Directional transport of centimeter-scale object on anisotropic microcilia surface under water

Natural organisms such as cactus spines or trachea cilia have unique directional transport ability, owing to their anisotropic surface structures or asymmetric motion. However, most artificial interfacial materials are incapable of transporting macroscale object underwater. Herein, we report that anisotropic microcilia arrays, composed of cobalt fine powder and PDMS, can successfully transport the centimeter-scale hydrogel underwater by periodically asymmetric stroke under alternative magnetic field. Reciprocal collective stroke of anisotropic microcilia can generate directional flow, propelling the centimeter-scale hydrogel slice forward. Accompanying computational simulation results are consistent with the directional transport behaviors observed in our experiments. This study provides a clue to design artificial anisotropic interfacial materials with capability of transporting macroscale object at low Reynolds number.