Surface Locomotion of Cell-Sized Microrobots Subject to Adhesive Heterogeneity

Chemically powered microrobots provide a promising route toward untethered operation at small length scales, but their motion near surfaces is often difficult to predict because it depends strongly on both particle design and the local interfacial environment. Here, we investigate the two-dimensional surface locomotion of cell-sized self-propelled microrobots in aqueous hydrogen peroxide. Planar 15 µm microrobots were fabricated by photolithography with different structural materials and electrode configurations, and their motion was examined on substrates with distinct surface conditions. Variations in microrobot structure and substrate environment produced differences in mobility and locomotion mode, including translational, circular, and spiral trajectories. Our force-balance analysis indicates that these behaviors reflect the combined effects of self-phoretic propulsion driven by ionic gradients, viscous drag, and surface interactions. We further find that translational velocity is coupled to trajectory curvature under different interfacial conditions. This relationship is captured by a reduced kinematic model and is consistent with both experiments and simulations. Together, these results provide an experimental and physical framework for understanding and tuning the surface locomotion of chemically powered microrobots.