Application of Hydrogel-Based Materials for Vascular Targeted Drug Delivery

Abstract

The design of vascular targeted carriers (VTCs) has continually been optimized in terms of size and shape, and recently, attention has also shifted to carrier elasticity, which has been shown to have significant impact on circulation time and immune cell clearance. Notably, soft materials such as hydrogels have been of interest because of their high water content and biocompatibility. In this thesis, we develop an enzyme-degradable hydrogel material suitable for use as a VTC and characterize its use as a carrier for NPs, followed by an in-depth investigation of interactions between elastic particles and human neutrophils. Finally, we developed a scalable, high-throughput technique to produce rod-shaped hydrogel particles. We first developed multiple reaction schemes to incorporate enzyme-sensitive peptides (VPM) into a polyethylene-glycol hydrogel (PEG) matrix and selected for a material that degraded completely in the presence of trypsin and MMP-2. Thiol-ene photopolymerization did not allow for reaction specificity of thiol to acrylate groups. Nucleophilic Michael addition instead allowed for greatly increased peptide incorporation (up to 95%), generating high-MW PEG-VPM macromers, yielding a hydrogel material capable of degrading completely in the presence of trypsin in the span of two hours. We pivoted to a multifunctional PEGVS molecule to increase crosslinking density, successfully developing an enzyme-degradable hydrogel material with physical properties suitable for vascular drug delivery. Using this material, we fabricated hydrogel particles for use as VTCs, and successfully demonstrated that they could degrade enzymatically, be functionalized with targeting ligands, be loaded with non-degradable PS NPs, and adhere to an inflamed monolayer of endothelial cells. 2 – 4 µm particles were generated using a water-in-oil emulsion and characterized using SEM. These particles were degraded using MMP-2, a more physiologically relevant enzyme compared to trypsin, and were found to degrade completely within 6 hours. Next, to demonstrate their utility as VTCs, we conjugated particles with avidin and biotin-anti-ICAM1 using a thiolated avidin protein to react with residual vinyl sulfone groups. We confirmed successful conjugation by staining with fluorescent tags and analyzing with flow cytometry. Finally, we perfused targeted particles over a layer of activated HUVEC and demonstrated that enzyme-degradable hydrogels had an 8-fold increase in particle adhesion compared to an untargeted particle control. We found neutrophils effectively phagocytose particles of various moduli, despite macrophages exhibiting a lowered ability to uptake soft particles compared to stiff particles. 2 µm and 500 nm PEG particles were taken up at an equivalent or greater rate by primary human neutrophils as compared to PS. We similarly saw equivalent uptake of HA-based particles (50 – 700 kPa) by human neutrophils. These trends were visually confirmed using optical tweezer assays. Surface conjugation of the particle resulted in notable reduced uptake, likely due to increased albumin adsorption, based on SDS-PAGE analysis of the protein corona of the particle. Finally, we successfully developed a novel fabrication technique for the shearing of polymer droplets and in situ crosslinking of deformed droplets to generate rod-shaped hydrogel particles. The displacement-flow driven shear system allowed us to fabricate elongated hydrogel particles with an average ESD of 5 µm and an AR between 1 – 3.5 from a shear rate of 0 – 1400 s-1. Overall, in this dissertation, we seek to demonstrate the utility of hydrogels specifically within the context of vascular targeted drug delivery and showcase the potential of soft materials for tissue engineering.