Physical and Chemical Signals That Promote Vascularization of Capillary-Scale Channels

Abstract

Proper vascularization remains critical to the clinical application of engineered tissues. To engineer microvessels in vitro, we and others have delivered endothelial cells through preformed channels into patterned extracellular matrix-based gels. This approach has been limited by the size of endothelial cells in suspension, and results in plugging of channels below ~30 μm in diameter. Here, we examine physical and chemical signals that can augment direct seeding, with the aim of rapidly vascularizing capillary-scale channels. By studying tapered microchannels in type I collagen gels under various conditions, we establish that stiff scaffolds, forward pressure, and elevated cyclic AMP levels promote endothelial stability and that reverse pressure promotes endothelial migration. We applied these results to uniform 20-μm-diameter channels and optimized the magnitudes of pressure, flow, and shear stress to best support endothelial migration and vascular stability. This vascularization strategy is able to form millimeter-long perfusable capillaries within three days. Our results indicate how to manipulate the physical and chemical environment to promote rapid vascularization of capillary-scale channels within type I collagen gels.

Construction of a patterned hydrogel—fibrous mat bilayer structure to mimic choroid and Bruch's membrane layers of retina

“…The vascularization of tissue engineering scaffolds is crucial since the integration of the construct with the tissues depends on the nutrient transfer . Similar to our results, the vascularization of biomaterials with microchannels was recently shown by bioprinting agarose template fibers and microfabricating type I collagen microchannels in gels by photolithography . However, to the best of our knowledge, no vascularization study that employed a microchannel network with a fractal tree design has been performed until now.…”

“…31 Similar to our results, the vascularization of biomaterials with microchannels was recently shown by bioprinting agarose template fibers 32 and microfabricating type I collagen microchannels in gels by photolithography. 33 However, to the best of our knowledge, no vascularization study that employed a microchannel network with a fractal tree design has been performed until now. This is the first study consisting of a bilayer, with a fractal tree pattern on a hydrogel activated with cell adhesion cues and a fibrous mat.…”

Vascularization and Angiogenesis in Tissue Engineering: Beyond Creating Static Networks

“…Perfusion of these channels with culture medium results in the active transport of nutrients within engineered tissues, resulting in increased cell survival in vitro [41]. A recent study shows that channels as narrow as 20 mm can be seeded successfully with endothelial cells, resulting in millimeter-long perfusable capillaries [42]. This development enables the creation of an engineered tissue with a vascular tree-like network, including a highly organized capillary bed, where all cells are within 200 mm from a vascular structure.…”

Tissue‐engineered 3D microvessel and capillary network models for the study of vascular phenomena

“…The templating method for microvessel formation is normally restricted to relatively large diameter vessels (>20 μm) due to the difficulty in seeding cells in small cylindrical tubes without clogging . However, capillary networks can be formed between two parallel microvessels by exploiting stimulated angiogenesis and anastomosis or self‐assembly (Figure A,B).…”

“…The templating method for microvessel formation is normally restricted to relatively large diameter vessels (>20 μm) due to the difficulty in seeding cells in small cylindrical tubes without clogging. 19,77 However, capillary networks can be formed between two parallel microvessels by exploiting stimulated angiogenesis and anastomosis or self-assembly 2,78,79 (Figure 8A The selection of ECM, concentration, and the extent of crosslinking all affect the degree of sprouting and capillary growth rate. [80][81][82] In general, low matrix concentrations promote angiogenic sprouting; however, higher concentrations are preferred to maintain robust microvessels that are stable under flow.…”