Nanosystems for targeted delivery and remote-controlled release of therapeutic agents has become a top priority in pharmaceutical science and drug development in recent decades. Application of a low frequency magnetic field (LFMF) as an external stimulus opens up opportunities to trigger release of the encapsulated bioactive substances with high locality and penetration ability without heating of biological tissue in vivo. Therefore, the development of novel microencapsulated drug formulations sensitive to LFMF is of paramount importance. Here, we report the result of LFMF-triggered release of the fluorescently labeled dextran from polyelectrolyte microcapsules modified with magnetic iron oxide nanoparticles. Polyelectrolyte microcapsules were obtained by a method of sequential deposition of oppositely charged poly(allylamine hydrochloride) (PAH) and poly(sodium 4-styrenesulfonate) (PSS) on the surface of colloidal vaterite particles. The synthesized single domain maghemite nanoparticles integrated into the polymer multilayers serve as magneto-mechanical actuators. We report the first systematic study of the effect of magnetic field with different frequencies on the permeability of the microcapsules. The in situ measurements of the optical density curves upon the 100 mT LFMF treatment were carried out for a range of frequencies from 30 to 150 Hz. Such fields do not cause any considerable heating of the magnetic nanoparticles but promote their rotating-oscillating mechanical motion that produces mechanical forces and deformations of the adjacent materials. We observed the changes in release of the encapsulated TRITC-dextran molecules from the PAH/PSS microcapsules upon application of the 50 Hz alternating magnetic field. The obtained results open new horizons for the design of polymer systems for triggered drug release without dangerous heating and overheating of tissues.
This work is devoted to the evaluation of a change in the barrier height in the case of an atom jump to the nearest vacancy site under strain and to obtaining the vacancy diffusion equation taking into consideration the strain influence. Earlier, we suggested a new approach to solving the problem of the influence of elastic stress on the vacancy jump rate for atomic diffusion in crystals. It was based on the simple observation that a stress field alters the surrounding configuration and on the assumption that the height of the activation barrier should be altered accordingly. The change of the activation barrier was shown to depend on the displacement field, the symmetry of the crystal, the atomic structure near point defects and the interatomic potential. Knowledge of this change makes it possible to calculate the jump rate. The expression for the vacancy flux was obtained with the help of the 'hole gas' method, by using the jump rate. In these nonlinear equations, the influence of the strain tensor component on diffusion flux is determined by coefficients, which depend on the atomic interaction and atomic structure of the saddle-point configuration. One of the aims of the present work is to generalize our approach taking into account N-body interatomic interaction. Now we present the diffusion equation for vacancy in FCC and BCC metals, obtained in a more general and convenient form.
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