The downsizing of mobile robots faces obstacles in power and control as conventional electromechanical systems do not scale favorably with mass and size. Despite recent advancements in functional materials, enabling efficient energy storage, structural integration, and on-demand energy release in small-scale robots remains a challenge. Inspired by metabolic strategies in animals, we designed a fuel carrier molecule for embodied energy in small-scale swimming robots. We integrated an ultralow surface tension unit into a photolabile o-nitrobenzyl derivative to yield a novel photoresponsive molecule for fuel storage and controlled release. Combining these two properties, carrier molecules undergo bond scission under UV light to release fuel and locally manipulate surface tension to generate Marangoni flows. We incorporated this fuel carrier into an easily processable polymer composite to enable its application as a structural component with embodied energy and control. We implemented this approach in Marangoni micropump systems, surface-tension-active particle transportation, and untethered hybrid microrobots that combine photochemical on-off propulsion with magnetic control. This materials platform serves as a versatile solution to store fuel and energy in structural components and release it on demand with precision, opening new opportunities for embodied energy design in microrobots, soft devices, and active matter systems.
Huang et al. (Sat,) studied this question.