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.

Investigation of Antibacterial Properties of Corrosion-Resistant 316L Steel Alloyed with 0.2 wt.% and 0.5 wt.% Ag.

The article is devoted to the study of melted ingots, plates rolled from them, and the resulting spherical powder made of corrosion-resistant 316L steel with the addition of 0.2 wt.% and 0.5 wt.% Ag. The study of antibacterial properties, microstructure, and distribution of silver concentrations, as well as qualitative analysis of silver content was carried out. The optimal mode of homogenization annealing of the ingot was 1050 °C for 9 h, which leads to the formation of an austenitic structure. It is shown that the addition of a small amount of silver does not affect the formation of the austenitic structure and silver is distributed evenly throughout the volume of the ingot. The austenitic structure also prevails in the plates after rolling. Silver is distributed evenly throughout the entire volume of the plate. It is noted that the addition of 0.2 wt.% Ag does not affect the strength, elongation, and microhardness of steel, and the addition of 0.5 wt.% Ag does not significantly reduce the strength of steel, however, all samples meet the mechanical characteristics according to the ASTM A240 standard. The qualitative chemical composition of samples made of corrosion-resistant steels was confirmed by X-ray fluorescence analysis methods. By the method of energy-dispersion analysis, the presence of a uniform distribution of silver over the entire volume of the powder particle was determined. The particles have a spherical shape with a minimum number of defects. The study of the antibacterial activity of plates and powder shows the presence of a clear antibacterial effect (bacteria of the genus Xanthomonas campestris, Erwinia carotovora, Pseudomonas marginalis, Clavibacter michiganensis) in samples No. 2 and No. 3 with the addition of 0.2 wt.% and 0.5 wt.% Ag.

Obtaining a Wire of Biocompatible Superelastic Alloy Ti-28Nb-5Zr.

Using the methods of electric arc melting, intermediate heat treatments, and consecutive intensive plastic deformation, a Ti-Nb-Zr alloy wire with a diameter of 1200 µm was obtained with a homogeneous chemical and phase (ß-Ti body-centered crystal lattice) composition corresponding to the presence of superelasticity and shape memory effect, corrosion resistance and biocompatibility. Perhaps the wire structure is represented by grains with a nanoscale diameter. For the wire obtained after stabilizing annealing, the proof strength Rp0.2 is 635 MPa, tensile strength is 840 MPa and Young's modulus is 22 GPa, relative elongation is 6.76%. No toxicity was detected. The resulting wire is considered to be promising for medical use.

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.

Ion Release and Surface Characterization of Nanostructured Nitinol during Long-Term Testing.

The corrosion resistance of nanostructured nitinol (NiTi) was investigated using long-term tests in solutions simulating physiological fluids at static conditions, reflecting the material structure and metal concentration in the solutions. Mechanical polishing reduced the ion release by a factor of two to three, whereas annealing deteriorated the corrosion resistance. The depassivation and repassivation of nitinol surfaces were considered. We found that nanostructured nitinol might increase the corrosion leaching of titanium into solutions, although the nickel release decreased. Metal dissolution did not occur in the alkaline environment or artificial plasma. A Ni-free surface with a protective 25 nm-thick titanium oxide film resulted from soaking mechanically treated samples of the NiTi wire in a saline solution for two years under static conditions. Hence, the medical application of nanostructured NiTi, such as for the production of medical devices and implants such as stents, shows potential compared with microstructured NiTi.

Biocompatibility of new materials based on nano-structured nitinol with titanium and tantalum composite surface layers: experimental analysis in vitro and in vivo.

A technology for obtaining materials from nanostructured nitinol with titanium- or tantalum-enriched surface layers was developed. Surface layers enriched with titanium or tantalum were shown to provide a decrease in the formation of reactive oxygen species and long-lived protein radicals in comparison to untreated nitinol. It was determined that human peripheral vessel myofibroblasts and human bone marrow mesenchymal stromal cells grown on nitinol bases coated with titanium or tantalum-enriched surface layers exhibit a nearly two times higher mitotic index. Response to implantation of pure nitinol, as well as nano-structure nitinol with titanium or tantalum-enriched surface layers, was expressed though formation of a mature uniform fibrous capsule peripherally to the fragment. The thickness of this capsule in the group of animals subjected to implantation of pure nitinol was 1.5 and 3.0-fold greater than that of the capsule in the groups implanted with nitinol fragments with titanium- or tantalum-enriched layers. No signs of calcinosis in the tissues surrounding implants with coatings were observed. The nature and structure of the formed capsules testify bioinertia of the implanted samples. It was shown that the morphology and composition of the surface of metal samples does not alter following biological tests. The obtained results indicate that nano-structure nitinol with titanium or tantalum enriched surface layers is a biocompatible material potentially suitable for medical applications.