A research team from Ulsan Institute of Science and Technology in South Korea has developed a new type of artificial muscle that can freely switch between "soft and flexible" and "hard and powerful" states. This innovative muscle can lift objects equivalent to 4000 times its own weight, and its energy output far exceeds that of human muscles. This achievement is expected to promote the development of soft robots, wearable devices, and medical assistive technologies. The relevant paper was published in the latest issue of the journal Advanced Functional Materials. This "variable stiffness" artificial muscle adopts a dual crosslinked polymer network structure. Among them, chemical bonds (covalent bonds) endow the material with structural strength, and physical bonds are formed or broken through thermal stimulation, enabling the material to change stiffness under different conditions. Experiments have shown that this miniature artificial muscle, weighing only 1.25 grams, can lift a weight of 5 kilograms in a rigid state, equivalent to about 4000 times its own weight. In a flexible state, the elongation can reach 12 times the original length. During the contraction process, its strain rate reaches 86.4%, which is twice that of human muscles (about 40%). Meanwhile, its unit volume power density is as high as 1150 kilojoules per cubic meter, which is 30 times that of human muscles. The team also added surface treated magnetic particles to this material, enabling it to achieve precise motion under external magnetic field control. The team stated that this composite material combines the characteristics of "softness" and "toughness", opening up new doors for the development of more flexible soft robots, wearable devices, and intuitive human-machine interaction systems. (New Society)