Advances in muscle-driven biohybrid robots: electrical, optical and neuromuscular junction-based stimulations

Abstract Muscle-driven biohybrid robotics has gained substantial attention for its potential to enable advanced mechanical systems with flexibility, high energy efficiency, self-healing capability and adaptability. Autonomous or stimulated muscle contractions have been used as driving forces of mechanical functions and have successfully demonstrated walking, swimming and crawling behaviours of biohybrid robots. Despite these advances, many opportunities exist to achieve greater actuation, precise control, longer-term viability, and programmability. This review provides insights into the next generation of biohybrid systems by examining prior studies on locomotive biohybrid robots specifically designed for walking and crawling locomotion. We introduce diverse biohybrid walker and crawler models and describe their design principles and operating mechanisms, and discuss key factors for optimal engineering strategies. Furthermore, we classify these models according to three primary muscle-stimulation techniques, i.e. electrical field, optical, and neuromuscular junction, and discuss their unique characteristics, including their advantages and limitations. We also highlight approaches for multi-directional locomotion and wireless control, which can contribute to achieving higher dynamic control of biohybrid robots.