Rats kept on a high-fat/high-sucrose diet (HFSD) for 10–12 weeks demonstrated the development of hyperglycemia and signs of visceral obesity. Compared to the control, extracellular action potentials (eAP) of subepicardial myocytes of the left ventricle (LV) of HFSD rats characterized by a significantly increased fraction of signals with a pronounced afterhyperpolarization (AHP) phase and an accelerated decline. Local delivery of apamin (a blocker of small conductance Ca2+-activated K+ channels (IKCa, SK channels) to the eAP registration cite at a concentration of 500 nM in the solution inside the pipette was accompanied by suppression of the AHP phase and prolongation of the eAP decline. The obtained data suggest that HFSD leads to an increase in the expression and/or activity of SK channels and, as a result, to the development of AHP and shortening of eAP in epicardial cardiomyocytes of the LV of the rat heart.

The role of small-conductance Ca2+-activated K+-channels (SK channels) in the pathogenesis of cardiomyopathies of various etiologies remains poorly understood. The purpose of this work was to evaluate the effect of the blocker of SK channels, apamin, on the extracellularly recorded action potentials (eAPs) of subepicardial myocytes in the left ventricles of sham-operated rats and rats with myocardial infarction caused by ischemia-reperfusion. It was found that local delivery of the SK channel blocker apamin at a concentration of 500 nM to the eAP recording area did not affect the eAP profiles in the group of sham-operated rats but caused a significant slowdown in the repolarization time and a decrease in the afterhyperpolarization phase of eAPs in the group of rats with myocardial infarction. These data suggest that changes in the waveform of eAPs after infarction are associated with increased expression and/or activity of SK channels in subepicardial myocytes. The possible role of these channels in the structural and functional remodeling of the myocardium of the left ventricle of the heart after ischemia-reperfusion is discussed.

The possibilities of a new class of adaptive X-ray optical elements based on bending piezoelectric actuators for practical implementation of time-resolved experiments using X rays and synchrotron radiation-fast high-resolution X-ray diffractometry and fast X-ray absorption spectroscopy-are described. Examples of studies and results obtained using the proposed elements and the corresponding techniques are presented.

A number of systemic heart diseases leading to the development of heart failure (aortic stenosis, hypertension, diabetic cardiomyopathy, reperfusion injury etc.) are accompanied by a pronounced reorganization of the T-system of cardiomyocytes, both in humans and animals. However, structural-functional changes within this membrane compartment of cardiomyocytes following ischemia-reperfusion (IR) have not been thoroughly studied. The aim of the work was to study the remodeling of the T-system in the subepicardial cardiomyocytes of the left ventricle (LV) of the rat heart after IR injury using confocal microscopy and extracellular recording methods. The study was carried out after 24 hours, two weeks, and four weeks following IR. A remodeling of extracellular action potentials, recorded in the cardiomyocyte membrane patches that are devoid of t-tubule entrances (a single negative peak, type 1 eAP), was observed. Starting from 24 hours up to 4 weeks after IR, there was an increase in the duration of their decline time ( T 90 ) and the formation of eAP after-hyperpolarization phase, reaching maximum values by the fourth week after IR. A decrease in the amplitude of the second peak of eAPs, recorded in the cardiomyocyte membrane patches that contained t-tubule openings (a double negative peak, type 2 eAP), was also noticed four weeks after IR. However, in this investigation, no observable changes in the structural organization of the T-system were found. These data suggest that functional modifications of the epicardial cardiomyocyte T-system after IR injury may precede its structural modifications.

In this work the effect of annealing in a constant magnetic field on the magnetoelectric (ME) coefficient in three-layered gradient composites is investigated. A technique of nickel electrochemical deposition on bidomain lithium niobate crystals was demonstrated. It is shown that the optimum temperature for the formation of the maximum remanent magnetization of the Ni layer in a constant magnetic field is 350 °C. In the samples annealed at this temperature, the maximum shift of the dependence of the ME coefficient on the external constant magnetic field relative to the value of 0 Oe was achieved. Quasistatic ME coefficient value was 1.2 V/(cm∙Oe) without applying of external DC magnetic field. The maximum value of the ME coefficient was reached 199.3 V/(cm∙Oe) at bending resonance of 278 Hz without external DC magnetic field. Obtained in this work values of ME coefficients don’t yield to most of ME composite materials which were published before.

