Multiple-Stimuli-Responsive and Cellulose Conductive Ionic Hydrogel for Smart Wearable Devices and Thermal Actuators

Abstract

Stimulus-responsive hydrogels, such as conductive hydrogels and thermoresponsive hydrogels, have been explored extensively and are considered promising candidates for smart materials such as wearable devices and artificial muscles. However, most of the existing studies on stimulus-responsive hydrogels have mainly focused on their single stimulus-responsive property and have not explored multistimulus-responsive or multifunction properties. Although some works involved multifunctionality, the prepared hydrogels were incompatible. In this work, a multistimulus-responsive and multifunctional hydrogel system (carboxymethyl cellulose/poly acrylic-acrylamide) with good elasticity, superior flexibility, and stable conductivity was prepared. The prepared hydrogel not only showed excellent human motion detection and physiological signal response but also possessed the ability to respond to environmental temperature changes. By integrating a conductive hydrogel with a thermoresponsive poly­(N-isopropylacrylamide) (PNIPAM) hydrogel to form a bilayer hydrogel, the prepared bilayer also functioned as two kinds of actuators owing to the different degrees of swelling and shrinking under different thermal stimuli. Furthermore, the different thermochromic properties of each layer in the bilayer hydrogel endowed the hydrogel with a thermoresponsive “smart” feature, the ability to display and conceal information. Therefore, the prepared hydrogel system has excellent prospects as a smart material in different applications, such as ionic skin, smart info-window, and soft robotics.

Ionic Conductive Organohydrogels with Dynamic Pattern Behavior and Multi‐Environmental Stability

“…Specifically, the CMC macromolecule mainly functioned as a skeleton of a double network, which improved the mechanical properties of the organohydrogel. [ 14,15 ] Al 3+ ions not only enhanced the organohydrogel strength through the formation of coordination bonds, [ 16 ] but they also served as conductive ions, [ 17 ] which endowed the organohydrogel with high electrical conductivity and mechanosensitivity. More importantly, the hydrophilic monomer and the hydrophobic monomer in the mixed solvent could be affected by the polarity of the solvent to form a microphase separation and hydrophobic association interactions, which endowed the organohydrogel with an optically tunable performance and solvent‐resistant properties.…”

“…Hence, Gel 5:5 showed sensitive and reliable strain sensing within the strain range of 2.5–500%, which was comparable to the mechanosensation performance of the hydrogel‐based sensors reported in the literature. [ 14,12b,17 ]…”

“…[ 13 ] Taking advantage of the transparency of an ionic conductive hydrogel, we previously reported a multiple‐stimuli‐responsive bilayer hydrogel comprising a transparent ionic conductive layer and a thermo‐responsive layer, which exhibited obvious thermochromic properties under thermo‐stimulus owing to the difference in transparency between the two hydrogel layers. [ 14 ] Hence, the highly transparent conductive hydrogel is a potential candidate for studying the changes in optical properties, from transparent to turbid.…”

Recent Application of Cellulose Gel in Flexible Sensing-A Review

“…After years of research and exploration of hydrogel materials, researchers can make hydrogel materials have high mechanical properties and adhesion properties at the same time. [116][117][118] Exceptional mechanical properties ensure that the hydrogel material remains intact under external force, and the adhesive properties can make it adhere closely to the skin. In addition, it can also give the hydrogel self-healing properties to extend the service life of electronic devices and reduce their maintenance costs.…”

Composites of functional polymers: Toward physical intelligence using flexible and soft materials

“…For a device that measures physiological changes, measurements of resistance over time are as important as the absolute change in resistance. For example, a device that could sense coughing, swallowing, and deep breathing [153] could distinguish these events by monitoring and filtering events deemed "healthy" or "recurring and ordinary." This filtering would also require improvements in data processing.…”