  Organisms use hair-like cilia that beat in a metachronal fashion to actively
transport fluid and suspended particles. Metachronal motion emerges due to a
phase difference between beating cycles of neighboring cilia and appears as
traveling waves propagating along ciliary carpet. In this work, we demonstrate
biomimetic artificial cilia capable of metachronal motion. The cilia are
micromachined magnetic thin filaments attached at one end to a substrate and
actuated by a uniform rotating magnetic field. We show that the difference in
magnetic cilium length controls the phase of the beating motion. We use this
property to induce metachronal waves within a ciliary array and explore the
effect of operation parameters on the wave motion. The metachronal motion in
our artificial system is shown to depend on the magnetic and elastic properties
of the filaments, unlike natural cilia, where metachronal motion arises due to
fluid coupling. Our approach enables an easy integration of metachronal
magnetic cilia in lab-on-a-chip devices for enhanced fluid and particle
manipulations.
