Matus Molcan

The single- and multicore iron oxide nanoparticles (IONPs) were synthesized, and their structural and magnetic properties were evaluated to assess their applicability in magnetic hyperthermia. Whereas the single-core IONPs obtained by the co-precipitation method consisted of roughly spherical particles with an average magnetic core diameter of ~ 10 nm, the multicore IONPs, prepared by applying the standard polyol protocol, exhibited a characteristic morphology: they looked like they were composed of smaller grains of ~ 9 nm, assembled in a flower shaped structure with an overall diameter of ~ 30 nm. The experimental evaluation of the specific absorption rate (SAR) of both single-core IONPs and multicore IONPs was conducted by calorimetric measurements. The SAR values of both samples increased with the applied magnetic fields H up to ~7.9 kA·m⁻¹, with multicore IONPs showing significantly higher SAR than single-core IONPs. These results highlight the potential of multicore IONPs as efficient nanoheaters for hyperthermia-based cancer treatment.

Liquid marbles are widely known for their potential biomedical applications, especially due to their versatility and ease of preparation. In the present work, we prepared liquid marbles with various cores composed of water, agar-based hydrogels, magnetic fluids, or non-aqueous substances. As a coating material, we used biocompatible particles of plant origin, such as turmeric grains and Lycopodium pollen. Additionally, we provided marbles with magnetic properties by incorporating either magnetosomes or iron oxide nanoparticles as a powder or by injecting another magnetic fluid. Structures obtained in this way were stable and susceptible to manipulation by an external magnetic field. The properties of the magnetic components of our marbles were verified using electron paramagnetic resonance (EPR) spectroscopy and vibrating sample magnetometry (VSM). Our approach to encapsulation of active substances such as antibiotics within a protective hydrogel core opens up new perspectives for the delivery of hydrophobic payloads to the inherently hydrophilic biological environment. Additionally, hydrogel marbles enriched with magnetic materials showed promise as biocompatible heating agents under alternating magnetic fields. A significant innovation of our research was also the fabrication of composite structures in which the gel-like core was surrounded without mixing by a magnetic fluid covered on the outside by the particle shell. Our liquid marbles, especially those with a hydrogel core and magnetic content, due to the ease of preparation and favorable properties, have great potential for biomedical use. The fact that we were able to simultaneously produce, functionalize (by filling with predefined cargo), and manipulate (by means of an external magnetic field) several marbles also seems to be important from an application point of view.

High-frequency components such as microprocessors, transistors, antennas, voltage-controlled oscillators, and many others generate a large amount of heat. In the absence of satisfactory cooling, these components may suffer damage or even destruction. Therefore, it is important to find effective ways to cool these components. A possible solution is to use oil-based magnetic fluids. Magnetic fluids contain magnetic particles dispersed in oil, and their properties, including viscosity, affect their cooling capabilities. Viscosity can be changed by adding various additives or by adjusting the concentration of magnetic particles. The advantage of using oil-based magnetic fluids for cooling is that they allow for precise dosing and control of the amount of fluid applied to the component, reducing thermal losses and increasing cooling efficiency. In addition, oil-based magnetic fluids can also act as a dielectric, reducing electrical noise and increasing electromagnetic compatibility with the components. Analyzing the heating rate of magnetic fluids consisting of mineral oils in an alternating magnetic field with a frequency of 500 kHz, we have shown the capability of controlling thermal losses by adjusting the viscosity of the carrier liquid.

