Browsing by Author "Radev L."
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Item Carbonate - apatite forming ability of polyphase glass - ceramics in the CaO - MgO - SiO2 system(2015-01-01) Mihailova I.; Radev L.; Aleksandrova V.; Colova I.; Salvado I.M.M.; Fernandes M.H.V.Several types of glass-ceramics in the CaO - MgO - SiO2 system are shown to be bioactive, biocompatible and exhibiting various advantages for bone regeneration. A polyphase calcium-magnesium-silicate glass-ceramics is prepared by the sol-gel method including a two-step thermal treatment procedure aiming to investigate the effect of its phase composition on the in-vitro bioactivity observed. The dried gels of a chemical composition 3CaO.MgO.2SiO2 corresponding to merwinite are thermally treated at 700°C and 1100°C. The structural behavior of the synthesized samples is examined by X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). Larnite as the main crystalline phase, accompanied by merwinite, akermanite and periclase are detected after heat treatment at 1100°C. The in-vitro bioactivity of the glass-ceramics is detected by investigating the apatite formation ability in Simulated Body Fluid (SBF) for different times of soaking. The changes on the surface of the immersed samples and the formation of Mg- and Si-substituted carbonated apatites are verified by FTIR, SEM and Energy Dispersive Spectroscopy (EDS) techniques. The dissolution behavior of the glass-ceramics in SBF is also carried out by Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). The results indicate fast degradation in SBF and high reactivity of the polyphase glass-ceramics. The latter might be used as a bioactive implant material.Item 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.Item DFT calculations, characterization and in vitro cytotoxicity of platinum(II) complex of 3-amino-1,2,4-triazole(2020-01-01) Yankova R.; Kostadinova A.; Radev L.A platinum(II) complex of 3-amino-1,2,4-triazole is synthesized and characterized by using 1H, 13C NMR and FT-IR spectroscopies. The molecular geometry and the chemical reactivity of the complex are studied using the Density Functional Theory at B3LYP/6-311++G(d, p) basis set of H, C, N, Cl and LANL2DZ for Pt. The molecular electrostatic potential surface, the natural bond orbital and the natural charge population are estimated. The frontier molecular orbital analyses are conducted. The intramolecular interactions in [Pt(3-amino-1,2,4-triazole)2Cl2] are investigated using the quantum theory Atoms in Molecules. It is observed that the complex is stabilized via two hydrogen bonds, N-H···Cl, which are weak and electrostatic in nature. They determine the different energy and bond length of Pt-Cl and Pt-N. The compound cytotoxicity is evaluated using 2 type eukaryotic cells: MDCK II kidney epithelial cell line and A549 cancer alveolar cell line. The results of this investigation demonstrate the high cytotoxic effect of [Pt(3-amino-1,2,4-triazole)2Cl2] especially to cancer cells. This Pt(II) complex is a promising nanomaterial for a variety of biomedical applications, including cancer therapy.Item In vitro bioactivity of 70 wt.% SiO2 - 30 wt.% CaO sol-gel glass, doped with 1, 3 and 5 wt.% NbF5(2012-02-01) Radev L.; Hristova K.; Jordanov V.; Fernandes M.; Salvado I.The 70SiO2-30CaO (wt.%) sol-gel glasses doped with 1, 3 and 5 NbF5 (wt.%) were prepared via polystep sol-gel route. The synthesized glasses were characterized by XRD, FTIR and SEM. Changes in 1.5 SBF solutions were measured by ICP-AES. XRD of the glasses stabilized at 700°C for 6 hours proved the presence of niocalite. FTIR was consistent with XRD data. The in vitro bioactivity study of all glasses prepared were carried out by soaking in 1.5 simulated body fluid (1.5 SBF) at 37°C for 6 and 12 days in static conditions. The FTIR reveals the formation of A-type and B-type carbonate containing hydroxyapatite (CO3HA) layer. Changes in 1.5 SBF solutions, after 6 days of soaking, show that the Ca concentration increased significantly, compared to the initial Ca content in the 1.5 SBF solution before in vitro test. After 12 days of immersion, the Ca concentration decreased, i.e., the formation of HA phase consumed Ca from 1.5 SBF solution. For all soaking times, the concentration of P is much lower than that the used 1.5 SBF. Based on these results we suggest that Ca and P play an active role in the future of the glasses. SEM depicts that the different morphology of hydroxyapatite can be formed as a function of soaking time. © 2011 Versita Warsaw and Springer-Verlag Wien.Item 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.Item 