2.1 Design and fabrication of lung on-a-chip device
The LOC device comprises three layers. The upper and lower layers, fabricated from polydimethylsiloxane (PDMS), each contain three chambers. The upper layer features three rectangular chambers (10 mm long × 5 mm wide × 100 μm height) connected by channels 3 mm wide. The lower layer includes three independent rectangular chambers (15 mm long × 8 mm wide×100 μm height) that partially overlap with those of the upper layer, allowing observation of cells adhering to the base. A 25 μm-thick porous polyethylene terephthalate (PET) membrane with 8 μm pores separates these layers, which is treated with Aminopropyltriethoxysilane (APTES) for enhanced bonding. The PDMS mixture, with a 10:1 base-to-curing agent ratio by weight, is cast into a mold and cured at 65°C for 2 hours. Afterward, the PDMS layers are punched out and all three layers are plasma-treated before being bonded together. Based on previous literature[59, 60], hydrostatic pressure was utilized to provide fluid dynamics to the upper chamber of the chip, specifically through a pump-free system tilted at a 20-degree angle with a cycle frequency of 5 seconds. The variation in liquid height from an external reservoir generates fluid dynamics in the upper channel of the chip, effectively simulating blood flow.