Tough and Fast Thermoresponsive Hydrogel Soft Actuators

Abstract

Thermoresponsive hydrogels hold significant potential for soft actuators due to their ability to undergo reversible shape deformation in response to temperature changes. However, the mechanical brittleness along with slow actuation responsiveness of such hydrogels limit their usage in high-stress environments. Herein, the design and fabrication of tough and fast-responding thermoresponsive double-network (DN) hydrogels, specifically developed for use in soft actuators, are introduced. Using a one-pot free-radical polymerization method, DN hydrogels composed of a poly(N-isopropylacrylamide) (PNIPAm) thermoresponsive first network and an ether-based polyurethane (EPU) second network, providing both mechanical strength and fast response to temperature variation are synthesized. The fabricated hydrogels exhibit excellent mechanical properties, with an ultimate compressive stress of ≈8 MPa, and demonstrate rapid actuation, achieving ≈30% linear contraction and ≈28% radial contraction within 2 min under hydrothermal conditions at 50 °C. Furthermore, tubular soft actuators fabricated from these hydrogels demonstrate the ability to act as fluidic temperature sensors, automatically switching fluid flow direction in response to temperature change. These DN hydrogels combine toughness, rapid actuation, and temperature sensing, offering substantial advancements for soft robotics and adaptive systems.