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Experimental dependences of inelastic deformations returned due to the effects of superelasticity and shape memory, and the development of plastic deformation during bending and torsion of coarse-grained samples of the Ti49.3Ni50.7 (at %) alloy are obtained. It was found that the total inelastic strain is ∼11% (which slightly exceeds the crystallographic resource of martensitic strain, typical for alloys of this composition) at a total strain of samples of 24%. The correlation of the total inelastic strain and plastic under bending strain and the calculated Mises equivalent values under torsion of the samples are shown. [ABSTRACT FROM AUTHOR]

In this work we presented development results for monocrystalline silicon macrosamples with porous silicon area. The area ensures mechanical impact stability. It is identified that there is the crack resistance increase of porous silicon in comparison with monocrystalline silicon during indentation. Porous structure parameters are defined as well. The macrosamples were used as carriers of anticancer drugs. The developed macrosamples' design was used as an anticancer drug carrier during the development of method for in vitro effectiveness assessment of drug behavior. The example of Doxorubicin usage shows that designed carriers ensure prolonged dosed influence of drugs on cancer cells. [ABSTRACT FROM AUTHOR]

The paper investigates the effect of isothermal (T=295 K, above Af) mechanical cycling by bending to a strain of 4.5% and 20.2% on the development of reversible inelastic deformation manifested as the shape memory and superelasticity effects (SE and SME, correspondingly) in binary alloy Ti49.3Ni50.7 (at.%). It is found that the increment of plastic strain and chnges of SE and SME are expressed brightly after seven cycles and absent practically at the increase of number cycles to 11 (independently of the value of total strain εt in cycles). The cycling with εt=4.5% leads to the weak accumulation of plastic strain (∼1%) and, correspondingly, to the decrease of SE from 4/5% to ∼3.5% (SME ≤ 0.2%). It is shown that the increase of εt to 20.2% leads to increases of SE to ∼6.2% and SME to ∼4.8% at the first bending cicle. The sharp decrease of SME (to ∼0.5%) is observed under subsequent mechanical cycling due to development of plastic strain. At the same time, SE becomes stable on high level (∼6.5%). The possible reasons of similar changes of SE and SME are discussed. [ABSTRACT FROM AUTHOR]

The paper analyzes the effect of friction stir processing (FSP) on the structure and phase state of two titanium– nickel alloys: Ti–50.9Ni and Ti–50.2Ni (at %). The analysis shows that with the FSP modes and equipment chosen, the treatment creates no macroscopic defects in the stir zone, dissolves the initial texture of the alloys, and weakly influences their structure and phase state. In the internal volumes of the track region, Ti–50.9Ni preserves its B2 phase and Ti– 50.2Ni undergoes R → B2 transition with its B19′ phase kept intact. The oxide layer thickness is smaller than 50 µm. [ABSTRACT FROM AUTHOR]

In present work porous structures with different geometrical parameters in silicon wafers were formed by the methods of metal-assisted chemical etching (MACE) and electrochemical etching. It has been found that using the MACE method with chemical solutions and etching parameters used in the present work, it is possible to purposefully form a porous structure in a layer up to 100 microns thick with a porosity from 24 to 57%, and using an electrochemical etching it is possible to obtain a porous structure with a porosity of 72% in a layer thick of 170 μm. It was concluded that the use of original chemical solutions and etching parameters for the manufacture of silicon samples with the required parameters of the porous structure is promising in order to study the possibility of their use as container materials for medicine drug. [ABSTRACT FROM AUTHOR]

Grain structure and substructure of a nanocrystalline Ti–50.9 at. % Ni alloy was investigated using the transmission electron microscopy. The regularities of recovery and recrystallization processes of the alloy structure after annealing at 500°C are revealed. It is shown that the subgrain structure inhibits recrystallization due to the presence of Ti3Ni4 coherent particles at the subgrain boundaries. The coalescence of subgrains is a main mechanism of recrystallization in a substructure. A relationship between recovery and recrystallization and the dissolution and coagulation of Ti3Ni4 particles was found. [ABSTRACT FROM AUTHOR]

Among the macroscopic characteristics of solids, elastic properties play a crucial role in the analysis of the loss in the phase transition stability of the crystal lattice of materials. For shear-type transitions, such as martensitic transformations in metals and alloys, the study of the elastic parameters of crystal structures: elastic moduli and constants, Poisson’s ratio, etc., is of particular significance. In this study obtained the central sections of the surfaces of Young’s modulus and shear surfaces, as well as the Poisson’s ratio of TiFe and TiNi intermetallide crystals, both stable and under martensitic transformations. The extremes of the elastic properties and the maximum-to-minimum ratio are determined. The effective values of the elastic moduli and Poisson’s ratio are calculated based on the data on elastic constants and the compliance coefficients of materials. [ABSTRACT FROM AUTHOR]

