  In this work we study the effect of metachronal waves on the flow created by
magnetically-driven plate-like artificial cilia in microchannels using
numerical simulations. The simulations are performed using a coupled
magneto-mechanical solid-fluid computational model that captures the physical
interactions between the fluid flow, ciliary deformation and applied magnetic
field. When a rotating magnetic field is applied to super-paramagnetic
artificial cilia, they mimic the asymmetric motion of natural cilia, consisting
of an effective and recovery stroke. When a phase-difference is prescribed
between neighbouring cilia, metachronal waves develop. Due to the discrete
nature of the cilia, the metachronal waves change direction when the phase
difference becomes sufficiently large, resulting in antiplectic as well as
symplectic metachrony. We show that the fluid flow created by the artificial
cilia is significantly enhanced in the presence of metachronal waves and that
the fluid flow becomes unidirectional. Antiplectic metachrony is observed to
lead to a considerable enhancement in flow compared to symplectic metachrony,
when the cilia spacing is small. Obstruction of flow in the direction of the
effective stroke for the case of symplectic metachrony was found to be the key
mechanism that governs this effect.
