In recent years, considerable effort has been devoted to the development and investigation of systems for controlled delivery of drugs. Targeted delivery of drugs significantly increases their efficacy and allows the total drug concentration in the organism to be considerably decreased. In order to solve this task, special containers/carriers have been designed possessing preset and controlled physicochemical and mechanical properties. The function of such containers can be performed, for example, by polymeric micelles [1][2][3][4], liposomes [5], emulsions [4, 6, 7], and colloidal particles. This class also includes polyelectrolyte (PE) microcapsules obtained by the method of polyion assembly, which consists in sequential adsorption of oppositely charged PE molecules on the surface of colloidal particles (templates), followed by the dissolution and removal of the initial core [8,9]. Using this approach, it is possible to obtain capsules with a broad range of preset dimensions (from 50 nm to 50 µ m) and a broad spectrum of shell materials. Indeed, the shells of microcapsules can be made of almost any synthetic and natural PEs [8,[10][11][12][13], lipid bilayers, inorganic nanoparticles (e.g., of silver, gold, or iron(III) oxide) [14][15][16], and polyvalent metal ions. The core (template) material can be selected from colloidal particles of various kinds with diameters ranging from tens of nanometers to several tens of microns [8,10,[17][18][19]. The capsule walls can also be controlled with respect to thickness, functional role, and permeability to any low-and high-molecular-mass compounds [20][21][22].The unique properties of PE microcapsules make it possible to use them in various fields of science and technology, such as biotechnology, cosmetics, the food industry, and medicine. The main advantage to such capsules in medical diagnostics is possibility of filling them with various drugs [23] and controlling their properties (e.g., elasticity and deformability) by varying the shell composition, template material, solvent [24], and the nature and number of PE layers. However, in order to ensure the desired result, a container must release the encapsulated drug in the immediate vicinity of damaged cells. For this purpose, inorganic magnetic nanoparticles of Fe 3 O 4 (magnetite) possessing pronounced magnetic properties can be introduced in the shell composition at the synthesis stage, which makes it possible to control the motion of capsules under an applied external magnetic field. Magnetite nanoparticles also possess certain advantages from a pharmaceutical standpoint: (i) the surface of these particles can be readily modified with compounds ensuring the biocompatibility and selective adsorption of microcapsules on damaged cells; (ii) the magnetic parameters of nanoparticles make their local concentration possible with the aid of magnetic fields [25][26][27]. The magnetic-fieldcontrolled delivery and localization of magnetic nanoparticles with a preset magnetic transition temperature Atomic Force Microscopy Ch...
