Muscle‐Mimetic Thermomechanical Adaptive Hydrogels Capable of Isometric Exercise

Abstract Muscles in the human body exhibit stronger performance when warmed as increased temperature enhances actin‐myosin cross‐bridge formation, leading to greater isometric force generation with minimal length change. However, the existing muscle‐mimetic materials predominantly emphasize isotonic exercise, characterized by large length or volume changes upon external stimuli. Developing soft yet freestanding synthetic hydrogels that exhibit isometric exercise behavior in response to temperature variations remains a challenge. Here, muscle‐like hydrogels are presented capable of isometric exercise, inspired by the structural changes in muscles during temperature changes and their associated thermomechanical adaptiveness. In this hydrogel system, linear poly(N‐isopropylacrylamide) chains are designed to intertwine within poly(vinyl alcohol) networks. At lower temperatures, the linear polymer chains remain untangled, but upon temperature elevation, they aggregate within the polymer networks, forming a strengthened polymer complex and thus generating isometric force. This reversible and repeatable behavior enables dynamic adaptation to temperature variations, evidenced by distinct, temperature‐dependent transitions between mechanical strengthening and weakening, as well as lubrication and friction. Closely mimicking the characteristics and behaviors of natural muscles, the developed hydrogel exhibits nearly a twofold increase in mechanical performance within the 20–30 °C range while maintaining stiffness in the tens of kPa.