The orientation dependence of the Poisson’s ratio of teeth dentin and enamel of tooth on the basis of matrices of elastic constants and the compliance coefficients of hexagonal crystals, such as crystals of dentine hydroxyapatite, was obtained. The results of calculating the Poisson’s ratios of dentin and enamel as a crystalline system with a hexagonal structure are presented in the form of tables and diagrams in the polar and Cartesian coordinate systems. It was shown that the maximum value of the Poisson’s ratio of dentin (0.54) is greater than the upper limit for the Poisson’s ratio of isotropic materials, including known restoration materials, which in some cases may reduce the quality of restorations. The effective elastic characteristics of dentine and enamel, including Poisson’s ratio using different averaging methods, were calculated. [ABSTRACT FROM AUTHOR]

In search of a container material for drugs placement to create the polymer-free stents with drug coatings (polymer-free drug-eluting stents), an analysis of the known literature data is carried out. It is shown that one of the promising materials for this purpose is porous silicon with mesoporous structure (transverse pore diameter 2–50 nm), which has high biocompatibility and biodegradation ability. The basic requirements to the characteristics of porous silicon coating on metal intravascular stents are formulated. The results of experimental studies, including those carried out by the authors of this article, show the possibility of applying a unbroken silicon coating up to 0.6 μm thick to the stents using magnetron sputtering or plasma-immersion ion implantation and deposition (PIII@D) methods. These methods provide high adhesion of the coating to the stent material and allow the coating to be applied to the outer and inner surface of the stent. [ABSTRACT FROM AUTHOR]

The thickness, chemical and phase composition, adhesion characteristics of the near-surface layers of model samples from TiNi alloy after their plasma-immersion treatment using a magnetron system with silicon ions at different values of bias voltage on the sample were studied. It was found that as a result of processing on the samples surface was formed a two-layer coating based on silicon up to 2 µm thickness. Near the surface there is a layer up to 20 nm thick, containing amorphous silicon and silicon oxide. In the deeper layers of silicon oxide is not found. It is shown that the coatings have a high adhesion to the substrate of NiTi alloy. The conclusion is made about the prospects of using the obtained silicon-based coatings to form a mesoporous structure in them for the purpose of placing therapeutic drugs in the pores in the manufacture of medical implants of NiTi alloy. [ABSTRACT FROM AUTHOR]

We have found that in TiNi alloys exposed to plasma immersion ion implantation with deposition, diffusion and martensite transformations occur the features of which are determined by the structural-phase state of the initial material. The coarse-grained material experiences low-temperature aging with release of Ti3Ni4 particles, while it is in the B2 + R state. The ultrafine-grained material containing a Ti3Ni4 phase in the initial state undergoes recrystallization, coagulation of Ti3Ni4 particles, and material transition to the B2 + R + B19 state. Inside its grains, no separations of Ti3Ni4 phases is detected. The formation of the Ti3Ni4 phase occurs along the grain boundaries and at the triple grain junctions. [ABSTRACT FROM AUTHOR]

The paper presents research data demonstrating the influence of equal channel angular pressing (ECAP) at 650 K on the structural-phase state of a Ti-0.16Pd-0.14Fe alloy (wt %) with initially microcrystalline structure (≺

The cytocompatibility of titanium nickelide (TiNi) with near-surface layers doped with silicon ions was studied on mesenchymal stem cells of rat bone marrow cultivated in vitro. The cytotoxic effect of eluted components of material on the mesenchymal stem cells was determined using a RTCA iCELLigence cellular analyzer. The proliferative activity of mesenchymal stem cells cultivated in the presence or on the surfaces of titanium nickelide samples was estimated from the cell mitochondrial respiration rate in MTT tests using [2-(4-Iodophenyl)-3- (4-nitrophenyl)-5-(2, 4- disulfophenyl)-2H-tetrazolium] tetrazolium salt. It is shown that ion plasma modification of near-surface layers of titanium nickelide with silicon improves the cytocompatibility of the alloy. [ABSTRACT FROM AUTHOR]

Self-expanding intravascular NiTi stents serve to recover the lumen of vessels suffered from atherosclerotic stenosis. During their manufacturing or functioning in blood vessels, the stents experience different strains and local stresses that may result in dangerous defects or fracture. Here, using the method of movable cellular automata, we analyze how the design of a stent influences its stress state during shaping to a desired diameter on a mandrel. We consider repeated segments of different stents under two loads: uniform diametric expansion of their crown and expansion with relative displacements. The simulation data agree well with experiments, revealing critical strain, stress, and their localization sites at the shaping stage, and provide the way toward optimum stent designs to minimize the critical stress during shaping. [ABSTRACT FROM AUTHOR]

