Flow-driven orientational self-organization of the bronchial epithelium

In human lungs, the long-range oriented transport of mucus by the bronchial epithelium multi-ciliated cells, a process referred to as muco-ciliary clearance, is a key self-defense mechanism protecting the respiratory tract from inhaled particles and pathogens. Yet, the biophysical processes allowing such orientational organization remain unclear. In this work, we show that in-vitro reconstituted human bronchial epithelia exhibit active orientational self-organization driven by the mucus-cilia coupling. The ciliary orientation typically forms circular patterns associated with mucus swirls, on length scales depending on the ciliary density and mucus properties. Numerical simulations are used to investigate the two-dimensional flow driven by streamwise-oriented local forces over a substrate, as a model for ciliary-driven flows. Simulations predict multi-scale swirls and the emergence of a long-range orientational order controlled by the viscosity/friction competition (setting the hydrodynamic length scale) and the ciliary density. Model-based predictions of the effect of the ciliary density on the transport length scale show quantitative similarities with in-vitro measurements.