Chestnut-Tannin-Crosslinked, Antibacterial, Antifreezing, Conductive Organohydrogel as a Strain Sensor for Motion Monitoring, Flexible Keyboards, and Velocity Monitoring

Abstract

Flexible sensing devices (FSDs) fabricated using conductive hydrogels have attracted researchers' extensive enthusiasm in recent years due to their versatility. Considering the complexity of their application environments, the integration of various functional characteristics (e.g., excellent mechanical, antibacterial, and antifreezing properties) is an important guarantee for FSDs to stably perform their applications in different environments. Herein, we developed a multifunctional conductive polyvinyl alcohol (PVA) organohydrogel PVA-CT-Ag-Al-Gly (PCAAG) by using a green, natural, and cheap biomass, chestnut tannin (CT), as a crosslinking agent, nano-silver particles (AgNPs) as an antimicrobial agent, aluminum trichloride (AlCl 3 ) as a conducting medium, and the mixed water−glycerol as the solvent system. In this organohydrogel system, CT acted not only as the reducing and stabilizing agent for the preparation of antibacterial AgNPs but also as the crosslinking agent owing to its strong multiple hydrogen bonding interactions with PVA, realizing its multifunctional application. The PCAAG organohydrogel possessed outstanding physical and mechanical properties (350.54% of the maximum fracture strain and 1.55 MPa of the maximum tensile strength), considerable bacteriostatic effects against both Escherichia coli and Staphylococcus aureus, and excellent freeze resistance (it could function normally at −20 °C). The motion-monitoring sensor based on the PCAAG organohydrogel exhibited excellent specificity recognition for both large-amplitude (e.g., elbow bending, wrist bending, finger bending, running and walking, etc.) and small-amplitude (frowning and swallowing) human movements. The flexible keyboard constructed by using the PCAAG organohydrogel could easily achieve the transformation between digital signals and electrical signals, and the signal output had both specificity and stability. The velocity-monitoring sensor fabricated by using the PCAAG organohydrogel could accurately measure the speed of the object movement (less than 3% of relative error). In short, the present PCAAG organohydrogel solves the problems of the single application environment and a few application scenarios of traditional conductive hydrogels and possesses remarkable application potential as a multifunctional FSD in many fields such as artificial intelligence, sport management, soft robots, and human−computer interface.

Collagen-Based Organohydrogel Strain Sensor with Self-Healing and Adhesive Properties for Detecting Human Motion

“…Following the reported method, 12 the conductivity of CDPAP organohydrogel was measured to be 3.4 S/m. The excellent electrical conductivity provides a prerequisite for the development of hydrogel-based strain sensors.…”

“…Additionally, the self-healed CDPAP organohydrogel also possessed the same sensing performance, which is crucial for the development of self-healable hydrogel-based strain sensors for their application in complex environments. Following the reported method, 12 the conductivity of CDPAP organohydrogel was measured to be 3.4 S/m. The excellent electrical conductivity provides a prerequisite for the development of hydrogel-based strain sensors.…”

“…Recently, flexible conductive sensors were increasingly investigated owing to their tremendous applied value in human–computer interaction, − electronic skin, − soft robots, , and health monitoring. − Conductive hydrogels, as a kind of conductive soft materials, have attracted much research interest due to their excellent flexibility, conductivity, lightweight, and other attractive characteristics. − The ideal conductive hydrogel-based flexible sensor is expected to possess multi-environmental applicability; thus, it can be applied in different real environments, such as warm, cold, and even underwater conditions. However, most of the current reports have mainly focused on the anti-freezing performance of conductive hydrogels.…”

“…In general, researchers can achieve self-healing and adhesion performance of conductive hydrogels in the air in different ways. 12,24 However, it is a challenging job to achieve satisfactory adhesion and self-healing performance simultaneously both in air and water. 25 This is because water can create a boundary layer between the hydrogel and the substrate, thus weakening the hydrogel's ability to form hydrogen bonds and thereby reducing its adhesion stress and self-healing ability.…”

“…However, it remains a daunting but meaningful task to simultaneously combine the above-mentioned multiple properties into a single hydrogel system to broaden the applied environmental range and lifetime of the resulting hydrogel sensors. In general, researchers can achieve self-healing and adhesion performance of conductive hydrogels in the air in different ways. , However, it is a challenging job to achieve satisfactory adhesion and self-healing performance simultaneously both in air and water . This is because water can create a boundary layer between the hydrogel and the substrate, thus weakening the hydrogel’s ability to form hydrogen bonds and thereby reducing its adhesion stress and self-healing ability. , Hence, it is a significant and challenging task to produce a multifunctional conductive hydrogel sensor that can be used in more complex environments (e.g., warm, cold, and underwater environments).…”