Self-Assembled (Nano)Structures of Human Serum Albumin with Thermoresponsive Chitosan-g-PNIPAM Graft Copolymer

Protein-polyelectrolyte entities (complex, coacervates, flocs, gels, etc.) are of great interest due to their potential applications in biological and medical fields. This study focuses on investigating the interactions between a model protein, human serum albumin (HSA) and a newly synthesized hybrid thermoresponsive copolymer based on chitosan polysaccharide grafted with poly(<i>N</i>-isopropylacrylamide) synthetic polymer chains (Chit-<i>g</i>-PNIPAM), in aqueous media, by mixing the individual component aqueous solutions. Depending on the mixing molar ratio and the order of addition of the two components (protein and copolymer), either stable nanostructured suspension or macrostructures' phase separation have been observed. Dynamic light scattering (DLS) results reveal that the Chit-g-PNIPAM/HSA_x (molar ratio 5:x, where x = 1, 2, 3, 5, 10 and 15) nanostructures' and HSA/Chit-g-PNIPAM_x (molar ratio 100:x, where x = 1, 2, 3, 10, 20, 30, 40 and 50) structures' formation depend on the molar ratio of the two components as well as on the order of addition, with first component amount being kept constant in aqueous solution and second component solution added drop-by-drop in the solution of the first component. Additional information regarding the thermoresponsiveness and stability vs time of the formed (nano)structures were acquired using turbidimetry and DLS measurements.