Imagine a material that can behave like both soft rubber and hard steel—stretchy and gentle when needed, yet powerful enough to lift thousands of times its own weight.
A team of engineers at the Ulsan National Institute of Science and Technology (UNIST) in South Korea has achieved just that, developing an artificial muscle that can switch between soft and rigid states while delivering an energy output far greater than that of human muscles.
Led by Professor Hoon Eui Jeong from UNIST’s Department of Mechanical Engineering, the research team has created a new kind of soft actuator—essentially an artificial muscle—that overcomes one of the biggest challenges in soft robotics: the trade-off between flexibility and strength.
Their results, published in Advanced Functional Materials, mark a major step forward for applications ranging from wearable robotics to medical assistive technologies.
Traditional artificial muscles have always faced a fundamental limitation.
They can either stretch easily, mimicking the flexibility of biological tissue, or they can generate strong forces to lift heavy objects—but rarely both at the same time.
The new UNIST design solves this problem with an innovative dual cross-linked polymer network that allows the muscle to adapt dynamically.
In practical terms, the artificial muscle can soften when it needs to move or bend and then stiffen instantly to handle heavy loads.
Despite weighing only 1.25 grams—lighter than a paperclip—it can support up to 5 kilograms, roughly 4,000 times its own weight.
When softened, it can stretch to 12 times its original length, demonstrating remarkable elasticity.
Even more impressive is its performance compared to human muscles. During contraction, the artificial muscle achieves a strain of 86.4%, more than double that of typical human tissue, which maxes out at about 40%.
Its work density, or the amount of energy it can deliver per unit volume, reaches 1,150 kilojoules per cubic meter—around 30 times higher than the human equivalent.
The key to this performance lies in the material’s chemistry. Its structure includes two types of bonds: strong covalent bonds that provide rigidity and weaker physical bonds that can break and reform with temperature changes, allowing flexibility.
To add another level of control, the researchers embedded magnetic microparticles into the polymer. By applying magnetic fields, they can precisely manipulate the muscle’s motion and stiffness, which they demonstrated in experiments where the muscle lifted objects through magnetic actuation.
“This research overcomes the fundamental limitation where artificial muscles were either flexible but weak, or strong but rigid,” said Professor Jeong. “Our material can do both, making it ideal for the next generation of soft robots, wearable devices, and human-assistive technologies.”
The breakthrough brings scientists a step closer to machines and prosthetics that move and react with the same versatility as natural muscle—strong when needed, soft when required, and ready to reshape the future of robotics.
