Constructing Dynamic Macropores in Thermo-Responsive Hydrogel Actuator for Large-Deformable Gripper.

Abstract

Poly(N-isopropyl acrylamide) (PNIPAm)-based smart hydrogels are widely employed in emerging applications such as drug delivery and tissue engineering, because their lower critical solution temperature (LCST) is close to physiological conditions. However, the dense chain collapse during the thermo-responsive phase transition restricts water diffusion, resulting in limited volumetric change. Here, a pure PNIPAm hydrogel that achieves a large-scale volume transition by incorporating PNIPAm microgels, is presented. During its thermo-responsive shrinkage, the microgels contract to 10% of their original volume, generating open macropores that serve as efficient water channels, thereby facilitating volume change of hydrogel bulk. In contrast to conventional PNIPAm hydrogels with static porous structures, these dynamic macropores disappear when the microgels return to their initial state at lower temperatures, preserving the mechanical integrity of the entire hydrogel. This enhanced deformability enables the bilayer hydrogel actuator to achieve bending angles exceeding 1150°, a sixfold increase over traditional PNIPAm-based actuators, allowing it to function as an intelligent gripper capable of capturing small, mobile organisms. This approach, which addresses the inherent challenge of achieving large-scale deformability in conventional bulk PNIPAm hydrogels, is distinct from existing strategies.