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 Open Access Bioinspired scaffold induced regeneration of neural tissue(PERGAMON-ELSEVIER SCIENCE LTD, 2019-05) EKREN, NAZMİ; Altun, Esra; Aydogdu, Mehmet O.; Togay, Sine O.; Sengil, Ahmet Z.; Ekren, Nazmi; Haskoylu, Merve E.; Oner, Ebru T.; Altuncu, Nese A.; Ozturk, Gurkan; Crabbe-Mann, Maryam; Ahmed, Jubair; Gunduz, Oguzhan; Edirisinghe, MohanIn the last decade, nerve tissue engineering has attracted much attention due to the incapability of self-regeneration. Nerve tissue regeneration is mainly based on scaffold induced nanofibrous structures using both bio and synthetic polymers. The produced nanofibrous scaffolds have to be similar to the natural extracellular matrix and should provide an appropriate environment for cells to attach onto. Nanofibrous scaffolds can support or regenerate cells of tissue. Electrospinning is an ideal method for producing the nanofibrous scaffolds. In this study, Bacterial cellulose (BC)/Poly (epsilon-caprolactone) (PCL) blend nanofibrous scaffolds were successfully prepared by electrospinning for nerve tissue induced repair. The produced nanofibrous scaffolds contain well defined interconnected nanofiber networks with hollow micro/nanobeads. Firstly, in-vitro biocompatibilities of nanofibrous scaffolds were tested with L2929 murine fibroblasts and improved cell adhesion and proliferation was observed with polymer blends compared with PCL only. The primary cell culture was performed with dorsal root ganglia (DRG) cells on nanofibrous samples and the samples were found suitable for enhancing neural growth and neurite outgrowth. Based on these results, the BC/PCL (50:50 wt.%) nanofibrous scaffolds exhibited nerve-like branching and are excellent candidate for potential biomimetic applications in nerve tissue engineering regeneration.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 Open Access A drug-eluting nanofibrous hyaluronic acid-keratin mat for diabetic wound dressing(2022-01-01) EKREN, NAZMİ; GÜNDÜZ, OĞUZHAN; Su S., Bedir T., KALKANDELEN C., Sasmazel H. T. , Basar A. O. , Chen J., EKREN N., GÜNDÜZ O.© 2022, Qatar University and Springer Nature Switzerland AG.Diabetes mellitus is a chronic metabolic disease associated with long-term multisystem complications, among which are non-healing diabetic foot ulcers (DFUs). Electrospinning is a sophisticated technique for the preparation of polymeric nanofibers impregnated with drugs for wound healing, burns, and diabetic ulcers. This study describes the fabrication and characterization of a novel drug-eluting dressing made of core–shell structured hyaluronic acid (HA)–keratin (KR)-polyethylene oxide (PEO) and polycaprolactone (PCL) nanofibers to treat diabetic wounds. The core–shell nanofibers produced by the emulsion electrospinning technique provide loading of metformin hydrochloride (MH), HA, and KR in the core of nanofibers, which in return improves the sustained long term release of the drug and prolongs the bioactivity. Morphological and chemical properties of the fibers were examined by SEM, FTIR, and XRD studies. It was observed that the fibers which contain HA and KR showed thin fiber structure, greater swelling capacity, fast degradation and increased cumulative drug release amount than neat emulsion fibers due to the hydrophilic nature of HA and KR. MH showed a sustained release from all fiber samples over 20 days and followed the first-order and Higuchi model kinetics and Fickian diffusion mechanism according to kinetic analysis results. In vitro cell culture studies showed that the developed mats exhibited enhanced biocompatibility performance with HA and KR incorporation. The results show that HA and KR-based emulsion electrospun fiber mats are potentially useful new nanofiber-based biomaterials in their use as drug carriers to treat diabetic wounds.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 Open Access Marine-derived bioceramics for orthopedic, reconstructive and dental surgery applications(2022-11-01) OKTAR, FAİK NÜZHET; ÜNAL YILDIRIM, SEMRA; GÜNDÜZ, OĞUZHAN; EKREN, NAZMİ; ALTAN, ERAY; OKTAR F. N. , Unal S., GÜNDÜZ O., Ben Nissan B., Macha I. J. , Akyol S., Duta L., EKREN N., ALTAN E., YETMEZ M.Bioceramics are a fast-growing materials group, which are widely used in orthopedics, maxillofacial, dental, and reconstructive surgeries. They are produced using raw materials either from synthetic or natural sources. As naturally originated resources, the bones of sheep and cows are used after converting to calcium phosphates. Human-originated sources in the past were obtained from human cadaver bones, however now-a-days this has been discontinued. On the other hand, the \"golden standard\" in the reconstruction surgery has been using patients own bones, -i.e., autogenous bones, which heal better than other alternatives. Besides natural products, synthetic materials are produced from a range of inorganic raw and natural materials based on marine sources, such as corals, and other marine-derived materials (i.e., seashells, nacre). These are used to produce bioceramics and hence implants, devices, and bone grafts. Although during the last four decades a number of excellent books and book chapters have been published, no comprehensive review has been yet reported to cover the available marine materials and to indicate the related work and corresponding references to allow for both medical and ceramic scientists to access directly and open new avenues for further research on marine structures and their applications in orthopedic, maxillofacial, and reconstructive surgery areas. Hence, this review covers the general marine structures, their locations and availability in different countries and, current research on production methods of these unique structures that are difficult to fabricate synthetically. The authors are confident that this comprehensive review will be an excellent source not only for the ceramists, but also for the medical scientists.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.