Table 1 Summary of quality control tests, purposes of the test and criteria for healthy models

Electrical resistance measurement (TEER measurement and impedance measurement)

TEER measurement: To quantify the integrity of cellular barriers during the development stages

Impedance measurement: To examine the growth and differentiation of the models as well as the integrity of cellular barriers of the models

TEER value falls into the range of 700–1200 Ω·cm² [21]

During the first stage of the growth of the models, the TEER value increases as the multilayers of cells are established in the models. During the second stage, the TEER value of the models decreases, and the capacitance of the models increases as the cells differentiate

Light microscopy

To observe and monitor the growth of cells during the cultures

High cellular confluency after a week of culture

Permeability assay

To assess the formation and function of cellular barriers

Decreased permeability of fluorescent dyes into the basal compartment

Histology and immunofluorescence staining (IF) in cross-section view

To visualise the cell layers in the cross-section view

Represent the key features of lungs such as ciliated cells, goblet cells, etc

Immunofluorescence staining (IF)

To detect and localise different antigens that are released from different types of cells and tissues in the models

Continuous and discrete tight junctions

Scanning electron microscopy (SEM)

To visualise the topological morphology and structure of the cells in the models

Fully ciliated cells and presence of goblet cells

Cytokine profiling

To quantify the expression level of released cytokines in the models

Different expression levels of cytokines in healthy and diseased models