How microplastics are transported and deposited in realistic upper airways?

Microplastics are tiny plastic debris in the environment from industrial processes, various consumer items, and the breakdown of industrial waste. Recently, microplastics have been found for the first time in the airways, which increases the concern about long-term exposure and corresponding impacts on respiratory health. To date, a precise understanding of the microplastic transport to the airways is missing in the literature. Therefore, this first-ever study aims to analyze the microplastic transport and deposition within the upper lung airways. A computational fluid dynamics-discrete phase model approach is used to analyze the fluid flow and microplastic transport in airways. The sphericity concept and shape factor values are used to define the non-spherical microplastics. An accurate mesh test is performed for the computational mesh. The numerical results report that the highly asymmetric and complex morphology of the upper airway influences the flow fields and microplastic motion along with the flow rate and microplastic shape. The nasal cavity, mouth-throat, and trachea have high pressure, while a high flow velocity is observed at the area after passing the trachea. The flow rates, shape, and size of microplastics influence the overall deposition pattern. A higher flow rate leads to a lower deposition efficiency for all microplastic shapes. The nasal cavity has a high deposition rate compared to other regions. The microplastic deposition hot spot is calculated for shape and size-specific microplastic at various flow conditions. The findings of this study and more case-specific analysis will improve the knowledge of microplastic transport in airways and benefit future therapeutics development. The future study will be focused on the effect of various microplastic shapes on the human lung airways under the healthy and diseased airways conditions.