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Öğe Biopolymers for Surgical Applications(Mdpi, 2022) Bibire, Tudor; Yilmaz, Onur; Ghiciuc, Cristina Mihaela; Bibire, Nela; Danila, RaduBiopolymers have gained significant attention as a class of polymer materials with a wide range of applications, especially in the medical and pharmaceutical field. Due to particular characteristics, such as biocompatibility, biodegradability, non-toxicity, and functionality, they have become promising candidates for various surgical applications, including as bioadhesives, sealants, wound dressings, sutures, drug carriers, coating materials, etc. Recent research shows that further modification of biopolymers by advanced techniques can improve their functionality i.e., antibacterial activity, cell viability, drug-releasing capability, good wet adhesion performance, and good mechanical properties. This mini review aims to provide a brief report on the type of biopolymers and recent developments regarding their use in various surgical applications.Öğe Chitosan-Graft-Poly(N-Isopropylacrylamide)/PVA Cryogels as Carriers for Mucosal Delivery of Voriconazole(Mdpi, 2019) Cheaburu-Yilmaz, Catalina Natalia; Yilmaz, Onur; Kose, Fadime Aydin; Bibire, NelaThe objective of this study was to prepare and characterize physically crosslinked gel formulations of chitosan (CS)-graft-poly(N-isopropyl acrylamide) (PNIPAAm) and polyvinyl alcohol (PVA) for smart delivery of an antifungal drug, Voriconazole, for mucosal applications. For this purpose, cryogels of CS-g-PNIPAAm/PVA and CS/PVA were tested by means of texture profile analysis and rheology to determine optimal matrix properties for topical application. the ratio of 75/25 v/v % CS-g-PNIPAAm/PVA was selected to be used for formulation since it gave low compressibility and hardness (1.2 and 0.6 N) as well as high adhesion properties and non-Newtonian flow behavior. the cryogels and formulations were further characterized by means of FTIR spectroscopy, swelling behavior, texture analysis, scanning electron microscopy (SEM), thermal (differential scanning calorimetry (DSC) and TGA), and rheological behavior. the drug loading capacity and in vitro release profile of the drug, storage stability, and cytotoxicity tests were also performed for the gel formulation. the FTIR, DSC, and TGA results verified the successful formation of cryogels. Swelling studies revealed a pH-dependent swelling ability with a maximum swelling degree of 1200% in acid and 990% in phosphate buffer (pH = 7.4). Thermal studies showed that CS-g-PNIPAAm/PVA 75/25 had higher thermal stability proving the structural complexity of the polymer. the loading capacity of Voriconazole was found to be 70% (w/w). the in vitro release profiles of Voriconazole showed Fickian release behavior for CS-g-PNIPAAm/PVA 75/25 gel with an approximate delivery of 38% within 8 h, slower than matrices containing unmodified chitosan. the storage stability test exhibited that the gel formulation was still stable even after aging for two months. Moreover, the cell culture assays revealed a non-toxic character of the polymeric matrix. Overall results showed that the CS-g-PNIPAAm/PVA 75/25 hydrogel has the potential to be used as a smart polymeric vehicle for topical applications.Öğe Comparison of different tanning agents on the stabilization of collagen via differential scanning calorimetry(Springer, 2017) Onem, Ersin; Yorgancioglu, Ali; Karavana, Huseyin Ata; Yilmaz, OnurLeather is composed of a three-dimensional weave of collagen fiber bundles. Collagen is a fibrous protein well organized in the formation of skin as building blocks. Leather production involves serial operations where the tanning plays the major role in improving the durability of leather products by stabilizing the triple helical structure of collagen matrix. In the leather-making industry, different tanning agents are used to produce different kind of leather goods. These tanning agents have varied efficiency on the stabilization of collagen. In this study, thermal stability of the leathers tanned with most commonly used tanning agents was evaluated by conventional shrinking test (CST) and differential scanning calorimetry (DSC) methods. The results showed that the thermal stability of leathers varied by the type of tanning agent which were in accordance with theoretical approaches. A distinct correlation was also observed between CST and DSC results of the tanned leathers.