Chain Length Effect of the Multidentate Block Copolymer Strategy to Stabilize Ultrasmall Fe3O4Nanoparticles

Abstract

A multidentate block copolymer (MDBC) strategy to stabilize ultrasmall superparamagnetic iron oxide nanoparticles (USNPs) as biocompatible T1-positive contrast agents for magnetic resonance imaging (MRI) is explored. The MDBC is designed with a poly(methacrylic acid) (PMAA) block having pendant carboxylates as multidentate anchoring groups and a hydrophilic polymethacrylate block having pendant oligo(ethylene oxide) chains (POEOMA). A series of multifunctional MDBCs with different chain lengths of POEOMA and PMAA blocks were synthesized by atom transfer radical polymerization and subsequent hydrolytic cleavage. The resultant aqueous MDBC/USNP colloids fabricated through a ligand-exchange process were characterized to investigate the effect of chain lengths of POEOMA-b-PMAA copolymers on size, morphology, and colloidal stability as well as relaxometric properties and in vitro MRI performance. The results suggest that the optimal design of chain lengths of both anchoring and hydrophilic blocks is required for enhanced colloidal stability under biologically relevant conditions as well as effective T1-weighted contrast enhancement.