Browsing by Author "Teodosieva R."

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    Biodecomposition of Jordan phosphorite by Phosphate-Solubilizing Fungi
    (2016-01-01) Teodosieva R.; Bojinova D.
    The bio-solubilization of Jordan phosphorite by the phosphate-solubilizing fungus Aspergillus Niger has been investigated. The effect of the phosphate concentration in the liquid medium, the duration of biodecomposition, titratable acidity and the effect of preliminary mechanical activation on the process of dissolution have been studied. The investigations indicate that almost complete extraction of P2O5 from Jordan Phosphorite in a form utilizable by plants can be achieved. A maximum degree of P2O5 extraction 99.10% was obtained on the 15-th day in a medium containing 0.5% w/v non-activated Jordan phosphorite. The preliminary mechanical activation of the phosphate facilitates the dissolution until a definite period of the bioconversion. Investigations with mechanically-activated Jordan phosphorite showed that a maximum extent of 92.40% of phosphate solubilization was observed on the 10-th day at a phosphorite concentration of 0.5% w/v.
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    New Glass-Ceramics in the System Ca2SiO4-Ca3(PO4)2—Phase Composition, Microstructure, and Effect on the Cell Viability
    (2025-08-01) Mihailova I.; Dimitrova P.; Avdeev G.; Ivanova R.; Georgiev H.; Nedkova-Shtipska M.; Teodosieva R.; Radev L.
    The CaO-SiO2-P2O5 system is one of the main systems studied aiming for the synthesis of new bioactive materials for bone regeneration. The interest in materials containing calcium-phosphate-silicate phases is determined by their biocompatibility, biodegradability, bioactivity, and osseointegration. The object of the present study is the synthesis by the sol-gel method of biocompatible glass-ceramics in the Ca2SiO4-Ca3(PO4)2 subsystem with the composition 6Ca2SiO4·Ca3(PO4)2 = Ca15(PO4)2(SiO4)6. The phase-structural evolution of the samples was monitored using X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and surface area analysis. A powder (20–30 µm) glass-ceramic material containing fine crystalline aggregates of dicalcium silicate and plates of silicon-substituted hydroxyapatite was obtained after heat treatment at 700 °C. After heat treatment at 1200 °C, Ca15(PO4)2(SiO4)6, silicocarnotite Ca5(PO4)2(SiO4), and pseudowollastonite CaSiO3 were identified by XRD, and the particle size varied between 20 and 70 µm. The compact glass-ceramic obtained at 1400 °C contained Ca2SiO4-Ca3(PO4)2 solid solutions with an α-Ca2SiO4 structure as a main crystalline phase. SEM showed the specific morphology of the crystalline phases and illustrated the trend of increasing particle size depending on the synthesis temperature. Effects of the glass-ceramic materials on cell viability of HL-60-derived osteoclast-like cells and on the expression of apoptotic and osteoclast-driven marker suggested that all materials at low concentrations, above 1 µg mL−1, are biocompatible, and S-1400 might have a potential application as a scaffold material for bone regeneration.