UK engineers build tiny pump that could let robots move without bulky motors

Engineers at the University of Bristol have developed a miniature liquid-metal pump weighing just 0.2 grams that could help soft robots move without bulky pumping systems. With a volume of 0.086 cubic centimetres, the device can drive a robotic butterfly’s flapping wings, change the colours of a bracelet and power a wearable that squeezes a fingertip to simulate touch.

The researchers say the pump operates at less than 1 volt, while the university’s announcement puts its operating voltage below 0.1 volts. The findings, published in Nature Communications on May 12, 2026, could open new possibilities for lightweight wearable devices and flexible robots.

How does the liquid-metal pump work?

The device, known as a liquid-metal magnetohydrodynamic (LIMA) pump, uses electromagnetic forces to move liquid through a small, flexible channel.

Its operation rests on magnetohydrodynamics, the physical principle describing how electrically conducting fluids respond to magnetic fields.The pump contains a tiny droplet of liquid metal, surrounded by sodium hydroxide solution, positioned between electrodes, with a small permanent magnet placed beneath the channel. When current passes through the liquid metal, the magnetic field produces a force known as the Lorentz force.

This moves the droplet back and forth, pushing the surrounding fluid and creating a pumping action. In the tests, the current reached about 8 amps at roughly 0.1 volts, for a maximum power draw of 0.8 watts.The resulting flow can inflate or deflate soft actuators, allowing them to bend, contract or move. Reversing the current’s polarity reverses the direction of pumping. Continuous one-way flow requires valves, and the portable version of the system pairs the pump with valves, a microcontroller and an AA battery.

There is no impeller or piston, the moving parts of a conventional mechanical pump.

A robotic butterfly demonstrates the technology

One demonstration involved a robotic butterfly whose wings could be raised and lowered using signals generated by the pump.The pump produces a stream of alternating liquid-metal and sodium hydroxide droplets that travels through a tube to a remote receptor. When a liquid-metal droplet bridges the receptor, it completes an electrical connection that activates shape-memory alloy actuators attached to the wings.

When a sodium hydroxide droplet passes through, the connection breaks and the wings relax. By adjusting the rate and duty cycle of the droplet stream, the researchers could control the wing-flapping pattern.The pump therefore does more than move fluid, since it also helps transmit control signals to components elsewhere in a soft robotic system. The wings themselves are moved by the shape-memory alloy actuators, not by the liquid metal acting as a motor.

A colour-changing bracelet and a wearable touch device

The researchers also demonstrated wearable uses. The colour-changing bracelet contains fluidic channels through which two differently coloured liquids can be pumped, and its colour changed in 28 seconds. That shows how fluid movement could alter the look of a flexible accessory without a conventional electronic display.Another prototype combined a wristband with a soft fingertip pouch. Shape-memory alloy actuators in the wristband squeezed the wrist, driven by coded signals from the pump.

The finger actuator delivered a gentle pressure sensation through hydraulic pumping and a stronger one through a gas-generating chemical reaction, in which citric acid and sodium bicarbonate pumped together produce carbon dioxide. In its current form, the chemical mode is single-use.In a preliminary test, a blindfolded participant correctly identified the three tactile modes. The timing of each mode was controlled manually with valves, and the authors state that the experiment is a prototype demonstration rather than a validated human-robot interaction study.

They say future work will test a larger group of participants.

Could it make robots lighter and more flexible?

Many soft robots use silicone or elastomer components that move when air or liquid is pumped into them. Conventional systems often depend on external compressors or rigid pumps, which add weight, occupy space and restrict movement. The Bristol design integrates the pumping mechanism into a unit of 0.2 grams and 0.086 cubic centimetres, small enough to distribute through a robot’s body rather than connecting every actuator to a central compressor.The researchers also used the pump to power flexible, jointed actuators inspired by arthropod legs. One of them deflected by more than 45 degrees from its starting position, showing that a very small pump can drive a larger soft component. The pump does not remove the need for other actuators, however: the butterfly prototype still relies on shape-memory alloy to move its wings.

Potential applications

Bristol’s press release points to uses ranging from robotic legs to haptic gloves in medical and industrial settings.

Firouznia said the pump could be deployed in lab-on-a-chip devices for disease diagnosis, as micropumps for robotic clothing and in tiny actuators for environmental sampling. Study co-author Jonathan Rossiter, professor of robotics at Bristol, said further research is under way on applications from smart bandages to edible robots.

What the research found

The study was led by Saba Firouznia, with colleagues at the University of Bristol and Bristol Robotics Laboratory.

It was published in Nature Communications on May 12, 2026, under the title “A flexible liquid metal magnetohydrodynamic pump for soft robotic systems.”The authors report bidirectional flow of up to 70 milligrams per second and a maximum blocked pressure of 3 kilopascals. They say the pump surpasses existing soft and commercial pumps when its output is measured per unit of volume. In a continuous test, it ran for 13.5 hours and 48,600 cycles with only minor drift in actuation, attributed to slight oxidation of the liquid metal.

The prototype’s actuation unit costs less than 50 pence in materials.The authors say future work will focus on optimising the design, adding integrated flat valves and simplifying the drive electronics, for instance by replacing the Arduino controller with a simple two-transistor oscillator. For now, the robotic butterfly and the two wearable prototypes offer an early demonstration of how a tiny pump could help flexible machines move, change appearance and deliver physical feedback.