Ultrathin and Highly Tough Hydrogel Films for Multifunctional Strain Sensors

Abstract

With good flexibility and biocompatibility, hydrogel-based sensors have been widely used in human motion detection, artificial intelligence, human–machine interface, and other fields. Previous research on hydrogel-based sensors has focused on improving the mechanical properties and signal transmission sensitivity. With the development of human smart devices, there is an increasing demand for hydrogel sensor comfort and more application functions, such as ultrathin structures and recognition functions for contact surfaces, which are realized with higher requirements for the thickness, flexibility, friction resistance, and biocompatibility of hydrogels. Inspired by the ultrathin and flexible characteristics of human organ biofilms, we constructed conductive hydrogel films by using the flim-casting and glycerol–H2O secondary hydration methods. This ultrathin structure enables the hydrogel films to have a high elongation at break of 523.3%, a stress of 3.5 MPa, and a good friction resistance. Combined with the excellent sensing properties (gauge factor = 2.1 and a response time of 200 ms), the hydrogel film-based sensor can not only record human motion signals but also recognize the surface texture and roughness of objects, such as glass, brushes, wood, and sandpaper with mesh sizes of 80, 50, and 24, accurately. In addition, this hydrogel film has a series of excellent properties such as UV shielding, antiswelling ability, and good biocompatibility. This research provides a novel way for the development of emerging soft-material smart devices, such as hydrogel-based electronic skin and soft robots.

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

“…Furthermore, the PAC hydrogel sensor is capable of detecting finger bending at different amplitudes at −20 °C (Figure d), attributed to its good flexibility and conductivity under cold conditions. Compared to previously reported skin-like sensors, − the PAC@200%-V hydrogel sensor shows obvious advantages in terms of ultrahigh stretchability, high transparency, and stable frost resistance. In addition, as a strain sensor, the present hydrogel sensor shows a wide sensing strain, high detection limit, and prominent strain responsiveness, demonstrating its great potential in wearable electronic skins.…”

Advances in ultrasound-responsive hydrogels for biomedical applications

“…Hydrogels, formed by physical or chemical cross-linking of hydrophilic polymers, are a class of materials with a threedimensional network structure and high content of water. 1 Due to the characteristics of smooth surface, elasticity, great water absorption and retention, and the ability to mimic the extracellular matrix, hydrogels have wide application potential in biomedical fields, such as tissue engineering, [2][3][4][5][6] wound dressings, [7][8][9][10][11] biological sensors, [12][13][14][15][16] drug delivery, [17][18][19][20][21][22][23][24][25] medical imaging, [26][27][28][29][30] etc. Initial research studies focused on the basic physicochemical properties of hydrogels, such as swelling/ swelling kinetics and equilibrium, solute diffusion, volume phase transformation and sliding friction, and mainly explored the applications of hydrogels in ophthalmology.…”

A Chewing Gum Residue‐Based Gel with Superior Mechanical Properties and Self‐Healability for Flexible Wearable Sensor

“…[13][14][15] Up to now, various materials, especially elastic gel, have been emerged to evaluate human motion. [16][17][18] Generally, the gel combined with metal, organic carbon, and nanophase materials can be fabricated as strain sensors. [19][20][21][22] Nonetheless, the method of compounding may reduce the tensile properties of the gel and also causes compatibility issues.…”