Fig. 2.

On-chip formation and mechanical stretching of an alveolar-capillary interface. (A) Long-term microfluidic co-culture produces a tissue-tissue interface consisting of a single layer of the alveolar epithelium (Epithelium; stained with CellTracker Green) closely apposed to a monolayer of the microvascular endothelium (Endothelium; stained with CellTracker Red), both of which express intercellular junctional structures stained with antibodies to Occludin or VE-cadherin, separated by a flexible ECM-coated PDMS membrane (bar, 50 μm). (B) Surfactant production by the alveolar epithelium during air-liquid interface culture in our device detected by cellular uptake of the fluorescent dye, quinacrine that labels lamellar bodies (white dots; bar, 25 μm). (C) Air-liquid interface (ALI) culture leads to a greater increase in trans-bilayer electrical resistance (TER) and produces tighter alveolar-capillary barriers with higher TER (over 800 Ω·cm²), as compared to the tissue layers formed under submerged liquid culture conditions. (D) Alveolar barrier permeability measured by quantitating the rate of fluorescent albumin transport is significantly reduced in air-liquid interface (ALI) cultures compared to liquid cultures (*p < 0.001). Data in (C) and (D) represent the mean ± SEM from three separate experiments. (E) Membrane stretching-induced mechanical strain visualized by the displacements of individual fluorescent quantum dots that were immobilized on the membrane in hexagonal and rectangular patterns before (red) and after (green) stretching (bar, 100 μm). (F) Membrane stretching exerts tension on the cells and causes them to distort in the direction of the applied force, as illustrated by the overlaid outlines of a single cell before (blue) and after (red) application of 15% strain. The pentagons in the micrographs represent microfabricated pores in the membrane. Endothelial cells were used for visualization of cell stretching.