Carboxyl-Assisted Coordination-Driven Self-Assembly for the Preparation of Magnetic Polymer Composite Microspheres

Magnetic polymer composite microspheres (MPCMs) with biocompatible coatings are increasingly being recognized as promising candidates for biologic separation, immunoassays, and drug delivery systems. Notwithstanding, conventional preparation methods primarily involve the simple stacking or disordered assembly of magnetic particles. In this study, carboxylate ligands of the poly(styrene-alt-maleic acid) sodium salt (PSMA-Na) facilitate the self-assembly preparation of PSDA@Fe3O4 composite microspheres through bidentate bridging coordination to surface metal ions of Fe3O4. The critical role of carboxyl groups within the amphiphilic alternating copolymer PSMA-Na can be determined so that (1) these can help to establish strong coordination bonds with Fe3O4, serving as a bridge between the magnetic nanoparticles and the polymer material, thereby facilitating the capture of magnetic components; (2) more intriguingly, the magnetic materials within this system undergo a self-assembly process transitioning from the core to the shell, where the strong coordination effect of carboxyl groups results in the formation of a core–shell structure with Fe3O4 uniformly dispersed on the surface of polymer microspheres. Consequently, the PSDA@Fe3O4 microspheres produced exhibit controllable particle size, high magnetic loading, and excellent biocompatibility, presenting potential biomaterial applications in magnetic resonance imaging and drug delivery systems. Significantly, this self-assembly method is straightforward, swift, and widely applicable to nanoparticles and carboxylate organic molecules, offering insights and inspiration for synthesizing additional composite materials.