(a) Schematic illustration of the FMi-OOC device, along with how DiO-labeled (green) exogenous exosomes are loaded into the outermost AEC compartment (chamber#1), where red fluorescent exosomes producing CD9-RFP-AECs cells are seeded so that both endogenous exosomes and engineered exosomes can be monitored for their trafficking. (b) Cartoon illustration of exosomes (red and green) trafficking throughout the cell layers. (c) Representative images of endogenous and exogenous exosomes trafficking through the fetal membrane cell layers (AMCs and CTCs, chamber#2 and chamber#3, respectively), and finally reaching the maternal DEC layer (chamber#4). Close up images are shown in the insets.