Enhancing energy conversion efficiency in entangled hydrogel actuators

Traditional hydrogels-based actuators are hindered by limitations such as low deliverable forces (∼2 kPa) and sluggish actuation speeds, culminating in persistent issues with low work density (∼0.01 kJ/m³). Furthermore, achieving low hysteresis and high strength presents significant challenges in both their synthesis and applications. Herein, we developed poly(acrylic acid) hydrogels characterized by sparse cross-linking and high entanglement, effectively addressing these issues. Inspired by the energy conversion mechanisms of mammalian muscle fibers, the hydrogels were utilized for storing and releasing elastic potential energy in polymer network. Notably, we achieved a remarkable contractile force of 60.6 kPa, an ultrahigh work density of 30.8 kJ/m³, and an energy conversion efficiency of up to 53.8%. Furthermore, the hydrogels exhibit unique dual-state functionality, seamlessly transitioning between elasticity and plasticity, which paves the way for adaptable and precisely controllable energy release mechanisms. These features hold significant potential for diverse practical applications, providing a promising advancement for hydrogel actuators.