In this work we mimic the efficient propulsion mechanism of natural cilia by magnetically actuating thin films in a cyclic but non-reciprocating manner. By simultaneously solving the elastodynamic, magnetostatic, and fluid mechanics equations, we show that the amount of fluid propelled is proportional to the area swept by the cilia. By using the intricate interplay between film magnetization and applied field we are able to generate a pronounced asymmetry and associated flow. We delineate the functional response of the system in terms of three dimensionless parameters that capture the relative contribution of elastic, inertial, viscous, and magnetic forces.

In this Brief Report we investigate biomimetic fluid propulsion due to an array of periodically beating artificial cilia. A generic model system is defined in which the effects of inertial fluid forces and the spatial, temporal, and orientational asymmetries of the ciliary motion can be individually controlled. We demonstrate that the so-far unexplored orientational asymmetry plays an important role in generating flow and that the flow increases sharply with Reynolds number and eventually becomes unidirectional. We introduce the concept of configurational symmetry that unifies the spatial, temporal, and orientational symmetries. The breaking of configurational symmetry leads to fluid propulsion in microfluidic channels.

The flow in a micro-mixer based on artificial cilia (J. M. J. den Toonder, F. M. Bos, D. J. Broer, L. Filippini, M. Gillies, J. de Goede, G. N. Mol, M. Reijme, W. Talen, J. T. A. Wilderbeek, V. Khatavkar and P. D. Anderson, Lab Chip, 2008, 8, 533-541) is studied. A numerical model is developed and simulations are performed for Reynolds numbers (Re), based on the cilium dimension, from 0 to 10. The mixing properties of the flow are investigated both quantitatively and qualitatively. Flow visualisation by optical coherence tomography (OCT) is performed, and experimental and numerical particle distributions are compared. It is found that for higher Reynolds numbers (Re > 0.1) inertial effects cause a flow reversal compared to lower Reynolds numbers (Re < 0.1). Flow inertia also results in a significant increase of the distributive mixing. The qualitative agreement between experiments and simulations at higher Re is good. This indicates that local inertia effects play a key role in the mixing effectiveness of the artificial cilia mixing.

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