New magnetic polymer design boosts force and stretch in soft robotics

Researchers at the Ulsan National Institute of Science and Technology in South Korea have developed a novel dual cross-linked magnetic polymer that significantly advances the performance of soft artificial muscles used in soft robotics. This new material overcomes a longstanding trade-off in artificial muscle technology, where actuators could either stretch extensively or generate strong force, but not both. The polymer achieves a record work density of 1,150 kJ/m³ and an actuation strain of 86.4%, enabling it to stretch over twelve times its original length and shift stiffness by more than a thousandfold—from a soft, rubber-like state to a rigid, plastic-like one. The breakthrough stems from a smart molecular design featuring two types of cross-links that allow the polymer to behave as both rubber and plastic. This dual-mode operation lets the material soften above about 99 °F to be manipulated by a magnetic field and then lock in the new shape below about 80 °F, storing mechanical energy. Reheating releases this stored