Engineering vascular development for tissue regeneration

Tissue engineering and regenerative medicine aim at restoring a damaged tissue by recreating in vitro or promoting its regeneratin in vovo. The vasculature is central to these therapies for the irrigation of the defective tissue (oxygen, nutrients or circulating regenerative cells) and as an inductive, trophic embedded organ. This thesis describes the in vitro formation of biological vascular networks for tissue engineering and regenerative medicine applications.\ud \ud In a first part, we show the in vitro formation of a vascularized tissue, using human mesenchymal stem cells and human umbilical vein endothelial cells for bone regeneration. Exogenous Sonic Hedgehog induced in vitro vascular development which was essential for the vasculature to robustly contribute to new bone tissue formation in vivo. The implant recapitulated a combination of intramembranous and endochondral ossification and matured into a bone organ including a large amount of trabecular bone, blood vessels and bone marrow cavities with apparent hematopoiesis. This approach, based on the regenerative paradigm of endochondral bone repair, opens new opportunities for the treatment of large bone defects.\ud \ud In a second part, we developed a microfabrication technique to form arrays of scaffold-free, three-dimensional, geometric tussies by sequential assembly. Using this method, we investigated a novel mechanism of vascular pattern formation in microfabricated tissue undergoing autonomous contraction and structural remodeling. Endogenous tissue contractility produced local tissue deformations and compactions and spatially regulated the VEGF production (gradient formation), the VEGFR2 expression and the formation of stereotyped patterns of blood capillaries. This experiment demonstrate the possibility to recapitulate and investigate tissue pattern formation mechanisms in microfabricated tissues. We propose that endogenous tissue contractility is a tissue-scale morphogenetic regulator of the angiogenic microenvironment and angiogenesis, a finding with wide implications in regenerative medicine and cancer biology.\ud \ud This thesis demonstrate possibilities to engineer vascularized tissue for (1) clinical applications (endochondral bone repair) and (2) as models to investigate mechanisms of vascular pattern formation