Self-organization of Long-lasting Human Endothelial Capillary Networks guided by DLP Bioprinting

Tissue engineering holds great promise for regenerative medicine, drug discovery and as an alternative to animal models. However, as soon as the dimensions of engineered tissue exceed the diffusion limit of oxygen and nutriments, a necrotic core forms leading to irreversible damage. To overcome this constraint, the establishment of a functional perfusion network is essential and is a major challenge to be met. In this work, we explore a promising Digital Light Processing (DLP) bioprinting approach to encapsulate endothelial progenitor cells (EPCs) in 3D photopolymerized hydrogel scaffolds to guide them towards vascular network formation. We observed that EPCs encapsulated in the appropriate photopolymerized hydrogel can proliferate and self-organize within a few days into branched tubular structures with predefined geometry, forming capillary-like vascular tubes or trees of various diameters (in the range of 10 to 100 m). Presenting a monolayer wall of endothelial cells strongly connected by tight junctions around a central lumen, these structures can be microinjected with fluorescent dye and are stable for several weeks in vitro. Interestingly, our technology has proven to be versatile in promoting the formation of vascular structures using a variety of vascular cell lines, including EPCs, human vascular endothelial cells (HUVECs) and human dermal lymphatic endothelial cells (HDLECs). We have also demonstrated that these vascular structures can be recovered and manipulated in an alginate patch without altering their shape or viability. This opens new opportunities for future applications, such as stacking these endothelial vascular structures with other cell sheets or multicellular constructs to yield bioengineered tissue with higher complexity and functionality.