Öğe Conversion of leather wastes to useful products(Elsevier Science Bv, 2007) Yilmaz, Onur; Kantarli, I. Cem; Yuksel, Mithat; Saglam, Mehmet; Yanik, JaleThe main objective of the present study is to investigate the production of useful materials from different kinds of leather waste. Three different types of tannery wastes (chromium- and vegetable-tanned shavings, and buffing dust) were pyrolyzed in a fixed bed reactor at temperatures of 450 and 600 C under NZ atmosphere. Gas, oil, ammonium carbonate and carboneous residue were obtained by pyrolysis. The effect of temperature and type of leather waste on product distribution of pyrolysis was investigated. Buffing dust gave the highest yield of oil (ca. 23%), while other wastes recorded yields of ca. 9%. Results of elemental analysis and column chromatography showed that pyrolysis oils could be used as fuel or chemical feedstock after re-treatment. The yields of carboneous residue (chars) were between 37.5% and 48.5% and their calorific value was between 4300 and 6000 kcal kg(-1), suitable for use as solid fuel. In addition, these chars were activated by CO2 to obtain the activated carbon. The activated carbon having highest surface area (799.5 m(2) g(-1)) was obtained from chromium-tanned shavings. Activated carbons prepared from chromium-tanned leather were presented as an adsorbant for the adsorption of dyes from aqueous solution. (c) 2006 Elsevier B.V. All rights reserved.Öğe Development, Characterization, and Evaluation of Potential Systemic Toxicity of a Novel Oral Melatonin Formulation(Mdpi, 2024) Cheaburu-Yilmaz, Catalina N.; Atmaca, Kemal; Yilmaz, Onur; Orhan, HilmiThe need to create safe materials for biomedical and pharmaceutical applications has become a significant driving force for the development of new systems. Therefore, a chitosan-coated copolymer of itaconic acid, acrylic acid, and N-vinyl caprolactam (IT-AA-NVC) was prepared by radical polymerization and subsequent coating via nanoprecipitation to give a system capable of sustained delivery of melatonin. Although melatonin brings undoubted benefits to the human body, aspects of the optimal dose, route, and time of administration for the obtaining of suitable treatment outcomes remain under discussion. The entrapment of melatonin in biocompatible polymeric systems can prevent its oxidation, decrease its toxicity, and provide an increased half-life, resulting in an enhanced pharmacokinetic profile with improved patient compliance. The structures of the biopolymer and conjugate were proven by FTIR, thermal properties were tested by DSC, and the morphologies were followed by SEM. The loading efficiency and in vitro release profile were studied by means of HPLC, and a delayed release profile with an initial burst was obtained. The potential systemic toxicity of the formulation was studied in vivo; a mild hepatotoxicity was observed following administration of the melatonin-loaded formulation to mice, both by histopathology and blood clinical biochemistry. Histopathology showed a mild nephrotoxicity as well; however, kidney clinical biochemistry did not support this.Öğe Effect of body condition score at mating on the reproductive performance of Kivircik sheep under an extensive production system(Springer, 2011) Yilmaz, Murat; Altin, Tufan; Karaca, Orhan; Cemal, Ibrahim; Bardakcioglu, Husnu Erbay; Yilmaz, Onur; Taskin, TurgayThe aim of this study was to determine the effects of the body condition score (BCS) of ewes before and during the mating season on their reproductive performance under an extensive production system. In this study, 240 Kivircik sheep from the flocks of two breeders were used for over a 2-year period. The flocks were fed under extensive conditions on natural pastures throughout the year. The ewes were synchronized in two different periods, one of which was 45 days before the other. Before the introduction of rams to the ewes, the ewes were weighed after measuring their BCS. Detailed records were kept for every flock in each year. We found significant effects of BCS on pregnancy rate, lambing rate (P<0.05) and fecundity (P<0.05). The BCS for the highest pregnancy, lambing rate, and fecundity was determined between 2.01 and 3.00, while the lowest rates for these traits were <= 1.50. The highest rates of the pregnancy rate, lambing rate, and fecundity and gestation productivity were 75.9%, 70.9%, 1.11 and 3.34 kg, respectively.Öğe The Effect of Different Soft Core/Hard Shell Ratios on the Coating Performance of Acrylic Copolymer Latexes(Mdpi, 2021) Cheaburu-Yilmaz, Catalina Natalia; Yilmaz, Onur; Darie-Nita, Raluca NicoletaCore-shell acrylic copolymer latexes containing bio resourced itaconic acid with different compositions in respect with the core and shell segments were synthesized, characterized, and applied as coating materials for leather. The purpose of the study was to evidence the high coating performance of the latexes when the ratio of the core/shell differed from 90/10 to 50/50 wt %. The copolymers were prepared via emulsion copolymerization technique and the products were isolated and characterized by means of structure identity, thermal behavior (DSC and DMTA), coating performance. The particle size of the latexes varied from 83 to 173 nm with the variation of the ratio of core/shell segments. The influence of the composition of soft part and hard part was highlighted in the thermal and coating properties. The optimal composition giving the best coating performance could be determined as DS 60/40. Further increase of the hard segment content, resulted in decreased emulsion stability and the coating performance on the leathers. The use of itaconic acid seemed to increase the emulsion stability as well the adhesion of the latexes to the substrate.