Figure 3.

(a) Schematic diagram and optical image of the permeability test setup. Flu‐Na solution in phosphate‐buffered saline (PBS) (2.5 mg/ml) and prewarmed PBS are infused into the top channel and the bottom (acceptor) channel at 100 µl/h, respectively. A 3 cm height difference (Δh) maintained between two outlets creates a constant pressure difference between two chambers (ΔP = PT‐out‐PB‐out = ρg Δh) to drive Flu‐Na diffusion. PT‐out: pressure at the end of the top channel tube; PB‐out: pressure at the end of the bottom channel tube. (b) Photo of the actual experimental setup