Pump-less, recirculating organ-on-a-chip (rOoC) platform

Current OoC systems mimic aspects of specific organ and tissue functions, however, many commercial and academic devices either exhibit an exceeding simplicity for advanced assays or require a complicated support set-up including external driving systems such as pumps and tubing that hamper scalability and robustness. We have developed an innovative, pump-less directional flow recirculating OoC (rOoC) platform that addresses central shortfalls of existing OoC devices in a robust and scalable configuration. The rOoC platform creates continuous or pulsed directional gravity-driven flow by a combination of a 3D-tilting system and an optimized microfluidic layout. The rOoC platform allows growing and connecting tissue or organ representations on-chip with the possibility of incorporating barrier functions, gradients, and circulating cells. Using the rOoC platform we demonstrate robust endothelialization, hepatic organoid integration, and vascularization of 3D organ representations on-chip and demonstrate its suitability as a drug testing platform applying a liver-toxicity assay. ### Competing Interest Statement The authors have declared no competing interest.