Development and functional characterization of a tissue-engineered blood-air barrier model for in vitro applications

The blood-air barrier (BAB) of the lung is a critical interface responsible for gas exchange and protection against external attempts, and acts as a selective barrier. Developing in vitro models that replicate its structural and functional properties is essential in studying pulmonary diseases and their therapy.

In this study, a model consisting of alveolar epithelial (A549) and primary endothelial (pHUVEC) cells seeded on opposite sides of a thin (11 ± 4 μm), electrospun poly(ε-caprolactone) mesh of nanofibers (140-800 nm) to represent the basal membrane, and the interstitial matrix of the native BAB when coated with collagen type I, fibronectin, and laminin 511 proteins. The dense, nanofibrous architecture of the mesh enabled the formation of cellular monolayers on opposite sides, allowing gas and nutrient exchange for 14 days at air-liquid interface.

The mesh had a Young's modulus of 8.0 ± 0.8 MPa, and upon coating with proteins, the water contact angles were decreased from 127.5°±2.6 to 94.4°±3.6. Epithelial and endothelial monolayers demonstrated tight junction formation as shown by ZO-1 and CD31 expression. TEER was measured as 44 ± 5.0 Ω·cm² with a permeability coefficient (P_app) of 2-5 × 10^-6 cm/s against fluorescein.

This study presents a physiologically relevant in vitro BAB model for respiratory research and therapies.