Lithium niobate (LiNbO3) and lithium tantalate (LiTaO3) are among the most important and most widely used materials of coherent and nonlinear optics, as well as acoustics. High degree of uniformity and reproducibility has become the foundation of technology for manufacturing high-quality crystals, absorbed by many suppliers around the world. However, the above areas do not limit the use of LiNbO3 and LiTaO3 due to their unique piezoelectric and ferroelectric properties. One promising application of crystals is the design of electromechanical transducers for precision sensors and actuators. In this respect, the high thermal stability of the piezoelectric and mechanical properties, the lack of hysteresis and creep make it possible to create electromechanical converters with wide operating temperature range, that is beyond the capability of commonly used ferroelectric ceramics. The main advantage of LiNbO3 and LiTaO3 over other single-crystal piezoelectrics is ferroelectric domain structure regulation toward targeted impact on the device characteristics. One of the most striking examples of electromechanical transducer design through domain engineering is the formation of a so-called bidomain ferroelectric structure in crystal. It represents a single-crystalline plate with two macrodomains with opposite directions of spontaneous polarization vectors separated by a charged domain wall. High switching fields make inversion domains stable at temperatures up to 1000 °C. This review summarizes the main achievements in the formation of bidomain structure and near surface inversion domains in LiNbO3 and LiTaO3 crystals. We present the domain structure virtualization methods in crystals and non-destructive methods for controlling the domain boundary position. The report contains a comparative analysis of the methods for forming inversion domains in crystals, and the patterns and technological control methods of the domain structure are discussed. The basic physical models have been proposed in the literature to explain the effect of the inversion domains formation. In the present paper we outline what one sees as strengths and weaknesses of these models. The strategies of crystallographic cut selection to create devices based on bidomain crystals are briefly discussed. We provide examples of the implementation of devices based on bidomain crystals such as actuators, sensors, acoustic transducers, and waste energy collection systems.

Composite multiferroics are materials in which electric polarization of the material is possible under the action of an external magnetic field and vice versa, a change in the magnetization of the structure when an electric field is applied. Such properties have a high practical potential for application in science and technology. Based on these materials, it is possible to manufacture a number of devices with unique properties, such as, for example, random access magnetoelectric (ME) memory, ME sensors of magnetic fields, current, magnetic nanoparticles, micromechanical ME antennas, voltage-adjustable microwave filters, resonators and phase shifters. Therefore, the search for new materials of composite multiferroics and the study of the ME effect in them is a priority and urgent task in the search and creation of new electronic devices. One of the most promising and close to practical implementation directions is the creation of highly sensitive sensors of ultra-weak magnetic fields on the basis of composite multiferroics. The absence of the need to cool such sensors is a significant technical advantage over superconducting quantum interferometers currently used for these purposes. To date, the best achieved limits for detecting magnetic fields using sensors based on composite magnetoelectrics are values of the order of pT/Hz(1/2), and new works are regularly published that reduce this threshold by improving processing electronics and changing the sensor design. This threshold of sensitivity is already sufficient for reliable detection of magnetic fields induced by alpha-rhythm currents of the brain with amplitudes of units of pT (magnetoencephalography) and for detecting the magnetic activity of the human heart. The review article is devoted to composite magnetoelectric structures with a focus on sensor structures capable of detecting ultra-weak magnetic fields. The comparison of the limiting sensitivity to the magnetic field of the existing ME composite structures is carried out, the ways of increasing the sensitivity to the magnetic field are shown.

The role of small conductance (SK) Ca2+-dependentpotassium channels in pathogenesis of diabetic cardiomyopathy remainsuncertain. In our studies in the rat model of streptozotocin-inducedtype 1 diabetess mellitus (STZ-DM1) a significant increase abovecontrol in the prevalence of extracellular action potentials (eAP)recorded from isolated heart left ventricles and terminating witha prominent phase of after-hyperpolarization was observed. In experimentswith local delivery to the site of recording of several tested potasssiumchannel blockers suppression of this phase of eAP after hyperpolarizationwas achieved only with application of apamin, the selective SK channelinhibitor. These data suggest that eAP afterhyperpolarization phaseis associated with activation of SK channels and that activity and/orexpression of these channels is increased in epicardial cardiomyocytesof left ventricles of STZ-DM1 rat hearts.

