Electrostatic Artificial Cilia

In lab‐on‐chip devices, on which complete (bio‐)chemical analysis laboratories are miniaturized and integrated, it is essential to manipulate fluids in sub‐millimetre channels and sub‐microlitre chambers. A special challenge in these small micro‐fluidic systems is to create good mixing flows, since it is almost impossible to generate turbulence. We propose an active micro‐fluidic mixing concept inspired by nature, namely by micro‐organisms that swim through a liquid by oscillating microscopic hairs, cilia, that cover their surface. We have fabricated artificial cilia consisting of electrostatically actuated polymer structures, and have integrated these in a micro‐fluidic channel. Flow visualization experiments show that the cilia can generate substantial fluid velocities, up to 0.6 mm s−1. In addition, very efficient mixing is obtained using specially designed geometrical cilia configurations in a micro‐channel. To explain the effectiveness of the electrostatically actuated cilia, we used a combination of numerical modelling and flow visualization. It was found that, even though the cilia are small, inertial effects do play a role since the cilia motion is extremely fast due to the large electrostatic forces acting on the cilia. Since the artificial cilia can be actively controlled using electrical signals, they have exciting applications in micro‐fluidic devices.