Fuel-Driven Redox Reactions in Electrolyte-Free Polymer Actuators for Soft Robotics

Polymers that undergo shape changes in response to externalstimulican serve as actuators and offer significant potential in a varietyof technologies, including biomimetic artificial muscles and softrobotics. Current polymer artificial muscles possess major challengesfor various applications as they often require extreme and non-practicalactuation conditions. Thus, exploring actuators with new or underutilizedstimuli may broaden the application of polymer-based artificial muscles.Here, we introduce an all-solid fuel-powered actuator that contractsand expands when exposed to H-2 and O-2 via redoxreactions. This actuator demonstrates a fully reversible actuationmagnitude of up to 3.8% and achieves a work capacity of 120 J/kg.Unlike traditional chemical actuators, our actuator eliminates theneed for electrolytes, electrodes, and the application of externalvoltage. Moreover, it offers athermal actuation by avoiding the drawbacksof thermal actuators. Remarkably, the actuator maintains its actuatedposition under load when not stimulated, without consuming energy(i.e., catch state). These fuel-powered fiber actuators were embeddedin a soft humanoid hand to demonstrate finger-bending motions. Interms of two main actuation metrics, stress-free contraction strainand blocking stress, the presented artificial muscle outperforms reportedpolymer redox actuators. The fuel-powered actuator developed in thiswork creates new avenues for the application of redox polymers insoft robotics and artificial muscles.