Left ventricles (LV) of isolated hearts of the control rats (n = 7) and rats injected with streptozotocin (STZ; n = 21) were studied on the four-week post-injection term using 5-µm tip (O.D.) glass extracellular microelectrodes. STZ-rats that maintained hyperglycemia by the time of the study (random glucose > 11 mM; n = 3) were designated as diabetic animals (diabetes mellitus group; STZ-DM). Remaining STZ-rats (n = 18) were designated as normoglycemic rats (STZ-NG group). In control and in STZ-rat hearts two main types of sinus rhythm action potentials (AP) of epicardial ventricular myocytes could be recorded: signals characterized by a single (AP1) or double negative peaks (AP2). Respective time parameters of AP1 (rise time, and 50% and 90% decay times (T50 and T90) not differed between studied groups of rats. However, T50 of AP2 of LV myocytes of STZ-NG and STZ-DM rats were statistically significantly longer than T50 of AP2 recorded in control rat hearts. Furthermore, in 28% of STZ-NG and in 67% of STZ-DM rat hearts additional type of AP (AP3) featuring a complex, multi-peak negative phase and prominent positive phase of after-hyperpolarization were recorded. Appearance of AP3 was associated with a proportional decrease in the relative frequency of AP2 recordings (from 80-85% to 55-60% of all recordings). Frequency of AP1 recordings remained stable, 15-20% in all experiments in all groups of rats. Tentatively, observed in this study modulation in electrical activity of ventricular myocytes of STZ-rat hearts results from structure-functional changes in organization of the T-system of these myocytes. Regardless of validity of this suggestion, it is important that changes in electrogenesis of cardiomyocytes develop fast (1 month) not only in STZ-DM rats, but also in hearts of STZ-rats with normal or moderately increased blood glucose levels, which may be considered as the state equivalent to the state of early prediabetes.

Disorganization of the T-system of cardiomyocytes is considered an early and critical step in the development of Diabetic Cardiomyopathy (DCM). To test this suggestion, male Wistar rats were injected with streptozotocin (STZ, 30 or 45 mg/kg) and studied one month later. STZ-rats that developed and maintained hyperglycemia (random blood glucose > 11 mM) were designated as hyperglycemic (STZ-HG) rats, while the remaining STZ-rats – as normoglycemic (STZ-NG) animals. The structural integrity of the T-system was investigated using an analysis of confocal images of the left ventricle (LV) sub-epicardium of isolated hearts, stained with the Di-8-ANEPPS. In control, T-system was organized into regular networks of t-tubules aligned with Z-discs of cardiomyocyte’s sarcomeres. Accordingly, the frequency distributions of intervals between neighboring t-tubules (INT, measured along the major cell axis) peaked at a 2 µm value with not more than 21% of INT (per cell) exceeding the 3 µm cut-off. Only 4±3% of the control cardiomyocytes (274 cells, 4 rats) could be considered as deficient, according to this parameter (>21% occurrence of long INT). Compared to control, in the hearts of STZ-NG and STZ-HG rats, the fractions of such deficient cardiomyocytes were statistically significantly higher: 48±13% (STZ-NG, 8 rats, 573 cells) and 76±8% (STZ-HG, 4 rats, 247 cells). Thus, structural changes in the T-system of the rat heart LV cardiomyocytes develop early during chronic hyperglycemia (overt diabetes) as well as during near-normoglycemic stages of diabetes (prediabetes). The relevance of these changes to the development of DCM in subjects with prediabetes remains to be studied.

