A new catechol-functionalized poly(amidoamine) as an effective nanoparticle stabilizer

Superparamagnetic iron oxide nanoparticles (SPIONs) have been in the spotlight in the last years as promising candidates for a plethora of different biomedical applications, for both imaging (magnetic resonance imaging, MRI) and therapeutic purposes (e.g. magnetofluidic hyperthermia, MFH). However, in order to impart the SPIONs the necessary stability and solubility, a coating of the iron oxide surface is needed. In this work we aimed at functionalizing SPIONs with a previously developed amphoteric poly(amidoamine), nicknamed ISA23: this polymer is synthesized by a stepwise Michael addition of 2-methylpiperazine onto bis(acryloamido)acetic acid, and was previously found to be biocompatible and to exhibit “stealth-like” properties once injected into animals, avoiding immediate identification and disposal after intravenous injection. These important characteristics would be imparted to the core/shell SPION@ISA23, improving this way their blood circulation times and, consequently, their potential usefulness for biomedical applications. Effective binding to the iron oxide surface was achieved functionalizing the polymer with cathecol moieties, whose high affinity towards iron is already exploited in a variety of natural siderophores. In order to introduce this functional group, nitrodopamine was chosen over dopamine thanks to its higher stability towards oxygen- and metal-catalyzed oxidation. Coupling of nitrodopamine to the free carboxylic group of the polymer, employing EDC-coupling chemistry, resulted in the functionalization of ca 15% of the repeating units. This polymer was then successfully employed for SPIONs coating, affording stable and water-dispersible nanoparticles, whose characterization is currently in progress.