The effect of embedded macrophages on intravascular coagulation in 3D vessels-on-chips

Macrophages are innate immune cells that prevent infections and help in wound healing and vascular inflammation. While these cells are natural helper cells, they also contribute to chronic diseases, e.g., by infiltrating the endothelial layer in early atherosclerosis and by promoting vascular inflammation. There is a crosstalk between inflammatory pathways and key players in thrombosis, such as platelets and endothelial cells – a phenomenon known as ‘thromboinflammation’. The role of the embedded macrophages on thromboinflammation in vascular disease is incompletely understood.
Blood perfusion assays are a good way to determine the state of an endothelial layer in a blood vessel-on-chip model. Multiple research projects have shown the advantages of using blood perfusion assays in blood vessel-on-chip models. These models are usually based on square microchannels that do not represent the in vivo geometries of a real blood vessel.
Using induced pluripotent stem cell derived endothelial cells and polarized THP-1 monocytes, we have developed a 3D blood vessel-on-chip with embedded macrophages, which is created using sequential cell seeding in viscous finger-patterned collagen hydrogels. We have set up a human whole blood perfusion assay for these 3D blood vessel-chips.
Platelet formation was seen in brightfield images, but were not observed in fixated samples, due to washing steps to clear the channels of residual blood. An increased formation of fibrin in the blood vessel-on-chip models containing (lipid loaden) macrophages was observed indicating an increasing in the blood clotting process in these channels.
In conclusion, we have developed a 3D vessel-on-chip model with embedded macrophages and have demonstrated that it can be perfused with human whole blood. With the first version of the 3D model established, we expect to use it in future studies of the role of macrophages in thromboinflammation.