Browsing by Author "Rangelova N."
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Item ANTIBACTERIAL ACTIVITY AND STRUCTURE OF SOL-GEL BASED SiO2/HPC/Zn NANOCOMPOSITES(2020-01-01) Angelova T.; Rangelova N.; Aleksandrov L.; Georgieva N.The present paper reports an investigation of the antibacterial activity of sol-gel derived silica/hydroxypropyl cellulose zinc doped nanocomposites. The thermal analysis shows that the crosslinking between cellulose ether and zinc ions is more thermally stable than the crosslinking of the precursors in the matrix. The optical investigation and the transmission electron microscopy (TEM) observation verify the existence of nano-dimentional zinc particles. The antibacterial properties of the composites are investigated by measuring the inhibition zones formed around the materials of a different zinc content in presence of reference strains of Gram-positive bacteria - Bacillus subtilis 3562 and Gram-negative bacteria - Escherichia coli K12 and by calculating the growth decrease percentage.Item Antibacterial activity of SiO 2/hydroxypropyl cellulose hybrid materials containing silver nanoparticles(2012-07-01) Angelova T.; Rangelova N.; Yuryev R.; Georgieva N.; Müller R.Silica hybrid materials containing tetraethyl orthosilicate (TEOS) as SiO 2 precursor, hydroxypropyl cellulose (HPC) as an organic compound with incorporation of silver were prepared, and their structure and surface morphology were examined by FTIR measurements and SEM. The quantity of organic substance was 5 wt.% and the silver concentration varied from 0.5 to 2.5 wt.%. It is suggested that the main structural units build an amorphous network of synthesized hybrids from depolymerized [SiO 4] tetrahedra giving strong bands at 1050 and 790 cm - 1. The surface morphology changed from smooth to rough with the increasing amount of silver. The possible antibacterial behavior of the hybrid materials was also studied. The results indicate pronounced antibacterial performance against Escherichia coli and Bacillus subtilis. Highest antibacterial activity was detected against B. subtilis. The increase of silver concentration up to 2.5 wt.% Ag leads to stronger antibacterial effects with both strains. © 2012 Elsevier B.V. All rights reserved.Item Antifungal effect of SiO2/cellulose ethers/Ag hybrid nanomaterials on the growth of Penicillium chrysogenum 2303(2016-01-01) Angelova T.; Mohamed R.A.A.E.; Rangelova N.; Georgieva N.Three types of silica hybrid nanomaterials, doped with silver, were studied for their antifungal effect against fungi Penicillium chrysogenum strain 2303. The hybrid nanomaterials based on SiO2 and cellulose ethers - hydroxypropyl cellulose, hydroxypropylmethyl cellulose and carboxymethyl cellulose, and silver were prepared by sol-gel method. The antifungal effect was quantified against P. chrysogenum 2303 based on the inhibition zone measurement by the agar diffusion test. The results showed that the hybrid nanomaterials containing hydroxypropylmethyl cellulose, doped with the highest silver concentration of 2.5 mass % Ag, have the most prominent antifungal effect towards the fungi in comparison to the other nanomaterials.Item BIOCOMPATIBILITY AND ANTIFUNGAL ACTIVITY OF SILVER DOPED SiO2/PECTIN COMPOSITE MATERIALS(2021-01-01) Angelova T.; Uzunova V.; Rangelova N.; Georgieva N.; Momchilova A.; Tzoneva R.The purpose of the study was to evaluate the biocompatibility and antifungal activity of silver doped SiO2/citrus pectin composite materials. The effect of the amount of silver content (0 - 2.5 wt. %) on biocompatibility using L929 fibroblast cells and antifungal activity against Candida albicans 74 was observed. It was established that composites containing 0.5 wt. % and 1 wt. % Ag exhibited biocompatibility as well as revealed low cytotoxicity, good cell adhesion and spreading and luck of apoptosis. The antifungal activity of the composites demonstrated that the size of formed inhibition zones depends on the amount of silver in the materials. Based on the obtained results, silver doped SiO2/ pectin composite materials were proven to be efficient for use as in vivo implants in tissue engineering applications.Item Cytotoxicity and antibiofilm activity of SiO2/cellulose derivative hybrid materials containing silver nanoparticles(2016-01-01) Angelova T.; Rangelova N.; Uzunova V.; Georgieva N.; Andreeva T.; Momchilova A.; Tzoneva R.; Müller R.Hybrid materials based on tetraethyl orthosilicate (TEOS), hydroxypropyl cellulose (HPC), or hydroxypropyl methyl cellulose (HPMC) with silver nanoparticles were synthesized. They were analyzed and characterized using differential thermal analysis and thermogravimetry, atomic force microscopy, and static contact angle measurements. It was experimentally demonstrated that the silverdoped hybrid materials have pronounced antibacterial behavior by studying the reduction of Pseudomonas aeruginosa PAO1 biofilm formation on the tested materials. The results revealed biofilm reduction of 35.7% and 30% by SiO2/HPC/2.5% Ag and SiO2/HPMC/2.5% Ag hybrid materials, respectively, compared to the control. Cytotoxicity of examined materials and actin cytoskeleton organization of fibroblasts seeded on the materials was studied as a function of material properties as the type of surface functional groups and silver content. The obtained hybrid materials with low silver content proved efficient in tissue engineering applications since they showed good antibacterial and noncytotoxic properties for eukaryotic cells.Item CYTOTOXICITY OF COPPER DOPED SiO2-HYDROXYPROPYL CELLULOSE COMPOSITES