Fluid Propulsion by Cilia in a Shear-thinning Fluid

Fluid propulsion by natural cilia is governed by their asymmetric motion. For artificial cilia driven by an external force, this asymmetry comes from the shape of the applied force and the initial shape of the cilium. For shear-thinning liquids such as saliva, which are deformation rate dependent, the motion can also become asymmetric due to different time-scales of the forward and the backward stroke. Using numerical simulations, we show that the time-scales can be controlled by the applied force amplitude. The model we use to describe the saliva behavior is based on rheological measurements we have performed on human whole saliva. We observe three times higher flow rates for saliva than for a Newtonian liquid with the same actuation and comparable cilia deflection. The dynamics of the cilium are also different.