The paper presents experimental results demonstrating the capabilities of plasma immersion ion implantation of silicon (Si) for surface treatment of complex branched structures such are self-expanding intravascular nickel-titanium (NiTi) stents. Using NiTi stents of diameter 4 and 8 mm, it is shown that plasma immersion ion implantation can provide rather homogeneous doping of their outer and inner surfaces with Si atoms. Also presented are research data on the processes that determine the thickness, composition, and structure of surface layers subjected to this type of treatment. [ABSTRACT FROM AUTHOR]

The data reported here show that recrystallization annealing at 973 K transforms the initial nanocrystalline structure of Ti49.1Ni50.9 (at %) into a microcrystalline structure with an average grain size of ≤11.4 μm and changes the sequence of martensite transformations from B2 → R→B19' to B2→19'. Also dependences of the superelasticity effect (SE), shape memory effect (SME), summary reversible inelastic strain (SIS = SE + SME), and plastic strain on total strain for the alloy exposed to bending in isothermal (295 K) loading-unloading cycles with post-unloading heating are presented. [ABSTRACT FROM AUTHOR]

This paper presents the results of the chemical, topographic and structural properties of the NiTi alloy surface and their changes after surface treatments by ion implantation techniques with use of ions Ta+ and Si+. The influence of physicochemical properties of the surface ion modified NiTi alloy was studied on in vitro cultured mesenchymal stem cells of the rats' bone marrow. It is shown that the ion surface modification improves histocompatibility of the NiTi alloy and leads to increase of proliferative activity of mesenchymal stem cells on its surface. It was experimentally found that a major contribution to viability improvement mesenchymal stem cells of rat marrow has the chemical composition and the microstructure of the surface area. [ABSTRACT FROM AUTHOR]

Here we investigated in vivo interaction of Si-modified titanium nickelide (TiNi) samples with adjacent tissues in a rat subcutaneous implant model to assess the impact of the modification on the biocompatibility of the implant. Modification was performed by plasma immersion ion processing, which allows doping of different elements into surface layers of complex-shaped articles. The aim of modification was to reduce the level of toxic Ni ions on the implant surface for increasing biocompatibility. We identified a thin connective tissue capsule, endothelial cells, and capillary-like structures around the Si-modified implants both 30 and 90 days postimplantation. No signs of inflammation were found. In conclusion, modification of TiNi samples with Si ions increases biocompatibility of the implant. [ABSTRACT FROM AUTHOR]

Cyclic voltammetry and potentiostatic polarization have been applied to study electrochemical behavior and to determine corrosion resistance of nitinol, which surface was modified with silicon using plasma-immersion ion implantation, in 0.9 % NaCl solution and in artificial blood plasma. It was found out that continuous, and also homogeneous in composition thin Si-containing layers are resistant to corrosion damage at high positive potentials in artificial physiological solutions due to formation of stable passive films. Breakdown potential Eb of Si-modified NiTi depends on the character of silicon and Ni distribution at the alloy surface, Eb values amounted to 0.9-1.5 V (Ag/AgCl/KCl sat.) for the alloy samples with continuous Si-containing surface layers and with decreased Ni surface concentration. [ABSTRACT FROM AUTHOR]

In this study, we compared pre- and postoperative parameters of the cardiac sympathetic innervation. The aim of the study was to examine the approaches to evaluating the quality of radiofrequency (RF)-induced cardiac denervation by using non-invasive and laboratory methods. The study included 32 people with long-lasting persistent atrial fibrillation (AF). The patients were divided into 2 groups according to the objectives of the study: group 1 (main) - 21 patients with mitral valve diseases, which simultaneously with radiofrequency ablation (RFA) AF carried out on the effects of the paraganglionic nervous plexuses by C. Pappone (2004) and N. Doll (2008) schemes. The second group (control) contained 11 patients with heart diseases in sinus rhythm (the RF denervation not been performed). All patients, who underwent surgical treatment, were received examination of cardiac sympathetic tone by using 123I-MIBG. All of them made blood analysis from ascending aorta and coronary sinus to determine the level of norepinephrine and its metabolites before and after cardiac denervation. Data of radionuclide examination are correlating with laboratory data. [ABSTRACT FROM AUTHOR]

