Person: EKREN, NAZMİ
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EKREN
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NAZMİ
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Publication Metadata only Preparation and characterization of electrospun polylactic acid/sodium alginate/orange oyster shell composite nanofiber for biomedical application(SPRINGER, 2020) BİLĞİÇ ALKAYA, DİLEK; Cesur, Sumeyye; Oktar, Faik Nuzhet; Ekren, Nazmi; Kilic, Osman; Alkaya, Dilek Bilgic; Seyhan, Serap Ayaz; Ege, Zeynep Ruya; Lin, Chi-Chang; Erdem, Serap; Erdemir, Gokce; Gunduz, OguzhanBone tissue engineering has begun to draw attention in recent years. The interactive combination of biomaterials and cells is part of bone tissue engineering. Sodium alginate (SA) is a biologically compatible, degradable, non-toxic natural polymer accepted by the human body and is widely used in the field of tissue engineering. Polylactic acid (PLA) is another type of biodegradable thermoplastic polyester derived from renewable sources which are used in bone tissue engineering and biomedical owing to its biocompatibility and biodegradability. Hydroxyapatite (HA) and tricalcium phosphate (TCP) derived from natural sources such as marine species and bovine bone are biocompatible and non-toxic biomaterials which are used to reconstruct many parts of the skeleton. In this study, PLA, SA with different compositions, and nanofibers obtained by adding orange spiny oyster shell powders (Spondylus barbatus) to them by using electrospining technique. Cell culture study, scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and physical analysis such as density, electrical conductivity, surface tension, viscosity measurement, and tensile strength measurement tests were carried out after the production process. Produced nanofibers showed smooth and beadless surface. The average diameters and distributions decreased with the addition of optimum PLA and TCP amount. The tensile strength of nanofibers was enhanced with the additional SA and TCP. The produced nanofibers are compatible with human bone tissue, which are not cytotoxic, and in addition, a high cell efficiency of SaOS-2 cells on the nanofibers was observed with SEM images.Publication Metadata only Fabrication and characterization of pla/sa/ha composite nanofiber by electrospinning for bone tissue engineering applications(2018-07-18) CESUR, SÜMEYYE; EKREN, NAZMİ; KILIÇ, OSMAN; OKTAR, FAİK NÜZHET; BİLĞİÇ ALKAYA, DİLEK; AYAZ SEYHAN, SERAP; GÜNDÜZ, OĞUZHAN; Cesur S., Ekren N., Kılıç O., Oktar F. N., Bilğiç Alkaya D., Ayaz Seyhan S., Ege Z. R., Gündüz O.Publication Metadata only A review of anti-reflection and self-cleaning coatings on photovoltaic panels(PERGAMON-ELSEVIER SCIENCE LTD, 2020) EKREN, NAZMİ; Sarkin, Ali Samet; Ekren, Nazmi; Saglam, SafakThe production of electrical energy from solar energy through the photovoltaic method has become increasingly widespread throughout the world in the last 20 years. The photovoltaic energy system generates electricity depending on the amount of sunlight reaching the solar cell, and the amount of sunlight that reaches the solar cells in a solar panel decreases due to factors such as soil and organic dirt. At the same time, sunlight is refracted and reflected due to the reflective effect of the cover glass surface, even if the surface of the photovoltaic panel is clean. The remaining solar rays are broken and reach the solar cell. Decreasing sunlight also causes a decrease in electrical power output. Thus, to overcome these problems, photovoltaic solar cells and cover glass are coated with anti-reflective and self-cleaning coatings. As observed in this study, SiO2, MgF2, TiO2, Si3N4, and ZrO2 materials are widely used in anti-reflection coatings. Common methods used are sol-gel + spin-coating or + dipcoating, sputtering, DC or RF magnetron, and electrospun methods. Regarding self-cleaning applications, fabricating superhydrophobic surfaces stands out among other methods. In self-cleaning applications, Al2O3, TiO2, and Si3N4 are the most suitable materials; the double- and triple-layer coatings yield successful results in terms of surface adhesion and durability. In multi-layer anti-reflection coatings, the reflectance was reduced in studies in which materials with low and high reflection indexes were applied and light transmittance