Highly Stretchable, Self-Healable, Freezing-Tolerant, and Transparent Polyacrylic Acid/Nanochitin Composite Hydrogel for Self-Powered Multifunctional Sensors

Abstract

To fulfill the current challenges in the hydrogel applications in wearable sensors including low sensitivity, lack of self-healing ability, and nontransparency, we synthesized a polyacrylic acid/nanochitin composite hydrogel with dual cross-linking networks for highly stretchable, transparent, self-healing, and anti-freezing sensors via an eco-friendly method. Dynamic metal-coordination bonds between Al 3+ and carboxyl groups and the hydrogen bonds contributed to the excellent self-healing efficiency of the hydrogel (97%). The dual cross-linking networks provide the composite hydrogel with 400 kPa tensile strength. The hydrogel-based sensors could detect multiple external stimuli, demonstrating a high gauge factor of 2.36 with the strain range of 0−500% and an ultrabroad temperature detection range (−35 to 50 °C). Significantly, the composite hydrogel demonstrates an ultrasensitive thermal response with a sensitivity of 252 %/°C during the cooling process. Moreover, the composite hydrogel was also assembled into a triboelectric nanogenerator to act as a self-powered pressure sensor. Therefore, the developed hydrogel sensors fabricated via a facile and green preparation approach hold great potential for sustainable wearable sensors in electronic skins and personal healthcare.

Hydrogels as Soft Ionic Conductors in Flexible and Wearable Triboelectric Nanogenerators

“…[ 54 ] This indicates the matched internal resistance of the device was only 3.3 MΩ, which is tens or hundreds times less than that of common reported TENGs. [ 55–58 ] Similar results have been observed from other H‐TENGs as well, [ 59–64 ] with intriguing applications such as wireless real‐time communication, large capacitors charging, temperature sensing, as well as human motion monitoring. The stronger mechanical adhesion and better reliability between the triboelectric layer and hydrogel resulted in the better charge induction.…”

“…As one of the most abundant biopolymers, chitin is the main structural component in living organisms, for instance, carb as seen in Figure 3l. Interestingly, a polyacrylic acid (PAA)/nanochitin hydrogel was synthesized via a facial and green approach by Jing et al [64] The developed chitin-based sensors and TENGs can be used to monitor throat movement during speaking, body joint bending, as well as finger gestures. This provides an alternative raw material presenting a direction that can move away from petroleum-based raw materials.…”

“…For example, it takes two hours for the poly-acrylic acid/nanochitin composite hydrogel to achieve a selfhealing efficiency of 97% based on the formation of dynamic metal-coordination bonds between aluminum ions and carboxyl groups. [64] This dynamic process is time consuming considering that TENGs undergo continuous contact and separation during mechanical energy harvesting. In this respect, Shuai et al [91] have developed a self-healing hydrogel with a high healing efficiency of 85% after only 10 min healing, but the healing temperature was as high as 60 °C.…”

Polyacrylic Acid Nanoplatforms: Antimicrobial, Tissue Engineering, and Cancer Theranostic Applications

“…Furthermore, cross-linked PAA can be employed as a medicinal adhesive due to its excellent bonding strength. PAA has hardness and barrier qualities in film form, making it ideal for packaged food [ 48 , 52 ]. Poly (acrylic acid) varies its characteristics in response to changes in ionic strength and pH; for example, at pH < 4, precipitate occurs in aqueous solutions due to the carboxylate groups’ protonation making the polymer sparsely soluble in water [ 53 ].…”

Recent Advances in Self-Powered Piezoelectric and Triboelectric Sensors: From Material and Structure Design to Frontier Applications of Artificial Intelligence

“…The excellent self-healing properties of the hydrogel were deemed to be the combined effect of the triple helix crosslinking of gelatin and the dynamic reversible crosslinking network formed by the dynamic hydrogen bond between PAA and Gel molecules. Jing et al [62] reported an ultra-stretchable and self-healing composite hydrogel based on polyacrylic acid/nanochitin (PAA/NCT) by introducing dual crosslinked networks. Due to the presence of dynamically reversible metal coordination bonds and multiple dynamic hydrogen bonds, it gave the hydrogel outstanding self-healing efficiency (97%).…”