THREE-DIMENSIONAL COMPUTATIONAL MODEL OF MULTIPHASE FLOW DRIVEN BY A BED OF ACTIVE CILIA
Bioinformatics Institute, Singapore
Physiological fluid propulsion on the micro-scale is often accomplished through channels and tubes whose walls are lined with arrays of actively beating cilia. It is wellknown that cilia arranged in arrays can spontaneously coordinate their beat patterns to form metachronal waves. However, while it is generally agreed upon that metachronal waves arise largely due to hydrodynamic coupling, their effects on fluid propulsion are still not thoroughly explored. There are at present complex, nonlinear models where cilia motion is modelled as a function of their internal biological mechanisms; however these models are often computationally challenging and expensive to perform. We therefore present a simplified computational model of a cilia array that has the ability to spontaneously produce metachronal waves. Each individual cilium is modelled as a one-dimensional elastic structure immersed in a stratified, two-fluid configuration. Such a configuration corresponds to physiological conditions similar to that on our respiratory epithelium, where cilia reside in a periciliary layer (PCL) below a mucus layer. Our model treats the mucus as a high-viscosity Newtonian fluid. Our model shows that, in the presence of surface tension between the PCL and mucus layer, the fluid velocity component perpendicular to the interface is suppressed. This suppression prevents the interface from deforming, leading to increased fluid flow along the cilia array and enhancing fluid transport. Conversely, in the absence of surface tension, the fluid velocity component perpendicular to the interface is not suppressed. The interface is severely deformed, forming a large interface area between the PCL and mucus layer, thus potentially resulting in enhanced mixing. We finally present a phase-space plot of viscosity ratio against surface tension, showing conditions under which fluid transport or mixing is enhanced.