Development of Jammed Microparticle-Based Materials for Embedded 3D Printing, Injectable Cell Delivery Applications, and In Vitro Cancer Cell Migration Studies

Granular microgel-based materials are an interesting and promising platform with uses in a wide range of biomedical applications. These material systems consist of particles packed together to form a material exhibiting solid-like behaviors at rest, but upon application of a force can fluidize, and thus provide advantages over traditional, continuous hydrogels in formulating injectable hydrogels and developing porous 3D in vitro models. Properties of granular materials can be tuned to improve biomanufacturing processes such as enhanced 3D printing resolution of complex features, deliver cells in a minimally-invasive manner, and to study key cell processes as a function of local mechanical changes to an environment, and are the focal points of this dissertation.

In my first study, gelatin and norbornene-modified hyaluronic acid (NorHA) were used to formulate microparticles for a removable ink and printing support, respectively, to create perfusable channels using embedded 3D printing. Printing of tunable diameter channels was demonstrated, along with diffusion of large proteins and small molecules from the perfused channels into the surrounding support structure. Human umbilical vein endothelial cells were used to line perfused channels and showed proliferation and flattening over time, demonstrating the potential for future in vitro vasculature development.

My second study examines the rheological characteristics, injectability, and cell delivery application of NorHA microparticles tethered together using dynamic electrostatic interactions. To do so, cationic gelatin was synthesized and mixed with anionic NorHA microgels. Rheological studies show poroelastic-like behaviors and strain-stiffening, both relevant to native tissues. These particle-based formulations were demonstrated to be injectable and have good filament formation, qualities important for hydrogel delivery and 3D printing applications. Lastly, cell viability in extruded and non-extruded groups was assessed as a function of cationic gelatin concentration.

My third study further tunes this electrostatically-stabilized granular platform to study cancer cell migration. Metastasis is heavily dependent on extracellular matrix (ECM) mechanics, and thus the development of an in vitro model in which cells can easily move, total polymer content is maintained, and combined with tunable mechanics, is crucial to further understand this process. Because bulk properties in granular systems are dependent on interparticle interactions, the zeta potential of interstitial gelatin is modulated, producing supports with altered rheological properties and microstructural characteristics. Cancer cell migratory behaviors such as speed and migratory path were measured and found to be dependent on gelatin zeta potential and porosity.