S. V. Smirnov

Cell-binding properties of glycoprotein B of Aujeszky's disease virus

The glycoprotein B (gB) of Aujeszkys disease virus (ADV) has a role in virus entry and cell-to-cell spread. In this report we examined the cell-binding properties of native ADV gB purified from the virus envelope by affinity chromatography. The binding of gB to the surface of susceptible cells BHK-21 and MDBK was specific, dose-dependent, and nearly saturable, which is characteristic of conventional receptor-ligand interactions. The purified gB was shown to specifically bind to immobilised heparin. The addition of soluble exogenous heparin and heparinase treatment of cells inhibited the binding of gB to the cells. Cell-associated gB could also be dissociated from the cells by soluble heparin. The results indicated that ADV gB binds specifically to cellular heparan sulphate. The binding of gB to cells inhibited the attachment of virus to cells and thus the formation of viral plaques. The results suggest that ADV gB may have a function in the initial attachment of ADV to the surface of susceptible cells.

Magnesium-substituted calcium phosphate cements with (Ca + Mg)/P = 2

The introduction of magnesium ions into bone calcium phosphate cements (CPCs) increases the strength and biodegradation rate of the materials. Cement powders with the (Ca + Mg)/P ratio of 2 and the degree of magnesium substitution for calcium of 0, 10, 20, and 40 wt % were used in the study. Sodium phosphate-based solutions were used as the cement fluids. Depending on the magnesium content, CPCs based on magnesium-substituted apatite and whitlockite phases were obtained. The phase composition, setting time, strength, and microstructure of the cements were determined. An increase in the acidity of the cement liquid was found to give cements with a greater content of amorphous phase and more homogeneous structure, resulting in higher strength.

Isolation of mutants of Aujeszky’s disease virus with antigenically altered glycoprotein E by affinity chromatography using monoclonal antibodies

An efficient method for isolation of virus mutants with antigenically altered proteins is described. The method is based on the separation of viruses with wild-type and antigenically altered proteins by affinity chromatography using monoclonal antibodies (MAbs). A nonessential glycoprotein E (gE) of Aujeszkys disease virus (ADV) was chosen as a model for introducing the antigenic changes. The ADV strain Ka mutagenised with 5-bromo-2-deoxyuridine was used for the selection of mutants that do not bind to gE-specific MAb conjugated to resin. After three rounds of isolation by affinity chromatography, the resulting viruses that escape the binding to MAb were plaque-purified by plating at limiting dilution, and virus isolates were tested by the gE-specific sandwich ELISA in which the selecting MAb was used as a capture antibody. About 70% of the ADV isolates tested were not recognised by the sandwich gE-ELISA. The analysis of some of virus isolates in indirect ELISA with a panel of 16 gE-specific MAbs revealed that at least several of the generated virus isolates were mutants expressing gE with alterations in the epitope of the selecting MAb 75/7, as well as in the majority of other conformation-dependent epitopes of gE. The method for the production of antigenically altered viruses by affinity chromatography using MAbs is simple and convenient, and can be utilised with MAbs irrespective of their virus-neutralising activity.

Study of liquid-phase sintering of materials based on zirconium dioxide containing alumina

The dependence of the sintering of zirconium dioxide on the aluminum oxide content and the use of additives forming the liquid phase during sintering is studied. Dense nanostructured ceramic materials based on zirconium dioxide containing aluminum oxide are synthesized. It is shown that the use of additives based on sodium silicate contributes to the sintering and the formation of a nonporous structure at 1330°C. It is revealed that aluminum oxide in the amount of 1 and 5 wt % increases the density of materials, while at the content of 16 wt % the sintering until the dense state does not occur even at temperatures up to 1550°C.

Effect of titanium and zirconium substitutions for calcium on the formation and structure of tricalcium phosphate and hydroxyapatite

The effect of Ti and Zr substitutions for Ca cations on the formation of tricalcium phosphate and hydroxyapatite has been studied in a wide concentration range: from 0.1 to 20 mol %. Upon the incorporation of Ti and Zr cations into tricalcium phosphate, the major forming phase is β-tricalcium phosphate. On the addition of low substituent concentrations to hydroxyapatite, we observe the formation of a single-phase material with the apatite structure. Increasing the substituent concentration to 10–20 mol % Ti or 20 mol % Zr leads to the formation of tricalcium phosphate. The unit-cell volume of the cation-substituted tricalcium phosphates has been shown to decrease with increasing substituent concentration. In the zirconium-containing hydroxyapatites, the unit-cell volume decreases with increasing zirconium concentration, whereas the titanium-containing hydroxyapatites exhibit an opposite tendency.

Sintering and microstructure of materials based on the fluorohydroxyapatite–ZrO2–Al2O3 system

We have studied the influence of the sintering temperature and modifying additives on the phase composition, microstructure, and mechanical strength of a fluorohydroxyapatite-based composite ceramic material containing 20 wt % zirconia. The addition of 5 wt % alumina has been shown to prevent recrystallization processes and contribute to phase composition stabilization. Moreover, the addition of a sintering aid (2 wt %) has made it possible to lower the sintering temperature to 1200°C and raise the bending strength of the material to 143 MPa.

Heat treatment-induced phase transformations of materials in a system of calcium phosphates and magnesium phosphates with (Ca + Mg)/P = 2

We have studied the effect of heat treatment in a wide temperature range (from 300 to 1500°C) on the phase composition, heat effects and weight loss of powder materials in a system of calcium phosphates and magnesium phosphates with (Ca + Mg)/P = 2. The results demonstrate that crystalline magnesium-substituted whitlockite phases begin to form at temperatures above 600°C. Raising the heat treatment temperature reduces the degree of magnesium substitution for calcium in the structure of the magnesium-substituted whitlockite. Tetracalcium phosphate, a high-temperature phase, is formed through apatite phase recrystallization.

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.

Agglomeration and Properties of Ceramics Based on Partially Stabilized Zirconium Dioxide Containing Oxides of Aluminum and Iron

Agglomeration of ceramics of partially stabilized zirconium dioxide containing 5 wt % of aluminum oxide depending on the amount of additive (iron oxide) was studied. It was shown that introduction of an additive promotes a decrease in agglomeration temperature to 1400–1450°С and formation of a dense structure, as well as acquisition of high strength up to 450 MPa (after agglomeration at 1400°С).

Influence of Lithium on the Structure and Phase Composition Formation in the Synthesis of Hydroxyapatite

The influence of lithium substitution for calcium over a broad concentration range (0–20 mol %) on the crystal lattice parameters, coherent scattering regions, and phase composition was studied for hydroxyapatite synthesized by precipitation from solutions and heat treatment at 900, 1200, and 1400°C. The lithium substitution in a more than 10 mol % concentration and increase in the heat treatment temperature to 1400°C give rise to a complex phase composition, which includes not only the apatite phase, but also two tricalcium phosphate phases and calcium pyrophosphate. The results are useful for the development of hydroxyapatite-based materials for bone surgery.