Synthesis of Clickable Poly(ethylene glycol) Derivatives for Fabrication of Modular Microsphere-Based Scaffolds to Promote Vascularization
Date of Award
Doctor of Philosophy (PhD)
Vascularization plays an important role in supporting transplanted tissues and cells in tissue engineering applications. Most tissues require access to blood vessels for the delivery of oxygen and nutrients, as well as the removal of carbon dioxide and cellular waste products. Without an adequate blood supply, cells within tissue-engineered constructs and scaffolds lose viability and fail to perform their intended functions. The goal of this dissertation was to design scaffolds that can promote vascularization of biomaterial implants for biomedical applications. In order to accomplish this goal, clickable poly(ethylene glycol) (PEG) derivatives were synthesized in order to fabricate modular microsphere-based scaffolds that could deliver angiogenic growth factors and molecules. Microspheres were formed by lowering the lower critical solution temperature (LCST) of PEG, inducing thermal phase separation, and forming spherical PEG-rich domains that increased in size until they reached the gel point. Using a PEG/dextran aqueous two-phase system, microspheres were crosslinked via click reactions to form scaffolds. Conjugation of these scaffolds with cell adhesion peptides and proteins allowed for cell attachment and migration. Subsequently, scaffolds were formed in the presence of cells to confirm cell attachment and demonstrate that the functionalized PEG and the scaffold fabrication process did not affect cell viability. To show that the scaffolds did not adversely affect the activity of loaded growth factor, biologically active vascular endothelial growth factor (VEGF) was successfully loaded into and delivered from the scaffolds in an endothelial cell migration assay. Finally, fibroblasts and endothelial cells were seeded into the scaffolds to determine if the scaffolds were able to support vascular formation. After 21 days, the scaffolds demonstrated small regions of vascularization. The vascularization in these scaffolds was comparable to what we had observed with similar scaffold implants in mice. To improve scaffold vascularization, future work will be done to adjust their porosity, growth factor delivery, and introduce scaffold degradability. Overall, this dissertation demonstrated that clickable PEG microsphere-based scaffolds have excellent potential for inducing vascularization in tissue engineering applications.
Steven George, Garland Marshall, Robert Mecham, Shelly Sakiyama-Elbert