ON CANCER AND NON-CANCEROUS CELLS(2023-01-01) Foteva T.; Vukova T.; Rangelova N.; Georgieva N.; Tzoneva R.In the present paper the cytotoxicity of series of sol-gel based copper doped SiO2/HPC composites on lung cancer cell line (A549) and primary human umbilical cord endothelial cells (HUVEC) was investigated. Hydroxypropyl cellulose (HPC), tetraethyl ortosilicate (TEOS) were used for preparation of amorphous matrix in which the copper was added as Cu(NO3)2*3H2O or CuSO4*5H2O in concentration range of 0 - 5 wt. %. We observed that the composite materials at low concentration of Cu (0.5 wt. %) showed no toxic effects on both cell types. The composite material with CuSO4*5H2O was found relatively more toxic, and furthermore, cancer cells are more sensitive to the copper concentration increase to non-cancer cells. The concentration of Cu ions of 2.5 and 5 wt. % were toxic to both cancer and non-cancer cells at 24th hour. At 72th hour of incubation some restoration of cell viability was observedItem Enzymatic decolorization of dyes by laccase immobilized on hybrid carriers(2018-01-01) Yaneva S.; Rangelova N.; Aleksandrov L.; Danalev D.The study focused on sol-gel synthesis of biopolymer-silica hybrids further used as materials for laccase immobilization. Silica was obtained from tetraethyl orthosilicate (TEOS), while pectin, derived from citrus fruits, was used as a biopolymer. The structure of the hybrids obtained was investigated by X-ray diffraction, Fourier transform infrared spectroscopy, Scanning electron microscopy and BET analysis. The results provided to conclude that the interaction between SiO2 network and the polysaccharide proceeding via H-bonds formation was successful. Laccase was immobilized by cross-linking, while the degradation ability was tested against several dyes - Rhodamine B, Methyl orange and Malachite green. The most effective decolorization was reached for Malachite green and Methyl orange.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 OCCUPATIONAL RISK ASSESSMENT TO EXPOSURE OF RESPIRABLE CRYSTALLINE SiO2 AT CEMENT MANUFACTURING(2024-01-01) Kirova V.; Yaneva S.; Rangelova N.According to the European Agency for Safety and Health at Work (EU - OSHA) and the Roadmap on Carcinogens about 120, 000 work - related cancer cases occur each year as a result exposure to carcinogens at the workplace in the EU, leading to approximately 80, 000 fatalities annually. Occupational risk assessment is used as a criterion for occupational safety. At the cement manufacturing sector, it was revealed that the main hazard is exposure to carcinogen substances such as respirable crystalline SiO2. In the present work, two methods were used for risk assessment in a cement production enterprise: the classical Fine - Kinney method and Flexible risk assessment method developed by Reinhold and Tint. The results of the joint application of these two methods show the advantages and disadvantages of each of them and point to the need to combine more than one method to effectively cover aspects of risk assessment. It was made the evaluation of applied existing control measures, as well as new measures for better protection have been proposed.Item Preparation, Characterization, and Antibacterial Properties of Cu-Fibreboards(2023-11-01) Aleksandrov L.; Rangelova N.; Lazarova-Zdravkova N.; Georgieva N.; Dragnevska M.; Nenkova S.In the present study, copper modified fibreboards were prepared and their existing phase, morphology, and antibacterial behaviour were investigated. The copper content and the physical and mechanical properties of fibreboards (thickness, bending strength, and swelling) were determined. X-ray diffraction analysis (XRD) showing diffraction peaks typical for cellulose, Cu2S, and Na2SO4, depended on the preparation conditions. The average size of the Cu2S crystals varied between 20 and 50 nm. The morphology of the obtained fibreboards, as well as the size and shape of copper particles, were observed by scanning electron microscopy (SEM) and transition electron microscopy (TEM). The antibacterial activity was tested against Gram-positive (Bacillus subtilis 3562) and Gram-negative (Escherichia coli K12 407) bacteria. The tests showed that the materials had higher antibacterial activity against E. coli, which depended on their preparation conditions. Based on these results, the obtained copper fibreboards can be used as antibacterial agents in the packaging and building industry.Item Synthesis, Characterization and antibacterial assessment of sio2-hydroxypropylmethyl cellulose hybrid materials with embedded silver nanoparticles(2014-10-22) Angelova T.; Rangelova N.; Dineva H.; Georgieva N.; Müller R.Antibacterial SiO2 hybrid materials based on tetraethyl orthosilicate (TEOS), hydroxypropylmethylcellulose (HPMC) and silver were prepared by the sol-gel method. The content of cellulose derivate was 5 wt% and the silver concentration varied from 0.5 wt% to 2.5 wt%. The amorphous nature, morphology and antibacterial behaviour were studied. Fourier transform infrared (FTIR) spectra of the hybrids showed characteristic peaks for SiO2 network. Scanning electron microscope (SEM) analysis confirmed the formation of spherically shaped silver nanoparticles with a size of 30 nm on the matrix surfaces. Bacillus subtilis and Escherichia coli K12 were used as model microorganisms. The hybrid materials demonstrated bacteriostatic and bactericidal effect on the tested bacteria. Highest sensitivity to the obtained hybrids was observed in B. subtilis with significant lag-phase delay and biggest inhibition zone sizes.