Meet the magnetic liquid metal robot: It merges and squeezes through tiny gaps like a living cell
Scientists have developed a remarkable liquid robot that blurs the line between machines and living organisms. Created by researchers from Seoul National University and Gachon University, the robot is made from liquid metal coated with a dense armour of microscopic particles and embedded with magnetic particles that allow it to be controlled remotely. Unlike conventional robots built from rigid components, this soft robot can dramatically change its shape, squeeze through openings smaller than its own diameter, split into multiple droplets, merge back into one body and even engulf foreign objects before carrying them away. The study, published in Science Advances, introduces a new class of particle-armoured liquid robots that combine the fluidity of liquids with the stability of solid materials. Inspired by the behaviour of biological cells, the technology could eventually transform fields ranging from minimally invasive medicine to industrial inspection and disaster response.
What makes the particle-armoured liquid robot different?
Soft robotics has advanced rapidly over the past decade, but one challenge has remained difficult to overcome: creating robots that are both highly deformable and mechanically stable. Traditional rigid robots are strong and predictable but cannot adapt to confined or irregular environments. Existing soft robots can bend and stretch, yet many lose their structural integrity when subjected to large deformations.The new robot addresses this problem by using a unique material architecture called a particle-armoured liquid robot (PB). At its core is a droplet of liquid metal, chosen for its excellent electrical conductivity, high surface tension and ability to flow like a liquid. The droplet is infused with magnetic particles, enabling scientists to manipulate it using external magnetic fields.
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The defining feature, however, is its outer shell. Instead of leaving the liquid metal exposed, the researchers surrounded it with an unusually dense layer of superhydrophobic, or water-repelling, particles. This microscopic armour gives the robot a protective skin that dramatically improves its stability without sacrificing its liquid nature.According to the researchers, the particle shell allows the robot to maintain its overall structure even while undergoing extreme compression, stretching and deformation. This enables movements that are impossible for conventional solid robots while preventing the droplet from breaking apart during operation.
A new manufacturing technique solved a long-standing problem
The study’s most significant innovations lies in how the particle shell is created. Previous liquid robots were typically produced by coating an already formed liquid droplet with particles. Although this method provided some protection, it often resulted in uneven particle coverage, limiting both durability and flexibility.To overcome this limitation, the researchers developed an entirely different fabrication process.They first froze the liquid into a solid ice template before coating its surface with hydrophobic particles. Once the coating was complete, the ice was allowed to melt, leaving behind an exceptionally dense and uniform particle shell surrounding the liquid metal core.This approach produced a much stronger protective layer than earlier methods. The researchers found that the dense armour significantly improved the robot’s ability to withstand repeated deformation while preserving its fluid behaviour.The paper explains that this fabrication strategy creates a robust liquid-particle composite capable of maintaining structural integrity during demanding robotic operations, making it suitable for tasks requiring repeated changes in shape.
Inspired by the remarkable abilities of living cells
Rather than taking inspiration from conventional machinery, the researchers looked to biology.Many living cells possess extraordinary capabilities. They can squeeze through microscopic openings, alter their shape depending on their environment, engulf foreign particles through phagocytosis and even divide before merging again under certain biological processes.The particle-armoured liquid robot reproduces several of these behaviours in an artificial system. During laboratory demonstrations, the robot successfully deformed itself to pass through narrow gaps formed by metal bars that were considerably smaller than its normal dimensions. Once it had crossed the obstacle, it naturally returned to its original shape.Researchers also demonstrated that a single robot could divide into several smaller droplets and later reunite into one larger robot without losing functionality. This ability to split and merge offers possibilities unavailable to conventional robots assembled from rigid mechanical components.Another striking demonstration showed the robot engulfing foreign objects before transporting them elsewhere. The behaviour resembles biological phagocytosis, the process by which immune cells surround and consume harmful particles or pathogens.These experiments illustrate how the liquid robot combines fluid motion with controlled manipulation, allowing it to perform complex physical tasks while maintaining a stable overall structure.
Controlled remotely using magnetic fields and acoustic waves
The robot contains magnetic particles dispersed throughout the liquid metal, allowing researchers to control its movement without any onboard electronics or power source.By applying external magnetic fields, the team guided the robot across solid surfaces, through confined spaces and around obstacles with high precision.The study also demonstrated that acoustic waves could influence the robot’s movement. By combining magnetic manipulation with ultrasound, researchers achieved greater control over how the robot travelled through different environments.Because the robot does not rely on internal motors, gears or batteries, its overall design remains extremely simple despite its sophisticated capabilities.The researchers also developed a theoretical model describing how the particle-armoured robot behaves under different conditions. This framework predicts changes in the robot’s shape, movement and interaction with external forces, providing engineers with a valuable tool for designing future liquid robotic systems.Rather than relying solely on trial-and-error experiments, scientists can now use this predictive model to optimise robot performance for specific applications.
Exceptional durability despite behaving like a liquid
One of the most surprising findings from the study is how mechanically resilient the particle-armoured robot proved to be.Liquids are generally associated with fragility because they easily change shape. However, the dense particle shell dramatically enhances the robot’s robustness.Laboratory tests showed that the robot could tolerate repeated compression and significant deformation while continuing to function normally. Even after passing through confined spaces or experiencing substantial external forces, it rapidly recovered its original droplet shape.This combination of deformability and resilience addresses one of the central challenges in soft robotics.Previous liquid robots often faced a trade-off between flexibility and stability. Designs that were highly deformable frequently lost their structural integrity, while more stable systems sacrificed adaptability.The particle-armoured design successfully balances both properties, creating a robotic platform capable of operating in environments where rigid machines would fail.
Potential medical applications inside the human body
One of the most promising applications highlighted in the study involves medicine. Many areas inside the human body are extremely difficult to reach using conventional surgical instruments. Blood vessels, narrow ducts and delicate tissues require tools that can navigate confined pathways without causing damage.Because the particle-armoured liquid robot can squeeze through tiny openings, deform around obstacles and recover its shape afterwards, it could eventually serve as a minimally invasive medical device.Researchers envision future versions capable of delivering drugs directly to diseased tissue, removing blockages, transporting therapeutic agents or assisting with microsurgical procedures.The magnetic control system offers another important advantage. Doctors could potentially steer these robots remotely using externally generated magnetic fields, reducing the need for invasive surgical access. Although the technology remains at the laboratory stage, the research demonstrates several physical behaviours required for future biomedical robots.
Beyond medicine: Industrial inspection and disaster response
The technology’s usefulness extends well beyond healthcare. Industrial facilities often contain narrow pipes, intricate machinery and hazardous environments that are difficult or dangerous for humans to inspect.Liquid robots capable of flowing through confined spaces could inspect structural damage, identify leaks or transport sensors into inaccessible areas.Similarly, disaster zones frequently contain collapsed buildings with tiny openings that prevent conventional robots from reaching trapped survivors.Because the particle-armoured robot can squeeze through narrow gaps while remaining structurally intact, future generations could help explore unstable environments following earthquakes or industrial accidents.The researchers also suggest applications involving environmental monitoring, micro-manufacturing, cargo transport and the manipulation of tiny objects within complex systems.Its ability to divide into multiple robots before reuniting later could prove particularly valuable for cooperative robotic tasks that require adaptability.
