A. S. Baikin

Properties of nanostructured titanium nickelide and composite based on it

The properties of nanostructured nitinol (Ni, 55.91 wt %; Ti, 44.03 wt %) in the initial state and after mechanical and the thermal treatment and a composite of nitinol with a tantalum surface layer obtained by magnetron sputtering have been studied. Compared with microstructured nitinol, the use of nanostructured nitinol for medical appliances, like stent, has great opportunities due to better corrosion resistance in solutions that model the physiological media of a human organism and the decreased diffusion of nickel ions into solution below the admitted average dietary intake of 200–300 mg/day in solutions of any acidity. Surface mechanical polishing increases its corrosion resistance by two to three times more. Compared with nitinol, the composite of nitinol with a tantalum surface layer is ∼7–11% better by strength, plasticity, and surface microhardness and characterized by the absence of a corrosion processes and diffusion of metal ions into solution.

Mechanical properties of nanostructured nitinol/chitosan composite material

The mechanical properties and degradation behavior of a composite material based on nanostructured nitinol and a biodegradable polymer surface coating of chitosan of various molecular weights are studied. The formation of a biodegradable surface layer of any composition does not change the properties of the base material. The created biodegradable polymer surface coating disintegrates upon applying the yield stress, i.e., within the operating range of loadings on medical items. The base disintegrates with the formation of a neck. Surface layer cracking is observed only near the fracture.

The shear strength of Ti–HA composite coatings for intraosseous implants

Plasma spraying of composite coatings is developed and investigated. Three-dimensional capillary porous titanium (3DCP Ti) coatings with a thickness of 1 mm are sprayed using a wire. Hydroxyapatite (HA) coatings with a thickness of 0.08–0.35 mm are sprayed on 3DCP Ti coatings at a temperature of 300–550°C. The joint between the coating and plastic is analyzed at shear. The plastic simulates bone tissue that grows into the coating surface. The heating of the 3DCP Ti coating to 550°С when the HA coating is being sprayed increases the shear strength of the coating with respect to the plastic to 9.8 MPa. Modeling approximations are proposed for the shear of the joint between the coating and the plastic.

Bone cements in the calcium phosphate–calcium sulfate system

Cement materials in the calcium phosphate–calcium sulfate system were proposed for bone tissue reconstruction. Mixtures of calcium sulfate and amorphous calcium sulfate in the weight ratios 20: 80, 40: 60, 60: 40, and 80: 20 were used as a cement flour, and an acidic solution of orthophosphoric acid was used as a setting liquid. Cement materials based on dicalcium phosphate dihydrate and calcium sulfate were obtained, and the phase composition, setting time, compressive strength, and microstructure of cements were studied. A phenomenon of dispersion strengthening of cements by adding 20 wt % calcium sulfate was detected. The obtained cement stone had a strength to 60 MPa, a setting time of 6–7 min, and uniform microstructure with a crystal size of 1–2 μm.

Long-term corrosion tests of nanostructural nitinol of (55.91 wt % Ni, 44.03 wt % Ti) composition under static conditions: Ion release

The corrosion resistance of nanostructural nitinol in solutions with pH from 1.68 to 9.18 for a long time is investigated. The metal concentration in solution was determined using atomic emission spectrometry with inductively coupled plasma. The ion yield is inhibited in NaCl and hardly so in acidic media, and corrosion is not observed in alkaline medium. The corrosion resistance increases by polishing and deteriorates with annealing. The nanostructure promotes a lower yield of nickel ions.

Long-term corrosion tests of nanostructural nitinol of (55.91 wt % Ni, 44.03 wt % Ti) composition under static conditions: Composition and structure before and after corrosion

Nanostructural nitinol is investigated before and after storage for a long time in solutions simulating pH of physiological liquids. The structure and composition are determined by SEM, TEM, and Auger spectroscopy. The material base is the B2 phase in the form of fibers 30–70 nm in diameter. Polishing promotes the formation of a thin homogeneous surface layer of titanium oxide, which thickens after solution storage; and annealing, the layer unchanging, thick, and heterogeneous.

Kinetics of the release of antibiotics from chitosan-based biodegradable biopolymer membranes

A process for manufacture of chitosan-based biodegradable biopolymer membranes suitable for medical applications was developed. A technology for inclusion of broad spectrum antibiotics into the chitosan membranes was elaborated. The effects of pH of the solution surrounding the membranes and the initial solvent chosen for chitosan on the kinetics of release of antibiotics from the membranes were studied. It was demonstrated that the kinetics of drug release from the chitosan-based biodegradable biopolymer membranes depends on the properties of substance immobilized in the membrane, the membrane manufacture process, and extraction conditions.

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

AbstractA 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.

The Production of a Thin Wire of Ti-Nb-Ta-Zr Shape Memory Alloy for Medical Devices

Alloys possessing a shape memory effect and mechanical characteristics similar to the behavior of living tissues have been already used for years as the material for production of medical devices, including implants, for example stents, without the need for additional devices except catheter-carrier. However, most of these alloys contain elements (including on its surface) which is toxic for organism. To satisfy the requirements of biochemical compatibility, the alloy should contain only safe elements as alloy components, which include: Ti, Nb, Ta, Zr. The possibility of obtaining of Ti-Nb-Ta-Zr thin wire was investigated. The structure was determined with the use of the optical microscope, X-ray diffractometer, scanning electron microscope (SEM) and Auger spectrometer. Optimal conditions for smelting were chosen. It was noted that a uniform structure was obtained for all compositions, before and after homogenizing annealing. The ingots have a dendritic structure. Niobium and zirconium were uniformly distributed throughout the sample, tantalum was concentrated in the dendrites themselves, titanium was predominantly in the regions between the dendritic axes, but is also found in it. X-ray diffractometry indicates that the elements of the alloy were not distributed in it by separate fragments, but were united in a single structure. The optimal annealing temperature of Ti-(20-30)Nb- (10-13)Ta-5Zr alloys was noted in the range from 600 to 900°C. The grain boundaries after plastic deformation and heat treatment were not identified in a microstructural analysis, which indicates that there was no recrystallization. It is possible that nanostructure was formed. The morphology of wires of any composition after drawing shows a high heterogeneity, two types of surfaces of different composition alternate - areas with a high content of carbon and with a high content of oxygen were observed. After mechanical treatment the surface, its uniformity increases.

Influence of the Surface Modification on the Mechanical Properties of NiTi (55.8 wt % Ni) Alloy Wire for Medical Purposes

The mechanical characteristics of a titanium nickelide alloy are studied depending on the surface machining. The additional processing improves the characteristics.