Bio-Inspired Fast Actuation by Mechanical Instability of Thermoresponding Hydrogel Structures

Abstract

Inspired by natural plants, thermoresponding hydrogel (TRH) structures have been designed to trigger mechanical instability with fast actuation. Tough Ca-alginate/poly(N-isopropylacrylamide) (PNIPAM) hydrogel has been synthesized by the hybrid of physically cross-linked alginate and covalently cross-linked PNIPAM. The tough Ca-alginate/PNIPAM hydrogel exhibits 30 kPa of elastic modulus, 280 J/m2 of fracture energies, and fivefold of uniaxial stretch. A multilayered structure made of (Ca-alginate/PNIPAM)/(Ca-alginate/poly (acrylamide)) hydrogels demonstrate fast actuation induced by mechanical instability. A finite-element simulation model is developed to investigate the deformation and to guide the structural design of the hydrogels. The instability-triggering mechanism can enhance the actuation performances of hydrogel structures in applications, such as drug delivery, microfluid control system, and soft biomimetic robotics.