Novel chitosan-based pH-sensitive and disintegrable polyelectrolyte nanogels

A novel approach to design pH-sensitive and disintegrable polyelectrolyte nanogels composed of citraconic-based N -(carboxyacyl) chitosan (polyanion) and quaternary chitosan (polycation) was reported. Firstly, the hydrolysis of citraconic-modified chitosan was monitored using fluorescamine assay and it could selectively dissociate in acidic media (e.g., pH ∼5.0) due to the isomerization during the addition of citraconic anhydride to chitosan. Secondly, the self-assembly behaviors of different polyelectrolyte pairs between citraconic-based chitosan and quaternary chitosan were investigated via colloidal titration assay. It was indicated that the difference in molecular weight (MW) of opposite charged polyelectrolytes played an important role on the formation of polyelectrolyte nanogels. Results showed that polyelectrolyte nanogels (ca. 300   nm in size) only formed when polyanion and polycation had a very large difference in MW. The pH-sensitive behavior of polyelectrolyte nanogels was comprehensively investigated by dynamic light scattering (DLS) and transmission electron microscope (TEM). The incorporation of charge-conversional citraconic-based chitosan into polyelectrolyte complexes has provided an effective approach to prepare polyelectrolyte nanogels which were very stable at neutral pH but disintegrated quickly in acidic media.