The magneto-mechanical actuation (MMA) of magnetic nanoparticles with a low-frequency alternating magnetic field (AMF) can be used to destroy cancer cells. So far, MMA was tested on different cells using different nanoparticles and different field characteristics, which makes comparisons and any generalizations about the results of MMA difficult. In this paper, we proposed the use of giant unilamellar vesicles (GUVs) as a simple model system to study the effect of MMA on a closed lipid bilayer membrane, i.e., a basic building block of any cell. The GUVs were exposed to barium-hexaferrite nanoplatelets (NPLs, 50 nm wide and 3 nm thick) with unique magnetic properties dominated by a permanent magnetic moment that is perpendicular to the platelet, at different concentrations (1–50 µg/mL) and pH values (4.2–7.4) of the aqueous suspension. The GUVs were observed with an optical microscope while being exposed to a uniaxial AMF (3–100 Hz, 2.2–10.6 mT). When the NPLs were electrostatically attached to the GUV membranes, the MMA induced cyclic fluctuations of the GUVs’ shape corresponding to the AMF frequency at the low NPL concentration (1 µm/mL), whereas the GUVs were bursting at the higher concentration (10 µg/mL). Theoretical considerations suggested that the bursting of the GUVs is a consequence of the local action of an assembly of several NPLs, rather than a collective effect of all the absorbed NPLs.
COBISS.SI-ID: 20924163
Atomic-resolution scanning-transmission electron microscopy showed that barium hexaferrite (BHF) nanoplatelets display a distinct structure, which represents a novel structural variation of hexaferrites stabilized on the nanoscale. The structure can be presented in terms of two alternating structural blocks stacked across the nanoplatelet: a hexagonal (BaFe6O11)2- R block and a cubic (Fe6O8)2+ spinel S block. The structure of a vast majority of the nanoplatelets can be described with an SR*S*RS stacking order, corresponding to a BaFe15O23 composition. The nanoplatelets display a large, uniaxial magnetic anisotropy with the easy axis perpendicular to the platelet, a crucial property enabling different novel applications based on aligning the nanoplatelets with applied magnetic fields. However, the HF nanoplatelets exhibit a modest saturation magnetization, Ms, of just over 30 emu/g. Given the cubic S block termination of the platelets, layers of maghemite (M), with a cubic spinel structure, can be easily grown epitaxially on the surfaces of the platelets, forming a sandwiched M/BHF/M platelet structure. The exchange-coupled composite nanoplatelets exhibit a remarkably uniform structure, with an enhanced Ms of more than 50 emu/g while essentially maintaining the out-of-plane easy axis. The enhanced Ms could pave the way for their use in diverse platelet-based magnetic applications.
COBISS.SI-ID: 30880551
An understanding of the adaptation of the crystal structure of materials confined at the nanoscale, the influences of their specific structures on the evolution of their morphologies and, finally, their functional properties is essential not only for expanding fundamental knowledge, but also for facilitating the designs of novel nanostructures for diverse technological and medical applications. We analysed how the distinct structure of barium-hexaferrite nanoplatelets evolves in a stepwise manner in parallel with the development of their size and morphology during hydrothermal synthesis. The nanoplatelets are formed by reactions between Ba- and Fe-hydroxides in an aqueous suspension at temperatures below 80 C. Scanning-transmission electron microscopy showed that the structure of the as-synthesized, discoid nanoplatelets (2.3 nm thick, 10 nm wide) terminates at the basal surfaces with Ba-containing planes. However, after subsequent washing of the nanoplatelets with water, the top two atomic layers dissolve from the surfaces. The final structure can be represented by a SRS* sequence of the barium-hexaferrite SRS*R* unit cell, where S and R represent a hexagonal (BaFe6O11)2- and a cubic (Fe6O8)2+ structural block, respectively. Due to the stable SRS* structure, the thickness of the primary nanoplatelets remains unchanged up to approximately 150 C, when some of the primary nanoplatelets start to grow exaggeratedly, and their thicknesses increase discretely with the addition of the RS segments to their structure. The SRS* structure of the primary nanoplatelets is too thin for the complete development of magnetic ordering. However, the addition of just one RS segment (SRS*R*S structure) gives the nanoplatelets hard magnetic properties.
COBISS.SI-ID: 31549735
In the paper, we presented a significant advance in the colloidal stabilization of nanoparticles in complex biological media that is one of the ongoing challenges for the usage of nanoparticles in biomedicine. A new strategy enabled the preparation of the first stable colloidal suspensions of permanently-magnetic nanoparticles with applicable properties in biological media. A very common solution is to coat the nanoparticles’ surfaces with dextran via an electrostatic or coordinative attachment. The dextran molecules can be subsequently crosslinked to form a biocompatible coating. However, these procedures are not suitable for nanoparticles with an extreme tendency for agglomeration that often occurs during the coating steps. The novel functionalisation strategy ensures the colloidal stability of the system in all the steps of the coating process. In addition to this, the robustness of the dextran coating, obtained by the covalent attachment of the dextran molecules via the 3-glycidyloxypropyl-trimethoxysilane linker to the surfaces of the silica-coated nanoparticles, ensures the colloidal stability of nanoparticles in complex biological media. As a case study we selected permanently magnetic barium hexaferrite nanoplatelets that are extremely prone to agglomeration due to the magnetic dipole-dipole interaction and their plate-like shape. At the same time, barium hexaferrite nanoplatelets are receiving increasing attention for their use in biomedical applications.
COBISS.SI-ID: 32311847
The suspensions of hexaferrite nanoplatelets developed in the project enabled the development of a new diagnostic method based on their magneto-mechanical actuation. Improving the actual clinical techniques for cardiovascular imaging is the first step towards the improvement of both the diagnosis and treatment of cardiovascular diseases that are, nowadays, the first cause of mortality in developed countries. One of the problems that cardiologists are encountering is the lack of high-enough contrast and the difficult interpretation of intracoronary images, especially those achieved with optically based techniques, such as intracoronary optical coherence tomography (IC-OCT). These two limitations could be simultaneously overcome if IC-OCT is combined with contrast agents capable of background removal (contrast enhancement) and of providing the contrast by complementary techniques (multimodal imaging). This last possibility would lead to a better image interpretation based on the synergy between different techniques such as IC-OCT and Magnetic Resonance Imaging (MRI). In this work, we demonstrated how magnetic nanoplatelets could be used to substantially increase the contrast of IC-OCT images and, at the same time, to obtain intracoronary images by MRI. Contrast improvement and multimodal imaging is achieved by exploiting their unique magneto-optical properties that allow for the straightforward application of dynamical optical contrast imaging principles. In addition, magnetic nanoplatelets are also demonstrated as excellent probes for high resolution, high contrast visualization of individual macrophages that play a fundamental role in the formation of arteriosclerosis plaques. Furthermore, we demonstrated how magnetic nanoplatelets enable remote manipulation of individual macrophages. Results included in this work identify magnetic nanoplatelets as unique contrast agents for high resolution multimodal cardiovascular imaging opening new avenues towards the advanced diagnosis and treatment of cardiovascular diseases.
COBISS.SI-ID: 32325415