Polyelectrolyte Complexes: The Effects of Charge Distribution and Charge Density

Abstract

Polyelectrolytes are widely used as components in biomaterial applications. This thesis focuses on the design, synthesis, and investigation of polyelectrolyte complexes and their respective properties based on charge arrangement and charge density. The tunability of ionic interactions in polyelectrolyte complexes was then demonstrated in applications including alginate-based polyelectrolyte complexation for microcapsules and in strong polyampholyte hydrogels. Polyelectrolytes comprising methacrylic acid (MAA) and N-(3-aminopropyl)methacrylamide hydrochloride (APM) in different ratios were prepared and used to explore the interactions of different single- and multicomponent PECs with different charge arrangements using turbidimetric/potentiometric titration, UV-vis spectroscopy, microscopy, and isothermal titration calorimetry. The complexes were shown to have isoelectric points (pH(I)) at which macroscopic phase separation is induced that are highly dependent on the polymer composition as well polymer mixing ratio for multi-component PECs. Additionally, these complexes have sensitivity to [NaCl] shielding effects that are dependent on charge separation, improving with charge compensation and shifting from solid precipitates to liquid coacervates in strong complexes. The PECs exhibit cloud point temperatures indicative of lower critical solution temperature behaviours. These polyelectrolytes were then used to bind model ionic dyes and were crosslinked using naturally occurring genipin, indicating their potential as drug delivery materials. The system of MAA-APM polyelectrolytes was further explored as betaines were introduced to the individual polymers for three distinct coacervates: charge-balanced polyampholytes, pairs of complementary, nonstoichiometric polyampholytes, and pairs of pure polyanion-polycations. 2-methacryloyloxyethyl phosphorylcholine (MPC) was introduced into the different polyelectrolytes and drastically increased the responsiveness of complexes to pH, [NaCl], and temperature. MPC notably enhances complex hydration in single-component polyampholyte coacervates, while complex coacervates are less effectively destabilized with greater coacervate stability by charge separation. The exploration of structure-property relationships in polyelectrolytes was then extended to alginate-based complexation for applications in cell encapsulation, as compositional distribution and charge dilution influence the formation and stability of the complexed polyanion-polycation surface coatings. A semi-batch approach was employed to limit compositional variability in the copolymerization of APM and MPC. Different copolymers were then explored as potential low-fouling, cationic shell formers capable of covalent crosslinking with different reagents, including naturally occurring genipin. The crosslinked capsules show good mechanical and low protein adsorption. Finally, the underlying principles of charge density effects were demonstrated in strong polyampholyte hydrogels. Using a styrenic system of charged monomers, a near-alternating copolymerization was achieved and generated physical hydrogels with stimuli-responsive properties and high mechanical strength. Both the physical and mechanical properties are highly dependent on monomer loading during gel preparation. To tune the hydrogel properties, charge-neutral termonomers were incorporated to reduce charge density but show that termonomer selection has significant impacts on the responsive and mechanical properties. These polyampholyte hydrogels appear capable of stimuli-responsive self-healing.