Developing a novel mucociliary clearance boundary condition (MCBC) to simulate micro-scale particle transfers inside the respiratory tract system without generating extra computational cells

The respiratory tract system is protected against pathogens and contaminants by the mucociliary clearance phenomenon. Simulating the effects of mucociliary clearance is an important numerical challenge besides the airflow inside the respiratory tract system. The open-source toolbox (OpenFOAM 7) is used to develop a novel method for modeling mucociliary clearance in the vicinity of airflow without extra computational cells. The new method is developed based on three components including inlet-outlet direction, cilia metachronal wave, and main flow core direction, and can be applied to any other respiratory geometries. The capability of the new method is assessed by applying it to the nasal cavity using the Eulerian-Lagrangian approach. The method is applied to the whole nasal surface except the vestibule region to model mucociliary clearance. The results show all deposited particles inside the nasal valve region are transferred alongside the nasal surface toward the main airway region within 12 min. Although mucociliary clearance does not affect the airflow and deposition location of particles due to its slight velocity, its effect on transferring deposited particles is significant. Particle tracking during 5 min inside a single nasal cavity shows 40 % of deposited particles inside the nasal valve are transferred to the main airway by mucociliary clearance. This novel numerical method can lead to the appearance of new insights into the discovery and development of mucosal-based therapies.