Simultaneously enhanced alginate-based hydrogel self-recovery and mechanical strength upon intramolecular nodes and nanoparticulate joints

The lack of self-recovery features and mechanical toughness has fundamentally limited the practical applications of ionic single-network hydrogels. Due to strong ionic interactions with Zr⁴⁺ cation crosslinkers, intramolecular crosslinking nodes are found to evolve via the folding of alginate segments, revolutionizing alginate hydrogels with substantial self-recovery capability and enhanced mechanical strength. Although being restricted by like-charge repulsion still, this new crosslinking mechanism triples the reachable tensile strain of alginate/polyacrylamide double-network hydrogels, and largely improves self-recovery efficiency. As the gold nanoparticles with adsorbed alginate segments are further introduced as nanoparticulate crosslinking joints, nanoparticle size and weight ratios emerge as new parameters of reached plateau modules and, thus, effective crosslinking density. The stretching-induced conformation alteration and stripping of adsorbed alginate segments are surprisingly associated with the detachment of capping ligands from gold nanoparticles instead of the cleavage of hydrogen bonding between ligands and alginates. As a result, the strong interactions between capping ligands and nanoparticles significantly stimulate the re-adsorption of stripped alginate segments on nanoparticles, leading to the extraordinary 90 % self-recovery of mechanical strength within 5 min with much promoted tensile strength and energy dissipation. For achieved self-recovery efficiency, adjustable partial destruction of intramolecular nodes and nanoparticulate crosslinking joints have been unveiled essential. Hence, new concepts regarding the evolution and partial destruction of newly identified crosslinking joints have been delivered, which together with disclosed influential factors, including the size and capping ligands of crosslinking joints, should stimulate innovative approaches to promote the use of ionic hydrogels.