Lagrangian transport by ciliary arrays

In many biological systems, from sinuses to airways, ciliary arrays are essential for transporting particles and bacteria. Challenging long-held assumptions, we show that the classical Eulerian view of cilia-induced flow overlooks a key feature of time-averaged transport. Using theoretical modeling and numerical simulations, we demonstrate that the drift generated by ciliary motion is not uniform, as previously predicted, but varies with distance from the ciliary surface in unexpected ways. This variation reveals drift stagnation points, offering a potential means to distinguish healthy from impaired ciliary beating and refines our understanding of fluid-driven transport.