Applications of Nanostructural NiTi Alloys for Medical Devices

New nanostructural shape memory alloy (55.91 wt% of Ni and 44.03 wt% of Ti) for the production of minimally invasive implantation medical devices (stents) was tested for corrosion resistance under static conditions by dipping it into solutions with various acidities (pH from 1.68 to 9.18) for 2 years, for static mechanical properties and for biocompatibility. The material for investigations was 280‐μm wires before and after thermal treatment at 450°C for 15 min in air and surface mechanical treatment. The characteristic image and size of grains were determined using the transmission electron microscope (TEM), and the phase composition; surface morphology; and the layer‐by‐layer composition were investigated using an X‐ray diffractometer; a scanning electron microscope (SEM); and an Auger spectrometer. The nickel release from the investigated nanostructural nitinol is less in comparison with data for microstructural nitinol in a solution of any acidity. Dissolution in the alkali medium is absent. A significant retardation of the nickel ion release (and insignificant concentration as a whole) and the absence of titanium ion release in the weakly acidic and neutral solutions with polished samples are observed. A simultaneous 7–11% increase in strength and plasticity in comparison with microstructural nitinol was attained. Toxicity of samples has not been revealed

Using of Magnetron Sputtering for Biocompatible Composites Creating

Biocompatible composites obtained using the magnetron sputtering for the production of minimally invasive implantation medical devices (stents) were investigated. Nano- and microdimensional surface layers of Ta, Ti, Ag, and Cu on flat and wire NiTi, Cu, Ti, and SiO2 substrates were created. The phase composition, surface morphology, and the layer-by-layer composition were investigated on an X-ray diffractometer, SEM, and Auger spectrometer. It was shown that the thickness and the structure of surface layers were affected by the sputtering distance, time, power, and the bias voltage at the substrate. The presence of the transition layer that contains both substrate and target elements and provides high adhesion of the surface layer to the substrate has been demonstrated. The material was tested for corrosion resistance under static conditions by dipping into solutions with various acidities (pH from 1.68 to 9.18) for 2 years, static mechanical properties, and biocompatibility in vitro and in vivo. A slight corrosive dissolution was observed only in a medium with a pH of 1.56. Dissolution in the other media is absent. An increase in strength and plasticity in comparison with substrate was attained depending on the nature of the sputtered substance and substrate. Toxicity of samples has not been revealed

Studying of the Polylactide or Polyglycylidactide Surface Layer Biodegradation in Neutral Media for the Subsequent Layered Composite Creation

  The processes of biodegradation in phosphate buffer with pH 7.4 and 0.9 wt.% NaCl of polymer polylactide or polyglycylidactide films for the subsequent creation of a layered composite with a biodegradable layer on the basis of a nickel-free shape memory alloy TiNbTaZr were studied. The structure of the samples was determined by SEM and an optical microscope. For polylactide films the rate of biodegradation did not depend on the mass of the film. A gradual decrease in the rate of biodegradation at any mass with a similar dependence on time is noted. With an increase in the mass of films based on poly(glycolide-lactide) the rate of biodegradation increased. And even at the initial stage the dissolution rate is 2-3 times higher than in pure polylactide. On day 180, complete dissolution of the polyglycolidelactide was observed (even a precipitate was not observed) and completely entire polylactide films, however, lost  their transparency, was noted

Biomechanical properties of the sclera in patients with different types of refraction

Purpose. To determine biomechanical age-specific features of the scleral tissue and the axial length of the eye.Material and methods. The study investigated 144 isolate d fragments of the sclera of 38 cadaver human eyes at the age from 40 to 75 years. [The average value of the axial length of eyes: 23.56±3.06mm (20.05-26.62).] Samples of sclera with a standard 5mm width were cut out with microsurgical blade from the anterior, equatorial and posterior areas of the eye. Biomechanical test of scleral samples was carried out using the universal testing Instron-3322 machine.Results. The highest indices of scleral strength and Jung’s Modulus (JM) were obtained at the age of over 60 years. A strength increase of the sclera was noted in all segments of the eyeball, amounting to 15.6±0.4MPa in the anterior segment in case of hyperopia; 12.3±0.5MPa in myopia; in norm: 15.2±0.8MPa; in the posterior pole of the eye these indices also increased and were 13.1±0.5MPa in hyperopia, 10.2±0.7MPa for myopia, in norm: 12.8±0.7МPа. The JM has significantly (p <0.05) the highest value in the anterior segment 49.21±4.1МPа in hyperopia, 37.05±5.5МPа for myopia, in norm: 48.29±5.3МPа; the lowest values were determined in the posterior pole of the eye amounting 37.25±2.2МPа in hyperopia, 24.07±7.1МPа for myopia, in norm: 36.78±1.5МPа.Conclusions. Biomechanical characteristics of scleral tissue fragments show that the strength and resilience of the scleral tissue increases with age, however, the heterogeneity of these indices remains by segments, that leads to a variability in its biomechanical status

