Description
Pulmonary bronchi are lined with a thin layer of mucus, which protects the airways from foreign particulate, such as dust and pathogens. In order to remove this mucus from the lung, the epithelium of the lung is covered in ciliated cells, which beat, moving the mucus up and out of the bronchi to the throat. Dysfunction in this mucociliary clearance can originate from both the cilia, such as cilia dyskinesia, and the mucus itself, such as in the case of cystic fibrosis, resulting in impaired breathing, infection and an increase in mortality [1]. One approach to studying mucociliary clearance has been using artificial cilia, and in particular microfabricated magnetic cilia [2].
We use artificial magnetic cilia which are fabricated using soft lithography, and filled with iron microparticles, lining a circular microchannel, as previously reported previously [3]. These artificial cilia are actuated by placing the microchannel above a rotating set of permanent magnets, which actuate with a slow active stroke, and a rapid recovery stroke, caused by a magneto-elastic instability [4]. The microchannel is filled with fluid which can be pumped by the cilia. In order to better mimic mucociliary clearance, we leave the top fluid surface open to air. To overcome surface tension effects, the microchannel is made hydrophilic by plasma activation, and surfactants are added to fluid solutions when necessary, resulting in a flat air-liquid interface.
Flow in our channel is measured using particle tracking velocimetry of suspended tracer particles. The flow profile in all fluids resembles that of fully developed flow with the maximum velocity achieved on the surface of the fluid. This flow is dependent upon the specifics of the cilia pathway, and proportional to their frequency. Flow generated is measured to decrease relative to viscosity in giant micelle solutions and in model snail slime mucus. Importantly, we show that the relationship between flow rate and viscosity is not the same in micelle and mucus solutions.
Bibliography:
[1] Bustamante-Marin, and Ostrowski, (2017), Cold Spring Harb Perspect Biol, 9:a028241.
[2] ul Islam, et al. (2022), Lab on a Chip, 22.9:1650-1679.
[3] Bolteau et al. (2024), ACS Appl Mater Interfaces 15.29 :35674-35683.
[4] Moore et al. (2025), Lab on a Chip, 25.12:2949-2960.