Person: KAYAMAN APOHAN, NİLHAN
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KAYAMAN APOHAN
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NİLHAN
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Publication Metadata only Synthesis and drug-release properties of biodegradable hydrogels having beta-cyclodextrin(SPRINGER, 2013) KAYAMAN APOHAN, NİLHAN; Kayaman-Apohan, Nilhan; Akyurek, EmelA new beta-cyclodextrin (beta-CD) methacrylated monomer was synthesized from the reaction of beta-CD, glycidyl methacrylate. Based on inclusion character of beta-CD, a series of hydrogels were prepared by irradiating the mixtures of beta-CD methacrylate monomer (beta-CD-Met), poly(ethylene glycol) monoacrylate, poly(ethylene glycol)diacrylate, fumaric acid monoethyl ester-functionalized poly(lactic-co-glycolic) acid, 1-vinyl-2-pyrrolidone, N,N'-methylene bisacrylamide, and the photoinitiator. Gel percentages and equilibrium swelling ratios (%) of hydrogels were investigated. It was observed that equilibrium-swelling ratio increased with increasing beta-CD-Met content in the hydrogel composition. SEM images demonstrated that beta-CD-Met-based hydrogel have lots of voids on the fractured surface. In this study, ibuprofen (IBU) which is capable of forming inclusion complex with beta-CD was chosen. For the hydrogel with maximum CD content, the IBU drug loading was found as 9 mg/g dry gel. It can be concluded that the inclusion complex-formation capability of beta-CD moiety increases the drug release by improving the aqueous solubility of hydrophilic drugs.Publication Metadata only Preparation and drug release properties of lignin-starch biodegradable films(WILEY-V C H VERLAG GMBH, 2012) OGAN, AYŞE; Calgeris, Ilker; Cakmakci, Emrah; Ogan, Ayse; Kahraman, M. Vezir; Kayaman-Apohan, NilhanStarch is one of the most commonly available natural polymers which are obtained from agro-sources. It is renewable and abundant in nature. Unfortunately due to its poor mechanical properties and hygroscopic nature, there are some strong limitations to the development of starch-based products. Usually blends of starch are prepared and plasticized with glycerol to improve some of its properties. In this study, lignin was extracted from hazelnut shells and investigated as a potential additive for starch biofilms. The structural characterization of hazelnut lignin was performed by employing UV spectroscopy and Fourier transform infrared (FTIR) spectroscopy. Lignin was blended with corn starch in different ratios to obtain biofilms. Mechanical and thermal properties of the biofilms were enhanced as the lignin amount was increased in the formulations. Water absorption tests were performed at pH 2.0, 4.0, and 6.0. The percent swelling values of the starch/lignin films increased as pH increased. Also, the biofilm exhibiting the best properties was chosen for the drug release studies. Biofilms showed a fast ciprofloxacin (CPF) release within an hour and then the drug release rate decreased. A pH dependent drug release mechanism was also observed according to KoshnerPeppas model. The drug release increased with a decrease in pH.Publication Metadata only Synthesis and characterization UV-curable organic-inorganic of flame retarding hybrid coatings(WILEY, 2006) KAYAMAN APOHAN, NİLHAN; Karatas, Sevim; Hosgor, Zuhal; Menceloglu, Yusuf; Kayaman-Apohan, Nilhan; Gungor, AtillaUV-curable, organic-inorganic hybrid materials were synthesized via sol-gel reactions for tetraethylorthosilicate, and methacryloxypropyl trimethoxysilane in the presence of the acrylated phenylphosphine oxide resin (APPO) and a bisphenol-A-based epoxy acrylate resin. The sol-gel precursor content in the hybrid coatings was varied from 0 to 30 wt %. The adhesion, flexibility, and hardness of the coatings were characterized. The influences of the amounts of inorganic component incorporated into the coatings were studied. Results from the mechanical measurements show that the properties of hybrid coatings improve with the increase in sol-gel precursor content. In addition, thermal properties of the hybrids were studied by thermogravimetric analysis in air atmosphere. The char yield of pure organic coating was 32% and that of 30 wt % silicate containing hybrid coating was 30% at 500 degrees C in air atmosphere. This result demonstrates the pronounced effect of APPO on the flame retardance of coatings. Gas chromatography/mass spectrometry analyses showed that the initial weight loss obtained in thermogravimetric analysis is due to the degradation products of the photoinitator and the reactive diluent. (c) 2006 Wiley Periodicals, Inc.Publication Metadata only Stimuli-responsive poly(hydroxyethyl methacrylate) hydrogels from carboxylic acid-functionalized crosslinkers(WILEY, 2019) KAYAMAN