Flexible Multimodal Sensor Based on Double‐network Hydrogel for Human and Robotic Applications

Abstract

With the development of wearable technology, there are higher requirements for wearable sensors, such as multimodal sensing, superior mechanical properties, and simple and easy‐to‐fabricate structures. However, it is difficult for existing flexible sensors to possess all these advantages simultaneously. Herein, a flexible multimodal sensor based on sodium alginate/polyvinyl alcohol/graphene oxide double‐network hydrogel was prepared. The multiple hydrogen bonds between the two networks provided the gel with great mechanical properties. In addition, the flexibility and easy‐to‐fabricate simple structure of hydrogels were ideal for wearable sensors. In particular, the hydrogel sensors have a temperature sensitivity of up to 2.81 %/°C between −20 °C and 55 °C and pressure sensitivity of 0.03 kPa−1, both of which have excellent properties of stability and repeatability. Besides, the sensor also presented a humidity sensitivity of 0.027 % RH−1. This work also applied hydrogel sensors to practical applications and provided a new idea for wearable technology.

Amphibious Multifunctional Hydrogel Flexible Haptic Sensor with Self-Compensation Mechanism

“…Figure 6c,d demonstrate the temperature sensitivity reproducibility of DN-SPEZ hydrogel at temperatures ranging from 25 • C to 60 • C and from −20 • C to 25•C, respectively, although it was different from that of the hydrogel of Zou et al[62], who proposed an SNPG multimodal hydrogel sensor, for which the degree of temperature response was relatively low (∆R/R 0 of SNPG is about 143% at −20 • C and 68% at 55 • C); the ∆R/R 0 of the DN-SPEZ hydrogel is 52.34% at −20 • C and 57.26% at 60 • C, but it still demonstrates a good temperature-sensing repeatability in temperature sensing. The wide temperature measurement range and stability further endow the hydrogel sensor with the potential to become a wearable device, e.g., for extreme ambient temperature detection or for helping the human body to collect elements of environmental information.…”

“…As the temperature increases, the resistance of the hydrogel decreases and exhibits a negative temperature coefficient (NTC) property, which also visualizes the temperature detection capability of the hydrogel sensor from the perspective of temperature sensitivity. Temperature sensitivity (TS) is defined as follows [Equation ( 1)] [62]:…”

“…Combining the mechanical properties and electrical conductivity of the hydrogels, we comprehensively analyzed and studied the pressure sensitivity and tensile sensitivity of DN-SPEZ hydrogels. As shown in Figure 7a, the relative resistance change of DN-SPEZ hydrogel changed significantly when it was squeezed, and since the trend of resistance change of DN-SPEZ under different pressure strains was not consistent, the pressure sensitivity (PS) of DN-SPEZ hydrogel was calculated by ∆R/R 0 with the pressure (P) applied to the hydrogel according to the following equation [Equation ( 4)] [62]:…”