Insitu magnesium calcium phosphate cements formation: From one pot powders precursors synthesis to in vitro investigations.

Calcium phosphate cements are of great interest for researchers and their applications in medical practice expanded. Nevertheless, they have a number of drawbacks including the insufficient level of mechanical properties and low degradation rate. Struvite (MgNH4PO4) -based cements, which grew in popularity in recent years, despite their neutral pH and acceptable mechanical performance, release undesirable NH4 + ions during their resorption. This issue could be avoided by replacement of ammonia ions in the cement liquid with sodium, however, such cements have a pH values of 9-10, leading to cytotoxicity. Thus, the main goal of this investigation is to optimize the composition of cements to achieve the combination of desirable properties: neutral pH, sufficient mechanical properties, and the absence of cytotoxicity, applying Na2HPO4-based cement liquid. For this purpose, cement powders precursors in the CaO-MgO-P2O5 system were synthesized by one-pot process in a wide composition range, and their properties were investigated. The optimal performance was observed for the cements with (Ca + Mg)/P ratio of 1.67, which are characterized by newberyite phase formation during setting reaction, pH values close to 7, sufficient compressive strength up to 22 ± 3 MPa (for 20 mol.% of Mg), dense microstructure and adequate matrix properties of the surface. This set of features make those materials promising candidates for medical applications.

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.

[Octacalcium phosphate--precursor of biomineralization, novel bone scaffold].

Review of the literature and our own investigations describes structure, synthesis, hydrolysis, participation in biomineralisation of bone and teeth of octacalcium phosphate, a new synthetic bone scaffold.

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, beta-tricalcium phosphate, carbonate-substituted hydroxyapatite with 0.59 and 5.9 wt% substitution with CO(3)(2-)) and biphasic (hydroxyapatite-tricalcium phosphate with various percentage of the components 80/20, 60/40, 20/80, silicon-substituted hydroxyapatite with 0.79 wt% SiO(2)) 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.

Energy dispersive X-ray diffraction study of phase development during hardening of calcium phosphate bone cements with addition of chitosan.

The aim of this work was to study the phase transformation during the setting reaction of two calcium phosphate bone cements based on either alpha tricalcium phosphate (alpha-TCP) or tetracalcium phosphate (TetCP) initial solid phase, and a magnesium carbonate-phosphoric acid solution as the hardening liquid. Low molecular weight (38.2 kDa) chitosan was used to retard the cement's setting reaction. To follow the kinetics of the phase development, an energy dispersive X-ray diffraction technique was applied. This technique allowed the collection of diffraction patterns from the cement pastes in situ starting from 1 min of the setting process. In the case of the TetCP-based cement, the appearance and evolution of an intermediate phase was detected.

Study of in vivo biocompatibility and dynamics of replacement of rat shin defect with porous granulated bioceramic materials.

Biocompatibility of porous granulated bioceramic materials (hydroxyapatite, beta-tricalcium phosphate, hydroxyapatite-b-tricalcium phosphate complex (80:20 wt%), carbonate-containing hydroxyapatite, and silicon-containing hydroxyapatite) was shown in a subcutaneous test on BDF1 mice. Dynamic (up to 8 months) observation showed gradual replacement of the granular substance with de novo forming bone tissue with hemopoiesis foci on a model of fenestral defect in the shin bone in Wistar rats. By the rate of resorption, the materials rank as follows: silicon-containing hydroxyapatite

[Development and laboratory analysis of new remineralizing means].

In laboratory research there were studied different combinations of remineralizing agents allowing production of substances close by chemical composition to hydroxyapatite of hard dental tissues. The most acceptable for practical use in case of demineralizing foci of hard dental tissues treatment can be only 2 calcium orthophosphates that may be synthesized under physiological conditions from solutions of calcium nitrate and twice-substituted ammonium phosphate, in particular, dicalcium phosphate dihydrate (structure of brushite, CaHP0(4) x 2H(2)O) and the so called precipitated hydroxyapatite (Ca(10-x) (HPO(4))(x)(PO(4))(6-x)(OH)(2-x)). The data are the bases for development of remineralizing agents and their further experimental and clinical studies.

