High Strength, Conductivity, and Bacteriostasis of the P(AM-co-AA)/Chitosan Quaternary Ammonium Salt Composite Hydrogel through Ionic Crosslinking and Hydrogen Bonding

Traditional hydrogels with a single-crosslinked networkstructuresuffer from poor stretchability, low sensitivity, and easy contamination,which seriously affect their practical application in the strain sensorfield. To overcome these shortcomings, herein, a multiphysical crosslinkingstrategy (ionic crosslinking and hydrogen bonding) was designed toprepare a hydrogel strain sensor based on chitosan quaternary ammoniumsalt (HACC)-modified P(AM-co-AA) (acrylamide-co-acrylic acid copolymer) hydrogels. The ionic crosslinkingfor the double-network P(AM-co-AA)/HACC hydrogelswas achieved by an immersion method with Fe3+ as crosslinkingsites, which crosslinked with the amino group (-NH2) on HACC and the carboxyl group (-COOH) on P(AM-co-AA) and enabled the hydrogels to recover and reorganize rapidly,resulting in a hydrogel-based strain sensor with excellent tensilestress (3 MPa), elongation (1390%), elastic modulus (0.42 MPa), andtoughness (25 MJ/m(3)). In addition, the prepared hydrogelexhibited high electrical conductivity (21.6 mS/cm) and sensitivity(GF = 5.02 at 0-20% strain, GF = 6.84 at 20-100% strain,and GF = 10.27 at 100-480% strain). Furthermore, the introductionof HACC endowed the hydrogel with excellent antibacterial properties(up to 99.5%) and excellent antibacterial activity against bacteriaof three forms, bacilli, cocci, and spores. The flexible, conductive,and antibacterial hydrogel can be applied as a strain sensor for real-timedetection of human motions such as joint movement, speech, and respiration,which exhibits a promising application prospect in wearable devices,soft robotic systems, and other fields.