A. Yu. Fedotov

Spontaneous explosive crystallization and phase transformations in a selenium/copper bilayer nanofilm

Spontaneous explosive crystallization in a selenium/copper bilayer nanofilm has been experimentally studied. It has been shown that the formation of a microcrack network in the selenium film is a decisive factor for spontaneous explosive crystallization. The microcrack network is an efficient channel for the relaxation of the collected energy of elastic stresses in the selenium film. The relaxation of this energy accelerates crystallization and transfers it to the explosive regime. It has been found that crystalline phases appearing in the products of the reaction after spontaneous explosive crystallization depend on the ratio of the thicknesses of the copper and selenium films.

Preparation of octacalcium phosphate from calcium carbonate powder

We have studied a process for the preparation of apatite precursors through calcium carbonate conversion into dicalcium phosphate dihydrate, which is then hydrolyzed to octacalcium phosphate. The process enables the preparation of both phase-pure octacalcium phosphate and calcium phosphate mixtures with variable dicalcium phosphate dihydrate : octacalcium phosphate and hydroxyapatite : octacalcium phosphate ratios.

Selective Laser Sintering of Bioactive Composite Matrices for Bone Tissue Engineering

A method for surface-selective laser sintering which produces mineral-polymeric materials based on calcium phosphates and aliphatic polyesters was developed. Three-dimensional matrices of the given architectonics for replacement of bone defects and bone tissue engineering were obtained. The microstructure of the experimental samples obtained and their surface morphology and internal structure were investigated by scanning electron microscopy (SEM). The characteristic values of the compressive strength and relative deformation of the mineral-polymer composite samples obtained by surface-selective laser sintering of fine powders consisting of 80 wt % ceramic granules based on tricalcium phosphate and 20 wt % D,L-polylactide PDL04 corresponded to the characteristic indices of the similar parameters for the trabecular bone tissue. As a result of the initial study of the biological properties of mineral-polymer composite scaffolds made by surface-selective laser sintering, it was shown that they had low cytotoxicity and no adverse effects on the proliferative potential of mesenchymal stem cells. The technology of surface-selective laser sintering suggested could be effectively used to create scaffolds for bone tissue engineering.

Structural changes during the hydrolysis of dicalcium phosphate dihydrate to octacalcium phosphate and hydroxyapatite

Powders prepared through dicalcium phosphate dihydrate (DCPD) hydrolysis to octacalcium phosphate (OCP) and hydroxyapatite (HA) in an aqueous sodium acetate solution have been characterized by X-ray diffraction. The lattice parameters of the synthesized OCP and HA phases have been determined as functions of holding time at synthesis temperatures of 37 and 60°C. The structure of the HA obtained through hydrolysis at 60°C has been refined, and the distortion of the elements of the crystal lattice of this compound has been assessed in terms of Baur indices. A model has been proposed for the heterogeneous nucleation and growth of the OCP phase on DCPD crystals, in which the structure of these compounds is represented as made up of groups similar in structure to Posner regions.

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.

Effect of hot pressing temperature on the microstructure and strength of hydroxyapatite ceramic

A hot pressing method was applied for production of a dense ceramic with homogeneous structure and enhanced strength characteristics. Comparative investigations were carried out for properties of a ceramic obtained by traditional sintering in air and sintering under pressure in a temperature range of 900–1300°C. The hot pressing made it possible to decrease the temperature of achieving the vitrified state by at least 200°C. The microhardness of such materials at 1000°C is 4.2 GPa at an average crystal size of 80–150 nm and open porosity of 4%.

Porous chitosan matrices reinforced by bioactive calcium compounds

In the last decade, a new technology for bone tissue regeneration after damage through accidental injury or surgical operation has been developed. The technology is based on implanting porous resorbable matrices with bone-forming cells cultivated therein at the bone defect site. This matrix is replaced with time by bone tissue de novo, being gradually resorbed in the body. The design of matrices with required microstructure parameters (porosity, pore size and interconnection) and mechanical and biological properties is a key problem. In recent years, considerable attention has been devoted to the development of matrices made of composite materials based on biopolymers [1, 2]. Chitosan-based materials are biocompatible and bioresorbable [3, 4]. Chitosan is prepared from natural chitin, a linear aminopolysaccharide (composed of N -acetyl-2-amino-2-deoxy- D -glycopyranose units). The main raw material sources of chitin are shells of marine and freshwater crustaceans, dead bees, and some fungi [3]. Chitosan is used in medicine both in pure form (films, fibers, capsules, sponges) and as a composite material, e.g., chitosan‐hydroxyapatite. The use as a matrix of porous composite materials based on chitosan containing as fillers bioactive calcium compounds is promising. These composites have higher porosity and elasticity than porous ceramics, which allows filling of a bone defect of any shape without gaps between the bone and the implant. Porous chitosan sponges are obtained most often by freeze-drying. Cross-linking of the chitosan structure after preparation of a porous structure is often performed using toxic compounds (e.g., glutaraldehyde) [4]. In this paper, we describe a simple method for production and the results of studies of structures and properties of porous composite sponges (PCSs) containing bioactive calcium compounds. The method is based on chitosan dissolution, introduction of a filler, foaming, and subsequent replacement of water by a liquid in which chitosan is insoluble. This gives sponges with a porosity of more than 90% containing up to 50 wt % of a filler: hydroxyapatite (HA), carbonate hydroxyapatite (CHA), or calcium carbonate (CC).

Hydroxyapatite-based coatings for intraosteal implants

Using the buy-to-fly ratio for sprayed material, we optimized the method of creating nanostructured plasma coatings based on hydroxyapatite. After plasma spraying, the coating contains 67–83% hydroxyapatite phase. We studied several case of hydrothermal treatment of coatings for the purpose of strengthening them and in order to increase the hydroxyapatite phase content. After hydrothermal treatment of the coating at 650°C, we achieved the value of hydroxyapatite content around 98%. The size of coherentscattering regions grew from 95 to 122 nm. We proved that, after the treatment, the shear strength of hydroxyapatite-based coatings in relation to the titanium substrate is 22.3 MPa.

Investigation of physicochemical and biological properties of composite matrices in a alginate–calcium phosphate system intended for use in prototyping technologies during replacement of bone defects

Materials for 3D printing of porous composite materials (CM) that are based on sodium alginate–tricalcium phosphate are developed. Physicochemical and biological studies of CM in vitro are performed using a model of two adherent cells lines, immortalized human fibroblasts (HF, strain 1608h TERT) and human osteosarcoma (MG-63) that are cultivated up to 21 days. The cytocompatibility and matrix properties are studied by an MTT assay.

Bone cements in the calcium phosphate-chitosan systems containing magnesium and zinc

Based on studying the possibility of the introduction of physiologically important cations into a cementing system, technology of fabrication of highly deformable calcium phosphate cements has been developed for bone tissue reconstruction in medicine. It has been elucidated that the method of introduction of metal cations (magnesium, zinc) into the cementing system has an effect on the formation of the microstructure and properties. The in vitro degradation of composite cements in simulated body fluids has been studied. Results have been obtained for the development of cements with tailored properties, which can be varied in different ranges.