Physical Intelligence in Small-Scale Robots and Machines.

Intelligent living organisms-from unicellular entities to plants-rely on body physical intelligence (PI) to autonomously adapt and thrive in dynamic and complex environments, bypassing neural processing. The paradigm of PI has become a pivotal framework for small-scale mobile robots and machines, where they have limited onboard powering, actuation, perception, computation, and control. However, the emerging PI capabilities remain rudimentary compared to biological counterparts in adaptability, multifunctionality, and evolvability. Here, the review systematically examines PI in small-scale mobile robots and machines, highlight the importance of PI in extreme environments, elucidate hierarchical PI manifestations, identify current challenges and future opportunities for further promoting the evolution of PI. Notably, Current research emphasizes that the human body, featuring confined spaces, active and uncertain fluid and organ movements, immunological reactions, and heterogeneous physicochemical conditions, can be an ultimate testing ground for the next-generation small-scale robotic systems with more advanced PI. Looking forward, the rapid evolution of PI benefits from the convergence of multiple disciplines, such as robotics, mechanics, materials, chemistry, biology, and medicine, toward creating autonomous intelligent machines for real-world applications.