Engineering Next-Generation Granular Hydrogels for Vasculogenesis

Advancing three-dimensional tissue scaffolds is central to creating in vitro models and engineered tissues that recapitulate biological tissues. Minimally invasive biomaterial delivery for tissue regeneration can be achieved through rapid stabilization after injection. Granular hydrogels offer a promising platform for injectability due to their microporous architecture, which facilitates cellular infiltration and nutrient transport. However, achieving high porosity without compromising structural integrity remains a key challenge. This dissertation explores two strategies to enhance porosity: (1) reducing microgel density in a non-crosslinked system and (2) incorporating electrospun nanofibers to reinforce hydrogel structure. A polyethylene glycol (PEG)-based granular hydrogel system was developed, integrating electrospun nanofibers and sacrificial gelatin microgels to achieve tunable porosity while maintaining mechanical stability. In vitro results revealed that porosity and the presence of cell adhesive ligand, RGD, significantly influence microvasculature network formations. Current clinical applications utilize injectable granular hydrogels that can be crosslinked via photoinitiation, offering precise control, but this process is limited due to its ineffectiveness in deep tissue applications. Other existing strategies for crosslinking include pH changes, electrostatic interactions, and enzymatic reactions, but these often lack spatiotemporal control. This work explores an alternative crosslinking approach using focused ultrasound (FUS). FUS is a controllable, noninvasive energy source offering deep tissue penetration that can induce hydrogel polymerization within minutes. In this work, crosslinking parameters were optimized and validated both in vitro and in a mouse cadaver model, demonstrating successful hydrogel formation in a minimally invasive context. The resulting granular hydrogels exhibited viscoelastic properties comparable to photocrosslinked systems, retained high porosity, and demonstrated potential avenues within drug delivery platforms. This dissertation establishes a novel PEG-based fiber-reinforced granular hydrogel system for vasculogenesis and highlights FUS as a noninvasive biomaterial crosslinking method. These findings provide new insights into hydrogel design for tissue engineering and therapeutic applications.