On the effect of mucus rheology on the muco-ciliary transport

• Numerical model is used to study the mucus rheology on the muco-ciliary transport.
• Mucus is considered as a viscoelastic fluid.
• An Oldroyd-B model is used as the constitutive equation of mucus.
• Immerse boundary method is used to study the propulsive effect of the cilia.
• Viscosity and viscosity ratio of mucus have great effects on its velocity.

A two dimensional numerical model is used to study the muco-ciliary transport process in human respiratory tract. Here, hybrid finite difference-lattice Boltzmann method is used to model the flow physics of the transport of mucus and periciliary liquid (PCL) layer in the airway surface liquid. The immersed boundary method is also used to implement the propulsive effect of the cilia and also the effects of the interface between the mucus and PCL layers. The main contribution of this study is on elucidating the role of the viscoelastic behavior of mucus on the muco-ciliary transport and for this purpose an Oldroyd-B model is used as the constitutive equation of mucus for the first time. Results show that the viscosity and viscosity ratio of mucus have an enormous effect on the muco-ciliary transport process. It is also seen that the mucus velocity is affected by mucus relaxation time when its value is less than 0.002 s. Results also indicate that the variation of these properties on the mucus velocity at lower values of viscosity ratio is more significant.