Synthesis of Ag/Ag₂S Nanoclusters Resistive Switches for Memory Cells

Resistive switching Ag/Ag2S nanoclusters were formed by sulphidation of melting-dispersed thin and continuous Ag films. The morphology, structure and electrical properties of the prepared clusters were characterized by scanning (SEM), transmitting electron (TEM), scanning resistance microscopes (SRM) and Raman scattering. Hysteretic resistive switching behavior was observed in the samples that were studied with ON/OFF switching voltage equal to 8 - 10 V respectively. Simple empirical numerical simulation model, based on Deal-Grove model assumptions and mechanisms, for silver nanoclusters sulphidation process, was proposed.

Investigation of the Effect of Local Electrical Stimulation on Cells Cultured on Conductive Single-Walled Carbon Nanotube/Albumin Films

In this study we have developed a biocompatible current-conductive coating based on carbon nanotubes and bovine serum albumin and have shown its efficiency in culturing cells in vitro. We investigate the proliferation of human embryonic fibroblast (HEF) cells, which were subjected to electrical stimulation when cultured on carbon nanotube surface. A weak increase in proliferation is demonstrated at stimulating field pulses up to 100 mV. It is assumed that the transport mechanism accompanied by higher synthesis of proteins and their polymerization may increase proliferative activity at low voltages. At higher voltages the motility and spatial organization of HEF cell is observed. As a result, a novel technique of supplying the cells with electric field through a system of micro- and nanosized electrodes and a biocompatible composite have been developed.

Electrical Properties of Fluoro-Containing Alicyclic Polyimides

The electrical, physical, mechanical and thermal properties of fluorine-containing alicyclic polyimides have been investigated. It was shown that the minimum value of the dielectric constant 1.91 at room temperature and 1 kHz frequency was achieved for polymers containing only one fluorine atom in the structure. The dielectric loss tangent of new polymers was （I -4）~ 103. Electro-physical parameters were stable during polymer heating up to 300 ~C, and at the frequency from 1 to 20 kHz. Resistivity by heating in the air up to 320-380 ~C has been investigated depending on the polyimides structure. The coefficient of moisture absorption for the fluorine-containing polyimide based on dianhydride with 4,4＇-oxydianiline was determined at 50% humidity and 25 ℃. It was around 0.6, but after immersion in the water for 24 and 48 h was 0.8% and 1.2%, respectively. Manufactured films had tensile strength to 160-170 MPa, and elongation up to 55%.

Construction of Energy-Optimal Smooth Monophasic Defibrillation Pulse Waveforms Using Cardiomyocyte Membrane Model

The goal is to help create smooth energy-optimal monophasic pulse waveforms for defibrillation using the Luo-Rudy cardiomyocyte membrane computer model. The waveforms were described with the help of the piecewise linear function. Each line segment provides a transition from one present level of the transmembrane potential to the next with a minimal energy value. The duration of the last segment was defined as a minimum duration at which an action potential occurs. Monophasic waveforms of segments 3, 10 and 29 were built using different increments of the transmembrane potential. The pulse energy efficiency was evaluated according to their threshold energy ratios in mA2·ms/cm4. There was virtually no difference between the threshold energy ratios of the three waveforms constructed and those of the previously studied energy-optimal half- sine waveform: 241 - 242 and 243 mA2·ms/cm4. The pulse waveform constructed is characterized by a low rise and fall as the duration of the rise is ~1.5 times longer than that of the fall. Conclusion: Energy-optimal smooth monophasic pulse waveforms have the same threshold energy ratio as the optimal half-sine one which was studied before. The latter is equivalent to the first phase of biphasic quasisinusoidal Gurvich-Venin pulse which has been used in Russia since 1972. Thus, the use of the Luo-Rudy cardiomyocyte membrane model appears to offer no possibilities for a substantial increase in the energy efficiency (threshold energy ratio reduction) of the classical monophasic defibrillation pulse waveforms.

Igor V. Venin Founder of Biphasic Waveform Defibrillators

Igor V. Venin since 1966 and up till now has been an outstanding engineer of the Soviet Union and Ukraine, who has dedicated all his life to defibrillators development. Under his guidance 16 models of DC defibrillators with different waveforms, including the world’s first defibrillator with biphasic waveform (1971) have been developed and put into commercial production.

Multilayered organic semiconductors for high performance optoelectronic stimulation of cells

The efficiency of devices for bioelectronic applications,including cell and tissue stimulation,is heavily dependent on the scale and the performance level.With miniaturization of stimulation electrodes,achieving a sufficiently high current pulse to elicit action potentials becomes an issue.Herein we report on our approach of vertically stacking organic p-n junctions to create highlyefficient multilayered organic semiconductor(MOS)photostimulation device.A tandem arrangement substantially increases the photovoltage and charge density without sacrificing lateral area,while not exceeding 200-500 nm of thickness.These devices generate 4 times higher voltages and at least double the charge densities over single p-n junction devices,which allow using lower light intensities for stimulation.MOS devices show an outstanding stability in the electrolyte that is extremely important for forthcoming in vivo experiments.Finally,we have validated MOS devices performance by photostimulating fibroblasts and neuroblasts,and found that using tandem devices leads to more effective action potential generation.As a result,we obtained up to 4 times enhanced effect in cell growth density using 3 p-n layered devices.These results corroborate the conclusion that MOS technology not only can achieve parity with state-of-the-art silicon devices,but also can exceed them in miniaturization and performance for biomedical applications.

Porous Shish-Kebab Structure Prepared from Oriented UHMWPE Films by Processing in Supercritical CO_(2)

For the first time, a highly crystalline porous shish-kebab structure with a high degree of crystallinity was obtained by using a combination of two methods for the formation of porous polymeric materials. A treatment procedure using supercritical carbon dioxide(sc CO_(2))was carried out for oriented ultrahigh molecular weight polyethylene(UHMWPE) films, which provided special conditions for the crystallization of dissolved UHMWPE macromolecules on the surface of oriented UHMWPE crystals. The prepared porous materials were investigated by scanning electron microscopy(SEM) and differential scanning calorimetry(DSC). The particularity of the obtained porous shish-kebab is the absence of the amorphous phase between lamellar crystals(kebabs). The obtained pores had an oval shape, and they were oriented in the orientation direction of the UHMWPE macromolecules. The pore size ranged from 0.05 μm to 4 μm. Controlling the conditions for the crystallization of the UHMWPE macromolecules using supercritical CO_(2) gives the possibility to control the size of both lamellar disks and pores formed.

Dielectric properties of composite based on ferroelectric copolymer of poly(vinylidene fluoride-trifluoroethylene)and ferroelectric ceramics of barium lead zirconate titanate

A study of dielectric properties of composite films on the base of poly(vinylidene fluoride-trifluoroethylene)copolymer P(VDFTrFE)and ferroelectric ceramics of barium lead zirconate titanate(BPZT)solid solution is presented in this work.The composite films containing up to 50 vol.%of BPZT grains with size
1
m were prepared by the solvent cast method.Frequency dependences of real and imaginary components of the complex permittivity were determined.The concentration dependence of the dielectric constant was discussed.

Electrical characterization of poly(vinylidene fluoride-trifluoroethylene) nanocrystals embedded in porous alumina matrix

In this work,the study of dielectric properties of composite structures on the base of poly(vinylidene fluoride-triflouroethylene)copolymer P(VDF-TrFE)and porous aluminum oxide layers produced by the melt-impregnation is presented.Frequency dependences of dielectric characteristics of the composite samples were determined.The dielectric dispersion and ferroelectric switching processes in the composite structures were discussed.