was increased.Publication Metadata only Continuous wavelet transform for ferroresonance phenomena in electric power systems(ELSEVIER SCI LTD, 2013) EKREN, NAZMİ; Akinci, Tahir Cetin; Ekren, Nazmi; Seker, Serhat; Yildirim, SezenThe common characteristics of a nonlinear system are multiple equilibrium points, limit cycles, jump resonance and sub-harmonic generation. Ferroresonance is also a nonlinear electrical phenomenon, which occurs frequently in power systems including no-load saturable transformers, transmission lines and single/three phase switching. In this work, we modeled the 380 kV West Anatolian Electric Power Network of Turkey, by performing numerical simulations using MATLAB-Simulink Power System Block-set. We generated the signals that are characteristics to the ferroresonance in order to exhibit the emergence of the nonlinear phenomenon. In addition, using the continuous wavelet transform (CWT), we observed the behavior of the ferroresonance both in time and frequency domains. Using the results of the CWT and Power Spectral Density (PSD) applications, the ferroresonance is determined from the emergence of the over voltage changes and the inter-harmonics of between +/- Delta integral Wand +/- Delta integral depending on frequency resolution +/- Delta integral. (C) 2012 Elsevier Ltd. All rights reserved.Publication Metadata only Cell studies on Electrohydrodynamic (EHD)-3D-bioprinted Bacterial Cellulose\Polycaprolactone scaffolds for tissue engineering(ELSEVIER SCIENCE BV, 2019) EKREN, NAZMİ; Altun, Esra; Ekren, Nazmi; Kuruca, Serap Erdem; Gunduz, OguzhanThe application of three-dimensional (3D) printed scaffolds for tissue engineering have gained significant attention in recent years. The biological activity of scaffolds used in tissue engineering applications depends on fabricating high-resolution patterns with fiber orientation and scale. In this study, Bacterial Cellulose (BC) and Polycaprolactone (PCL) composite scaffolds with the line spacing of 100 mu m are produced using Electrohydrodynamic (EHD)-3D-bioprinting technique. The composite scaffolds exhibit enhanced biocompatibility with facilitated cell attachment and proliferation in vitro. The results of this work have demonstrated that EHD-3D-bioprinting method shows great potential for the preparation of BC/PCL composite scaffold and patterns for tissue engineering with enhanced bioactivity. (C) 2018 Published by Elsevier B.V.Publication Metadata only Production and Characterization of Antimicrobial Electrospun Nanofibers Containing Polyurethane, Zirconium Oxide and Zeolite(SPRINGER, 2018) OKTAR, FAİK NÜZHET; Aydogdu, Mehmet Onur; Oprea, Alexandra Elena; Trusca, Roxana; Surdu, Adrian Vasile; Ficai, Anton; Holban, Alina Maria; Iordache, Florin; Paduraru, Andrei Viorel; Filip, Diana Georgiana; Altun, Esra; Ekren, Nazmi; Oktar, Faik Nuzhet; Gunduz, OguzhanIn this study, electrospinning technique has been utilized to prepare composite nanofiber mats of polyurethane (PU)/zirconium dioxide (ZrO2) and PU/zeolite, consisted by antimicrobial properties. Tensile strength measurement test was performed for the mechanical analysis of the nanofibers. Scanning electron microscopy (SEM) were performed for displaying the morphological features of the fiber structure. XRD tests were performed for revealing the chemical structure. Antimicrobial tests were also performed to display antimicrobial effects of the produced materials. In vitro test was also performed to determine cytotoxicity and biocompatibility. The present PU/ZrO2 and PU/zeolite composite nanofibers resulted with improved mechanical properties and good antimicrobial properties against either their pure forms or other studies. Cell proliferation and viability also increased significantly with increase in zeolite and ZrO2 ratio. It is concluded that this composition provides a novel alternative as an antimicrobial material which can be suitable as a wound dressing or a coating material for various healthcare engineering applications.Publication Metadata only Energy saving in lighting system with fuzzy logic controller which uses light-pipe and dimmable ballast(ELSEVIER SCIENCE SA, 2013) EKREN, NAZMİ; Gorgulu, Sertac; Ekren, NazmiApproximately, 20% of the electricity consumed in the world is spent for lighting. More efficient utilization of the sun, as a natural source of