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.Item In vitro surface biocompatibility of high-content silicon-substituted calcium phosphate ceramics(2013-02-01) Mostafa N.Y.; Shaltout A.A.; Radev L.; Hassan H.M.The present work investigates surface biocompatibility of silicon-substituted calcium phosphate ceramics. Different silicon-substituted calcium phosphate ceramic bodies were prepared from co-precipitated powders by sintering at 1300 C. The in vitro bioactivity of the ceramics was assessed in simulated body fluid (SBF) at 37 C for periods up to 4 weeks. The changes in the surface morphology and composition were determined by scanning electron microscopy (SEM) coupled with electron probe microanalysis and energy dispersive spectrometer (EDX). Inductively coupled plasma optical emission spectroscopy (ICP-OES) was used to observe the change in ionic concentration of SBF after removal of the samples. The bioactivity of the ceramics increased with an increasing silicate ion substitution in a systematic way. The surface of ceramics with 2.23% silicon substitution was partially covered with apatite layer after one week, while ceramics with 8.1% silicon substitution were completely covered with apatite in the first week. The porous microstructure of high-concentration Si-substituted ceramics helps the dissolution of surface ions and the leaching process. This allows SBF to reach supersaturation in a short time and accelerate the deposition of apatite layer. © 2013 Versita Warsaw and Springer-Verlag Wien.Item Influence of thermal treatment on the structure and in vitro bioactivity of sol-gel prepared CaO-SiO2-P2O5 glass-ceramics(2014-01-01) Radev L.Nowadays there is a substantial practical interest in the in vitro bioactivity of calcium silicate phosphate (CSP) glass-ceramics and carbonate apatite (CO3HA) formation on their surfaces after in vitro test in simulated body fluid (SBF). The main purpose of the presented article is the evaluation of the chemical composition of the gel with nominal composition 70.59 CaO:28.23 SiO2:1.18 P2O5 (mol.%) on the structure, crystallization behaviour and in vitro bioactivity in SBF solution for 14 and 28 days. The prepared glass-ceramics have been synthesized via a polystep sol-gel method. The structure of the obtaining samples was studied by X-ray diffraction (XRD) analysis, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX). After thermal treatment of the samples XRD confirmed the presence of β-Ca2SiO4 and Ca15(PO4)2(SiO4)6, and indicated that at 1500 °C Ca15(PO4)2(SiO4)6 becomes predominant phase. FTIR revealed the presence of all characteristics bands for calcium silicate phosphate (CSP) bonds. SEM monitors the presence of particles with different morphology. After in vitro test in SBF, FTIR depicted that B-type carbonate containing hydroxyapatite (CO3HA) is preferentially formed on the immersed glass-ceramics. SEMof the precipitated layers showed the presence of HA spheres. The changes in SBF solution after soaking the samples were recorded by inductively coupled plasma atomic emission spectroscopy (ICP-AES).Item Methylcellulose/SiO2 hybrids: Sol-gel preparation and characterization by XRD, FTIR and AFM(2011-03-21) Rangelova N.; Radev L.; Nenkova S.; Salvado I.M.M.; Fernandes M.H.V.; Herzog M.Methylcellulose (MC)/SiO2 organic/inorganic hybrid materials have been prepared from MC and methyltriethoxysilane or ethyltrimethoxysilane, and characterized by XRD, FTIR and AFM. XRD showed peak shifts. FTIR shows intermolecular hydrogen bonding between MC and SiO2. AFM depicts surface roughness which depends on the silica precursor and MC content. © Versita Sp. z o.o.Item Organic/inorganic bioactive materials part I: Synthesis, structure and in vitro assessment of collagen/silicocarnotite biocoatings(2009-10-19) Hristov V.; Radev L.; Samuneva B.; Apostolov G.The silicocarnotite, as an inorganic part of the coatings, has been synthesized using a polystep sol-gel method. The chemical composition of the prepared silicocarnotite sol is described as 58.12 CaO, 29.42 P2O5, 12.45 SiO2 (wt%), where Ca/P+Si = 1,67. The acid soluble type I collagen, as an organic part of the obtained coatings, was mixed with silicocarnotite powder in a weight ratio of 25:75 and 75:25 weight ratio without cross-linkage. The acidity of the obtained mixture was readjust with 25% NH4OH to pH = 9.0. The mixture was then dried at 37°C for 12 h. The growth of B-type carbonate containing hydroxyapatite (B-type CO3HA) in which CO32+ → PO43- on the surface of collagen/silicocarnotite coatings soaked in 1.5 simulated body fluid (1.5 SBF) was observed. The nucleation of B-type CO3HA was estimated on the obtained coatings