Regulating Growth Factor Activity via Biomimetic Materials

Growth factor (GF) sequestering to the native extracellular matrix (ECM) regulates GF bioavailability and activity. Vascular endothelial growth factor (VEGF) is a particular growth factor that initiates angiogenesis during wound healing, and VEGF spatial and temporal activity is tightly controlled by sequestering to the ECM. Aberrant VEGF signaling to vascular endothelial cells promotes pathological angiogenesis during tumor growth and macular degeneration, which motivates the need to spatially regulate VEGF activity with biomaterials. ECM-derived hydrogels have been shown to regulate the activity of VEGF, but naturally-derived materials promiscuously bind GFs and thus are limited their ability to regulate the activity of a particular GF. In contrast, poly(ethylene glycol) represents a "blank slate" hydrogel due to its non-fouling properties and ease of functionalization with macromolecules. In this thesis, we describe an approach to specifically regulate VEGF activity using PEG hydrogel microspheres with pendant, biomimetic VEGF binding peptides (VBPs) derived from VEGFR2. We systematically varied the chemical composition of VBP microspheres and demonstrated that a particular formulation of VBP microspheres specifically sequestered VEGF and regulated VEGF-dependent endothelial cell function in serum-containing culture. We demonstrated the ability to control VEGF activity by engineering VBP microsphere degradation rate using modular chemical crosslinking groups. Degradable VBP microspheres reduced vascular growth in a choroidal neovascularization model in vivo, which demonstrates a clinical application of degradable VEGF sequestering microspheres as a therapy for pathological angiogenesis. We demonstrated the general nature of this GF sequestering approach by designing biomimetic peptides and peptide-containing microspheres that sequestered transforming growth factor beta1(TGFbeta1) and regulated TGFbeta1 activity in culture. Finally, based on the complexity of endothelial cell behavior during angiogenesis, we sought to design a quantitative, hydrogel-based model of sprouting angiogenesis in vitro to deconstruct the molecular control of endothelial sprouting behavior in vitro. We systematically examined the influence of 13 distinct hydrogel and a full concentration range of 9 pharmacological inhibitors on endothelial sprouting behavior in vitro. Taken together, the modular PEG hydrogel platforms described here enabled the design of therapeutic VEGF sequestering microspheres for regenerative medicine applications and the design of a novel endothelial sprouting assay for drug screening applications.