Design and Fabrication of Cell-laden Hydrogel Microparticles for Cell Therapy Applications

Abstract

Hydrogels have been widely explored for cell therapy applications due to their favourable biochemical and mechanical properties. However, the dimensions of bulk hydrogels limit the diffusion of nutrients to cells and cell products to the surrounding environment, negatively affecting cell viability and the therapeutic potential of the encapsulated cells. In addition, invasive procedures are often required for the administration of bulk hydrogels into patients that pose a practical barrier to cell therapy. To address these issues, micrometer sized hydrogels (microgels) have been designed with controlled shapes, sizes, and structures to enable sufficient biomolecule diffusion and injectable administration. In this thesis, in situ gelling poly(oligoethylene glycol methacrylate) (POEGMA) and zwitterionic microgels are fabricated based on delayed dynamic hydrazone crosslinking between cell friendly functionalized polymers without the need for any additional crosslinking agents. Two microgel fabrication strategies were explored: (1) droplet-based microfluidics and (2) droplet extrusion printing. In the first case, microgels with controlled degrees of porosity were fabricated via the incorporation of a non-toxic evaporable porogen into a microfluidic device. Porous microgels had significantly improved diffusion of small molecules compared to nonporous microgels, and cells encapsulated in the porous microgels showed significantly increased viability over 10 days. In the second case, droplet extrusion printing was employed to print a bioink on a hydrophobic surface, resulting in the fabrication of disk-shaped microgels with a height below the maximum pathlength of oxygen and nutrient diffusion. Cells encapsulated in the microgels maintained high viability, with the microgels also supporting effective cell proliferation over 10 days. Overall, the work presented in this thesis poses solutions to challenges around nutrient/cell product diffusion and the invasive procedures typically associated with hydrogel-based cell therapy, providing potentially new translatable therapeutic options for disease treatment.