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To date, there is only a fragmentary understanding of the fundamental mechanisms of airway mucociliary transport. Application of the latest measurement techniques can aid in deciphering the complex interplay between ciliary beat and airway surface liquid (ASL) transport. In the present study, direct, quasi-simultaneous measurements of the cilia-induced fluid and bead transport were performed to gain a better insight into both transport mechanisms. In this study cilia-induced periciliary liquid (PCL) transport is measured by means of micro Particle Image Velocimetry (?PIV?PIV) with neutrally buoyant tracers. Particle Tracking Velocimetry (PTV) with heavier polystyrene-ferrite beads is performed to simulate particle transport. Contrary to recent literature, in which the presence of mucus was deemed necessary to maintain periciliary liquid (PCL) transport, effective particle and fluid transport was measured in our experiments in the absence of mucus. In response to muscarine or ATP stimulation, maximum fluid transport rates of View the MathML source250?m/s at View the MathML source15?m distance to the tracheal epithelia were measured while bead transport rates over the epithelia surfaces reached View the MathML source200?m/s. We estimated that the mean bead transport is dominated by viscous drag compared to inertial fluid forces. Furthermore, mean bead transport velocities appear to be two orders of magnitude larger compared to bead sedimentation velocities. Therefore, beads are expected to closely follow the mean PCL flow in non-ciliated epithelium regions. Based on our results, we have shown that PCL transport can be directly driven by the cilia beat and that the PCL motion may be capable of driving bead transport by fluid drag., Process and Energy, Mechanical, Maritime and Materials Engineering

In this numerical study we investigate the flow induced by metachronal coordination between beating cilia arranged in a densely packed layer by means of a continuum model. The continuum approach allows us to treat the problem as two-dimensional as well as stationary, in a reference frame moving with the speed of the metachronal wave. The model is used as a computationally efficient design tool to investigate cilia-induced transport of a Newtonian fluid in a plane channel. Contrary to prior continuum models, the present approach accounts for spatial variations in the porosity along the metachronal wave and thus ensures conservation of mass within the cilia layer. Using porous-media theory the governing volume-averaged Navier–Stokes (VANS) equations are derived and closure formulations are given explicitly for the model. This makes it possible to investigate cilia-induced flow with a continuum model in both the viscous regime and the inertial regime. The results show that metachronal coordination can act as a transport mechanism in both regimes. Porosity variations appear to be the key mechanism for correct prediction of the fluid transport in the viscous flow regime. The reason is that spatial variations in the porosity break the symmetry of the drag distribution along the metachronal wave. A new insight that has been gained is that the fluid transport reverses, thus switches from plectic to antiplectic metachronism, for the same cilia beat cycle when the wavespeed is increased such that inertial effects occur. Based on a parameter study, the net transport in the channel is described by a power-law relation of the amplitude, length and speed of the metachronal wave. It is found that the wavelength has the strongest effect on the viscosity-dominated fluid transport., Process and Energy, Mechanical, Maritime and Materials Engineering

Artificial cilia-driven fluid transport in microfluidic devices is a newly emerging research topic that came into focus during the last five years. Artificial cilia can be described as wall-attached elongated structures that perform an externally actuated periodic beat cycle to manipulate fluids on sub-millimeter scale. The periodic motion of the cilia can be used to transport, mix or filter fluids. It is the variety of potential microfluidic manipulation processes that makes artificial cilia-induced microfluidic manipulation so attractive, and it probably is one of the main reasons for the rapid growth in the number of recent scientific papers in this field. The main research objective of this thesis is to study the influence of beating artificial cilia on the fluid transport. To this purpose, the research was done in three main steps. Firstly, fluid and particle velocities above a surface of natural cilia were measured to determine typical transport rates. This served as guideline for the second step in which a novel artificial cilia device was utilized and critically evaluated experimentally. While a nearly synchronized cilia beat was investigated in the experiments, in a third step the influence of a coordinated but phase-shifted beating of cilia on the fluid transport was studied numerically., Laboratory for Aero and Hydrodynamics, Mechanical, Maritime and Materials Engineering