Guided sprouting from endothelial spheroids in fibrin gels aligned by magnetic fields and cell-induced gel compaction.

An aligned engineered microvascular network is critical to the culture of thick or highly metabolic tissue in vitro due to the need for inlet and outlet sides for perfusion of the network. Contact guidance may be a way to achieve aligned networks, but the relationship between the alignment of endothelial sprouts and the alignment of extracellular matrix fibers has yet to be fully elucidated. The data presented here show that sprouts from human blood outgrowth endothelial cell spheroids align with fibrin fibrils, and that the extent to which the sprouts align depends upon the strength of the fibril alignment. This was true for both magnetically-aligned fibrin and fibrin aligned via cell-induced gel compaction, although magnetically-aligned fibrin was more effective over the same culture period. The data also demonstrate that longer sprouts are grown when the fibrils, and thus the sprouts, are more strongly aligned. The formation of aligned endothelial sprouts using these methods can be an essential step in the generation of aligned microvascular networks.