Engineering of vascular conduits

The best vascular substitutes are autologous materials but their unavailability or their poor quality are not uncommon, which then requires the use of synthetic prostheses. If these prostheses yield an excellent efficacy record in large diameters, such is not longer the case when small-caliber vessels have to be grafted and it is in this setting that vascular engineering techniques are electively indicated. Based on the variable combination of cells and natural or synthetic scaffolds, these techniques rely on diverse strategies: seeding of synthetic grafts; use of serosal cavities as natural bioreactors; seeding of degradable biomaterials; autologous self-assembled cellularized tubes; cell-free scaffolds. Each of these techniques has advantages and drawbacks but all share in common the observation that the grafted cells are rapidly cleared from their supportive scaffold. The paradigm has then shifted from the use of cells as presumed constituents of a neo-tissue to that of cells considered as mediators of vascular remodeling through the recruitment of host cells. The identification of the key factors involved in this recruitment opens a new field in vascular engineering based on the harnessing of the endogenous neovascularization capacity. This concept technically translates into the development of acellular degradable scaffolds functionalized with motifs that can induce the repopulation of the graft by the recipient cells, thereby minimizing the deleterious effects at the blood-material interface (thrombosis, intimal hyperplasia) without compromising the elasticity and compliance of the neo-vessel.