Programmable shape deformation actuated bilayer hydrogel based on mixed metal ions

Abstract

The intelligent hydrogel actuators that respond to temperature have great application prospects in many fields. At the same time, the intelligent hydrogel actuators still have challenges in driving force, deformation intensity, and programming deformation. Herein, we fabricated a bilayer hydrogel actuator using a two-step photopolymerization method, which consists of a poly(N-isopropylacrylamide)-chitosan-N-2-hydroxypropyl trimethylammonium chloride (PNIPAm-HACC) layer with an LCST-type volume phase change and an alginate-polyacrylamide (SA-PAm) layer. We employed mixed metal ions (trivalent/divalent cations) to cross-link alginate-based hydrogels to construct two-dimensional and three-dimensional cross-linked structure units, resulting in a synergistic effect. The Zn2+/Fe3+(1:1)-SA-PAm/PNIPAm-HACC bilayer-actuated hydrogels have excellent antibacterial properties, shape fixation (85.4 %), fatigue resistance, and reversibility, and showed rapid, reversible, and reproducible thermoresponsive bending/unbending properties, which can be prepared as an actuator, such as a gripper to capture, transport, and release an object, or a temperature-controlled device to turn on and off indicator lights. Overall, this hybrid ion-crosslinked bilayer hydrogel can provide new insights into the design and fabrication of smart actuators.