(324h) Hybrid Electrostatic-Covalent Hydrogels

Polyelectrolyte complexes (PEC) form when oppositely charged polyelectrolyte chains spontaneously associate and phase separate in aqueous media. Combining one or both polyelectrolyte chains with a neutral polymer restricts bulk phase separation of the PECs, and thus leads to self-assembled micelles and hydrogels with PEC domains surrounded by neutral polymer coronae. The PEC domains can encapsulate charged therapeutics, genetic materials and proteins, thus enabling and enhancing the utility of PEC hydrogels for diverse biomedical applications. The use of these self-assembled hydrogels in drug delivery, tissue engineering and bioadhesion applications, however, requires the establishment of elaborate fundamental mappings interrelating the hydrogel mesoscale structures, nanoscale relaxation processes and bulk material properties. In this presentation, we will highlight our current understanding of the equilibrium structure and bulk rheology of PEC hydrogel assemblages comprising oppositely charged triblock polyelectrolytes. A comprehensive structural description of these materials will be presented, indicating large-scale ordering of the nanoscale PEC domains, characterized by a disorder-order transition, followed by morphological transitions with increasing polymer loading. Further, we will discuss our investigations on hybrid hydrogels comprising interpenetrating electrostatic (PEC) and covalent networks. Minimal influence of incorporation of the covalent network on the equilibrium hierarchical structure of PEC networks will be demonstrated, conserving the gel’s ability to encapsulate biomolecules and other charged cargo. At the same time, we will highlight marked improvements in the shear and the tensile strengths of the PEC hydrogels upon incorporation of the covalent network, even as a minor component, in the hybrid hydrogels. The decoupling of hydrogel structure and rheology, along with improved resistance to salt and controllable swelling, will be argued to further broaden the utility of the PEC hydrogels in diverse biomedical applications.