Researchers in South Korea have developed a soft artificial muscle that can transition from a flexible state to a rigid one, enabling it to support a load of approximately 4,000 times its own weight. A team at the Ulsan National Institute of Science and Technology (UNIST), led by Professor Hoon Eui Jeong, announced the creation on October 14, 2025. The new material, weighing only 1.25 grams, demonstrated the ability to lift 5 kilograms. This innovation addresses a long-standing challenge in the field of soft robotics, where materials have typically been either highly stretchable or capable of high energy output, but not both.
The core of this breakthrough lies in a novel composite material that effectively merges the properties of rubber and steel, allowing it to be soft and pliable for movement and then rigid and strong for support. This dual-character artificial muscle has the potential to revolutionize various fields, including advanced robotics, wearable technology, and next-generation prosthetics. The research, supported by the National Research Foundation of Korea, was published in the journal *Advanced Functional Materials* on September 7. The device not only demonstrates incredible strength but also exhibits a remarkable energy output, approximately 30 times greater than that of human muscle, opening the door to new possibilities for machines that can mimic biological systems with enhanced capabilities.
Resolving a Core Engineering Paradox
The development of soft artificial muscles has been constrained by a fundamental trade-off between mechanical properties. Materials that offered high stretchability, allowing for a wide range of motion, typically lacked the strength and energy output required for practical applications. Conversely, materials that could generate significant force were often rigid and limited in their flexibility. This has been a persistent obstacle in the quest to create soft robots and devices that can interact with the world in a gentle, yet powerful, manner. The UNIST team’s research directly confronts this limitation by engineering a material that does not compromise one quality for the other.
The new artificial muscle achieves its unique abilities through a composite structure that can alter its internal state in response to external stimuli. When in a soft state, the muscle can be stretched and moved with ease, similar to natural muscle tissue. However, when required to bear a load, it can stiffen to provide a strong, stable support structure. This ability to switch between states of high flexibility and high rigidity is what allows the device to perform tasks that were previously impossible for a single soft material. The development marks a significant step forward in the design of dynamic materials that can adapt to changing functional requirements.
Advanced Composite Material Design
The innovative material is a composite that combines two key components: shape-memory polymers and ferromagnetic particles. Shape-memory polymers are materials that can be deformed and then returned to their original shape upon the application of an external trigger, such as heat. This property allows the artificial muscle to be programmed for specific movements and to maintain a given shape without continuous energy input. The inclusion of these polymers is crucial for the muscle’s ability to fix its shape with over 99% accuracy, providing stability and reliability to its movements.
The ferromagnetic particles embedded within the polymer matrix are the key to the material’s remote-control capabilities and its ability to perform complex motions. When exposed to a magnetic field, these particles can be precisely manipulated, allowing for the control of the muscle’s movement without physical contact. This not only simplifies the control systems for potential robotic applications but also allows for a level of dexterity and complexity in movement that would be difficult to achieve with other methods. The combination of these two materials results in a composite that is greater than the sum of its parts, offering a unique set of properties that are ideal for advanced artificial muscle applications.
Record-Breaking Performance Metrics
The performance of the new artificial muscle, as detailed by the research team, sets a new standard in the field. The device delivers a work density of 1,150 kilojoules per cubic meter, a measure of the energy it can output per unit volume. This is a significant figure, indicating a high level of efficiency in converting input energy into mechanical work. Furthermore, the muscle exhibits an actuation strain of 86.4%, meaning it can contract to a significant portion of its original length, allowing for a wide range of motion. This is complemented by an elongation at break of 1274%, a measure of how much the material can be stretched before it fails, highlighting its remarkable durability and flexibility.
The most striking feature of the artificial muscle is its strength-to-weight ratio. The ability of a 1.25-gram device to support a 5-kilogram load is a testament to the effectiveness of the material’s stiffening mechanism. The stiffness of the composite can be increased to approximately 2,700 times that of traditional soft materials, which is what enables it to handle such significant loads. This level of performance is not just an incremental improvement over existing technologies but a substantial leap forward, opening up new avenues for the practical application of soft robotics in real-world scenarios where both strength and flexibility are paramount.
Enabling a New Generation of Robotics
The capabilities of this new artificial muscle have profound implications for the future of robotics and human-assistive devices. In the field of soft robotics, the material could be used to create robots that are not only gentle and safe for interaction with humans but also strong enough to perform meaningful physical tasks. This could lead to advancements in areas such as collaborative robotics in manufacturing, search and rescue robots that can navigate complex and delicate environments, and medical robots capable of performing intricate surgical procedures with a soft touch.
For wearable technology and prosthetics, the artificial muscle offers the potential for devices that are more comfortable, responsive, and capable than ever before. Prosthetic limbs could be designed to more closely mimic the natural movement and strength of human limbs, providing a greater sense of control and a more natural user experience. Exoskeletons and other assistive devices could become lighter, more powerful, and more adaptable to the needs of the user, enhancing mobility and quality of life for individuals with physical impairments. The ability to remotely control these devices could also lead to new possibilities in telemedicine and remote assistance.
The Path Forward for Dynamic Materials
The research from the UNIST team represents a significant milestone, but it also lays the groundwork for future innovations in the field of dynamic materials. The principles demonstrated in this work could be expanded upon to create a wider range of materials with tunable properties, tailored for specific applications. Future research may focus on refining the control systems for these materials, exploring new combinations of polymers and functional particles, and scaling up the manufacturing processes to make these advanced materials more widely available.
As the line between materials science and robotics continues to blur, the development of intelligent and responsive materials like this artificial muscle will be a key driver of technological progress. The ability to create devices that can physically adapt to their environment and the tasks they are required to perform is a long-sought-after goal in engineering. This new artificial muscle is a significant step towards achieving that goal, and its impact is likely to be felt across a wide range of industries in the years to come.