Bioactive Poly(ethylene glycol)-based Hydrogels for Angiogenesis in Tissue Engineering
Saik, Jennifer Elaine
West, Jennifer L.
Doctor of Philosophy
Because engineered tissue constructs are inherently limited by their lack of microvascularization, which is essential to provide oxygen for cell survival, this thesis presents rationally designed materials and cell culture techniques capable of supporting functional tubule formation and stabilization. Combining a synthetic scaffold material with cells and their cell-secreted signals instigated tubule formation throughout the scaffold. Poly(ethylene glycol) (PEG) based hydrogels, biocompatible polymers which resist protein adsorption and subsequent nonspecific cellular adhesion, were modified to induce desired cell characteristics. Human umbilical vein endothelial cells were used as a reproducible and readily available cell type. Several tubule-stabilization signals, including platelet derived growth factor-BB (PDGF-BB) and ephrinA1, were covalently immobilized via conjugation to PEG to enable prolonged bioactive signaling and controlled local delivery. All hydrogels were further tested in a mouse cornea micropocket angiogenesis assay, a naturally avascular tissue for easy imaging in a reproducible and quantifiable assay. Hydrogels containing soluble growth factors induced vessel formation in the hydrogel, and the resulting vessel morphology was modulated using different growth factor concentrations. Immobilized PDGF-BB led to tubule formation in two dimensions, three dimensions, and in the mouse cornea while immobilized ephrinA1 stimulated secretion of extracellular matrix proteins laminin and collagen IV to stabilize the newly formed tubules. Finally, a co-culture of endothelial and pericyte cells encapsulated into hydrogels formed tubules that anastomosed to the host vasculature and contained red blood cells. PEG-based hydrogels represent a promising technique to induce microvascular formation in engineered constructs, leading to stable and functional vessel formation using covalently immobilized growth factors and encapsulated cells. These materials can be used for replacement of damaged or diseased tissues as the current supply of cadaveric donations cannot meet the demand of tissues for the 110,000 people awaiting an organ in the US.