Synthetic blood vessels and in vitro modelling of the blood-brain-barrier

Author(s): Kyle A. DiVito

Traditional in vitro models have examined the blood brain barrier (BBB) using 2D Transwell® assays, however this approach fails to address the full functionality of the BBB largely due to the absence of active perfusion. An improved model would integrate multiple human cell types into a tunable organ system that would permit blood vessel perfusion and facilitate heterotypic cell-cell interactions, such as tight junctions analogous to those observed in vivo. Here, we report the ability to create 3D microvessels composed of biocompatible polymers such as polyethylene (glycol) and gelatin methacrylamide (GelMA) which contain either traditional endothelial cells (HUVEC) or specialized brain microvascular endothelial cells (hCMEC). Using photo-polymerization, these polymers form hollow microvessels that replicate the human BBB and support perfusion. The created blood vessels are ~200 µm in O.D., yet capillary outgrowths derived from the original vessels are <10um in O.D. mimicking brain capillaries observed in vivo. Endothelial cells integrated within the blood vessel express typical markers such as CD31 and von Willibrand factor (vWF). When placed into an extracellular matrix containing normal human astrocytes these microvessels display advanced developmental features such as angiogenesis and the development of astrocytic foot processes. We also describe a novel manifold device that houses the BBB tissue construct and enables the collection of perfusate over various time points, thus making significant advances beyond traditional assays. In conclusion, updated 3D models such as this will better recapitulate the BBB and greatly improve the ability to interrogate barrier function.
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