The paper presents a microfluidic platform designed to integrate functional vascular networks around mesenchymal and pancreatic islet spheroids, as well as blood vessel organoids (BVOs) generated from pluripotent stem cells. The platform aims to address the challenge of vascularizing organoids-on-chips, which is crucial for long-term culture of three-dimensional cell aggregates. The microfluidic chip, fabricated using cyclic olefin copolymer (COC), features 10 microchannels with a serpentine-shaped microchannel serving as a trap for organoids. Human umbilical vein endothelial cells (HUVECs) and fibroblasts are seeded into a fibrin hydrogel, which is then introduced into the microchannel. Continuous perfusion with growth medium is established, and the hydrogel remains inside the trap site, surrounding the organoid and providing a stable environment for endothelial network formation. The study demonstrates that the platform successfully establishes functional connections between the endothelium-rich spheroids and vascular organoids, enabling intravascular perfusion. Key findings include: 1. **Enhanced Organoid Growth and Maturation**: Organoids cultured on-chip using the vascularization method show improved growth, maturation, and function compared to those cultured under static conditions. 2. **Functional Anastomosis**: Effective anastomosis between HUVEC networks and BVOs is observed, allowing for interconnected networks. 3. **Enhanced Functionality**: Pre-vascularized pancreatic islet spheroids exhibit improved insulin secretion in response to glucose stimulation when cultured on-chip under flow conditions and embedded in a HUVEC vascular bed. The platform's robustness, scalability, and adaptability make it a promising tool for vascularizing diverse biological 3D tissues and establishing organoid perfusions using advanced microfluidics.The paper presents a microfluidic platform designed to integrate functional vascular networks around mesenchymal and pancreatic islet spheroids, as well as blood vessel organoids (BVOs) generated from pluripotent stem cells. The platform aims to address the challenge of vascularizing organoids-on-chips, which is crucial for long-term culture of three-dimensional cell aggregates. The microfluidic chip, fabricated using cyclic olefin copolymer (COC), features 10 microchannels with a serpentine-shaped microchannel serving as a trap for organoids. Human umbilical vein endothelial cells (HUVECs) and fibroblasts are seeded into a fibrin hydrogel, which is then introduced into the microchannel. Continuous perfusion with growth medium is established, and the hydrogel remains inside the trap site, surrounding the organoid and providing a stable environment for endothelial network formation. The study demonstrates that the platform successfully establishes functional connections between the endothelium-rich spheroids and vascular organoids, enabling intravascular perfusion. Key findings include: 1. **Enhanced Organoid Growth and Maturation**: Organoids cultured on-chip using the vascularization method show improved growth, maturation, and function compared to those cultured under static conditions. 2. **Functional Anastomosis**: Effective anastomosis between HUVEC networks and BVOs is observed, allowing for interconnected networks. 3. **Enhanced Functionality**: Pre-vascularized pancreatic islet spheroids exhibit improved insulin secretion in response to glucose stimulation when cultured on-chip under flow conditions and embedded in a HUVEC vascular bed. The platform's robustness, scalability, and adaptability make it a promising tool for vascularizing diverse biological 3D tissues and establishing organoid perfusions using advanced microfluidics.