A. V. Severin

Electron microscopy of biomaterials based on hydroxyapatite

Three types of biomaterials based on hydroxyapatite are synthesized and investigated. Hydroxyapatite nanocrystals or microcrystals precipitated from low-temperature aqueous solutions serve as the initial material used for preparing spherical porous granules approximately 300–500 μm in diameter. Sintering of hydroxyapatite crystals at a temperature of 870°C for 2 h or at 1000°C (for 3 h) + 1200°C (for 2 h) brings about the formation of solid ceramics with different internal structures. According to the electron microscopic data, the ceramic material prepared at 870°C is formed by agglomerated hydroxyapatite nanocrystals, whereas the ceramics sintered at 1200°C (with a bending strength of the order of 100 MPa) are composed of crystal blocks as large as 2 μm. It is established that all the biomaterials have a single-phase composition and consist of the hydroxyapatite with a structure retained up to a temperature of 1200°C.

Sonodynamic therapy of cancer. A comprehensive experimental study

Sonodynamic therapy in combination with antitumor drugs and sonosensitizers (theraphthal and its derivatives) was studied in preclinical testing against malignant tumors. The use of this therapy scheme enhances the destructive effect of ultrasound on tumors, promotes no metastasis, and make therapeutic drugs more bioavailable. The scheme was recommended for clinical use. A solid-phase sonosensitization mechanism was proposed. A possible system of laboratory and in vitro testing for selection of efficient sonosensitizers was outlined.

An X-ray electron study of nanodisperse hydroxyapatite

Two states of surface valence electrons localized on faces with different molecular reliefs were observed for nanodisperse hydroxyapatite. Thermal treatment of nanocrystals caused a shift ΔEb = 0.5 eV of the spectrum of valence electrons on molecularly rough faces and a shift of 0.8 eV of the spectrum from smooth faces. Similar electron spectrum shifts were observed for sorption, in particular, of sodium succinate. These results are of importance for the diagnostics of various hydroxyapatite kinds, since hydroxyapatite is a constituent mineral component of living organisms, and for the synthesis of medicines with enhanced biological activity used in treatment of various bone diseases.

Self-organization processes and phase transitions in nanocrystalline hydroxyapatite according to exoemission data

Low-temperature (20–360°C) exoemission of negative charges from nanocrystalline hydroxyapatite Ca10(PO4)6(OH)2 was studied. Thermal cycling and storage at 20°C were found to induce self-organization processes with charge separation and the formation of a negatively charged layer on the surface. The negative charge formed was long retained at elevated temperatures and only decreased during cooling in the temperature region of the structural transition, as is characteristic of thermoelectrets. No stable electrets formed in hydroxyapatite samples calcined at a high temperature (>800°C).

Ultrasonic synthesis of hydroxyapatite in non-cavitation and cavitation modes

The size control of materials is of great importance in research and technology because materials of different size and shape have different properties and applications. This paper focuses on the synthesis of hydroxyapatite in ultrasound fields of different frequencies and intensities with the aim to find the conditions which allow control of the particles size. The results are evaluated by X-ray diffraction, Transmission Electron Microscopy, morphological and sedimentation analyses. It is shown that the hydroxyapatite particles synthesized at low intensity non-cavitation regime of ultrasound have smaller size than those prepared at high intensity cavitation regime. The explanation of observed results is based on the idea of formation of vortices at the interface between phosphoric acid and calcium hydroxide solution where the nucleation of hydroxyapatite particles is taken place. Smaller vortices formed at high frequency non-cavitation ultrasound regime provide smaller nucleation sites and smaller resulting particles, compared to vortices and particles obtained without ultrasound. Discovered method has a potential of industrial application of ultrasound for the controlled synthesis of nanoparticles.

Sorption and cytotoxicity of zinc on hydroxyapatite

The preparation, physicochemical properties, and cytotoxicity of zinc-containing hydroxyapatites (HAP) were considered for further using HAP as carriers for zinc-containing drugs and radiopharmaceuticals.

Physicochemical aspects of the antiseptic action of nanohydroxyapatite

The mechanism of interaction of nanocrystals of hydroxyapatite with Staphylococcus aureus bacteria has been investigated. It was shown that the growth of bacteria and their colonies both in the presence and absence of hydroxyapatite nanocrystals can be described using the Fokker-Planck equation. It was found that hydroxyapatite nanocrystals adhere in a particular orientation on the surface of bacteria, decreasing substantially their colony-forming ability.

Fluctuations in growth rate of gypsum crystals

Growth of needlelike gypsum crystals from highly supersaturated aqueous solutions has been studied by the methods of the optical and electron microscopies. The average growth rates of the end faces and their fluctuations are determined. It is shown that the fluctuations in the growth rates of end faces are described by the Fokker-Planck equation and that the end faces of gypsum crystals grow by the layer mechanism with the layer nucleation in the vicinity of one of the crystal vertices.

The complex of zinc with N-(5,6-dihydro-4H-1,3-thiazine-2-yl)benzamide

A complex of zinc with N-(5,6-dihydro-4H-1,3-thiazin-2-yl)benzamide (L) ligand, LZnCl2, was synthesized for subsequent medical trials. The molar extinction coefficients were determined for LHBr solutions in water and physiological saline, and for LZnCl2 ethanol solution. The ligand stability in various solvents was evaluated and the value of its protonation constant was found for the physiological saline solution, logK = 5.3±0.2. The impossibility of determination of the complex stability constant by the potentiometric titration method was demonstrated. The complex exhibited an insufficient stability in aqueous and physiological saline solutions, but was stable as the solution in alcohol. There was no sorption observed upon the treatment of ligand with hydroxyapatite nanoparticles, which could be a potential carrier for the therapeutic form of LZnCl2, providing additional degrees of freedom for the interaction of ligand with cell membranes and a prolonged action of zinc ions.

A radionuclide-microscopic study of sorption of sodium [3H]succinate on textured nanohydroxyapatite

Specific features of sorption of sodium [3H]succinate on nanohydroxyapatite (HAP) and its hierarchic textures were studied by radionuclide-microscopic diagnostics. Chemisorption of sodium succinate leads to structural-morphological modification of HAP, manifested, in particular, in changes in the habit of individual nanocrystals and in the internal texture of HAP macrospheroids. The dynamics of sorption penetration of sodium succinate into macrospherical HAP granules was monitored by autoradiogarphy. The results obtained suggest that nanohydroxyapatite and textured products based on it can be used for the development of materials for drug transport and of complex succinic acid containing preparations for medical purpose.