Nanogel-type nano-objects from a random polyelectrolyte through intermolecular cross-linking

Abstract

Polyelectrolyte nanogel-like nano-objects were synthesized from poly((2-dimethylamino) ethyl methacrylate-co-oligoethylene glycol methacrylate), P(DMAEMA-co-OEGMA), random copolymers through covalent cross-linking with the hydrophobic 1,12-dibromododecane difunctional quaternizing agent, with varying degrees of cross-linking, corresponding to different dimethylamino group molar conversions to quaternized, permanently cationic amino groups. Physicochemical characterization, employing dynamic and electrophoretic light scattering (DLS, ELS), along with fluorescence spectroscopy (FS) measurements under various solution conditions elucidated distinct self-assembled structures of the formed polymer networks, most probably due to the utilization of the hydrophilic random copolymers as precursor macromolecules. The nanogels demonstrated pH responsiveness and temperature sensitivity, advantageous for applications requiring controlled release or environmental adaptability, while the stability under high ionic strength conditions indicated their resilience in complex physiological environments and varying salinities. Furthermore, Nanogel 2, displaying a balanced response to environmental factors, was successfully complexed with protein ovalbumin (OVA). The produced OVA/Nanogel 2 complexes maintained their size under high salt concentrations and sustained colloidal stability over time, even under ultrasound exposure. Further characterization through Cryo-TEM and ATR-FTIR spectroscopy highlighted the efficient complexation of OVA, revealing varying co-assembled structures, including irregular nano-objects consisting of thread-like structures and sphere-like morphologies comprised of branched-like internal structures, dependent on the protein concentration. We expect that such hybrid nanostructures may be promising for enzyme immobilization and as vaccine-delivering vehicles with special morphologies.