Polyelectrolyte multilayers fabricated from ‘charge-shifting’ anionic polymers: a new approach to controlled film disruption and the release of cationic agents from surfaces

We report an approach to the design of ‘charge-shifting’ anionic polymers that provides control over the disruption of ultrathin polyelectrolyte multilayers in aqueous media. We demonstrate that the addition of citraconic anhydride to poly(allylamine) yields an anionic, carboxylate-functionalized polymer (polymer 2) that can be converted readily back to cationic poly(allylamine) in acidic environments. The incorporation of polymer 2 into polyelectrolyte multilayers thus provides an approach to the fabrication of films that are stable at neutral pH but that erode over a period of several days in acidic media (e.g., pH 5). Experiments using a structural analog of polymer 2 with carboxylate side chains that do not hydrolyze readily provided support for the view that the disruption of these films occurred as a result of polymer side chain hydrolysis and a resulting change in the net charge of the polymers. Because this approach is based upon the use of anionic polymers to induce film instability, it provides a platform for the design of multilayers that can be used to provide control over the release of cationic film components. As proof of concept, we demonstrated that ultrathin films 100 nm thick fabricated using polymer 2 sustain the release of fluorescently labeled PAH for up to four days when incubated at pH 5.0. The synthetic approach used here is modular and tunable and can be used to introduce anionic ‘charge-shifting’ character to a broad range of other polyamines. With further development, this approach could expand significantly the range of different cationic agents (e.g., cationic proteins, peptides, polymers, nanoparticles, etc.) that can be released or delivered from surfaces using polyelectrolyte multilayers.