Robust Conductive Hydrogels with Ultrafast Self-Recovery and Nearly Zero Response Hysteresis for Epidermal Sensors.

Xiuru Xu,Chubin He,Hao Wang,Zhengchun Peng,Feng Luo

doi:10.3390/nano11071854

Abstract

Robust conductive hydrogels are in great demand for the practical applications of smart soft robots, epidermal electronics, and human–machine interactions. We successfully prepared nanoparticles enhanced polyacrylamide/hydroxypropyl guar gum/acryloyl-grafted chitosan quaternary ammonium salt/calcium ions/SiO2 nanoparticles (PHC/Ca2+/SiO2 NPs) conductive hydrogels. Owing to the stable chemical and physical hybrid crosslinking networks and reversible non-covalent interactions, the PHC/Ca2+/SiO2 NPs conductive hydrogel showed good conductivity (~3.39 S/m), excellent toughness (6.71 MJ/m3), high stretchability (2256%), fast self-recovery (80% within 10 s, and 100% within 30 s), and good fatigue resistance. The maximum gauge factor as high as 66.99 was obtained, with a wide detectable strain range (from 0.25% to 500% strain), the fast response (25.00 ms) and recovery time (86.12 ms), excellent negligible response hysteresis, and good response stability. The applications of monitoring the human’s body movements were demonstrated, such as wrist bending and pulse tracking.

Highlights

Conductive hydrogels have shown great potential in wearable bioelectronic devices, human–machine interactions, health monitoring, flexible electronic skins, and medical bandages [1,2,3,4,5], owing to their softness, wetness, stretchability, biocompatibility, and wide tunable conductivity
Since the surface of the chitosan quaternary ammonium salt (CQAS) is rich in hydroxyl groups, functional groups can be grafted to the surface of the CQAS molecules
We further evaluated the influence of different SiO2 NPs contents on the mechanical properties of the PAAm-HPG/acryloylgrafted CQAS hydrogels (PHC)/Ca2+ /SiO2 NPs conductive hydrogels (Table 1)

Summary

Introduction

Conductive hydrogels have shown great potential in wearable bioelectronic devices, human–machine interactions, health monitoring, flexible electronic skins, and medical bandages [1,2,3,4,5], owing to their softness, wetness, stretchability, biocompatibility, and wide tunable conductivity. Li et al [9] reported a double network hydrogel from polyacrylamide (PAAm) and gelatin as frameworks. It showed 1.66 MPa tensile strength, 849% tensile strain, up to 1.5 S/m conductivity, and about 70% within 1 min self-recovery rate, but went along a large hysteresis. Wei et al [10] utilized a hydrogel network by building weak non-covalent bonds and strong covalently cross-linked semiflexible electrospun fibrous nets. It exhibited about maximum 0.38 MPa tensile strength, ~1560 J/m2 toughness.

Methods

Results

Conclusion