[Application of cell technologies to tissue defect closure in oncology].

In vivo and in vitro experiments on the application of cell technologies to tissue defect closure were conducted; autologic mesenchymal stem cells on 3-demensional matrices were used. The authors analyze the results of the application of bioengineering tissue equivalents for the closure of soft tissue and upper airway defects after extensive resections performed in 52 oncological patients. Tissue equivalents with stem cells provide engraftment and long-term graft functioning; they also modify wound surface, thus stimulating wound epithelization. In this study the application of tissue equivalents led to wound healing and functional recovery in 87% of patients.

Carbonate release from carbonated hydroxyapatite in the wide temperature rage.

Synthetic carbonated apatite ceramics are considered as promising alternative to auto- and allograft materials for bone substitute. The aim of this study was to investigate the thermal stability of an AB-type carbonated apatite in the wide temperature range. The data on the thermal stability have to allow the conditions of the sintering of the ceramics to be controlled. Initial carbonated apatite powders were prepared by interaction between calcium oxide and ammonium hydrogen phosphate with addition of ammonium carbonate. Decomposition process was monitored by infra red spectroscopy, weight loss and X-ray diffraction of solid, and by infra red analysis of condensed gas phase resulted from the thermal decomposition of the sample in equilibrium conditions. Features of carbon monoxide and carbon dioxide release were revealed. The synthesized AB-type carbonated apatite is started to decompose at about 400 degrees Celsius releasing mainly carbon dioxide, but retained some carbonate groups and apatite structure at the temperature 1100 degrees Celsius useful to prepare porous carbonate-apatite ceramics intended for bone tissue engineering scaffolds.

FTIR study of carbonate loss from carbonated apatites in the wide temperature range.

The mineral constituent of bone tissue is a carbonate-substituted apatite (CHA). The thermal stability of the CHA has been revealed to depend on the substitution type and degree, although relatively little is known about this behavior. The aim of this study was to investigate the carbonate loss from synthetic CHAs in equilibrium conditions in a wide temperature range. An approach based on FTIR spectroscopy of condensed gas phase was applied to evaluate the CO and CO2 release with increasing temperature. Four different CHAs were studied, which were prepared by either precipitation from solution or the solid-state interaction. The samples differ from each other by the substitution degree. In one of the samples calcium was partially substituted by magnesium. Decomposition was shown to start at surprisingly low temperature, about 400 degrees C, and the CO content increases monotonously with the increase of temperature. The CO2 content goes through a maximum due to its decomposition into carbon monoxide and oxygen, the temperature of this maximum being strongly dependent on the chemical synthesis route. Therefore, control of the sintering atmosphere with respect to the CO2/CO ratio is needed when preparing the carbonated apatite bioceramics.

Influence of fluorapatite minor additions on behavior of hydroxyapatite ceramics.

Fluorinated hydroxyapatite is known to be less soluble by body fluids, resulting in enhanced resistance to biodegradation in vivo conditions, as compared to the pure hydroxyapatite ceramics. The present work was aimed at the investigation of the effect of minor additions of ultrafine fluorapatite (up to 10 wt%) on the sintering behavior and mechanical properties of hydroxyapatite ceramics. In vitro testing for the osteoblast-like cells viability and proliferation was performed with the samples of varying fluorapatite content. It was found that the fluorapatite addition hinders the sintering shrinkage and lowers the strength, but does not generally affect negatively the viability of the cells.

Porous hydroxyapatite ceramics of bi-modal pore size distribution.

A route for the fabrication of porous hydroxyapatite ceramics having two populations of open pores is reported. The bodies are prepared by sintering the spherical gelatin/hydroxyapatite granules. As the result, ceramics containing intragranular small-size pores and intergranular large-size interconnecting pores are obtained. The pore size and content are dependent on the route. Ceramics can generally be applied as bone replacement materials where the interconnections in the intergranular pores are the pathway to conduct cells and vessels for the bone ingrowth, whereas the intragranular pores can be filled with a drug, e.g. to eliminate infections.