a Soon after implantation, EVTs begin to differentiate from precursor cells in the cytotrophoblast shell (CS) and invade into the uterus, a process that continues through the first half of pregnancy. b Compartmentalized design of the implantation-on-a-chip device for in vitro modeling of EVTs and a maternal SA separated by maternal endometrium. c Architecture of the implantation-on-a-chip microdevice. The center and two side lanes have dimensions of 0.5 mm (width) × 0.3 mm (height) and 0.25 mm (width) × 0.3 mm (height), respectively. d Sequential steps of model construction. e Time-lapse imaging of ECM hydrogel precursor (colored black) injection into the center lane of the device. f Images of device cross-section to show capillary pinning-based physical confinement of injected hydrogel solution (dark solution) in the center lane. Scale bar, 500 μm g (Top row) Photos of first trimester termination tissue and EVT outgrowth from the tissue explants. Scale bars, 1 mm (middle) and 200 μm (right). (Bottom row) The purity of the population was confirmed by immunostaining for cytokeratin 7, a trophoblast marker (magenta) and HLA-G, an EVT-specific marker (green). The representative images of the villous tissue are from five independent experiments. Scale bars, 200 μm. h Immunostaining of HLA-G (green) and Ki67 (magenta) expression by EVTs cultured on coverslips in a 6 well plate, after 3 passages. The representative images of EVTs are from four independent experiments. Scale bars, 50 μm. i Top-down confocal projection of the microengineered maternal-fetal interface at Day 1. EVTs in the fetal chamber were labeled with CellTracker Green (green). ECs were stained for VE-cadherin (magenta). The representative image is from three independent devices. Scale bar, 200 μm. j Endothelial tube in the vascular compartment at Day 1. Magenta and blue show VE-cadherin and nuclear staining, respectively. The representative images are from three independent devices. Scale bars, 100 μm (top) and 50 μm (bottom). EVTs: Extravillous trophoblasts, CS: Cytotrophoblastic shell, ECs: Endothelial cells, ECM: Extracellular matrix, CK7: Cytokerain 7, HLA-G: human leukocyte antigen G.. Reproduced under Creative Commons Attribution 4.0 International License from Park, J.Y., Mani, S., Clair, G. et al. A microphysiological model of human trophoblast invasion during implantation. Nat Commun 13, 1252 (2022).