Polyelectrolyte - Multivalent Ion Interactions In Jammed Granular Microgels

Hydrogel particles, commonly called microgels, often rely on charged polyelectrolytes to drive swelling at low polymer concentrations. These highly swollen microgels have found applications across industrial and academic fields as rheological modifiers, drug delivery systems, 3D printing supports, and 3D cell culture media. However, interactions between the polyelectrolytes and multivalent ions in the solvent can limit their applications. Charged polyelectrolytes are strongly sensitive to multivalent ions and can dramatically deswell or collapse driven by osmotic pressure or condensation of counterions. For example, microgels have been swollen in cell growth media to study the behavior of cells in a 3D environment. However, the presence of multivalent ions in cell growth media, including Ca²⁺ and Mg²⁺, can have drastic effects on the rheological properties of the microgels as well as the behavior of suspended cells. To mitigate these problems, we create polyacrylamide microgels with anionic, cationic, and zwitterionic comonomers at varying charge densities and investigate the effects of Ca²⁺ ions on their rheological properties. We extend our findings to 3D cell cultures to explore the effects on cell viability and functionality.