after 3 days immersion in 1.5 SBF. The negatively charged carboxylate groups from the collagen surface may be responsible for the HA deposition. This was confirmed by the ``red shift`` of carboxylate groups of collagen molecules in the FTIR spectra. After soaking in 1.5 SBF, the morphology of prepared coatings and HA formation was observed by SEM. © Versita Warsaw and Springer-Verlag Berlin Heidelberg 2009.Item Organic/inorganic bioactive materials part II: In vitro bioactivity of Collagen-Calcium Phosphate Silicate/Wollastonite hybrids(2009-10-19) Radev L.; Hristov V.; Samuneva B.; Ivanova D.In the present study, novel hybrid materials of Collagen (C) and Calcium Phosphate Silicate/Wollastonite (CPS/W) were synthesized. The CPS/W ceramic was prepared via polystep sol-gel method. The dissolution test of CPS/W ceramic was filled with TRIS-HCl buffer. FTIR depicts that hydroxyl carbonate apatite (OHCO3HA) was observed after 3 days of immersion in TRIS-HCl buffer. Biohybrids of C-CPS/W were produced from diluted hydrochloric acid collagen type I and ceramic powder with different ratios of C and CPS/W equal to 25:75 and 75:25 wt.%. The synthesized hybrids were characterized by FTIR, XRD and SEM. FTIR depicts a ``red shift`` if amide I could be attributed to the fact that the collagen prefers to chelate Ca2+ from partial dissolution of CPS/W ceramic. The growth of B-type carbonate containing hydroxyapatite (B-CO3HA) on the C-CPS/W hybrids soaked in 1.5SBF was observed. The negatively charged carboxylate groups from the collagen may be responsible for hydroxyapatite (HA) deposition. This fact was confirmed by the ``red shift`` of carboxylate groups of collagen in FTIR spectra. The formation of HA was observed by FTIR, XRD and SEM. © Versita Warsaw and Springer-Verlag Berlin Heidelberg 2009.Item Organic/inorganic bioactive materials part III: In vitro bioactivity of gelatin/silicocarnotite hybrids(2009-10-19) Radev L.; Fernandes M.; Salvado I.; Kovacheva D.In this work we present our experimental results on synthesis, structure evolution and in vitro bioactivity assessment of new gelatin/ silicocarnotite hybrid materials. The hybrids were obtained by diluting gelatin (G) and silicocarnotite (S) ceramic powder with G:S ratios of 75:25 and 25:75 wt.% in hot (40°C) water. The hybrids were characterized using XRD, FTIR, SEM/EDS and XPS. FTIR depicts that the ``red shift`` of amide I and COO- could be attributed to the fact that the gelatin prefers to chelate Ca2+ from S. The growth of calcium phosphates on the surface of the hybrids synthesized and then immersed in 1.5 SBF for 3 days was studied by using of FTIR, XRD and SEM/EDS. According to FTIR results, after an immersion of 3 days, A and B-type CO3HA can be observed on the surface. XRD results indicate the presence of hydroxyapatite with well defined crystallinity. SEM/EDS of the precipitated layers show the presence of CO3HA and amorphous calcium phosphate on the surface of samples with different G/S content when immersed in 1.5 SBF. XPS of the G/S hybrid with 25:75 wt.% proved the presence of Ca-deficient hydroxyapatite after an in vitro test for 3 days. © Versita Warsaw and Springer-Verlag Berlin Heidelberg 2009.Item Organic/inorganic bioactive materials part IV: In vitro assessment of bioactivity of gelatin-calcium phosphate silicate/wollastonite hybrids(2010-04-01) Radev L.; Hristov V.; Fernandes M.H.V.; Salvado I.M.M.Biohybrids consisting of gelatin (G) and calcium phosphate silicate/wollastonite (CPS/W) have not been prepared so far. In this work our results are focused on the possibility of obtaining G-CPS/W bioactive hybrids in vitro. XRD, FTIR, SEM/EDS techniques were employed to characterize the synthesized hybrid materials. FTIR shows that before immersion in 1.5 SBF the ``red shift`` of COO- band for pure G is observed. The presence of this bond could be attributed to the formation of COO-Ca2+ via non-biomimetic route. After immersion in 1.5 SBF, FTIR shows the presence of A- and B-type carbonate containing hydroxyapatite (A/B-CO3HA). ESD and FTIR show that small amount of calcite (CaCO3) are present after in vitro test in 1.5 SBF for 3 days. XRD reveals that CO3HA and small amounts of CaCO3 can be detected after in vitro test. SEM results obtained for immersed samples show that hydroxyapatite (HA) particles fully covered the surface of the hybrids by a layer composed of spherulites. At higher magnification, very small elongated crystallites could be observed. © 2010 Versita Warsaw and Springer-Verlag Wien.Item Phase composition, structure and catalytic activity in oxidation reactions of fayalite waste from the flotation of copper slag(2017-01-01) Mihailova