A. A. Egorov

High-temperature hydroxyapatite-titanium interaction

Hydroxyapatite-titanium interaction has been studied in the temperature range 700 to 1200°C with a view to designing biocompatible dispersion-hardened hydroxyapatite-matrix materials for bone implants. The sequence of phase transformations in hydroxyapatite-titanium powder mixtures during heating in air has been identified using IR spectroscopy, differential thermal analysis, and X-ray diffraction. It is shown that hydroxyapatite decomposition can be inhibited via heat treatment in an atmosphere containing carbon monoxide.

Silver-Doped Calcium Phosphate Bone Cements with Antibacterial Properties.

Calcium phosphate bone cements (CPCs) with antibacterial properties are demanded for clinical applications. In this study, we demonstrated the use of a relatively simple processing route based on preparation of silver-doped CPCs (CPCs-Ag) through the preparation of solid dispersed active powder phase. Real-time monitoring of structural transformations and kinetics of several CPCs-Ag formulations (Ag = 0 wt %, 0.6 wt % and 1.0 wt %) was performed by the Energy Dispersive X-ray Diffraction technique. The partial conversion of β-tricalcium phosphate (TCP) phase into the dicalcium phosphate dihydrate (DCPD) took place in all the investigated cement systems. In the pristine cement powders, Ag in its metallic form was found, whereas for CPC-Ag 0.6 wt % and CPC-Ag 1.0 wt % cements, CaAg(PO3)3 was detected and Ag (met.) was no longer present. The CPC-Ag 0 wt % cement exhibited a compressive strength of 6.5 ± 1.0 MPa, whereas for the doped cements (CPC-Ag 0.6 wt % and CPC-Ag 1.0 wt %) the reduced values of the compressive strength 4.0 ± 1.0 and 1.5 ± 1.0 MPa, respectively, were detected. Silver-ion release from CPC-Ag 0.6 wt % and CPC-Ag 1.0 wt % cements, measured by the Atomic Emission Spectroscopy, corresponds to the average values of 25 µg/L and 43 µg/L, respectively, rising a plateau after 15 days. The results of the antibacterial test proved the inhibitory effect towards pathogenic Escherichia coli for both CPC-Ag 0.6 wt % and CPC-Ag 1.0 wt % cements, better performances being observed for the cement with a higher Ag-content.

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%.

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.

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.

Microstructure formation in porous calcium phosphate-chitosan bone cements

We have studied the microstructure formation in composite cement materials consisting of amorphous calcium phosphate and chitosan and reinforced with sodium alginate granules, their compressive strength, and the kinetics of their dissolution in an isotonic solution. Hardening in air allowed us to obtain a cement stone with a strength of up to 18 MPa and limiting strain of 6–8%. During hardening in simulated body fluid, the maximum strength decreased to 0.8 MPa, and the strain increased to 25–30%, which was due to the dissolution of the granules and the increase in the elasticity of the chitosan framework. The calcium ion release to the isotonic solution varied nonmonotonically, with a maximum in the initial stage of hardening. The cements are intended for the fabrication of porous matrices in bone tissue regeneration.

Three-dimensional printing of osteoconductive ceramic matrices for tissue engineering

The developments of three-dimensional printing of osteoconductive ceramic matrices based on tricalcium phosphate for tissue engineering constructions intended for acceleration of the reparative processes and effective osteointegration with tissues of the living body are studied in the present work.

High-temperature fluorohydroxyapatite-titanium interaction

We have studied chemical interaction between fluorine-substituted hydroxyapatite and metallic titanium in the temperature range 700–1000°C. The results indicate that the phase relations in this system differ markedly from those in the hydroxyapatite-titanium system under similar conditions. The most important result is that the apatite phase persists in the former system, whereas in the hydroxyapatite-titanium system the hydroxyapatite decomposes at 900°C to form calcium titanate. The process common to the two systems is the complete oxidation of titanium and the formation of rutile at temperatures above 800°C.

The Microctructure Formation and the Composite Properties Based on Alginate with Antibacterial Activity

The alginate gels microstructure formation regularities that were prepared in situ in a multicomponent system were determined, and their properties were studied. To produce experimental specimens, a combination of cross-linking agents of calcium and zinc salts with inhibitors based on a denatured protein and tricalciumphosphate granules was used. The antibacterial properties of the hydrogels were studied as a function of their composition.

X-ray investigation of the powders of tricalcium phosphate exposed to processing in planetary mill

Using the Rietveld X-ray method, the powders of tricalcium phosphate (α-TCP) were analyzed after their treatment in a planetary mill in various liquids (butanol, isobutyl alcohol, acetone, and ethanol). No features of the decomposition of α-TCP were detected and the parameters of its atomic-crystal structure did not change significantly. The reduction of the coherent scattering domains (DS) (d ~ 800 Å) was a major contribution to X-ray line broadening, while its value did not depend on physical properties of liquids. Particles dispersed during their processing in the mill owing to their brittle destruction by chipping. After 60 min of powder processing in butanol, mean particle size decreased by a factor of five (from 9.7 to 2 μm). After annealing at 1300°C, the fluorohydroxyapatite phase was detected in powders, whose formation was assisted by the impurities from fluorine-containing structural elements of the mill.