Muco-ciliary transport: Effect of mucus viscosity, cilia beat frequency and cilia density

In this paper, a two-layer Newtonian fluid model consisting of an upper mucus layer and a lower periciliary layer (PCL) is developed to simulate the muco-ciliary transport process. The objective is to investigate the important factors that may affect the muco-ciliary transport and to understand better the underlying mechanics of some respiratory diseases such as cystic fibrosis. The numerical technique implemented in this study is the projection method combined with the Immersed Boundary Method (IBM) for prescribed ciliary beating patterns. A systematic study of the muco-ciliary transport measured in terms of the mean mucus velocity is performed by changing (i) the viscosity of the mucus, (ii) the cilia beat frequency, (iii) the numbers of cilia, (iv) the thickness of PCL, and (v) the surface tension at the interface between the mucus and PCL. We conclude that the cilia beat frequency, the number of cilia, and the depth of PCL are the critical factors affecting the muco-ciliary transport. Moreover, the present results show that the velocity of mucus layer will be reduced when the length of cilia is larger than the depth of PCL.