Browsing by Author "Michailova I."

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    Carbonate apatite formation on novel multiphase CaO-SiO2-P2O5- MgO glass-ceramics in TRIS-HCl buffer
    (2016-01-01) Radev L.; Michailova I.; Georgiev H.; Zaimova D.
    The main purpose of the presented article is the preparation of novel glass-ceramics in CaO-SiO2-P2O5-MgO system and evaluation of carbonate apatite formation after soaking in TRIS-HCl buffer solution for 14 days. The investigated samples were prepared via sol-gel method and structure of the obtained samples was studied using XRD, FTIR, SEM, XPS and ICP-AES. XRD of the thermally treated samples showed that the presence of some crystalline phases is depended on the gel composition. FTIR revealed the existence of all characteristic bands for the observed crystalline phases. SEM monitored the presence of particles with different morphology. After soaking in TRIS-HCl solution, FTIR confirmed that carbonate apatite was formed on the soaked surface. The obtained data are in a good agreement with XPS analysis. The change of ions concentrations in TRIS-HCl buffer solution after immersion of the prepared glass-ceramics was recorded by ICP-AES measurements.
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    In vitro bioactivity of glass-ceramic/fibroin composites
    (2017-01-01) Radev L.; Michailova I.; Stateva S.; Zaimova D.; Georgiev H.; Apostolova M.
    Bioactive composite materials were prepared by mixing 20 wt.% of silk fibroin (SF) and 80 wt.% of glassceramics from CaO-SiO2-P2O5-MgO system. In vitro bioactivity of the prepared composites was evaluated in 1.5 simulated body fluid (1.5 SBF) in static conditions. The obtained samples before and after in vitro tests were characterized by X-ray diffraction (XRD) analysis, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The changes in 1.5 SBF solutions after soaking the samples were evaluated by inductively coupled plasma atomic emission spectroscopy (ICP-AES). MG63 osteosarcoma cells were used for the biological experiments. The obtained experimental data proved that the synthesized composites exhibit excellent in vitro bioactivity.
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    In vitro bioactivity of Polyurethane/85S Bioglass composite scaffolds
    (2013-09-01) Radev L.; Zheleva D.; Michailova I.
    In the present work Polyurethane (PU)/Bioglass (BG) composite materials were synthesized with different content of BG (10 and 20 mol.%) as filler. The 85S Bioglass was synthesized via polystep sol-gel method. The chemical composition of BG is 85SiO2-10CaO-5P2O5 (wt.%). The synthesis of PU was carried out by a two-step polyaddition reaction. The 85S BG was added in situ during the polymerization reaction. In vitro bioactivity of the prepared composites was examined in the presence of 1.5 SBF for 7 days in static conditions. The structure of synthesized PU/BG composites before and after in vitro test was determined by XRD, FTIR and SEM. XRD of the samples before in vitro test proved that the phase of γCa 2P2O7 in the PU/20BG is visible. FTIR revealed the presence of urethane bond between OH-(from BG) and NCO groups (from PU). Based on FTIR results after in vitro test in 1.5 SBF solutions, A/B-carbonate containing hydroxyapatite (CO3HA) was formed. XRD proved that HA was formed on the surface of the samples, but Ca2P2O 7 does not undergo any changes in the 1.5 SBF solution. SEM depicted the nano-HA agglomerated in spherical particles after immersion in 1.5 SBF for 7 days. © 2013 Versita Warsaw and Springer-Verlag Wien.
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    Sol-gel bioactive glass-ceramics Part I: Calcium phosphate silicate/ wollastonite glass-ceramics
    (2009-04-08) Radev L.; Hristov V.; Michailova I.; Samuneva B.
    In this work we present experimental results about synthesis, structure evolution and in vitro bioactivity of new calcium phosphate silicate/ wollastonite (CPS/W) glass-ceramics. The samples obtained were synthesized via polystep sol-gel process with different Ca/P+Si molar ratio (R). The structure of the materials obtained was studied by XRD, FTIR spectroscopy and SEM. XRD showed the presence of Ca15 (PO4)2(SiO4)6, β-CaSiO3 and α-CaSiO3 for the sample with R=1.89 after thermal treatment at 1200°C/2h. The XRD results are in good agreement with FTIR analysis. SEM denotes that apatite formation can be observed after soaking in simulated body fluid (SBF). © Versita Warsaw and Springer-Verlag Berlin Heidelberg 2009.
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    Sol-gel bioactive glass-ceramics Part II: Glass-ceramics in the CaO-SiO2-P2O5-MgO system
    (2009-04-08) Radev L.; Hristov V.; Michailova I.; Samuneva B.
    Ceramics, with basic composition based on the CaO-SiO2- P2O5-MgO system with different Ca+ Mg/P+Si molar ratio (R), were prepared via polystep sol-gel technique. The structure of the obtained ceramic materials has been studied by XRD, FTIR spectroscopy, and SEM. X-ray diffraction showed the presence of akermanite and HA for the sample with R = 1.68 and Mg substituted β-TCP and silicocarnotite for the sample with R = 2.16, after thermal treatment at 1200°C/2 h. The obtained results are in good agreement with FTIR. In vitro test for bioactivity in static condition proved that the carbonate containing hydroxyapatite (CO3HA) can be formed on the surface of the synthesized samples. CO3 HA consisted of both A- and B-type CO32- ions. SEM micrographs depicted different forms of HA particles, precipitated on the surface after soaking in 1.5 simulated body fluid (SBF). © Versita Warsaw and Springer-Verlag Berlin Heidelberg 2009.