Formation of Human CapillariesIn Vitro: The Engineering of Prevascularized Matrices

Abstract

Initial take, development, and function of transplanted engineered tissue substitutes are crucially dependent on rapid and adequate blood perfusion. Therefore, the development of rapidly and efficiently vascularized tissue grafts is vital for tissue engineering and regenerative medicine. Here we report on the construction of a network of highly organotypic capillaries in engineered tissue substitutes. We employed a three-dimensional culture system consisting of human microvascular endothelial cells. These were reproducibly expanded at high purity and subsequently seeded into biodegradable, fibrin-based hydrogels. The process of capillary formation in vitro followed the principles of both angiogenesis and postnatal vasculogenesis and a distinct sequence of other developmental steps that closely resemble embryonic neovascularization. Capillary lumen formation in vitro was initiated by the deposition of a basement membrane and intensive pinocytosis, followed by the generation of intracellular vacuoles, successive fusion of these vacuoles, and finally the formation of a long, continuous lumen. After transplantation the vascular structures were stabilized by mural cells of the recipient animal. Our findings suggest that the in vitro engineering of prevascularized matrices is within reach.

Mechanotransduction of fluid stresses governs 3D cell migration

“…For example, cell contraction induces deformation of the local matrix, and this deformation is propagated through the ECM to neighboring cells (42). For endothelial cells on 2D surfaces, traction generated by one cell can be transmitted to a neighboring cell inducing protrusion formation and migration toward the contractile cell (43).…”

Hydrogel-based microfluidics for vascular tissue engineering

“…There are two explicit mechanisms of blood vessel growth: vasculogenesis, the de novo formation of blood vessels by endothelial progenitor cells, and angiogenesis, the sprouting of new vessels from preexisting ones. For engineering of microvasculature within a 3-D cell laden biomaterial construct, many biological extracellular matrix (ECM) materials and cell co-cultures have been studied with respect to their vasculogenic potential [1][2][3][4]. Mimicking the embryonic environment for vasculogenesis is a popular strategy; for example, experiments on encapsulation of vascular progenitor cells within 3-D biological ECM have been undertaken, in which angioblasts and mesenchymal stem cells self-organize into a microvascular network and form a capillary bed [5].…”

Skin and hair on-a-chip: in vitro skin models versus ex vivo tissue maintenance with dynamic perfusion

“…Further bioengineering is particularly necessary for the implementation of adipose tissue, hair follicles and a functional vascular network. [4][5][6][7] Notably, adipose-derived stromal cells are not only important for lipid metabolism, but also have a major impact on the regulation of fibroblast and keratinocyte proliferation by cytokine secretion. 8 In addition, the hair follicle serves as a considerable storage area, takes a substantial role in skin metabolism, contains multiple stem cell lineages with regenerative capacity, and constitutes the major penetration route of topically applied substances to the skin.…”

“…Therefore, endothelial cells have been integrated into the dermal portion of fullthickness skin substitutes. 12,6,7 However, because of the lack of shear stress in existing in vitro systems, no mature blood vessels have been produced and no skin substitute with an artificial blood stream at micro-scale has been described so far. Such an improved skin equivalent needs to be implemented in a culture system which permits a constant oxygen and nutrient supply, measures and removes toxic metabolites, and can be intravitally monitored for sustainability over weeks and even months.…”