To the theory of mechano-magnetic effects in ferrogels

The paper deals with theoretical study of effect of ferrogels uniaxial elongation on magnetic susceptibilities of these composite materials. We have considered the systems with magnetically soft ellipsoidal and spherical particles. The results show that elongation of the composites with the ellipsoidal particles enhances the susceptibility in the direction of the elongation, whereas the deformation of ferrogels with the spherical particles decreases the susceptibility when the particles concentration is small enough and increases it when the concentration exceeds some threshold magnitude.This work has been supported by Russian Foundation for Basic Research (projects 18-08-00178, 19-52-12028); by the Program of the Ministry of Education and Science of the Russian Federation, projects 02.A03.21.0006; 3.1438.2017/4.6; 3.5214.2017/6.7. MTLL is grateful to proyect FIS2017-85954-R (Agencia Estatal de Investigación, AEI, Spain, co-funded by Fondo Europeo de Desarrollo Regional, ERDF, European Union)

Mechanoelectrical transduction in the hydrogel-based biomimetic sensors

The study addresses the phenomenon of mechanoelectrical transduction in polyelectrolyte hydrogelsand, in particular, the search of the driving force for the change of the electrical potential of a gel underthe applied mechanical stretch. Polyelectrolyte gels of calcium and magnesium salts of polymethacrylicacid were synthesized by the radical polymerization in water solution. Their electrical potential mea-sured by microcapillary electrodes was negative and fall within 100–140 mV range depending on thenature of a counterion and the networking density of a gel. The rectangular samples (∼10 mm in lengthand 2 × 2 mm in cross-section) of gel-based sensors underwent the dynamic axial deformation, and thesimultaneous monitoring of their geometrical dimensions and the electrical potential was performed.Sensor elongation resulted in the overall increase of gel volume, and it was always accompanied by thegel potential change toward the depolarization (diminishing of the negative values). Theoretical modelbased on the assumption of the total electrical charge conservation in the course of the dynamic defor-mation of a filament was proposed to describe the dependence of the electrical potential of a gel on itsvolume. Good agreement between the predictions of the model and the experimental trend was shown.The proposed mechanism of mechanoelectrical transduction based on the stretch-dependant volumechanges in polyelectrolyte hydrogels might be useful to understand the nature of mechanical sensing inmuch more complex biological gels like the cell cytoskeleton.This work has been done under the financial support of theRussian Scientific Fund, project 14-19-00989. One of us (M.T.Lopez-Lopez) has been supported by the Grant FIS2013-41821-R(MINECO, Spain)

Quantal Sarcomere-length Changes in Relaxed Single Myofibrils

We carried out experiments on single isolated myofibrils in which thin filaments had been functionally removed, leaving the connecting (titin) filaments as the sole agent taking up the length change. With technical advances that gave sub-nanometer detectability we examined the time course of single sarcomere-length change when the myofibril was ramp-released or ramp-stretched by a motor. The sarcomere-length change was stepwise. Step sizes followed a consistent pattern: the smallest was ∼2.3 nm, and others were integer multiples of that value. The ∼2.3-nm step quantum is the smallest consistent biomechanical event ever demonstrated. Although the length change must involve the connecting filament, the size of the quantum is an order of magnitude smaller than anticipated from folding of Ig- or fibronectin-like domains, implying either that folding occurs in sub-domain units or that other mechanisms are involved

Ferrogels based on commertial microparticles of magnetite or strontium ferrite

This work was supported by Russian Science Foundation grant 18-19-00090

Biological Impact of γ-Fe2O3 Magnetic Nanoparticles Obtained by Laser Target Evaporation: Focus on Magnetic Biosensor Applications

The biological activity of γ-Fe2O3 magnetic nanoparticles (MNPs), obtained by the laser target evaporation technique, was studied, with a focus on their possible use in biosensor applications. The biological effect of the MNPs was investigated in vitro on the primary cultures of human dermal fibroblasts. The effects of the MNPs contained in culture medium or MNPs already uptaken by cells were evaluated for the cases of the fibroblast’s proliferation and secretion of cytokines and collagen. For the tests related to the contribution of the constant magnetic field to the biological activity of MNPs, a magnetic system for the creation of the external magnetic field (having no commercial analogues) was designed, calibrated, and used. It was adapted to the size of standard 24-well cell culture plates. At low concentrations of MNPs, uptake by fibroblasts had stimulated their proliferation. Extracellular MNPs stimulated the release of pro-inflammatory cytokines (Interleukin-6 (IL-6) and Interleukin-8 (IL-8) or chemokine (C-X-C motif) ligand 8 (CXCL8)) in a concentration-dependent manner. However, the presence of MNPs did not increase the collagen secretion. The exposure to the uniform constant magnetic field (H ≈ 630 or 320 Oe), oriented in the plane of the well, did not cause considerable changes in fibroblasts proliferation and secretion, regardless of presence of MNPs. Statistically significant differences were detected only in the levels of IL-8/CXCL8 release.The study was supported by the program of the Ministry of Health of the Russian Federation (project 121032300335-1). This work was financially supported, in part, by the Ministry of Science and Higher Education of the RF (grant FEUZ-2020-0051) (G.Yu. Melnikov) and University of the Basque Country Research Groups Funding (grant IT1245-19) (G.V. Kurlyandskaya)

Regularities of ultrasonography of suspensions of alumina nanoparticles in biological media

This paper studies the echo-contrast properties of an alumina nanopowder suspension using ultrasonography (US) fully corresponding in its characteristics to the techniques of medical ultrasound diagnostics of organs and tissues. The purpose of this study was to search for the possible effect of the ionic and protein composition of the biological medium on the intensity of the reflected echo signal of the contrast material based on nanoparticles. It was found that the pH of the blood promotes the maximum use of echo contrast options of alumina nanopowder suspensions. Particle size measurements in the suspension using the dynamic light scattering technique showed the stabilizing effect of blood serum and plasma on the nanopowder suspension, resulting in the attenuation of the echo signal. The data offer a basis for the development of new contrast materials based on nanoparticles for the ultrasound imaging of the heart and blood vessels. The considered mechanisms of the established phenomena make it possible to elucidate the processes of interaction of metal oxide nanoparticles with biological molecules. © 2013 Pleiades Publishing, Ltd