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Simulations numériques du transport et du mélange de mucus bronchique par battement ciliaire métachronal

Abstract : The mucociliary clearance is a physico-chemical process whose aim is to transport and eliminate bronchial mucus. To achieve this, billions of microsized appendices, called cilia, cover the respiratory tracts. The cilia propel the mucus by following a periodical pattern, which includes a stroke phase where the cilia tip can enter the mucus layer, and a recovery phase where the cilia are completely immersed in the periciliary liquid. A dysfunction of this process can cause several respiratory diseases. It has been observed that cilia do not beat randomly, but instead synchronize their beatings accordingly to their neighbours, which results in the so-called metachronal waves. However, since experimental observations are extremely difficult to perform, the properties of these waves remain poorly understood. In this thesis, we use numerical simulations in order to reproduce a model bronchial epithelium and study the emergence, as well as the transport and mixing capacities, of these waves. In a first time, we consider carpets of cilia with a random phase lag between them. We observe that a purely hydrodynamical feedback from the fluids onto the cilia leads to ciliary synchronization, forming either antiplectic, symplectic, or synchronous waves. In a second time, we analyze the transport and mixing capacities of these three kinds of wave. The antiplectic waves are found to be the best for displacing and mixing fluids, and the more efficient from an energetical perspective. For the three kinds of ciliary coordination, the mixing is found to be chaotic. It is strong near the ciliated area, and weak in the regions far away. Then, we explain the better efficiency of the antiplectic metachronal waves over the synchronous and symplectic ones by a blowing-suction mechanism which occurs at the interface between the mucus and the periciliary liquid. This mechanism allows the tips of cilia beating in an antiplectic manner to better enter the mucus phase during the stroke phase, and to be more immersed in the periciliary liquid during the recovery phase. The competition between this phenomenon and the lubrification of the mucus due to the periciliary layer is also studied by varying several parameters. After that, the effects of the temporal asymetry present in the beating pattern of the cilia are studied. We find that a stroke phase which lasts 30 % of the total beating period, as observed in nature, leads to an energetical optimum in the case of antiplectic metachrony. Finally, we conclude on the work done during this thesis, and discuss the potential perspectives.
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Sylvain Chateau. Simulations numériques du transport et du mélange de mucus bronchique par battement ciliaire métachronal. Mécanique des fluides [physics.class-ph]. ED 353 Sciences pour l’ingénieur : Mécanique, Physique, Micro et Nanoélectronique; Université de Sherbrooke, 2018. Français. ⟨tel-01948125⟩

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