Öğe Effect of Finishing Density on the Physico-Mechanical Properties of Leather(Soc Leather Technol Chemists, 2016) Nalbat, Sevgi; Onem, Ersin; Basaran, Bahri; Yorgancioglu, Ali; Yilmaz, OnurFinishing is the process in which a polymeric coating is applied in order to improve the appearance and resistance of leather products. The applications at this stage greatly affect the use and appeal of the final product. In this study, the effect of different coating compositions on the physico-mechanical properties of leather was investigated. For this purpose, three different types of finishing formulations including semi-aniline, lightly pigmented and opaque finishes having different covering powers rated from light to heavy, respectively, were applied to the leathers and results were compared with uncoated counterparts. The findings of the study revealed that the application of lightly pigmented finishing statistically increased the tensile strength, single and double edge tear loads, and stitch tear resistance of the leather to a large extent. Semi-aniline and opaque finishing gave lower or, in some cases, statistically insignificant increases in the physico-mechanical properties of the leathers.Öğe THE EFFECT OF VALONEA AND HENNA TREATMENT AND POST-MORDANTING ON CR (VI) AND FREE FORMALDEHYDE FORMATION IN LEATHER(Ege Universitesi, 2016) Ozgunay, Hasan; Yilmaz, Onur; Dandar, Urana; Colak, Selime; Zengin, Gokhan; Afsar, Altan; Simion, Demetra; Gaidau, CarmenPresent study aims the use of natural vegetable tannins as antioxidant phenolic materials in the processing of chromium tanned leathers and to investigate their effect on Cr(VI) and free formaldehyde formation. For this purpose valonea and henna were selected as tannins and their antioxidant capacities were determined by FRAP and TEAC/ABTS methods. These vegetable tannins were used in retanning process of chromium leathers in combination with copper, aluminium and iron based mordants to evaluate their potential on reduction of Cr(VI) and formaldehyde content of the leathers as well as their effect on colour tones.Öğe Functionalization of chitosan by click chemistry(Amer Inst Physics, 2017) Cheaburu-Yilmazi, Catalina Natalia; Karavana, Sinem Yaprak; Yilmaz, Onur; Lepadatescu, BChitosan modification represents a challenge nowadays. The variety of compounds which can be obtained with various architectures and different functionalities made it attractive to be used in fields like pharmacy and material science. Presents study deals with the chemical modification of chitosan by using click chemistry technique. The study adopted the approach of clicking azidated chitosan with a synthesized alkyne terminated polymer i.e. poly N isopropylacrylamide with thennoresponsive properties. Structures were confirmed by the FT-IR and HNMR spectra. Thermal characterization was performed showing different thermal behaviour with the chemical modification. The final synthesized graft copolymer can play important role within pharmaceutical formulations carrying drugs for topical or oral treatments.Öğe Functionalized Chitosan for Pharmaceutical Applications(Bentham Science Publ Ltd, 2017) Cheaburu-Yilmaz, Catalina Natalia; Karavana, Sinem Yaprak; Yilmaz, OnurBackground: Chitosan structure versatility toward a change in an external stimulus represents a "must have" for the pharmaceutical applications, especially for the pharmaceutical formulations. Chemical modification can open new ways to obtain materials with tailored properties. Despite the great interest for conventional graft modifications, controlled/ living free radical polymerizations (i.e. RAFT, ATRP, etc.) and advanced chemistry techniques (i.e. click chemistry) seem more attractive nowadays and involve facile and fast procedure, high regioselectivity, quantitative yield, mild reaction conditions without generation of by-products. Objective: The present review provides a detailed state of art of the chemical modification of chitosan i.e. tailored side-chain functionalization using RAFT polymerization and click chemistry for specific applications within pharmaceutical formulations taking into account the applicative aspect regarding the need of pharmaceuticals. Conclusion: The review showed the routes of current approaches for side chain modification of chitosan including graft, block copolymers or other structural variations. The esterification of RAFT agents on chitosan by using carbonyl activating reagents enables producing chitosan graft and block copolymers with controlled architectures while the development of protection/ deprotection chemistry of chitosan made possible the regioselective modification of chitosan or other polysaccharides. Although these developments increased the potential of chitosan, still the chemical functionality and architectural diversity of the derivatives are limited. Application of modern techniques e.g. RAFT polymerization, "click" chemistry has opened new "doors" for the science of controlled and chemoselective synthesis of well-tailored derivatives with unique and superior properties.