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

Abstract

Wearable strain sensors of conductive hydrogels have very broad application prospects in electronic skins and human–machine interfaces. However, conductive hydrogels suffer from unstable signal transmission due to environmental humidity and inherent shortcomings of their materials. Herein, we introduce a novel moisture-proof conductive hydrogel with high toughness (2.89 MJ m–3), mechanical strength (1.00 MPa), and high moisture-proof sensing performance by using dopamine-functionalized gold nanoparticles as conductive fillers into carboxymethyl guar gum and acrylamide. Moreover, the hydrogel can realize real-time monitoring of major and subtle human movements with good sensitivity and repeatability. In addition, the hydrogel-assembled strain sensor exhibits stable sensing signals after being left for 1 h, and the relative resistance change rate under different strains (25–300%) shows no obvious noise signal up to 99% relative humidity. Notably, the wearable strain sensing is suitable for wearable sensor devices with high relative humidity.

Multifunctional Conductive Double-Network Hydrogel Sensors for Multiscale Motion Detection and Temperature Monitoring

“…As illustrated in Figure f, the fracture strain and strength increase with the extension of healing time, which is due to the reconstruction of hydrogen bonds and borate ester bonds requiring time. The healing efficiency (HE) is an important parameter to assess the self-healing ability, which is defined as the ratio of the healed strain (ε) to the initial strain (ε 0 ), HE = ε ε 0 × 100 % . After healing for 1 h, the hydrogel could be stretched to 220% with a tensile strength of 7.94 kPa and the HE is 29.36%.…”

“…The healing efficiency (HE) is an important parameter to assess the self-healing ability, which is defined as the ratio of the healed strain (ε) to the initial strain (ε 0 ), HE 100% 0 = × . 48 After healing for 1 h, the hydrogel could be stretched to 220% with a tensile strength of 7.94 kPa and the HE is 29.36%. When the healing time reaches 24 h, the fracture strain recovers to 97.03% of its original state, which surpasses many other reported hydrogels.…”

“…The results are much better than some of the reported hydrogels (Figure 5d). 16,31,37,39,47,48 Under the small strain, stretching causes an increase in inhomogeneity of the hydrogel network and a reduction in the cross-section area, which impedes the ion transfer and leads to an increase in resistance, whereas the free ions are still in contact with each other, resulting in a low GF (Figure 5c). With the increasing tensile strain, the ions separate from each other and the narrowing ion conductive pathway further increases the resistance, leading to a higher GF.…”