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Progress in artificial muscles relies on new architectures that combine soft matter with transduction mechanisms for converting controlled stimuli into mechanical work. Liquid metal, in particular eutectic gallium–indium (EGaIn), is promising for creating an artificial muscle since it is intrinsically deformable and capable of generating significant force and shape change through low voltage stimulation. In this work, a muscle‐inspired structure for designing liquid metal actuators is presented, where EGaIn droplets are configured with copper pads to linearly contract. By theory and experiments, it is demonstrated that this design enables higher work densities and stress, making it a favorable actuator at smaller length scales. Furthermore, higher frequency (up to 5 Hz) operation is achieved by prestretching an antagonistic pair of actuators, where energy bistability enables fast‐switching actuation. Overall, this muscle‐inspired architecture shows a unique combination of low voltage operation, higher energy density at smaller scales, structural scalability, and higher frequency actuation.

A muscle-inspired soft actuator is constructed from a liquid metal bridge, whose force and shape are controllable by electrochemical tuning of the surface energy using low voltages.

without altering their natural mechanics. [5] These batteries should be compliant and deformable so that they can conform to rounded and irregularly shaped surfaces, such as the contours the human body, and be capable of supplying stable voltage and current under mechanical strain, bending, and dynamic motions. Recent studies have successfully fabricated highly deformable lithium-ion batteries, zinc-air batteries, and supercapacitors. [6][7][8][9][10] However, further progress requires advancements in materials selection and design to address challenges of existing battery technologies: (i) eliminate dependency on rigid electrodes so that batteries can be stretchable rather than only flexible, and (ii) reduce the potential for battery failure/explosion caused by dendrite growth.Metal electrodes that are commonly used in batteries, such as lithium, zinc, aluminum metal anode, or copper current collectors, are rigid and can interfere with the mechanical compliance of soft devices that are designed to be flexible and stretchable. [11,12] One approach to overcoming this challenge is to pattern the metal anode into thin flexible sheets or stretchable spring-like coils or nanowires, which allow batteries to exhibit a strain limit of up to 30%. [13][14][15] Such a deterministic approach to obtain stretchable functionality has been extended to island-bridge architectures. However, such architectures require complex fabrication steps, such as electron beam evaporation and photolithography, that can be time consuming or require expensive equipment. [16,17] Moreover, batteries with wavy structures obtained by prestretching the surrounding substrate could exhibit a reduction in internal conductivity during stretching, which may lead to a decrease in electrochemical performance. [18][19][20][21] Another obstacle to the practical application of metal anode batteries is the formation of dendrites during charging, which can penetrate the separator and result in an internal shortcircuit that causes safety issues. [22,23] Even though dendrites do not penetrate the separator, they hasten adverse reactions between the electrolyte and metal anode, leading to fast electrolyte decomposition, for example, low current efficiency ascribed to hydrogen evolution reaction during zinc-air battery charging process. [24] Modifying the anode, electrolyte, and their interface can suppress dendrite growth. For example, electrolytic additives have been introduced to help form a stable artificial solid electrolyte interface (SEI); [25,26] rigid/elastic layer can A rechargeable, stretchable battery composed of a liquid metal alloy (eutectic gallium-indium; EGaIn) anode, a carbon paste, and MnO 2 slurry cathode, an alkaline electrolytic hydrogel, and a soft elastomeric package is presented. The battery can stably cycle within a voltage range of 1.40-1.86 V at 1 mA cm −2 while being subject to 100% tensile strain. This is accomplished through a mechanism that involves reversible stripping and plating of gallium along with MnO 2 chemical conversion. Mor...

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