V. V. Smirnov

Effect of the concentration of carbonate groups in a carbonate hydroxyapatite ceramic on its in vivo behavior

Carbonate-substituted hydroxyapatites containing up to 9 wt % of carbonate groups were synthesized and fabricated in the form of porous granules with a view to developing materials for use in bone tissue repairs. The use of sintering additives forming a liquid phase allowed the granule sintering temperature to be reduced by 400–450°C. It was found that the carbonate groups enter into the structure of the ceramic by a mixed AB-type substitution; the microstructure of the granules depends substantially on the concentration of the carbonate groups; introduction of 6 wt % of carbonate groups into apatite ensures high biological properties of the granules in experiments in vivo.

Hydroxyapatite-Calcium Carbonate Ceramic Composite Materials

Hydroxyapatite/calcium carbonate (CC) composite powders containing up to 50 wt % CO32−, have been prepared via precipitation from aqueous solutions. According to chemical analysis data, the CO32− content of the powders coincides with the intended one over the entire composition range studied. With increasing CO32− content, the specific surface area of the powders decreases because of the formation and growth of large needlelike CC crystals up to 1.5 μm in size. The addition of low-melting-point alkali carbonates to the starting powder mixture reduces the sintering temperature of the powders to below 720°C, thereby preventing the thermal decomposition of CC. The highest bending strength, up to 76 MPa, is offered by the materials with the lowest CC content, about 20 wt %, and an average crystal size of 100 nm. The solubility of the composites gradually increases with CC content. In vitro experiments with a human fibroblast model (MTT test) demonstrate that the composites have zero cytotoxicity.

Temperature fluctuations in turbulent flame measured using coherent anti-Stokes Raman scattering

Local temperatures and amplitudes of their temporal fluctuations caused by instabilities of the reacting medium composition and of the combustion process itself were measured for turbulent diffusion combustion of decane–air vapor–gaseous mixtures in a flame of a laboratory burner using a coherent anti-Stokes Raman scattering diagnostic system with nanosecond pulse duration of the pump lasers and broad modeless spectrum of Stokes radiation. The relative error of thermometry of nitrogen-containing mixtures in the range 100–2000 K during one laser pulse (10 ns) was 3.1%.

Study of collisional deactivation of O2(b1Σg+) molecules in a hydrogen-oxygen mixture at high temperatures using laser-induced gratings

Collisional deactivation of O2(b1Σg+) molecules resonantly excited by a 10 ns pulse of laser radiation with a wavelength of 762 nm in H2/O2 mixtures is experimentally studied. The radiation intensity and hence the molecule excitation efficiency have a spatially periodic modulation that leads to the formation of laser-induced gratings (LIGs) of the refractive index. The study of LIG temporal evolution allows collisional relaxation rates of molecular excited states and gas temperature to be determined. In this work, the b1Σg+ state of O2 molecules deactivation rates are measured in a 4.3 vol % H2 mixture at the number density of 2 amg in the temperature range 291–850 K. The physical deactivation is shown to dominate in the collisions of H2 with O2(b1Σg+) and O2(a1Δg) up to temperatures of 780–790 K at time delays up to 10 μs after the excitation pulse. The parameters of the obtained temperature dependence of the (b1Σg+ state deactivation rate agree well with the data of independent measurements performed earlier at lower temperatures (200–400 K). Tunable diode laser absorption spectroscopy is used to measure the temperature dependence of the number density of the H2O molecules which appear as the mixture, as the result of the dark gross reaction with O2 molecules in the ground state, O2 + 2H2 → 2H2O. The measurements show that this reaction results in complete transformation of H2 into H2O at temperatures of 790–810 K.

Nanocrystalline hydroxyapatite ceramics

The possibility of using high pressures in uniaxial pressing and rolling of nanopowders is investigated. Obtainment of a nanocrystalline hydroxyapatite ceramic intended for use in medicine is studied. The sintering temperature is reduced by approximately 600°C, and a ceramic with a grain size of less than 50 nm and high values of microhardness (up to 5.7 GPa) after annealing at 750°C is obtained. A substantial collective recrystallization of crystallite powder is overcome.

In Vitro Study of Matrix Surface Properties of Porous Granulated Calcium Phosphate Ceramic Materials Made in Russia

We performed in vitro screening of monophasic (hydroxyapatite, β-tricalcium phosphate, carbonate-substituted hydroxyapatite with 0.59 and 5.9 wt% substitution with CO32−) and biphasic (hydroxyapatite-tricalcium phosphate with various percentage of the components 80/20, 60/40, 20/80, silicon-substituted hydroxyapatite with 0.79 wt% SiO2) porous granulated ceramics composed of calcium phosphate powders synthesized by methods of heterophasic interaction of reagents and precipitation from aqueous solutions using MTT test and cultured human fibroblasts. Acute toxicity of materials (24-h incubation with cell culture) and matrix properties (3, 5, 7, 14, 18, 21, 28 days in culture) were evaluated. We selected a batch of materials obtained by precipitation from aqueous solutions, which were non-toxic and were characterized by good matrix properties (for cells). Biphasic ceramics with hydroxyapatite-tricalcium phosphate ratio of 80/20 exhibited best characteristics, and ceramics on the basis of silicon-substituted hydroxyapatite showed moderate characteristics.

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).

Laser Spectrometric Measurement System for Local Express Diagnostics of Flame at Combustion of Liquid Hydrocarbon Fuels

A laboratory laser spectrometric measurement system for investigation of spatial distributions of local temperatures in a flame at combustion of vapors of various liquid hydrocarbon fuels in oxygen or air at atmospheric pressure is presented. The system incorporates a coherent anti-Stokes Raman spectrometer with high spatial resolution for local thermometry of nitrogen-containing gas mixtures in a single laser shot and a continuous operation burner with a laminar diffusion flame. The system test results are presented for measurements of spatial distributions of local temperatures in various flame zones at combustion of vapor—gas n-decane/nitrogen mixtures in air. Its applicability for accomplishing practical tasks in comparative laboratory investigation of characteristics of various fuels and for research on combustion in turbulent flames is discussed.

Effect of Calcium Phosphate Materials on Multipotent Mesenchymal Cells from Exfoliated Deciduous Teeth (SHED Cells) in Vitro

Various calcium phosphate ceramic materials were created and their effect on cultured mesenchymal cells from exfoliated deciduous tooth pulp was evaluated. Tricalcium phosphate ceramics provides best cell survival and is an optimal material for bone tissue engineering. Analysis of the effects of tricalcium phosphate ceramics on osteogenic differentiation of SHED cells suggests that this material potentiated dexamethasone-induced osteogenic differentiation, which manifested in the increased number of ossification foci and enhanced extracellular matrix production by cells. Thus, the tricalcium phosphate ceramics created by us is a promising biomedical material that can be used for tissue-engineered bone analogs.

Measurements of temperature spatial distribution and fluctuations in a hydrogen-oxygen flame at high pressures by means of coherent anti-Stokes Raman spectroscopy

The results of measurements of the temperature field in a hydrogen-oxygen flame by means of broadband coherent anti-Stokes Raman spectroscopy are presented. The measurements were performed at pressures up to 1.7 MPa and temperatures ~3000 K with the spatial resolution of ~0.04 × 0.04 × 2.5 mm3. The duration of a single measurement was 10 ns and the sampling rate was 10 Hz. The error of the temperature determination was ~4% for the single-shot measurements and ∼0.15% for the measurements of the average values during 100 s under quasi-stationary burning conditions.