Cardiac disruption and development of a diabetic cardiomyopathy (DCM) are a direct consequence of diabetes. In work activity Na/K-ATPase in a myocardium of rats with different extent of diabetic impairment was studied. Suppression of activity of Na/K-ATPase in the cardiomyocytes the left ventricle of rats was revealed at strongly developed diabetes, but not at a prediabetes stage. It was concluded, that development of DCM breaks transport processes in a membrane of rats cardiomyocytes, and the expressiveness of observed changes depends on diabetes degree.

Action potentials (APs) were recorded extracellularly from ventricular and atrial cardiomyocytes using isolated rat heart preparations and narrow-tipped (5-µm O.D.) recording pipettes. The negative phase of the AP waveform in ventricular cardiomyocytes exhibited a prolonged and, in about 60% of records, double-peak AP deflection, while that of APs in atrial cardiomyocytes regularly consisted of a single and relatively short peak. Confocal imaging and Monte-Carlo simulations suggest a stochastic variation in the number of t-tubule mouths under the lumen of randomly positioned extracellular recording pipette as the leading determinant of both, between and within, ventricular/atrial AP waveform variations.

The influence of a charged domain wall on the formation of the induced domain structures in congruent x -cut lithium niobate crystals (LiNbO 3 ) is studied. By diffusion annealing in air ambient near Curie temperature, as well as infrared annealing in oxygen-free ambient bi- and multidomain ferroelectric structures containing charged domain walls «head-to-head» and «tail-to-tail» were formed. By Kelvin probe mode of atomic force microscopy (AFM) surface potential near the charged domain walls was investigated. We studied surface needle-shaped induced microdomains which were formed in a vicinity of the domain boundary and far from it by applying of voltage to the cantilever being in a contact with the surface of the sample. Dependence of morphology of the induced domain structure on the crystal’s electric conductivity was demonstrated. Screening effect of charged «head-to-head» domain wall on a shape and size of the domain, that was induced near the boundary is shown. We described partition of the single needle-shaped domains formed by AFM cantilever to several microdomains having a shape of several beams based in a common nucleation point. We found an influence of the charged domain wall on the topography of the samples, which consisted in the appearance of a long groove corresponding to the domain boundary after the reducing annealing.

In the current study, we have developed a mathematical model describing the frequency response of a sensor or energy harvester based on a cantilever made of a ferroelectric bidomain single-crystal plate with metal electrodes deposited on opposite faces. The structure is subjected to vibrational excitations. The model allows to predict the dependence of the voltage between the electrodes vs. the vibration frequency and amplitude as well as resonance frequency of the sensor fabricated in form of a rectangular plate, normally with a seismic mass on its free end. The device is placed on a vibration table, whose vibration parameters are set. The relevant differential equation was composed, and an analytic solution describing the required dependencies was obtained. To validate the proposed model, we created a single-crystal bimorph by annealing a lithium niobate (LiNbO3) wafer in air to promote Li out-diffusion and formation of a bidomain ferroelectric structure, i.e. two oppositely polarized domains within the plate (the so called “headto-head” structure). Such a crystal demonstrates a bimorph-like behavior but does not comprise any interface except for an interdomain wall. Thus, our bimorph is not a commonly used structure, typically consisting of two bonded piezoelectric plates (generally made of PZT piezoceramics), but a homogeneous continuous medium. Being made of a lithium niobate (or lithium tantalate) ferroelectric single crystal, the cantilever sensor or energy harvester demonstrates a strong dependence of the voltage between the electrodes on the bending deformations, with almost totally absent hysteresis and ageing in a wide temperature range. The comparison made between the results of the modeling and the experiment shows that the proposed model is in good agreement with the experiment. We have demonstrated that the vibration sensors based on bidomain single-crystal plates possess an exceptionally high sensitivity. The proposed model can be used to estimate and predict the parameters of vibration sensors, accelerometers and waste energy harvesters based on bidomain ferroelectric crystals.

the microstructure, value of self-polarization, and local piezoelectric hysteresis loops of LiNbO3 thin films synthesized on silicon substrates with a native SiOx layer and with a platinum layer are compared via scanning probe microscopy. It is found that smoother surfaces, smaller grain sizes, and a simultaneous higher self-polarization value and effective piezoelectric coefficient are typical of LiNbO3 films applied to a silicon substrate with a platinum sublayer.