Multifunctional Ionic Conductive Double-Network Hydrogel as a Long-Term Flexible Strain Sensor

Abstract

Hydrogel-based sensors have attracted a lot of attention owing to their promising applications in human−machine interfaces, personal health monitoring, and soft robotics. However, there is still a great challenge in the fabrication of conductive hydrogel sensors with good mechanical strength, self-healing property, transparency, self-adhesiveness, antibacterial performance, high conductivity, and sensitivity. To meet these requirements, a multifunctional ionic conductive double-network (DN) hydrogel was prepared via in situ freeradical polymerization using a simple one-pot method based on AlCl 3 , acrylic acid, oxide sodium alginate, and aminated gelatin. The hydrogel network was constructed via metal coordination and Schiff base. The resultant DN hydrogel showed self-healing behavior in an ambient environment and underwater with high healing efficiency. Notably, the water environment can effectually accelerate the self-healing process of the hydrogel. Moreover, the corresponding hydrogel displayed good self-adhesiveness, transparency (over 90%), stretchability, antibacterial ability, and high conductivity and sensitivity. This hydrogel was further utilized as a sensor to monitor various human movements and object deformations in daily life. Significantly, the hydrogel that was placed in a closed environment for 10 days still possessed those performances mentioned above. Additionally, the healed hydrogel also maintained the sensing behavior. This work may enlighten future research to design fully functional hydrogel-based sensors to adapt to the environment.

Tough, Anti-Swelling Supramolecular Hydrogels Mediated by Surfactant–Polymer Interactions for Underwater Sensors

“…In aqueous environments, water molecules are prone to penetrate into the sensor–substrate interface and cause interfacial debonding, resulting in distorted or interrupted detection signals. It is greatly vital for underwater sensors to possess robust and durable wet adhesion, which can avoid sensor detachment, making signal acquisition and output more reliable and accurate . An appealing feature of the P­(AA- co -LMA) CTAB -58.5% hydrogel is that although it shows no self-adhesion in air, it demonstrates remarkable adhesiveness after surface treatment with a thin layer of anhydrous ethanol and can adhere to diverse materials robustly (including natural rubber, plastic, glass, ceramic, steel, and pigskin) both in air and underwater, as displayed in Figure a.…”

“…It is greatly vital for underwater sensors to possess robust and durable wet adhesion, which can avoid sensor detachment, making signal acquisition and output more reliable and accurate. 51 An appealing feature of the P(AA-co-LMA) CTAB -58.5% hydrogel is that although it shows no self-adhesion in air, it demonstrates remarkable adhesiveness after surface treatment with a thin layer of anhydrous ethanol and can adhere to diverse materials robustly (including natural rubber, plastic, glass, ceramic, steel, and pigskin) both in air and underwater, as displayed in Figure 5a. Besides, the anhydrous ethanol treated hydrogel can achieve rapid bonding to the substrate, for example, blocking the hole on the plastic bag to prevent water leakage (Figure 5b).…”

Ultrastretchable, Adhesive, Anti-freezing, Conductive, and Self-Healing Hydrogel for Wearable Devices

“…However, the traditional hydrogel-based strain sensor was easy to fall off or damage during the complex and continual motion of the human body, , which largely limit its application in human healthcare detection. Therefore, various methods had been developed to prepare conductive hydrogel with combining qualities of adhesiveness and self-healing properties. − Adhesive and self-healing hydrogel could be fabricated via the introduction of multiple reversible physical interactions. − In our previous work, CS/SiW-PAM and HPMC/SiW-PDMAEMA/Fe 3+ hydrogels with excellent repeatable adhesive capacity and outstanding self-healing property were prepared. , The multiple physical interactions inside the hydrogel, such as hydrophobic interaction, hydrogen bonding, metal coordination, and electrostatic interaction, might arise simultaneously inside the hydrogel matrix and also at the hydrogel–substrate interface, endowing the hydrogels with excellent self-healing and adhesive performances. However, these hydrogels had no anti-freezing property, which would lose conductivity and stretchability and adhesive and self-healing properties at subzero temperature.…”

Hydrophobically Associated Functionalized CNT-Reinforced Double-Network Hydrogels as Advanced Flexible Strain Sensors

“…These properties include good stretchability, high conductivity, low hysteresis energy, biocompatibility, and so forth. Due to these tunable functional properties, hydrogels are considered one of the favorable materials for flexible strain sensors. − Hydrogels are three-dimensional polymer networks that are physically or chemically crosslinked. Improvements continue to remain necessary for the use of hydrogels in flexible sensors and medical technologies.…”