughout the whole stretching process, indicating that the hydrogel could be used as a flexible strain sensor for both fine amplitude motion and macroscopic deformation sensing. Given the sensing capability of the H-A-CP-3 hydrogel, the hydrogel strain sensor was compared with similar sensing materials previously reported in order to confirm the excellent characteristics in the field of flexible sign language interpreting devices. ,,,− Figure c illustrates the hydrogel in terms of its stretchability, adhesiveness, sensitivity, and responsiveness, exhibiting a skin-like mechanical performance and excellent sensing properties.…”

Self-healing liquid metal hydrogel for human–computer interaction and infrared camouflage

“…The GF value of LM hydrogel-1.0 is about 3.42 in the strain range of 0-500%, and the GF value reaches 7.21 after the strain exceeds 500%, as shown in Fig. 4c, which is superior to most of reported hydrogel sensors 30,41,[47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64][65][66] (Fig. 4f).…”

3D printed microstructured ultra-sensitive pressure sensors based on microgel-reinforced double network hydrogels for biomechanical applications

“…These results demonstrate that sharp structures are beneficial to the high sensitivity and low limit of detection since they enable a significant increase of contact area under low-pressure loading and exhibit stress concentration. Compared with cylindrical hydrogel, the pyramid microstructure improves the pressure sensitivity by a factor of 50; such a high sensitivity is superior to most existing pressure sensors based on tough hydrogels with a high Young's modulus [37][38][39][40][41][42][43][44][45][46][47] (Fig. 6(d) and Table S2, ESI †), which expands its stable sensing application under low load.…”