Magnetically-actuated artificial cilia for microfluidic propulsion

Natural cilia are hair-like microtubule-based structures that are able to move fluid at low Reynolds number through asymmetric motion. In this paper we follow a biomimetic approach to design artificial cilia lining the inner surface of microfluidic channels with the goal to propel fluid. The artificial cilia consist of polymer films filled with magnetic nanoparticles. The asymmetric, non-reciprocating motion is generated by tuning an external magnetic field. To obtain the magnetic field and associated magnetization local to the cilia we solve the Maxwell equations, from which the magnetic torques can be deduced. To obtain the ciliary motion we solve the dynamic equations of motion which are then fully coupled to the fluid dynamic equations that describe fluid flow around the cilia. By doing so we show that by properly tuning the applied magnetic field, asymmetric ciliary motion can be generated that is able to propel fluid in a microchannel. The results are presented in terms of three dimensionless parameters that fully delineate the asymmetry and cycle time as a function of the relative contribution of elastic, inertial, magnetic and viscous fluid forces.