I.; Radev L.; Mehandjiev D.The study examines the phase composition and structure of fayalite waste (FW), as well as the changes that occur during heat treatment applied in the temperature range of 500 - 1000 °C. Differential thermal analysis, X-Ray diffraction analysis, Fourier transform infrared spectroscopy, Optical microscopy, Scanning electron microscopy and Energy dispersive spectroscopy have been used. The main crystalline phase in waste was fayalite, accompanied by magnetite, amorphous silicate phase and a small amount of copper-iron sulfides. Phase-structural changes were found in all heat treated samples. Their extent was temperature dependent. Fayalite transformed to hematite, magnetite and silica. Magnetite transformed to hematite through oxidation. Glass phase underwent oxidation too. In oxidation at 1000°C FW baseline phases were fully replaced by hematite, magnetite, cristobalite and amorphous silicate phase. At this heat treatment temperature the sample exhibited the highest catalytic activity towards the oxidation of CO.Item SIGNIFICANCE OF ASSESSMENT AND COMMUNICATION WITH THE TEACHER IN THE CHEMICAL TECHNOLOGY LEARNING PROCESS(2024-01-01) Traykova S.; Radev L.Given the complexity of the learning content, in modern engineering education, the need for feedback from the students is also relevant. Not only during an exam when they demonstrate the outcomes of their studying. There is a need to research students’ opinions on effective communication with teachers, teaching methods and assessment. The goal of this publication is to show the results of a study conducted with students in the Fundamentals of Chemical and Metallurgical Technologies (FCME) major at the University of Chemical Technology and Metallurgy (UCTM), Sofia. Students’ opinions are presented regarding the teacher’s requirements for independent work and presentation of results, teaching methods and assessment of knowledge and skills. Respondents were third year full-time and part-time students at the Faculty of Chemical Technologies, major FCME. The outcomes of the study we conducted demonstrate that the use of different methods of teaching and assessment, as part of it, including giving tasks for self-assessment, increase students’ understanding and satisfaction of the learning process. Good communication between teachers and students, clear work requirements and criteria make the course content and assessment more understandable and meaningful for the students. They become active participants in the learning process, which leads to exhibited responsibility and commitment towards it.Item 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.Item 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.Item α/β-TCP silicate glass-ceramic obtained by sol–gel: Structure and in vitro bioactivity Vitrocerámica α/β-TCP obtenida por método sol-gel: estructura y bioactividad in vitro(2024-01-01) Mihailova I.; Dimitrova P.; Radev L.A glass-ceramic in the CaO–P2O5–SiO2 system, which contains two polymorphic modifications of tricalcium phosphate – whitlockite, β-Ca3(PO4)2 and α-Ca3(PO4)2, has been synthesized by the sol–gel method and thermal treatment up to 1200 °C. The phase composition and microstructure of the glass-ceramic were investigated with X-ray diffraction analysis (XRD), Fourier-transformed infrared spectroscopy (FTIR), scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS). An in vitro bioactivity test of the glass-ceramic in a simulated body fluid (SBF) was conducted for up to 21 days. α-Ca3(PO4) dissolved almost completely in SBF after 7 days. The experimental results of XRD, FTIR, SEM and EDS clearly validated the ability of the glass-ceramic samples to form a layer of hydroxyapatite on their surface in an SBF environment. We also studied the cytotoxic effect of the glass-ceramic on murine bone marrow (BM) cells and pre-osteoclasts in vitro. The glass-ceramic reduced the viability of BM cells in a dose-dependent manner being less toxic at concentrations below 0.1 mg/ml. It modestly affected the viability of pre-osteoclasts cultured in osteoclast differentiation media. The obtained sample increased the percentage of pre-osteoclasts expressing the receptors involved in osteoclastogenesis (RANK) and apoptosis (TRAIL). In conclusion, the glass-ceramic showed the potential to affect the survival/differentiation of pre-osteoclasts at early stage of osteoclastogenesis. It might be suitable for tissue engineering including implants coating or scaffold as it can interfere with early stage of osteoclastogenesis which is required for proper bone remodelling and repair upon a long-term application of biomaterials.