UC Berkeley

Biomaterials play a crucial role in studying and influencing a range of cellular behaviors, including stem cell differentiation, organogenesis, and tumor invasion. Hyaluronic acid (HA), the primary component of brain extracellular matrix, occupies a unique position in modeling neurological processes, including glioblastoma (GBM) tumor invasion. Traditional synthetic HA hydrogels typically rely on chemical modification to the HA backbone, where low-molecular-weight (LMW) HA is often chosen for its low viscosity to facilitate chemical modification, assembly, and use in cell culture. The modified HA polymers enable efficient molecular binding, allowing for the precise tuning of material properties, from the creation of soft and stiff platforms to the incorporation of adhesion motifs. However, extensive modifications may disrupt critical biological functions, such as the binding efficiency of HA to CD44, a transmembrane receptor essential for HA activity. Additionally, the covalent bonds typically found in standard HA hydrogels also limits the system's viscoelastic capabilities. In contrast, brain tissue is naturally viscoelastic and abundant in high-MW (HMW) HA, whose backbone is devoid of modification. To address these challenges, we have developed a diverse set of hydrogels that more closely mimics brain tissue and investigated how their material properties influence 3D neurological processes, such as cell invasion.

In this dissertation, we explore the tunability of biomaterial properties--ranging from stress relaxation to the degree of polymer modification--and study how these properties influence cell invasion. We begin by surveying the viscoelastic properties of several commonly used biomaterials: collagen I, alginate, HA, and electrospun fibers. We then introduce a novel material design that leverages the natural entanglements of HMW HA chains. This hydrogel not only relaxes stresses quickly, but also does so to a similar extent as brain tissue, surpassing many conventional HA-based scaffolds. Our findings reveal that GBM tumoroids invade much more rapidly in the highly stress-relaxing HMW hydrogel than in its LMW HA counterpart, as well as exhibit distinct leader-follower dynamics where HYAL2-rich deposits trail behind leader cells.

Next, we explore the tunability of HA methacrylation, focusing on hydrogel formation and its effects on cell invasion. While we observe rapid tumoroid growth in hydrogels made of low-modified HA, these hydrogels are also prone to collapse during extended cell culture experiments. In contrast, hydrogels comprised of medium-modified HA not only retain their structural integrity during long cell culture experiments, but also facilitate faster tumoroid invasion in soft hydrogel conditions than in hydrogels made of high-modified HA, a standard hydrogel for 3D cell culture. Finally, we combine our insights on stress relaxation and polymer modification to develop semi-interpenetrating networks (sIPNs) of modified and unmodified HA, providing more precise control over stress relaxation properties. These studies provide valuable insights into how HA hydrogel properties can be manipulated to enhance cell invasion while also highlighting the importance of thoughtful material design in studying neurological processes. Our discovery of distinct leader-follower dynamics and HYAL2-rich deposits, arising from the rapid invasion observed in HMW HA hydrogels, exemplifies the potential of these brain-mimetic materials. Their use provides an enhanced platform for studying neurological processes, paving the way for groundbreaking insights and promising therapeutic advancements.