Öğe High performance nanocomposite coatings based on soft core-reactive shell polyacrylic latex/modified halloysite nanotubes(Elsevier Science Sa, 2019) Yilmaz, OnurHigh performance coatings based on aqueous systems is highly demanded for many industrial applications. One attempt to improve the performance of coatings is the addition of nanoparticles to the main coating polymer. In the present study nanocomposite coatings based on polymethacrylic acid (PMAA) grafted halloysite nanotubes (HNTs) and epoxy functional core/shell polyacrylic latex have been prepared. The modification of HNTs was done via "grafting from" technique including the attachment of a chain transfer agent on the HNTs surface followed by RAFT (reversible addition-fragmentation chain transfer) polymerization of methacrylic acid (MAA). Main acrylic copolymer composed of butyl acrylate/methyl methacrylate soft core and glydicyl methacrylate reactive shell was synthesized via seeded emulsion polymerization. Final crosslinked nanocomposite coatings were prepared by mixing PMAA-modified HNTs (HNTs-PMAA) and acrylic latex in different ratios (2.5 and 5.0 wt.%) followed by drying and curing process. Dynamic mechanical analyses showed that the nanocomposites had significantly increased elastic moduli and tensile strength values as well as enhanced solvent resistance in comparison to the pure acrylic copolymer. The obtained nanocomposite coating system was found to be used in many applications as ductile high performance waterborne functional coatings.Öğe A hybrid polyacrylate/OMMT nanocomposite latex: Synthesis, characterization and its application as a coating binder(Elsevier Science Sa, 2014) Yilmaz, OnurHybrid latex particles have an increasing importance in industrial applications especially for high performance waterborne coatings. They provide combined properties of different phase compositions for the final polymer which can also be enhanced by additives such as nanoclays. The present study describes the preparation of a hybrid polyacrylate/OMMT nanocomposite latex via two stage in situ emulsion polymerization with a low emulsifier content (1 wt%) which is usually a challenge for the preparation of stable polymer/OMMT nanocomposite latexes. The obtained nanocomposite latex was stable and had a fine average size diameter of 151 nm with a very narrow size distribution. The copolymer films exhibited a well exfoliated structure observed by WAXD and TEM. Other polymer properties were investigated by FTIR, DSC, TGA, DMTA and rheological measurements. The results indicated that the addition of clay even in low amount (2 wt%) yielded significantly improved mechanical and thermal properties of the final polymer. In addition, the nanocomposite latex was also applied on leathers as coating binder in a finishing formulation and the results of the performance tests revealed substantially increased rubbing and heat resistance whereas a slight decrease was observed at water vapor permeability of the coated leathers. (C) 2013 Elsevier B.V. All rights reserved.Öğe Influence of the Chitosan and Rosemary Extract on Fungal Biodegradation of Some Plasticized PLA-Based Materials(Mdpi, 2020) Stoleru, Elena; Vasile, Cornelia; Oprica, Lacramioara; Yilmaz, OnurThe fungal degradation of the complex polymeric systems based on poly(lactic acid) (PLA) and natural bioactive compounds (chitosan and powdered rosemary alcoholic extract) was studied. Two fungal strains, Chaetomium globosum and Phanerochaete chrysosporium were tested. Both fungi characteristics and changes in morphology, structure and thermal properties were monitored. Biochemical parameters as superoxide dismutase, catalase, soluble protein and malondialdehyde have been determined at different time periods of fungal degradation. the fungi extracellular enzyme activities are slightly decreased in the case of composites containing bioactive compounds. the presence of natural compounds in the PLA-based polymeric system determines an acceleration of fungal degradation and probably the chemical hydrolysis, which further helps the attachment of fungi on the surface of polymeric samples. Significant decreases in average molecular mass of the polymeric samples were observed by fungi action; accompanied by structural changes, increase in crystallinity and decrease of thermal properties and the loss of the physical integrity and finally to degradation and integration of fungal degradation products into environmental medium. It was found that both fungi tested are efficient for PLA-based materials degradation, the most active from them being Chaetomium globosum fungus.