Electroosmosis-Driven Hydrogel Actuators Using Hydrophobic/Hydrophilic Layer-By-Layer Assembly-Induced Crack Electrodes

Development
of soft actuators with higher performance and more
versatile controllability has been strongly required for further innovative
advancement of various soft applications. Among various soft actuators,
electrochemical actuators have attracted much attention due to their
lightweight, simple device configuration, and facile low-voltage control.
However, the reported performances have not been satisfactory because
their working mechanism depends on the limited electrode expansion
by conventional electrochemical reactions. Herein, we report an electroosmosis-driven
hydrogel actuator with a fully soft monolithic structure-based whole-body
actuation mechanism using an amphiphilic interaction-induced layer-by-layer
assembly. For this study, cracked electrodes with interconnected metal
nanoparticles are prepared on hydrogels through layer-by-layer assembly
and shape transformation of metal nanoparticles at hydrophobic/hydrophilic
solvent interfaces. Electroosmotic pumping by cracked electrodes instantaneously
induces hydrogel swelling through reversible and substantial hydraulic
flow. The resultant actuator exhibits actuation strain of higher than
20% and energy density of 1.06 × 105 J m–3, allowing various geometries (e.g., curved-planar and square-pillared
structures) and motions (e.g., slow-relaxation, spring-out, and two
degree of freedom bending). In particular, the energy density of our
actuators shows about 10-fold improvement than those of skeletal muscle,
electrochemical actuators, and various stimuli-responsive hydrogel
actuators reported to date.