Study On The Multifunctional Composite Microcapsules Fabricated From A Template-free Self-assembly Approach

The composite microcapsules comprised from biomacromolecules andmagnetite nanoparticles (MNPs) possess not only a good magneticresponsivity but alsoa characteristic acoustic responsivity throughencapsulating appropriate gas in it. Therefore, it has the ability of enhancingboth ultrasound and magnetic resonance imaging (MRI) in medical diagnosis,which could improve the accuracy of diagnosis by combining the twodifferent medical imaging means. Usually speaking, the compositemicrocapsules were often prepared by the complex method based on"template surface layers assembly-template removal". However, there wasno report studying the preparation of magnetic microcapsules bytemplate-free self-assembling approach, especially the study involvingthefabrication of the "acoustic/magnetic" dual response microcapsules.Therefore, this paper presents a novel template-free self-assembly method tobuild acoustic/magnetic dual responsive microcapsules. In this way, thesuperparamagnetic Fe3O4nanoparticles (MNPs) coated with polycarboxylicligand were synthesized via a ligand-exchange approach, and the magneticcomposite microcapusles were prepared with MNPs and poly(allyamine)(PAH) through a template-free approach. After encapsulating fluorocarbon gas, the composite microcapusles possess the property of acoustic/magneticdual responses. In this study, the mechanism of template-free assemblymethod and the regularity in preparing microcapusles were systematicallydiscussed. Our studies are concluded asfollows.Firstly, magnetic Fe3O4nanoparticles (MNPs-OA) capped with oleic acidwere synthesized through a thermal decomposition method, which had meandiameter of15nm and narrow size distribution according to the observationby transmission electron microscopy (TEM). On this basis, water dispersibleFe3O4nanoparticles were prepared via a ligand exchange approach, in whichthe oil acid on the surface of MNPs was replaced by polycarboxylic molecule.After the ligand exchange reaction, the phase composition and crystallineform of MNPs kept unchanged from X-ray diffraction (XRD) analysis.Moreover, the dispersibility of water-soluble MNPs in their aqueous solutionswas characterized. The results show that the polycarboxylic ligand cappedMNPs display high dispersion stability in their aqueous solutions. Even if theMNPs solution was stored as long as four months, there was no precipitation.This paper also designed a distinctive template-free self-assemblyprocess. The magnetic composite microcapsules were successfully preparedfrom the self-assembly of cationic biomacromolecules (PAH), multivalentanionic salt (Sodium citrate, Na3Cit), the water-soluble MNPs and polyacrylicacid. The relationships between the microcapsules size,the shell thickness andthe preparation conditions were systematically studied. It was found thediameter of microcapsules could be controlled between400nm and2μm, andthe shell thickness of the microcapsules increased linearly with the increasingdiameter. The magnetic composite microcapsules had superparamagneticmagnetic properties, and its magnetic content and saturation magnetizationwere in45%~65%and20~30emu/g, respectively. The encapsulating ofperfluorohexane, which could enchance ultrasond imaging, endow theultrasonic/Magnetic dual imaging ability to the composite microcapsules. Asconfirmed by our study on ultrasound and magnetic resonance imaging invitro, the magnetite composite microcapsules had abilities of enchancing both ultrasond imaging and MRI. Its T2relaxation rates was up to125.9mM-1s-1.Therefore, the as prepared magnetic composite microcapsules have an greatpotential working as ultrasonic/MRI dual contrast agents.