Anisotropic nanocomposite hydrogels with enhanced actuating performance through aligned polymer networks

Anisotropic composite hydrogels have wide applications in the fields of materials for actuators and sensors. Herein, we report an anisotropic composite hydrogel prepared by a mechanical-strain-induced method. Polymer networks including poly(N-isopropylacrylamide) (PNIPAM) and sodium alginate (SA), as well as carbon nanotubes (CNTs) are found to align simultaneously by stretching, and then fixed by physical crosslinking through non-covalent bonds. Composite hydrogels with doubly aligned polymer networks showed anisotropic optical and mechanical properties. The actuation performance of the anisotropic composite hydrogels as compared with the isotropic ones was found to be enhanced, which showed the capability of lifting 100 times its weight with 20% contraction strain. Besides, a bilayer hydrogel was designed to bend with a maximum of 390° to mimic the tendril behavior of plants.