Fluorescence imaging of 3D SAF/A549 was performed by staining with AOPI dye (Nexcelom Bioscience, Lawrence, MA) as previously reported.27 (link) Briefly, at different time points, cultured media was aspirated from the wells, and the microcapsules were washed with DPBS twice to remove FBS. They were then stained with 15 μL of dye and incubated at 37 °C for 10 min. Z-stack fluorescence images were photographed under an Olympus IX83 microscope using Olympus cell Sens Dimension software (Olympus Corporation, Shinjuku, Tokyo, Japan).