Bioinspired Robotic Actuators by Electrochemical Oxidation of Liquid Metal Droplets*

Progress in artificial muscles rely on new architectures that combine soft matter with mechanisms for converting stimuli into mechanical work. These architectures depend on the intrinsic compliance of soft materials and liquids that matches natural muscles. Liquid metal, in particular eutectic gallium-indium (EGaIn), is promising for creating an artificial muscle because of its ability to generate significant force and shape change by low voltage stimulation, which electrochemically modifies the surface tension. Thanks to their tendency to alloy with metals such as copper, surfaces of EGaIn droplets can be locally constrained such that their deformation is translated into motion of copper, which enables a wide range of motions for robotic actuation.

We present a generalized framework for designing liquid metal actuators (LMA), where the EGaIn droplets are configured with copper pads to generate a desired robotic actuation. We demonstrate by theory and experiments that LMA performs with higher work densities at smaller length scales, making them a favorable actuator at smaller scales with volume constraints. We also show that common actuation modalities, including linear contraction, rotation, bending, and twisting, are achievable using a variety of biologically-inspired designs.