Stretchable, Reversible, and Self-Healable Poly(acrylic acid) and Cement Hydrate Nanocomposite Hydrogel for Pressure and Motion Sensing

Nanocomposite hydrogels have seen significant advancements owing to the unique structural enhancements facilitated by nanoparticles. However, a persistent challenge arises because of the conflicts between the plasticity and shapeability that accompany nanoparticle integration. Hereby, we present an approach that involves the in situ formation of the primary cement hydrate, i.e., calcium silicate hydrogel (C–S–H), in the presence of poly(acrylic acid) (PAA) to fabricate a nanocomposite hydrogel PAA/CSH. Notably, the resulting nanocomposite hydrogel demonstrates remarkable attributes: stretchable, reversible, shapeable, and self-healable in its wet state, while exhibiting a relatively high hardness and nonflammability upon drying. The amorphous C–S–H nanoparticles establish strong interactions with PAA by forming a robust hydrogen bond network and calcium coordination, which allows C–S–H to serve as a physical cross-linker enhancing the overall properties of PAA/CSH nanocomposite hydrogels, alongside calcium complexation. The excellent stretchability, shapeability, and self-healability render the PAA/CSH hydrogel suitable as pressure/human motion sensors, which exhibit superior response/recovery sensitivity holding considerable promise for applications in artificial intelligence, soft robotics, personal healthcare, among others.