Novel method to improve vascularization of tissue engineered constructs with biodegradable fibers.

Tissue engineered grafts lack adequate vascularization and suffer from poor perfusion in vivo curtailing clinical application. Improving vascularization in any tissue implants would hence increase their survivability and treatment efficacy. Many prevascularization strategies established to date involves the angiogenic induction of endothelial progenitor cells in thick tissue engineered scaffolds to obtain vascularization. These 3D scaffolds typically require a dynamic cell culturing system involving/needful of bioreactors to obtain vascularization in thick tissue engineered scaffolds. Herein, we developed a novel method to engineer a vessel network without bioreactor, where 3D blood vessels could be simply obtained in a 2D static cell culturing system. This network could be used to augment the prevascularization of tissue engineered grafts. Endothelial cells (HUVECs) were confluently cultured on resorbable electrospun poly (D, L-lactide-co-glycolide) microfibers of capillary dimensions. These cell encapsulated capillary fibers were further embedded in collagen with HUVECs and vascular endothelial growth factor. Green fluorescent protein and red fluorescent protein expressing HUVECs were used to label cells on fiber and in collagen respectively for visualization and monitoring of capillary network formation. Seeded HUVECs in the hybrid construct were subsequently cultured for 30 days before implantation. Vessel density was measured by the total tubule length per unit area at different time points. In vitro results indicated that the fibers provide contact guidance to form primary networks to direct more vessels branching of HUVECs in hybrid constructs and the vessel integrity of microvasculature was retained after fiber degradation. In addition, these preformed engineered capillaries could capably inosculate with de novo capillaries in collagen when combined, giving rise to a hybrid pre-vascularized scaffold of more extensive vessel network and interconnections, thereby markedly improved prevascularization. When implanted onto the dorsal skin of immune-deficient mice, vessels of hybrid pre-vascularized scaffold also rapidly anastomosed with mice vasculature within a day as confirmed with the immunostaining of endothelial cell markers CD31 and von Willebrand factor. This proof of concept study showed that artificial capillaries formed through contact guidance of endothelial cells on resorbable capillary sized microfibers can significantly enhance prevascularization in tissue engineered constructs intended for surgical implantation.