Background: As vascularization represents the rate-limiting step in permanent incorporation of hydrogel-based tissue-regeneration templates, the authors sought to identify the material chemistry that would optimize endothelial cell adhesion and invasion into custom hydrogel constructs. The authors further investigated induction of endothelial tubule formation by growth factor supplementation and paracrine stimulation.
Methods: Hydrogel scaffolds consisting of combinations of alginate, collagen type I, and chitosan were seeded with human umbilical vein endothelial cells and maintained under standard conditions for 14 days. Cell density and invasion were then evaluated. Tubule formation was evaluated following basic fibroblast growth factor addition or co-culture with human aortic smooth muscle cells.
Results: Human umbilical vein endothelial cells demonstrated greatest cell-surface density and invasion volumes with alginate and collagen (10:1 weight/weight) scaffolds (p < 0.05). Supplementation with basic fibroblast growth factor increased surface density but neither invasion nor tubule formation. A significant increase in tubule content/organization was observed with increasing human aortic smooth muscle cell-to-human umbilical vein endothelial cell ratio co-culture.
Conclusions: Alginate and collagen 10:1 scaffolds allow for maximal cellularization compared with other combinations studied. Growth factor supplementation did not affect human umbilical vein endothelial cell invasion or morphology. Paracrine signaling by means of co-culture with human umbilical vein endothelial cells stimulated endothelial tubule formation and vascular protonetwork organization. These findings serve to guide future endeavors toward fabrication of prevascularized tissue constructs.