Öğe Interactions Between Collagen and Alternative Leather Tanning Systems to Chromium Salts by Comparative Thermal Analysis Methods Thermal stabilisation of collagen by tanning process(Johnson Matthey Publ Ltd Co, 2022) Yorgancioglu, Ali; Onem, Ersin; Yilmaz, Onur; Karavana, Huseyin Ata[No Abstract Available]Öğe Localization-free and energy-efficient hole bypassing techniques for fault-tolerant sensor networks(Academic Press Ltd- Elsevier Science Ltd, 2014) Yilmaz, Onur; Dagdeviren, Orhan; Erciyes, KayhanNowadays, since wireless sensor networks (WSNs) are increasingly being used in challenged environments such as underground mines, tunnels, oceans and the outer space, fault-tolerance need has become a major requirement for routing protocols. So far, the proposed fault-tolerance methods or algorithms aim to recover the isolated failures which occur at different parts of the network in different times. However, there is another type of failure for WSNs which is more destructive for the applications. By collapsing sensor nodes as a group at the same time, a hole can appear at the network which may cut the data delivery drastically. In the literature, previous studies for bypassing holes are based on localization which may have significant energy and economic costs. In this paper, two localization-free and energy-efficient algorithms are proposed for bypassing the holes formed by group collapse. We realized that when holes are modeled with clusters, hole bypassing can be solved by cluster bypassing. Our algorithms, intra-cluster bypass and inter-cluster bypass, aim to heal the corrupted communication links in the presence of holes. We show the operation of the algorithms, analyze them and provide extensive simulation results in an ns-2 environment. We compare our proposed algorithms with the other approaches and show that our algorithms significantly improve the fault recovery percentages while consuming a reasonable amount of energy even in the presence of high collapse ratio. Crown Copyright (C) 2013 Published by Elsevier Ltd. All rights reserved.Öğe Meat quality characteristics in Kivircik lambs(Scientific Technical Research Council Turkey-Tubitak, 2014) Yarali, Engin; Yilmaz, Onur; Cemal, Ibrahim; Karaca, Orhan; Taskin, TurgayEsme District in Usak Province has a special role in western Anatolia sheep husbandry due to its number of animals and large pastures. A genotype with the characteristics of the Kivircik breed has emerged and became common in the region in the last 20-30 years. This study aimed to determine the meat quality characteristics of Kivricik lambs reared in the locality, which has a large market share. The study determined parameters about water and cooking loss and shear force in M. longissimus dorsi, M. longissimus thoracis, and M. semitendinosus muscles taken from the left half of lamb carcasses. Furthermore, meat quality characteristics such as pH, color, and fatty acid composition characteristics in the M. longissimus dorsi muscle were determined. In conclusion, the low shear force values (mean 2.27) obtained from Kivircik meat showed that it was tender. This result is consistent with the high demand from consumers for the meat of this breed.Öğe Modeling and Simulation Tools for Mobile Ad Hoc Networks(Crc Press-Taylor & Francis Group, 2012) Erciyes, Kayhan; Dagdeviren, Orhan; Cokuslu, Deniz; Yilmaz, Onur; Gumus, Hasan; Loo, J; Mauri, JL; Ortiz, JHÖğe NANOCOATINGS: PREPARATION, PROPERTIES, AND BIOMEDICAL APPLICATIONS(Elsevier Science Bv, 2019) Yilmaz, Onur; Yorgancioglu, Ali; Vasile, CÖğe Nanocomposites Based on Crosslinked Polyacrylic Latex/Silver Nanoparticles for Waterborne High-Performance Antibacterial Coatings(Wiley, 2014) Yilmaz, Onur; Karesoja, Mikko; Adiguzel, A. Candas; Zengin, Gokhan; Tenhu, HeikkiFunctional polymer/AgNPs nanocomposites have been prepared. Silver nanoparticles (NPs) were synthesized to which polyacrylamide, PAAm, was covalently bound. PAAm was synthesized via a RAFT reaction and carried thiol and carboxylic acid end groups. Thiol was used to bind the polymer to the metal surface and carboxyl for further reactions. The AgNPs were used in a post-crosslinking reaction with a separately synthesized poly(butyl acrylate-co-methyl methacrylate)/polyglycidyl methacrylate core/shell latex bearing epoxy functional groups. Dynamic mechanical analysis showed that the functional AgNPs effectively crosslinked the latex polymer, and that the final product had excellent mechanical strength. Antibacterial tests revealed that the nanocomposite films had strong antibacterial activity against all types of the bacteria and the immobilization of silver NPs by crosslinking retarded the release of silver in comparison to the uncrosslinked ones. With the presented method, it is possible to obtain ductile antibacterial nanocomposites to be used as waterborne functional coatings. (c) 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 1435-1447
