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Remote navigation and targeted delivery of biologically active compounds is one of the current challenges in the development of drug delivery systems. Modern methods of micro- and nanofabrication give us new opportunities to produce particles and capsules bearing cargo to deploy and possess magnetic properties to be externally navigated. In this work we explore multilayer composite magnetic microcapsules as targeted delivery systems in vitro and in vivo studies under natural conditions of living organism. Herein, we demonstrate magnetic addressing of fluorescent composite microcapsules with embedded magnetite nanoparticles in blood flow environment. First, the visualization and capture of the capsules at the defined blood flow by the magnetic field are shown in vitro in an artificial glass capillary employing a wide-field fluorescence microscope. Afterward, the capsules are visualized and successfully trapped in vivo into externally exposed rat mesentery microvessels. Histological analysis shows that capsules infiltrate small mesenteric vessels whereas large vessels preserve the blood microcirculation. The effect of the magnetic field on capsule preferential localization in bifurcation areas of vasculature, including capsule retention at the site once external magnet is switched off is discussed. The research outcome demonstrates that microcapsules can be effectively addressed in a blood flow, which makes them a promising delivery system with remote navigation by the magnetic field.

Nanocomposite coatings are promising for a range of practical applications, and layer-by-layer assembly (LbL) is a versatile tool for nanocomposite formation. However, conventional LbL is a quite laborious procedure taking a lot of time to reach a sufficient thickness of the coatings required for practical applications. Herein, we proposed a novel variant of the LbL approach based on the deposition of hydrophilic polyelectrolyte molecules from a polar solvent and hydrophobic magnetite nanoparticles (NPs) from a nonpolar dispersion medium with an intermediate washing in the same polar solvent. The composite multilayers formed in this way exhibit exponential growth of the thickness and mass. On the basis of quartz crystal microbalance (QCM), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), atomic force microscopy (AFM), and surface profile measurements, we propose a model describing the driving force of multilayer formation and the factors leading to nonlinear growth of their mass and thickness. The results allow one to expand the understanding of the mechanism of the LbL assembly in order to form multifunctional nanocomposites in a more efficient way.