Advances in skeletal muscle-inspired actuation using functional stimuli-responsive materials

Abstract

Skeletal muscles are fundamental biological systems that convert biochemical energy into mechanical work, enabling movement, force generation, and multifunctional tasks such as self-sensing and adaptive control. Artificial muscles based on stimuli-responsive materials have been developed to replicate these versatile functions. This review reorganizes existing literature from the perspective of skeletal-muscle mimetics by outlining three representative actuation strategies. The first involves contractile or extensional actuation that mirrors sarcomere motion. The second focuses on bending or twisting actuators that reproduce joint motions or localized muscle bending. The third highlights coiled fiber structures that directly imitate fascicles, reproducing both the motion and functional performance of the skeletal muscle. For each category, the advantages, limitations, and distinctive features of various material systems are summarized. In addition, representative studies are highlighted to demonstrate how these materials have been engineered to achieve skeletal-muscle-like performance. Beyond motion replication, advanced strategies are discussed that aim to realize realistic skeletal-muscle functions, including the integration of multi-stimuli-responsive materials and use of structural constraints to enable complex multimodal actuation. These material- and structure-level strategies are designed to be complementary, working synergistically to achieve more lifelike skeletal-muscle behavior. Finally, an outlook is provided on future research directions, with emphasis on material innovations, multifunctional integration, and adaptive design principles that support the transition from stimuli-responsive actuators to practical applications in soft robotics, wearable systems, and biomedical devices.