Enhanced degradation and peptide specificity of MMP-sensitive scaffolds for neovascularization of engineered tissues

Biomaterial strategies for engineering tissues of clinically relevant size require the formation of rapid and stable neovascularization. The ability of an engineered scaffold to induce vascularization is highly dependent on its degradation rate. Matrix metalloproteinases (MMPs) plan an important role in mediating cell-induced proteolytic matrix degradation, remodeling and controlled neovascularization. Poly (ethylene glycol) PEG hydrogels have been extensively investigated as scaffolds for tissue engineered applications due to their ease of chemical modification to recapitulate key aspects of the neovascularization process. The goal of the work described in this thesis was to develop strategies to enhance and control the degradation of MMP-sensitive PEG diacrylate (PEGDA) hydrogels without inducing changes in the bulk physical and mechanical properties of the material and to study the effect of cleavage site concentration and MMPsensitive peptide substrate specificity on the rate of neovascularization and tissue remodeling in vitro and in vivo. In the first part, a detailed investigation was completed to investigate the effects of the mechanical and physical properties of the scaffolds and the role of proteolytically mediated hydrogel degradation and acidic fibroblast growth factor (FGF-1) on 3D fibroblast invasion within MMP-sensitive PEGDA hydrogels. In the second part, a novel and controllable technique was developed to generate scaffolds with controlled cleavage site concentration, and tunable degradative properties without alterations in the bulk physical and mechanical properties, which showed controlled enhancement in degradation and neovascularization in vitro. In the final study, the effect of the cleavage site concentration and specificity of MMP-sensitive peptide substrates to degradation by MMPs expressed during neovascularization were investigated for degradation, neovascularization and tissue remodeling. Results showed that vascularization and tissue invasion was supported in all MMP-sensitive hydrogel groups regardless of the MMP-sensitive peptide substrate embedded in the matrix and that the cleavage site concentration had a profound impact in enhancing vascularization and tissue invasion.;These studies provide insight into the effect of the physical, mechanical, and degradative properties of these systems and how the concentration of cleavage sites, sensitivity to degradation, and specificity of MMP substrates affect the neovascularization and tissue invasion process.