Microfabricated blood vessels undergo neoangiogenesis

Abstract

The greatest ambition and promise of tissue engineering is to manufacture human organs. Before "made-to-measure" tissues can become a reality [1-3], however, three-dimensional tissues must be reconstructed and characterized. The current inability to manufacture operational vasculature has limited the growth of engineered tissues. Here, free-standing, small diameter blood vessels with organized cell layers that recapitulate normal biological functionality are fabricated using microfluidic technology. Over time in culture, the endothelial cells form a monolayer on the luminal wall and remodel the scaffold with human extracellular matrix proteins. After integration into three-dimensional gels containing fibroblasts, the microvessels sprout and generate extended hollow branches that anastomose with neighboring capillaries to form a network. Both the microfabricated vessels and the extended sprouts support perfusion of fluids and particles. The ability to create cellularized microvessels that can be designed with a diameter of choice, produced by the meter, and undergo angiogenesis and anastomoses will be an extremely valuable tool for vascularization of engineered tissues. To summarize, ultraviolet (UV) photo-crosslinkable poly(ethylene glycol) and gelatin methacrylate polymers used in combination with sheath-flow microfluidics allow for the fabrication of small diameter blood vessels which undergo neoangiogenesis as well as other developmental processes associated with normal human blood vessel maturation. Once mature, these vessels can be embedded; perfused; cryogenically stored and respond to stimuli such as chemokines and shear stresses to mimic native human blood vessels. The applications range from tissue-on-chip systems for drug screening, characterization of normal and pathologic processes, and creation and characterization of engineered tissues for organ repair.

Recapitulating the Vasculature Using Organ-On-Chip Technology

“…However, the process becomes more complex and the printed networks are less accurate. Examples taken from: left [67] (scale bar 500 µm), right [64] (scale bar 5 mm). Angiogenesis-based platforms: This method employs angiogenesis from an existing vessel or an endothelial layer into a matrix, either by a chemotactic gradient or by activating angiogenesis in the endothelial layer.…”

“…Examples taken from: left [79] (scale bar 500 µm), right [87] (scale bar 200 µm). Images based on [1,41,47,49,51,57,59,64,67,72,73,79,87].…”

“…An alternative to layer-by-layer printing is directly printing vessels by coaxial extrusion, using a smaller diameter nozzle inside another nozzle to dual extrude two materials in a fibre and sleeve manner. This coaxial extrusion creates multi-layered tube structures that can be arranged in specific patterns [66,67]. Despite the inability of fabricating in-plane bifurcations with this method, junctions can still be obtained via the remodelling of the matrix by the cells, connecting adjacent vessels [66].…”

Fabrication Techniques for Vascular and Vascularized Tissue Engineering

“…These capillary networks can then anastomose with the sprouting vessels stemming the host BVs in vitro . Another study also showed that neighboring capillary sprouts stemming from the same large BV can undergo anastomosis and form a closed‐loop system for blood circulation …”

“…Capillary anastomosis is a recently developed approach for fabricating hierarchical vasculature that relies on connecting sprouts from a large vasculature with a capillary network that is formed within a surrounding matrix ( Figure A). The larger BVs can be fabricated within a gel through microfluidic approaches, 3D sacrificial printing, or hydraulic focusing, and seeded with ECs to first form a confluent monolayer and induce angiogenesis to form sprouts. Concurrently, ECs and supporting cells form capillary networks in the gel through vasculogenesis.…”