Electrolysis-Driven Reversible Actuation using Micromachined pH-sensitive Hydrogel

While volume changing hydrogel is well studied for a sensing application, its mechanical actuation can also be implemented for a reversible actuation. In this paper, we present an electrolytically controllable soft actuator that utilizes a chemo-mechanical volume changing property of hydrogel. By incorporating micropatterning and electrolysis electrodes on a hydrogel surface, environmental stimuli (i.e., pH) can be localized, resulting in a precisely controlled, large displacement, reversible actuation. Patterned and non-patterned pH-sensitive poly(methacrylic acid-co-acrylamide) hydrogel is studied using a DC voltage (5 V). The hydrogel with a dimension of 5 mm by 5 mm by 0.5 mm with line patterns (t = 40 μm) via a laser machining demonstrated 2 mm in maximum actuation displacement, which is a three-fold improvement in the range of motion compared to a non-patterned hydrogel. It is anticipated that the presented actuator design and mechanism can be applied to an underwater walker or gripper.