Preparation and Structural Evaluation of Epithelial Cell Monolayers in a Physiologically Sized Microfluidic Culture Device

In vitro microfluidic experimentation holds great potential to reveal many insights into the microphysiological phenomena occurring in conditions such as acute respiratory distress syndrome (ARDS) and ventilator-induced lung injury (VILI). However, studies in microfluidic channels with dimensions physiologically relevant to the terminal bronchioles of the human lung currently face several challenges, especially due to difficulties in establishing appropriate cell culture conditions, including media flow rates, within a given culture environment. The presented protocol describes an image-based approach to evaluate the structure of NCI-H441 human lung epithelial cells cultured in an oxygen-impermeable microfluidic channel with dimensions physiologically relevant to the terminal bronchioles of the human lung. Using phalloidin-based filamentous-actin staining, the cytoskeletal structures of the cells are revealed by confocal laser scanning microscopy, allowing for the visualization of individual as well as layered cells. Subsequent quantification determines whether the cell culture conditions being employed are producing uniform monolayers suitable for further experimentation. The protocol describes cell culture and layer evaluation methods in microfluidic channels and traditional fixed-well environments. This includes channel construction, cell culture and requisite conditions, fixation, permeabilization and staining, confocal microscopic imaging, image processing, and data analysis.