Rapid Preparation of Dual Cross-Linked Mechanical Strengthening Hydrogels via Frontal Polymerization for use as Shape Deformable Actuators

The hydrogel artificial muscle has demonstrated enormous potential in various applications, such as soft robotics and actuators. However, the poor mechanical properties have always limited the practical applications of hydrogels. Here, we designed a Zr4+ coordinated and vinyl hybrid silica nanoparticle (VSNP) grafted poly(acrylamide-co-2-acrylamido-2-methyl-1-propanesulfonic acid) (VSNP@poly(AM-co-AMPS)-Zr4+) via frontal polymerization (FP). Benefiting from the synergistic effect of the polymer-nanocomposite interaction (VSNP nanocomposite) and metal ion-ligand interactions (Zr4+-sulfonate group coordination), the mechanical properties of hydrogels can be extremely improved. In addition, a deformable hydrogel with gradient structure and swelling ratio was designed through introducing Zr4+ to one side of the hydrogel, which can serve as an artificial muscle to accomplish multiple moving activities, such as bending and grabbing. This work offers an easy-to-perform strategy to construct mechanically strong hydrogels, which might promote the development of artificial muscle materials.