A number of materials are studied in the field of magnetic hyperthermia. In general, the most promising ones appear to be iron oxide particle nanosystems. This is also indicated in some clinical trial studies where iron-based oxides were used. On the other hand, the type of material itself provides a number of variations on how to tune hyperthermia indicators. In this paper, magnetite nanoparticles in various forms were analyzed. The nanoparticles differed in the core size as well as in the form of their arrangement. The arrangement was determined by the nature of the surfactant. The individual particles were covered chemically by dextran; in the case of chain-like particles, they were encapsulated naturally in a lipid bilayer. It was shown that in the case of chain-like nanoparticles, except for relaxation, a contribution from magnetic hysteresis to the heating process also appears. The influence of the chosen methodology of magnetic field generation was also analyzed. In addition, the influence of the chosen methodology of magnetic field generation was analyzed. The application of a rotating magnetic field was shown to be more efficient in generating heat than the application of an alternating magnetic field. However, the degree of efficiency depended on the arrangement of the magnetite nanoparticles. The difference in the efficiency of the rotating magnetic field versus the alternating magnetic field was much more pronounced for individual nanoparticles (in the form of a magnetic fluid) than for systems containing chain nanoparticles (magnetosomes and a mix of magnetic fluid with magnetosomes in a ratio 1:1).

The effect of the liquid crystalline host on structural changes in magnetosomes based on ferronematics is studied using the surface acoustic wave (SAW) technique supported by some capacitance and light transmission measurements. The measurement of the attenuation response of SAW propagating along the interface between LC and the piezoelectric substrate is used to study processes of structural changes under magnetic field. The magnetosome nanoparticles of the same volume concentration were added to three different nematic LCs, 5CB, 6CB, and E7. Unlike to undoped LCs, the different responses of SAW attenuation under the influence of magnetic and electric fields in LCs doped with magnetosomes were observed due to characteristic structural changes. The decrease of the threshold field for doped LCs as compared with pure LCs and slight effects on structural changes were registered. The threshold magnetic fields of LCs and composites were determined from capacitance measurements, and the slight shift to lower values was registered for doped LCs. The shift of nematic-isotropic transition was registered from dependencies of SAW attenuation on temperature. The acoustic anisotropy measurement approved the previous supposition about the role of bulk viscosity in used SAW measurements. In addition, capacitance and light transmition investigations supported SAW results and pointed out conclusions about their magnetic field behavior. Obtained results are discussed and confronted with previous ones and coincide well with those observed using acoustic, optical, or dielectric techniques.

Dextran-coated magnetic nanoparticles are promising biocompatible agents in various biomedical applications, including hyperthermia and magnetic resonance imaging (MRI). However, the influence of dextran molecular weight on the physical properties of dextran-coated magnetic nanoparticles has not been described sufficiently. We synthesise magnetite nanoparticles with a dextran coating using a co-precipitation method and study their physical properties as a function of dextran molecular weight. Several different methods are used to determine the size distribution of the particles, including microscopy, dynamic light scattering, differential centrifugal sedimentation and magnetic measurements. The size of the dextran-coated particles increases with increasing dextran molecular weight. We find that the molecular weight of dextran has a significant effect on the particle size, efficiency, magnetic properties and specific absorption rate. Magnetic hyperthermia measurements show that heating is faster for dextran-coated particles with higher molecular weight. The different molecular weights of the coating also significantly affected its MRI relaxation properties, especially the transversal relaxivity r₂. Linear regression analysis reveals a statistically significant dependence of r₂ on the differential centrifugal sedimentation diameter. This allows the targeted preparation of dextran-coated magnetic nanoparticles with the desired MRI properties. These results will aid the development of functionalised magnetic nanoparticles for hyperthermia and MRI applications.

Several methodologies for the preparation of nanofibrous materials exist. Electrospinning is currently the most popular technique due to its versatility and simplicity. Nanofibrous materials prepared in such a way are widely studied in medicine and material engineering. Polyvinyl butyral (PVB) nanofibers were generated by a rod-shaped spinning-electrode. Nanofibers were modified by a magnetic fluid (MF) added into the PVB solution. These magnetic nanofibers can be considered as a material for magnetic hyperthermia applications, either as implants or for the surface heating. The samples with various magnetic particle concentrations were tested in the alternating magnetic field. An immediate increase in the temperature after the field application was observed. The nature of the temperature rise is interesting: a non-linear increase could be seen, which is in contrast to the rising temperature for pure magnetic fluids.