Perfusable branching microvessel bed for vascularization of engineered tissues

Abstract

Vascularization is critical for the survival of engineered tissues in vitro and in vivo. In vivo, angiogenesis involves endothelial cell proliferation and sprouting followed by connection of extended cellular processes and subsequent lumen propagation through vacuole fusion. We mimicked this process in engineering an organized capillary network anchored by an artery and a vein. The network was generated by inducing directed capillary sprouting from vascular explants on micropatterned substrates containing thymosin β4-hydrogel. The capillary outgrowths connected between the parent explants by day 21, a process that was accelerated to 14 d by application of soluble VEGF and hepatocyte growth factor. Confocal microscopy and transmission electron microscopy indicated the presence of tubules with lumens formed by endothelial cells expressing CD31, VE-cadherin, and von Willebrand factor. Cardiac tissues engineered around the resulting vasculature exhibited improved functional properties, cell striations, and cell-cell junctions compared with tissues without prevascularization. This approach uniquely allows easy removal of the vasculature from the microfabricated substrate and easy seeding of the tissue specific cell types in the parenchymal space.microvasculature | contact guidance | controlled release | angiogenic factors | cardiac tissue engineering

Harnessing developmental processes for vascular engineering and regeneration

“…Radisic and colleagues developed collagen hydrogel materials for controlled release of Tβ4 over 28 days (Chiu and Radisic, 2011). They observed increased EC migration and tube formation in a hydrogel containing Tβ4 and enhanced vascularization when injected in vivo (Chiu et al, 2012a). Moreover, they applied the hydrogel/Tβ4 system to myocardial infarction in rats, which resulted in improved angiogenesis, reduced tissue loss and retained left ventricular wall thickness after infarction compared with Tβ4-free and soluble controls (Chiu et al, 2012b).…”

Cardiac Tissue Engineering

“…Blood vessels grew into the sheets and allowed repeated implantations and the generation of thicker, fully vascularized grafts that survived after connection to a recipient's circulation and transplantation in the neck region of rats ( Figure 1G). Radisic et al 58 developed an elegant in vitro approach in which 2 blood vessel explants are embedded on 2 opposing sides of a collagen-chitosan hydrogel-releasing thymosin β4, layered on micropatterned silicone surfaces. This stimulated the longitudinally directed outgrowth of capillaries from the vessels, which after ≈2 weeks started to connect the 2 explant vessels, allowing directed perfusion.…”

“…In a second step, cardiac myocytes were then cultured on top of the vascularized hydrogel-bed (Figure 2A-2E). 58 Whereas in the latter approach endothelial cells from blood vessels explants are used to form capillaries that support cardiac myocytes, endothelial cells contained in cardiac cell sheets were also shown to be able to connect to noncellularized microchannels in collagen Figure 2F). 59 Similarly, microchannels in EHTs generated by enzymatically dissolving alginate-fibers embedded in the EHT reconstitution mix during casting were populated by endothelial cells.…”

Oscillatory Strain Promotes Vessel Stabilization and Alignment through Fibroblast YAP‐Mediated Mechanosensitivity

“…During vascularization, endothelial cells (ECs) sense two forms of mechanical stimulation, shear stress, as a consequence of blood flow, and mechanical strain, as a consequence of rhythmic heart beating and tissue contraction 1, 2, 3, 4. While many studies have focused on the effect of shear stress on vessel mechanotransduction, there is much less information on the effect of mechanical strain on vascularization‐related processes 4…”