Liquid Metal Pumps Supercharge Soft Robotics

Study lead author Saba Firouznia holding the flexible pump embedded with a tiny liquid-metal droplet, which supercharges its performance capability.
Photo Credit: Saba Firouznia

Scientific Frontline: Extended "At a Glance" Summary: Electrocapillary-Enhanced Magnetohydrodynamic Pumps

The Core Concept: An electrocapillary-enhanced magnetohydrodynamic pump (EMP) is a fluidic system utilizing a liquid metal droplet charged with a low electrical voltage to generate and amplify power and fluid flow in soft robotic systems.

Key Distinction/Mechanism: Unlike conventional robotics that require larger mechanical motors or compressors to increase force, the EMP manipulates the physics of the liquid metal interface. Applying a low electrical voltage (0.5 to 2 volts) alters the shape and surface tension of the active droplet, amplifying the pump's output by up to 3.5 times with a negligible (0.083%) increase in the required electrical charge.

Major Frameworks/Components:

• Active liquid metal droplet for continuous shape-shifting fluid generation.
• Electrocapillary modulation to manipulate interfacial tension.
• Magnetohydrodynamic propulsion functioning without solid mechanical parts.

Branch of Science: Soft Robotics, Fluid Dynamics, Materials Science, and Biomedical Engineering.

Future Application: The technology enables lightweight and flexible wearable assistive devices for rehabilitation, advanced lab-on-a-chip diagnostic tools, miniature targeted drug delivery mechanisms, and rapid fluidic skin layers for environmental protection.

Why It Matters: This advancement allows for the development of substantially more powerful and efficient soft machines without adding mechanical complexity, size, or significant power requirements, directly overcoming a major bottleneck in soft robotics and wearable biomedical device design.

The wristwatch-powered fluidic skin, which deploys the pioneering pump technology to provide faster, greater UV protection via the white fluid as pictured.
Photo Credit: Saba Firouznia

Researchers have found an ingenious way to make soft robots and wearable technology more than three times more powerful by harnessing the surface tension of a tiny liquid-metal droplet smaller than a raindrop.

Their breakthrough, demonstrated in a new study led by the University of Bristol in collaboration with North Carolina State University, shows how charging a metal droplet with even a low electrical voltage can hugely boost the performance power of an artificial muscle, soft robot, and other assistive devices in a range of settings from drug delivery to wearables.

The discovery is important because, until now, if engineers wanted a device to have greater force or movement, it would need to become larger, more complex, and consume extra power.

Lead author Saba Firouznia, research associate at the University of Bristol Soft Robotics Lab, said, "In nature, muscles use internal biological mechanisms to amplify force and movement. We have demonstrated a similar concept in an engineered system, where a very small electrical signal can significantly increase the force and movement generated by the device without requiring larger motors, pumps, or additional mechanical complexity."

The charged liquid-metal droplet technology—called an electrocapillary-enhanced magnetohydrodynamic pump (EMP)—could be deployed in soft robotic systems, inspired by insects, fish, and other organisms, to generate stronger movement. For instance, wearable assistive devices used by rehabilitation patients could be more lightweight, flexible, compact, and comfortable with this pioneering fluidic system. Similarly, miniature biomedical technologies and lab-on-a-chip devices could transport fluids more effectively in very small spaces, enhancing the capability of diagnostic medical devices and drug delivery systems.

Image shows a close-up of the flexible pump embedded with the tiny liquid-metal droplet, called an electrocapillary-enhanced magnetohydrodynamic pump (EMP).
Photo Credit: Saba Firouznia

Findings in the study showed that even a low electrical voltage of between 0.5 and 2 volts can act as an amplifier, increasing the EMP’s output by up to 3.5 times, while requiring a negligible amount (0.083%) of extra charge.

Firouznia explained, "The pump uses a droplet of liquid metal as its active component, which continuously shapeshifts to generate fluid flow. We improved its performance by simply manipulating the physics of the liquid-metal interface, avoiding the need to add any mechanical complexity."

In their previous work, the team demonstrated the feasibility of integrating such transduction technology into wearable devices by developing a wristwatch equipped with a miniature liquid-metal-based pump. The wristwatch powered a fluidic skin, which can be used to provide protection against UV light. Only a small electrical charge enabled the pump to circulate the fluid faster and cover a larger expanse, improving the level of protection.

Study co-author Jonathan Rossiter, professor of robotics at the University of Bristol, who is famed for developing a pair of pioneering robotic trousers dubbed "the right trousers," and head of the Soft Robotics Research Group, added, "The system can generate greater pressure and flow without requiring larger motors, compressors, or batteries. Overall, the work presents a new way to amplify fluidic power in soft machines, which paves the way for more capable soft robots, wearable devices, and compact biomedical technologies."

Published in journal: Advanced Functional Materials

Title: Electrocapillary Modulated Interfacial Tension Amplifies Liquid Metal Transduction

Authors: Saba Firouznia, Ciqun Xu, Michael D. Dickey, and Jonathan Rossiter

Source/Credit: University of Bristol

Edited by: Scientific Frontline

Reference Number: ms070626_02

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