The clamped fibrinogen scaffolds were transferred into prepared wells using forceps and silicone rings were placed on top of the PVC rings for cell seeding. In a first step, the endothelial cells were seeded onto the scaffolds and incubated for 3 h at 37 °C and 5% CO2. Then, the clamped scaffolds were turned and the mesenchymal cells were seeded onto the other side of the scaffolds. To enable cell adhesion, the scaffolds were again incubated for 3 h at 37 °C and 5% CO2. In a last step, HSPCs were seeded on top of the endothelial or mesenchymal cells to complete the triple culture.