Scientists Found the "Social" Behavior of Magnetic Nanoparticles

09:41, May 17, 2022

Discovery applicable to targeted medication delivery and cancer treatment technologies

Magnetic nanoparticles evenly distributed in ferrofluids show unusual behavior: small particles obey the collective behavior of large particles. This is reported in an article published in the Journal of Molecular Liquids scientific journal. The discovery plays an important role in applications of magnetic nanoparticles, such as magnetic technologies for targeted medication delivery and treatment of cancer. The work was financially supported by the Ministry of Science and Higher Education of the Russian Federation as part of the Priority 2030 program.

During the study, the co-authors of the article, Aleksey Ivanov, professor at the Ural Federal University, and Philip Camp, professor at the University of Edinburgh, first in mathematical calculations and then in computer simulations ordered magnetic nanoparticles of different sizes by the influence of an external magnetic field, and then turned it off.

"An unexpected effect was discovered. It is known that the smaller the magnetic particles, the faster their disordering (relaxation) occurs, and vice versa: the larger the particles, the longer their relaxation takes. However, our theoretical calculations and the following computer simulations show that in the presence of large particles, relaxation of small particles occurs irregularly. In the state of low residual magnetization of small particles, i.e. when 5-10% of these particles are unordered, they suddenly begin to obey the collective behavior of large particles. Relaxation time of small particles lengthens and approaches the relaxation time of large particles. Although the number of small particles in ferrofluids is always many times greater than the large ones. This is similar to the behavior of naughty children. The smaller the child, the faster he goes wild in the absence of adults. However, under the influence of adults, looking back at them, fidgety one behaves much more modestly," explains Aleksey Ivanov.

Another effect discovered: at low temperatures, long chains of nanoparticles form ring-shaped aggregates in which the magnetic moments of the particles, closing in a circle, cease to respond to a weak external magnetic field.

"This is important to consider in magnetic hyperthermia, when magnetic particles are used to provide local heating of areas of an organ affected by cancerous cells. The larger the particles, the greater the heating, at the same time for a greater therapeutic effect the particles must be distributed so that they do not stick together and do not form large aggregates, lumps. In other words, it is necessary to look for the golden mean," emphasizes Aleksey Ivanov.

Further research by the article's co-authors will focus on identifying the causes of the detected phenomena. The discovery by Aleksey Ivanov and Philip Camp is of great practical importance for the development of so-called smart materials-capable of changing their properties in a controlled manner under the influence of a constant or alternating magnetic field. In addition to magnetic hyperthermia, such materials are used to increase the contrast of X-rays and tomographic images of internal organs, in technologies for targeted medication delivery to specific areas of the body, in the manufacture of liquid crystal screens, photodetectors, heat conductors, sealants, and hydraulic shock absorbers.

Reference

In earlier works, Aleksey Ivanov, Philip Camp, and their colleague Ekaterina Elfimova, Head of the Department of Theoretical and Mathematical Physics at UrFU, have identified other effects of "social" behavior of magnetic nanoparticles - particles of magnetic materials 10-15 nanometers in size, which is a hundred times smaller than the thinnest human hair. Scientists found that the particles respond not only to the external magnetic field, but also to each other, so their "collective behavior" is not reduced to the sum of "individual" reactions and represents a special phenomenon.

The subject of the study was magnetic nanoparticles introduced into biological tissue, for example, into the intercellular space or into the polymer matrix of a composite. In this state, the particles are immobilized and cannot move in space, but their magnetic moments rotate chaotically (this phenomenon is called superparamagnetism). When a constant external magnetic field is applied, energy competition arises: the field tends to turn the magnetic moments of particles toward itself, while they want to turn along the axes of light magnetization - the most energetically advantageous directions of magnetic moments. At the same time, it turned out that particles, being small magnets that create their own magnetic field around themselves, react not only to the applied external magnetic field, but also to each other, taking into account the interaction with the ensemble of other magnetized particles.

Scientists at the UrFU were the first to calculate formulas for such "group behavior" of particles, and Philip Camp confirmed the truth of the calculations on computer models.

The news article was translated by UrFU International Marketing Office
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