Strong, ultrafast, reprogrammable hydrogel actuators with muscle-mimetic aligned fibrous structures

Hydrogel actuators displaying programmable shape transformations promise to be core components in future biomedical and soft robotic devices. However, current hydrogel actuators have shortcomings, including poor mechanical properties, slow response, and lack of shape reprogrammability, which limit their practical applications . Existing molecular designs offer limited efficiency in synergistically addressing these issues in a single hydrogel system. Herein, we propose a strategy to develop hydrogel actuators with muscle-mimetic aligned microfibrillar morphology, combining thermoinduced microphase separation and mechanical alignment. The key to our design is the introduction of metal–phenolic complexes, which not only induce irreversible sol–gel transition via the concentrated coordinate ions above lower critical solution temperature (LCST) but also fix the alignment of bundle network due to dynamic network rearrangement. Our design concept is observed to simultaneously achieve excellent mechanical properties (tensile strength ≈ 1.27 MPa, toughness ≈ 2.0 MJ m–3) and ultrafast actuation (40.1% thermal contraction as short as 1 s), which is a long-lasting challenge in the field. In addition, the dynamic hydrogels can be reprogrammed into spiral, helical, and biomimetic actuators. This work opens new opportunities to realize real-world applications for smart hydrogels as soft machines by fundamentally breaking the current property limit.