Pumping Induced By Bio-Mimetic Magnetic Micro-Cilia in Creeping Flows

Abstract

The inertial effects in creeping flow regimes are negligible. Most motile micro-organisms manipulate fluid by oscillatory Cilia or Flagella. The pumping action by a cilium is attributed to the asymmetry in the power and recovery strokes. Further, the ratio of viscous forces to Elastic forces (given by sperm-number) on a cilium determines the efficiency of the pumping. In this presentation we demonstrate magnetic micro-cilia based pumping techniques. We experimentally determine the optimum sperm-number for maximum pumping efficiency. For this, we surface micro-machine high aspect ratio cilia, which are actuated magnetically. These micro-features are fabricated by evaporating NiFe alloy at room temperature, on to patterned photoresist. The evaporated alloy curls upwards when the seed layer is removed to release the cilia, thus making a free standing ‘C’ shaped magnetic microstructure. This is actuated using an external rotating permanent magnet. The time period for the power stroke and recovery stroke are different, which determines the asymmetry in the cilium trajectory. This manipulates the fluid around it. We also demonstrate the active mixing these cilia can produce in the microchannel. We suggest the use of these micro-cilia in capturing bacteria. Selective immobilization of the cilia can lead to highly specific capture of bacteria. We predict high capture rates which will enable easy detection. These simple to fabricate micro cilia can easily be incorporated into many microfluidic systems which require high pumping, mixing and capture efficiencies. The figure bellow shows an image of Cilia actuated by an external magnetic field. Figure 1