Nanocomposite capsules containing magnetite nanoparticles (MNPs) are promising multifunctional drug delivery systems for various biomedical applications. The presence of MNPs allows one to visualize these capsules via magnetic resonance imaging (MRI) and optoacoustic (photoacoustic) imaging. Moreover, we can ensure precise navigation and remote release via a magnetic field gradient and alternating magnetic fields, respectively. Magnetic dipole–dipole interaction between single capsules is important when a magnetic field is applied, and it is determined by a magnetic moment of each individual capsule. However, there is a lack of experimental data on the magnetic moment of a single capsule. Physical properties of capsules vary due to the change in the volume fraction of MNPs, as well as the capsule shell architecture. Therefore, two types of submicron capsules with different amounts of MNPs were synthesized. The first type of capsules was prepared by freezing-induced loading and layer-by-layer (LbL) assembly. The amount of MNPs varied by the number of freezing-induced loading cycles: two, four, and six. The second type of capsules is a nanocomposite shell formed using the LbL assembly of the oppositely charged polyelectrolytes and MNPs. Structural properties of both types of submicron capsules and MNPs were studied using transmission electron microscopy. Magnetic moments of nanocomposite shells placed in an external magnetic field were directly measured by optical tweezers and calculated based on vibrating-sample magnetometer measurements of the water suspension of nanocomposite shells. The magnetic moment of an individual shell depends on the amount of MNPs and increases as the number of MNPs per shell grows. Magnetic coupling parameters and the specific absorption rate were calculated. The obtained results can be applied while preparing drug carrier systems sensitive to alternating magnetic fields and navigated by gradient magnetic fields. They can also be taken into account in device development for navigating drug delivery systems and for the treatment based on alternating magnetic field-induced hyperthermia.

In this work, the preparation procedure and properties of anionic magnetic microgels loaded with antitumor drug doxorubicin are described. The functional microgels were produced via the in situ formation of iron nanoparticles in an aqueous dispersion of polymer microgels based on poly(N-isopropylacrylamide-co-acrylic acid) (PNIPAM-PAA). The composition and morphology of the resulting composite microgels were studied by means of X-ray diffraction, Mössbauer spectroscopy, IR spectroscopy, scanning electron microscopy, atomic-force microscopy, laser microelectrophoresis, and static and dynamic light scattering. The forming nanoparticles were found to be β-FeO(OH). In physiological pH and ionic strength, the obtained composite microgels were shown to possess high colloid stability. The average size of the composites was 200 nm, while the zeta-potential was −27.5 mV. An optical tweezers study has demonstrated the possibility of manipulation with microgel using external magnetic fields. Loading of the composite microgel with doxorubicin did not lead to any change in particle size and colloidal stability. Magnetic-driven interaction of the drug-loaded microgel with model cell membranes was demonstrated by fluorescence microscopy. The described magnetic microgels demonstrate the potential for the controlled delivery of biologically active substances.

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