(A) Experimental outline. (B) Live-cell staining with LysoTracker. Scale bar: 100 μm. (C) Transmission electron micrograph of an ODAEC chip. Scale bar: 250 nm. LB, lamellar body; MV, microvilli. (D) Immunofluorescence staining of AT1 marker HTI-56 (magenta) and tight junction marker ZO-1 (yellow). Scale bar: 100 μm. Mean fluorescence intensities (MFI). Different symbols indicate independent experiments. Two-tailed paired t tests (P < 0.05). (E) Relative expression of AT1 and AT2 marker genes in CPAECs and ODAECs, normalized to GAPDH, measured by qPCR. Data are shown as the mean ± SEM, with data points from 3 independent experiments. DL, detection limit. One-way ANOVA (P < 0.05). (F) Uniform manifold approximation and projection (UMAP) plot of identified cell populations estimated from single-cell RNA-sequencing data from 1 CPAEC and 1 ODAEC donor each on-a-chip (5% and 10% stretch) integrated with a previously generated dataset of alveolar organoids (ref. 4; accession GSE197949). (G) Volcano plot of differentially expressed genes in 10% vs. 5% stretched AT1-like cells from the chip. (H) Immunofluorescence images of Pseudomonas (green) in the vascular channel (VE-Cadherin, orange) and quantification of bacterial load (CFU/mL) at 12 hpi. Scale bar: 150 μm (I) Apparent permeability (P_app) at 12 hpi. (H and I) In bar graphs, data are shown as the mean ± SEM, with data points of all chip replicates over 4 independent experiments and 3 different donors for CPAECs and ODAECs. One-way ANOVA. In paired line plots, data are shown as the mean of chip replicates of each independent experiment. Two-tailed paired t tests (*P < 0.05, **P < 0.005).