Mechanoresponsive self-reinforcement composite hydrogels with triple-network structures

Composite hydrogels featuring multiple-network structures hold immense potential owing to their superior mechanical attributes and exceptional capacity for dissipating energy. Nonetheless, many multiple-network hydrogels lack mechanoresponsive self-reinforcement capabilities, rendering them susceptible to enduring structural fractures. Hence, it exists a critical need to engineer composite hydrogels with both multiple-network structures and mechanoresponsive self-reinforcement abilities. In this study, we devised a triple-network (TN) hydrogel employing poly (2-acrylamido-2-methylpropane sulfonic acid) sodium salt (PNaAMPS) as the first network, which can generate mechanical radicals upon fracture. While polyvinyl alcohol (PVA) and carboxymethyl cellulose (CMC)-Al³⁺ served as the secondary and tertiary networks, respectively, so that to optimize its mechanical properties effectively. Upon breakage, the fragmented PNaAMPS chains could act as radical initiators, catalyzing the polymerization of the N-isopropyl acrylamide (NIPAM) monomers within the TN hydrogels to form PNIPAM chains. Furthermore, through successive network disruptions and the infusion of NIPAM monomers, the mechanical strength of the triple-network gel could be significantly enhanced. Furthermore, we evaluated the extent of mechanoresponsive self-reinforcement using the fluorochrome 8-Anilino-1-naphthalene sulfonic acid (ANS) as a fluorescent probe. This probe enabled the quantification of the PNIPAM production visually, which provided valuable feedback of the mechanical strength self-reinforcement levels by the fluorescence signals. Our approach set the stage for the development of mechanoresponsive composite hydrogels with fluorescence feedback capabilities for self-reinforcement assessment.