  Most microorganisms use hair-like cilia with asymmetric beating to perform
vital bio-physical processes. In this paper, we demonstrate a novel fabrication
method for creating magnetic artificial cilia capable of such biologically
inspired asymmetrical beating pattern essential for creating microfluidic
transport in low Reynolds number. The cilia are fabricated using a lithographic
process in conjunction with deposition of magnetic nickel-iron permalloy to
create flexible filaments that can be manipulated by varying an external
magnetic field. A rotating permanent magnet is used to actuate the cilia. We
examine the kinematics of a cilium and demonstrate that the cilium motion is
defined by an interplay among elastic, magnetic, and viscous forces.
Specifically, the forward stroke is induced by the rotation of the magnet which
bends the cilium, whereas the recovery stroke is defined by the straightening
of the deformed cilium, releasing the accumulated elastic potential energy.
This difference in dominating forces acting during the forward stroke and the
recovery stroke leads to an asymmetrical beating pattern of the cilium. Such
magnetic cilia can find applications in microfluidic pumping, mixing, and other
fluid handling processes.