Polylactide-Based Stent Coatings: Biodegradable Polymeric Coatings Capable of Maintaining Sustained Release of the Thrombolytic Enzyme Prourokinase

The novelty of the study is the development, creation, and investigation of biodegradable polymeric membranes based on polylactide, that are capable of directed release of large molecular weight biomolecules, particularly, prourokinase protein (MW = 46 kDa). Prourokinase is a medication with significant thrombolytic activity. The created membranes possess the required mechanical properties (relative extension value from 2% to 10%, tensile strength from 40 to 85 MPa). The membranes are biodegradable, but in the absence of living cells in a water solution they decompose by less than 10% in half a year. The created membranes are capable of controlled prourokinase release into intercellular space, and the total enzymatic activity of prourokinase does not decrease by more than 12%. The daily release of prourokinase from one square centimeter of the membrane ranges from 1 to 40 μg per day depending on the technique of membrane preparation. The membranes have no acute toxic effect on cells accreting these surfaces de novo. The number of viable cells is at least 96%−97% of the overall cell count. The mitotic index of the cells growing on the surface of the polymeric films comprised around 1.5%. Histological examination did not reveal any disorders in tissues of the animals after the implantation of polymer membranes based on polylactide, both alone and as components of stent cover. Implantation of stents covered with prourokinase-containing polymers led to the formation of a mature connective tissue capsule that is thicker than in the case of uncovered stents. Thus, various polylactide-based biodegradable polymeric membranes possessing the required mechanical properties and capable of prolonged and directed release of prourokinase macromolecules are developed and investigated in the study

Preparation and Investigation of Spherical Powder Made from Corrosion-Resistant 316L Steel with the Addition of 0.2% and 0.5% Ag

The paper describes the production and study of spherical powder made from corrosion-resistant 316L steel with the addition of 0.2% and 0.5% Ag. The study of granulometric composition, morphology, fluidity and bulk density, phase composition, microhardness and impurity composition of the spherical powders was carried out. The study showed compliance of the spherical powders with the requirements for powders used for additive manufacturing. The fluidity of the powders was 17.9 s, and the bulk density was 3.76 g/cm3. The particles have a spherical shape with a minimum number of defects and an austenitic-ferritic structure. The study of the phase composition of ingots, wires and powders showed that the ingot structure of all samples consists of austenite. According to the results of studies of the phase composition of the wire, there is a decrease in γ–Fe and an increase in α–Fe and σ–NiCr in going from wire No. 1 to wire No. 3. According to the results of studies of the phase composition of the powder particles, there are three phases, γ-Fe, α-Fe, and Fe3O4. The study of microhardness showed a decrease in HV depending on the increase in silver. The hardness of the powder is lower than that of the ingot by 16–24% due to the presence of a ferritic phase in the powder. As a result of plasma spraying, an increase in residual oxygen is observed, which is associated with the oxidation of the melt during plasma dispersion. The amount of nitrogen and sulfur does not change, while the amount of carbon and hydrogen decreases, and the impurities content corresponds to the standards for corrosion-resistant steel. Qualitative and quantitative analysis of the silver content in the samples indicates that it was not affected by the stages involved in obtaining the spherical powder

Bacteriostatic and Cytotoxic Properties of Composite Material Based on ZnO Nanoparticles in PLGA Obtained by Low Temperature Method

A low-temperature technology was developed for producing a nanocomposite based on poly (lactic-co-glycolic acid) and zinc oxide nanoparticles (ZnO-NPs), synthesized by laser ablation. Nanocomposites were created containing 0.001, 0.01, and 0.1% of zinc oxide nanoparticles with rod-like morphology and a size of 40–70 nm. The surface of the films from the obtained nanomaterial was uniform, without significant defects. Clustering of ZnO-NPs in the PLGA matrix was noted, which increased with an increase in the concentration of the dopant in the polymer. The resulting nanomaterial was capable of generating reactive oxygen species (ROS), such as hydrogen peroxide and hydroxyl radicals. The rate of ROS generation increased with an increase in the concentration of the dopant. It was shown that the synthesized nanocomposite promotes the formation of long-lived reactive protein species, and is also the reason for the appearance of a key biomarker of oxidative stress, 8-oxoguanine, in DNA. The intensity of the process increased with an increase in the concentration of nanoparticles in the matrix. It was found that the nanocomposite exhibits significant bacteriostatic properties, the severity of which depends on the concentration of nanoparticles. In particular, on the surface of the PLGA–ZnO-NPs composite film containing 0.001% nanoparticles, the number of bacterial cells was 50% lower than that of pure PLGA. The surface of the composite is non-toxic to eukaryotic cells and does not interfere with their adhesion, growth, and division. Due to its low cytotoxicity and bacteriostatic properties, this nanocomposite can be used as coatings for packaging in the food industry, additives for textiles, and also as a material for biomedicine