3D locomotion of surface-rolling microrobots: a trade-off between hydrodynamic wall and gravitational effects

Abstract

Synthetic microrobots have gained significant attention due to their potential in various applications in biomedicine and lab-on-a-chip technologies. As a fundamental requirement, microrobots must navigate in 3D, effectively counteracting gravity to execute their tasks. However, locomotion at small scales presents numerous counterintuitive behaviors, primarily governed by the interactions between the microrobot's body and its surrounding boundaries. In this study, the locomotion of surface-rolling microrobots is investigated in 3D, particularly focusing on their ability to climb walls. Through a combination of experiments and computational fluid dynamics analyzes, it is demonstrated that the influence of gravity plays a secondary role in enabling surface-rolling microrobots to climb walls. Instead, locomotion capability in 3D settings is primarily determined by interactions with surrounding boundaries. The fundamental principles of surface-rolling locomotion in 3D spaces is elucidated and a design strategy aimed at optimizing fluid flow for efficient propulsion in future applications is proposed.