The martensitic transformation, Debye–Waller factor, mean-square atomic displacements and the coefficient of thermal expansion on cooling of the Ti49.5Ni50.5 shape memory alloy were examined using in-situ X-ray diffraction. It was revealed B2→R (TR ≡ T = 273 ± 10 K) along with B2→B19' (Ms ≡ T = 273 ± 10 K) transitions occur. It was found that Debye–Waller factor and mean-square displacement of B2 phase undergo significant increase as functions of temperature when phase transition B2→R and B2→B19' take place. The analysis of the thermal expansion coefficient of the B2 phase indicates that the value of α increases almost linearly while cooling. [ABSTRACT FROM AUTHOR]

The paper reports on a study of regularities of formation gradient nano-, submicron and microstructural conditions in the surface layers of the samples after pulsed electron-beam melting of tantalum coating on the substrate NiTi alloy. Experimentally revealed the presence of submicron columnar structure in the upper layers of the tantalum coating. After irradiation modified NiTi surface takes on a layered structure in which each layer differs in phase composition and structural phase state. [ABSTRACT FROM AUTHOR]

By transmission electron microscopy method the evolution of structural-phase states on a depth of close to equiatomic NiTi modified layer has been studied. Modification performed by pulse impact on its surface low-energy high-current electron beam (beam energy density 10 J/sm2, 10 pulses, pulse duration 50mks). It is established that during the treatment in the layer thickness of 8–10 µm, the melting of primary B2 phase and contained therein as Ti2Ni phase particles occurs. The result is change in the concentration ratio of titanium and nickel in the direction of increasing titanium content, which was confirmed by X-ray analysis in the form of increased unit cell parameter B2 phase. Analysis of the electron diffraction pattern showed that the modified layer is characterized as a highly distorted structure on the basis of bcc lattice. Lattice distortions are maximal near the surface and extends to a depth of melt. In subjacent layer there is gradual decline lattice distortions is observed. [ABSTRACT FROM AUTHOR]

The paper studies the influence of chemical and phase compositions of NiTi surface layers modified with Si ions by plasma immersion implantation on their interaction with endothelial cells. It is shown that certain technological modes of Si ion implantation enhance the adhesion, proliferation, and viability of endothelial cells. It is found that the Si-modified NiTi surface is capable of stimulating the formation of capillary-like structures in the cell culture. [ABSTRACT FROM AUTHOR]

This paper studies the processes of fracture of barriers using the fracture criterion, allowing for consideration of large anisotropy for ultimate values of total plastic strains in various symmetry axes of an anisotropic material in conditions of sign-variable strain. All calculations were performed using the finite-element method under conditions of dynamic loading in three-dimensional graphics with the use of original software. It was shown that when modeling processes of fracture in barriers made of anisotropic and isotropic materials the differences in size and localization of fracture zones increase with the increase in the initial speed of shock loading of barriers. [ABSTRACT FROM AUTHOR]

The paper reports on a study of NiTi-based alloys used for manufacturing self-expanding intravascular stents to elucidate how the technological modes of plasma immersion ion implantation with silicon influence the chemical and phase composition of their surface layers. It is shown that two types of surface structure can be obtained depending on the mode of plasma immersion implantation: quasi-amorphous Si coating and Si-doped surface layer. The Si-doped surface layer contains new phases: a phase structured as the main B2 phase of NiTi but with a lower lattice parameter, R phase, and phase of highly dispersed SiO2 precipitates. [ABSTRACT FROM AUTHOR]

Cyclic voltammetry and potentiostatic polarization have been applied to study electrochemical behavior and to determine corrosion resistance of nitinol, which surface was modified with silicon using plasma-immersion ion implantation, in 0.9% NaCl solution and in artificial blood plasma. It was found out that continuous, and also homogeneous in composition, thin Si-containing layers are resistant to corrosion damage at high positive potentials in artificial physiological solutions due to formation of stable passive films. Breakdown potential Eb of Si-modified NiTi depends on the character of silicon and Ni distribution at the alloy surface, Eb values amounted to 0.9–1.5 V (Ag/AgCl/KCl sat.) for the alloy samples with continuous Si-containing surface layers and with decreased Ni surface concentration. [ABSTRACT FROM AUTHOR]

The paper reports on an experimental study of inelastic strain recovery, due to superelasticity and shapememory effects, and plastic deformation under torsion and bending in a binary TiNi alloy containing 50.9 at % of Ni. It is found that the material under torsion and bending displays an anomalously high superelasticity of 16.4% and 13.5% and total recovery strain of 24.6% and 16.4% which exceed the theoretical limit of recoverable strain equal to 10.3% in the alloy involved in a cubic B2 to monoclinic B19' phase transformation. The correlation between the high recovery strains and the intensity and mechanisms of plastic deformation with increasing total strain is discussed. [ABSTRACT FROM AUTHOR]