Wearable, Antifreezing, and Healable Epidermal Sensor Assembled from Long-Lasting Moist Conductive Nanocomposite Organohydrogel

Abstract

Flexible wearable soft epidermal sensors assembled from conductive hydrogels have recently attracted tremendous research attention because of their extensive and significant applications in body-attachable healthcare monitoring, ultrasensitive electronic skins, and personal healthcare diagnosis. However, traditional conductive hydrogels inevitably face the challenge of long-term usage under room temperature and cold conditions, due to the lost water, elasticity, and conductivity at room temperature, and freezing at the water icing temperatures. It severely limits the applications in flexible electronics at room temperature or cold environment. Herein, we report a flexible, wearable, antifreezing, and healable epidermal sensor assembled from an antifreezing, long-lasting moist, and conductive organohydrogel. The nanocomposite organohydrogel is prepared from the conformal coating of functionalized reduced graphene oxide network by the hydrogel polymer networks consisting of poly­(vinyl alcohol), phenylboronic acid grafted alginate, and polyacrylamide in the binary ethylene glycol (EG)/H2O solvent system. The obtained organohydrogel exhibits excellent temperature tolerance (−40 °C), long-lasting moisture (20 days), reliable self-healing ability, and can be assembled as wearable sensor for an accurate detection of both large and tiny human activities under extreme environment. Thus, it paves the way for the design of highly sensitive wearable epidermal sensors with reliable long-lasting moisture and excellent temperature tolerance for potential versatile applications in electronic skins, wearable healthcare monitoring, and human–machine interaction.

PVA/Agar Interpenetrating Network Hydrogel with Fast Healing, High Strength, Antifreeze, and Water Retention

“…The instability of traditional hydrogels at room temperature and cold conditions seriously limits the application of compliant products, which are due to the loss of water, elasticity at room temperature and freezing of water at freezing temperatures. At present, there are two main solutions to solve these problems, one is to reduce the freezing point of the system by using a solvent, [41,42] and the other is to reduce the freezing point by using an inorganic salt. [43,44] The strategy of using an EG/H 2 O binary solvent instead of a distilled water solvent endowed the hydrogel with superb anti-freezing properties.…”

Flexible Self‐Repairing Materials for Wearable Sensing Applications: Elastomers and Hydrogels

“…Ion conductive hydrogels consist of a large number of free ions in a 3D polymer network with similar flexibility as biological systems, making them ideal candidates for wearable flexible devices. In recent studies of self-healing ionic conductive hydrogel flexible sensors, conductive ions such as Fe 3+ , [124,125] Na + , [126][127][128][129] [110] glycerol-plasticized polyvinyl alcohol-borax (PVA-borax) / 0.05 [111] polyvinyl alcohol, phenylboronic acid grafted alginate, and polyacrylamide 1.1 × 10 −2 0.064 [112] polyvinyl alcohol and borax / 0.23 [74] Carbon nanotubes polyacrylamide /chitosan hybrid / 0.06 [113] hydrophobic associated polyacrylamide hydrogel / 0.3 [114] Polyacrylamide hydrogels 0.5 0.91 [115] Silver nanoparticles polyion complex/polyaniline hybrid / 3. Al 3+ , [130] ammonium persulfate, [131] sulfuric acid, [132] and lithium chloride [133,134] have been reported.…”

“…As shown in Tables 2 and 3, flexible sensors with the same flexible matrices are more sensitive than those with low conductivity within a certain range, whether in elastomers [91,96] or hydrogels. [112,117] For different flexible matrices, for example, hydrogels exhibit superior sensing sensitivity due to their ultrahigh elasticity at the same conductivity compared to elastomeric flexible sensors. Similarly, for flexible sensors that pursue high conductivity and ignore the elasticity of flexible matrix, the sensitivity of sensing is greatly discounted.…”

Synthesis Antifreezing and Antidehydration Organohydrogels: One-Step In-Situ Gelling versus Two-Step Solvent Displacement

“…At the same time, Lu and coworkers synthesized the adhesive and conductive organohydrogel with long-lasting liquid retention at the temperature range from −20 to 60 • C by in situ polymerization in the glycerol-water binary solvent [14]. Since then, various organohydrogels were prepared by in-situ gelling in the organic-water binary solvent [25,26,[29][30][31][32][33][35][36][37][38][39]. The second synthesis strategy is to soak the preformed hydrogel in the organic or organic-water binary solvent for solvent displacement [15].…”