02171nas a2200289   4500000000100000000000100001008004100002260001500043100001800058700002700076700001400103700001500117700001900132700002700151700001900178700001900197700002200216700002100238700001600259700001800275245006100293856007000354300001200424490000700436520142400443022001401867       2023                            d  c2023-02-141 aMathias Busek1 aAleksandra Aizenshtadt1 aTimo Koch1 aAnna Frank1 aLudivine Delon1 aMikel Amirola Martinez1 aAlexey Golovin1 aClotilde Dumas1 aJustyna Stokowiec1 aStefan Gruenzner1 aEspen Melum1 aStefan Krauss00aPump-less, recirculating organ-on-a-chip (rOoC) platform  uhttps://pubs.rsc.org/en/content/articlelanding/2023/lc/d2lc00919f  a591-6080 v233 aWe developed a novel, pump-less directional flow recirculating organ-on-a-chip (rOoC) platform that creates controlled unidirectional gravity-driven flow by a combination of a 3D-tilting system and an optimized microfluidic layout. The rOoC platform was assembled utilizing a layer-to-layer fabrication technology based on thermoplastic materials. It features two organoid compartments supported by two independent perfusion channels and separated by a hydrogel barrier. We developed a computational model to predict wall shear stress values and then measured the flow rate in the microfluidic channels with micro-Particle-Image-Velocimetry (μPIV). The suitability of the rOoC for functional culture of endothelial cells was tested using HUVECs seeded in the perfusion channels. HUVECs aligned in response to the directional flow, formed a barrier and were able to sprout into the organoid compartments. Next, we demonstrated the viability of human stem-cell derived liver organoids in the organoid compartments. Finally, we show the possibility to circulate immune cells in the microfluidic channels that retain viability without being trapped or activated. The rOoC platform allows growing and connecting of two or more tissue or organ representations on-chip with the possibility of applying gradients, endothelial barriers, microvasculature and circulating cells independent of external tubing and support systems.  a1473-0189