Core-shell nanogel of PEG-poly(aspartic acid) and its pH-responsive release of rh-insulin

A new synthesis approach for the preparation of pH-responsive nanogels via core hydrolysis of cross-linked polymer micelles is proposed. The core-shell nanogels of poly(ethylene glycol)-poly(aspartic acid) exhibited a pH-responsive swelling behavior attributed to the ionization of aspartic acids, and the swelling of the nanogels depended on the cross-linking density. Small-angle neutron scattering (SANS) data were used to investigate the structure and swelling behavior of the nanogels via fitting analysis based on a new model equation that describes two distinguishable scattering intensities that arise from the particle structure and the fluctuation of polymer networks. We estimated that the nanogel core can absorb a volume of water molecules up to 30 times the volume of the polymer itself. The hydrophilic nanogels were able to entrap a protein drug, rh-insulin, and the drug release was retarded under acidic conditions due to deswelling of the nanogels.