light, for lighting would save electricity used for lighting. The aim of this study is to illuminate a windowless room via a light-pipe and dimmable electronic ballasts. Light-pipe is used for the illumination of the space during the daytime. In case of inadequate daylight, artificial lighting is made via dimmable electronic ballasts and fluorescence lamps. Artificial lighting is supervised by a fuzzy logic control system to keep the illumination level at 350 lux. When there is a motion in the room, the system works with the message of the motion sensor, which, thereby, enables energy saving. Additionally, dimming the lamps result in conversation of the electrical energy used for illumination. After the experimental studies, 350 lux value targeted in the work plane is achieved with +/- 10 lux error. (c) 2013 Elsevier B.V. All rights reserved.Publication Metadata only Patch-Based Technology for Corneal Microbial Keratitis(Springer, 2020) AKSU, MEHMET BURAK; Ulag S., Ilhan E., Aksu B., Sengor M., Ekren N., Kilic O., Gunduz O.Corneal opacities, which happened mainly due to microbial keratitis, are the fourth cause of blindness worldwide. Antimicrobial therapy is an alternative solution for microbial keratitis caused by Staphylococcus aureus and Pseudomonas Aeruginosa. The aim of this study, to develop patches for the treatment of corneal keratitis which caused significant corneal blindness by using electrospinning method. Polyvinyl-alcohol (PVA) patches with Gelatine (GEL) studied in various ratios. Different amounts of gelatine added to PVA to resemble the collagen fibril structure of the cornea. To enable the patches to the antimicrobial effect against the bacterias, the special plant extract was used. The produced corneal patches were examined separately for chemical, morphological, and antimicrobial properties. Scanning electron microscope (SEM), Fourier-transform infrared (FT-IR) spectroscopy were performed to observe the surface morphology and chemical structure of the patches, respectively. © Springer Nature Switzerland AG 2020.Publication Metadata only Effect of yttria-doping on mechanical properties of bovine hydroxyapatite (BHA)(SAGE PUBLICATIONS LTD, 2008) OKTAR, FAİK NÜZHET; Gunduz, O.; Daglilar, S.; Salman, S.; Ekren, N.; Agathopoulos, S.; Oktar, F. N.Sintered bodies of hydroxyapatite, derived from calcinated bovine bone (BHA) and doped with 0.5 and 1wt% Y2O3, were prepared. Measurements of density, compression strength, and microhardness, along with scanning electron microscopy (SEM) and X-ray diffraction (XRD) were carried out. The experimental results showed that BHA doping with yttria favors formation of glassy phase, which advances sintering and results in a dense and reinforced BHA matrix. The best mechanical properties were achieved after sintering at 1200 degrees C for compressive strength (82 MPa) and 1300 degrees C for microhardness (672 HV). These results are better than pure BHA or composites of hydroxyapatite with Y2O3-stablized zirconia, qualifying yttria (as dopant of BHA) for further in vitro and in vivo experimentation.Publication Metadata only Investigation of light transmittance of coatings containing sio2 and tio2 nano-particle made by electrospinning technique(2022-04-07) EKREN, NAZMİ; SAĞLAM, ŞAFAK; SARKIN A. S., EKREN N., SAĞLAM Ş.The electrospinning technique is a coating method with controllable parameters. This study aims to make a coating that increases light transmission, reduces reflection, and has self-cleaning properties on laboratory slide glasses by the electrospinning method. Studies in the literature were investigated that had been used SiO2, TiO2, polymers for it. PLA and PMMA were used as polymers, SiO2 and TiO2 were used as nanoparticles, and Chloroform was used as the solvent. Solutions were prepared at different mixtures and ratios. The solutions were applied with different electrospinning parameters. The coatings were examined in terms of surface adhesion and surface distribution, and some were found to be successful. The light transmittance was the highest with 66.2% in solution-6 containing 1.6 g PLA and 0.05 g SiO2. In coatings containing SiO2 and TiO2, the light transmittance of solution-7 with 1.6 g PLA, 0.025 g SiO2, and 0.025 g TiO2 was 64.8%, and solution-10 with 2 g PLA and 0.05 g SiO2, and 0.05 g TiO2 had 64.4% light transmission.