The rate of resorption of calcium phosphate self-hardening materials for bone regeneration can be changed by changing the phase composition. The Ca3(PO4)2/CaCO3/Ca(H2PO4)2·H2O/Na2HPO4·12H2O system is important for the synthesis of self-curing bioactive materials with variable resorption rates by changing the ratios of the initial components. Cement compositions in twelve figurative points of a four-component composition diagram at a fixed content in the α-Ca3(PO4)2 system were studied with XRD, FTIR, SEM, calorimetric, and volumetric methods to obtain an idea of the effect of composition on solubility in vitro and resorption in vivo. It was found that the presence of the highly resorbable phase of dicalcium phosphate dihydrate in cement and the substitution of phosphate ions with the carbonate ions of hydroxyapatite increased solubility in vitro and resorption in vivo. The obtained results confirm the possibility of changing the solubility of a final product in the Ca3(PO4)2/CaCO3/Ca(H2PO4)2·H2O/Na2HPO4·12H2O system by changing the ratio of the initial components.
Low-temperature ceramics based on magnesium calcium phosphate cement are a promising resorbable material for bone tissue restoration with the possibility of functionalization. The replacement of the magnesium Mg2+ ion with a calcium Ca2+ ion at the stage of preparation of the precursor leads to the production of multiphase ceramics containing phases of brushite, monetite, and newberyite, with different dissolution rates. Multiphase ceramics leads to volumetric resorption with preservation of their geometric shape, which was confirmed by the results of an evaluation of the output of magnesium Mg2+ and calcium Ca2+ ions into the contact solution of the ceramics and the X-ray density of ceramic samples during subcutaneous implantation. The combined introduction of sodium pyrophosphate decahydrate and citric acid monohydrate as setting inhibitors neutralizes their insignificant negative effect on the physico-chemical properties of ceramics (strength, pH, porosity), determining the optimal composition. In vivo experiments with setting inhibitors in the composition of ceramics showed a different biological response, affecting the rate of resorption on par with magnesium ions. Preliminary data on biocompatibility and solubility determined magnesium-calcium phosphate ceramics containing additives that regulate setting to be a potential material for bone tissue restoration and a vector for further research, including in orthotopic implantation models.
Introduction. The heat emission of concrete during its hardening in adiabatic conditions is typically determined according to the GOST 24316 State Satndard. This method is quite limited in research possibilities, since under the conditions of constantly increasing temperature, it appears impossible to adequately assess the influence of various components or hardening conditions on the processes occurring during the concrete hardening. The assessment of the heat emission during the isothermal hardening allows much more information about the hardening process of the studied material to be obtained. The direct determination of the concrete heat emission during hardening in isothermal conditions appears to be extremely difficult in technical aspect.Aim. The study is aimed at developing a method for determining the heat emission of the concrete in isothermal conditions.Materials and methods. The GOST 31108-2016 TsEM I 52.5N portland cement, quartz sand, crushed gabbrodiabase, and the GOST 23732-2011 mixing water were used in the study. The strength of concrete samples was determined in accordance with the GOST 10180-2012 State Standard. The TAM Air (TA Instruments) isothermal calorimeter was used for calorimetric studies.Results. As a result of the performed studies, a method for determining the concrete heat emission in isothermal conditions was developed on the basis of assessment of the heat emission during the hardening of model mixtures reflecting the composition of the studied concrete. The optimal particle size of the sand and crushed stone fractions for model mixtures comprises 0.16–0.315 mm. The heat emission during the isothermal hardening of 10 model mixtures reflecting the composition of the studied concrete grades was determined. The strength class of 10 concrete compositions differing in cement content was established. The dependence of the heat emitted by model mixtures on the strength classes of the studied concrete compositions was determined. The heat emission of model mixtures during the isothermal hardening was established to be directly dependent on the strength of the studied concrete compositions.Conclusions. The determination of the amount of heat emitted by model mixtures reflecting the composition of concrete mixtures during the isothermal hardening represents a useful cost-effective test significantly accelerating and facilitating the process of control and design of concrete compositions.
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