Recent Advances in Variable‐Stiffness Robotic Systems Enabled by Phase‐Change Materials

Abstract

Robotic systems have become indispensable across various domains, enhancing efficiency, safety, and convenience in everyday life. While rigid robots excel in precision and load‐bearing tasks, their lack of adaptability poses challenges in human interaction and unstructured environments. Soft robots, constructed from flexible materials, offer safer and more adaptive solutions but often lack the rigidity needed for high‐force applications. To bridge this gap, stiffness‐tunable robotic systems have emerged, with phase‐change materials (PCMs) gaining significant attention due to their ability to transition between soft and rigid phases, enabling dynamic stiffness modulation. Unlike conventional stiffness‐tuning methods that require bulky external components, PCM‐based soft robots provide a lightweight and compact alternative, making them highly suitable for applications that demand both adaptability and load‐bearing capabilities. However, slow phase transition rates remain a key limitation, prompting research into advanced thermal management and phase control strategies to enhance responsiveness. This review explores recent advancements in PCM‐enabled robotics, focusing on their underlying mechanisms, key applications in gripping, minimally invasive surgery, shape morphing, and locomotion, and the challenges that must be addressed to unlock their full potential. By summarizing the latest developments, this review highlights the promising role of PCMs in the evolution of multifunctional, adaptable soft robotic systems.