APOHAN, NİLHAN; Bingol, H. Betul; Agopcan-Cinar, Sesil; Bal, Tugba; Oran, D. Ceren; Kizilel, Seda; Kayaman-Apohan, Nilhan; Avci, DuyguTailoring hydrogel properties by modifications of the crosslinker structure is a good method for the design of hydrogels with a wide range of properties. In this study, two novel carboxylic acid-functionalized dimethacrylate crosslinkers (1a and 2a) are synthesized by the reaction of poly(ethylene glycol) or 2-hydroxyethyl disulfide with tert-butyl alpha-bromomethacrylate followed by cleavage of tert-butyl groups using trifluoroacetic acid. Their copolymerization reactivity with 2-hydroxyethyl methacrylate (HEMA) investigated by photopolymerization studies performed on photo-differential scanning calorimetry shows higher reactivity of 2a compared to 1a. These crosslinkers are then used at different ratios for fabrication of pH- and redox-responsive poly(2-hydroxyethyl methacrylate)-based hydrogels. The swelling behavior of the hydrogels is found to be dependent on the structure of the crosslinker, degree of crosslinking, pH, and CaCl2 concentration. The redox-responsive behavior is demonstrated by degradation of the hydrogel upon exposure to 1,4-dithiothreitol. The dye Rhodamine 6G and the drug resorcinol are used as models to demonstrate the pH and redox dependent release of loaded compounds from the hydrogels. The electrostatic interactions between the carboxylate groups and the positively charged R6G are found to govern the release profile in DTT and counteract the diffusion of dye molecules and significant amount of release (79% in 120 hr) occurs only at highly acidic conditions. The degradation mediated release in DTT is observed better in case of resorcinol (around 88% in 5 hr). Overall, these hydrogels can be regarded as good candidates for several applications, such as matrices for controlled release, tissue repair, and regeneration.Publication Metadata only Synthesis and characterization of polyimide/hexagonal boron nitride composite(WILEY-BLACKWELL, 2012) KAHRAMAN, MEMET VEZİR; Kizilkaya, Canan; Mulazim, Yusuf; Kahraman, Memet Vezir; Apohan, Nilhan Kayaman; Gungor, AtillaPolyimide (PI)/hexagonal boron nitride (h-BN) composites were produced via the thermal imidization procedure from solution mixtures of a polyamicacid, which is prepared from 3,3',4,4'-benzophenonetetracarboxylic dianhydride and 3,3'-diaminodiphenyl sulfone (DADPS) in N-methyl-2-pyrrolidone (NMP), and alkoxysilane functionalized h-BN. The structure, thermostability, thermal behavior, and surface properties of the resulting materials were characterized by means of Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), scanning electron microscopy (SEM). The thermal characteristics of PI/h-BN films were better than the pure PIs. The physical and mechanical properties of the films were evaluated by various techniques such as contact angle, chemical resistance, and tensile tests. The flame retardancy of the composite materials was also examined by the limiting oxygen index (LOI). The experiments showed that the LOI values of PIs increased from 32 to 43 for the materials containing hexagonal boron nitride. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012Publication Metadata only Phosphoric acid functional UV-cured proton conducting polymer membranes for fuel cells(SPRINGER HEIDELBERG, 2015) KAYAMAN APOHAN, NİLHAN; Ugur, Mustafa Hulusi; Kayaman-Apohan, Nilhan; Avci, Duygu; Gungor, AtillaThis paper reports the preparation and characterization of 10-methacryloyloxydecyl-dihydrogenphosphate (MDP)-based UV-curable proton-conducting polymer membranes (UVcPMs). Poly(ethylene glycol diacrylate) (PEGDA), as cross-linking agent, and N-vinyl-2-pyrrolidone (NVP), as reactive diluent, were used to arrange the mechanical and physical properties of the resulting membrane. The membrane formulation polymerized under UV irradiation and membranes were characterized by using Fourier transform infrared (FT-IR), thermal gravimetric analysis (TGA) and electrochemical impedans spectroscopy (EIS). The water uptakes, the volume swelling ratio and ion exchange capacity (IEC) measurement of the membranes were performed. The IEC values increase with an increase in MDP monomer content. Proton conductivities were measured as a function of the weight fraction of MDP content of the membrane. The conductivities are of the order of 10(-4)-10(-3) Scm(-1). The morphology of the membranes was also investigated by Atomic Force Microscopy (AFM). MDP-based UV-cured polymers are first reported as polyelectrolyte membranes.Publication Metadata only Synthesis and characterization of UV-curable dual hybrid oligomers based on epoxy acrylate containing pendant alkoxysilane groups(ELSEVIER SCIENCE SA, 2006) KAHRAMAN, MEMET VEZİR; Bayramoglu, Gulay; Kahraman, M. Vezir; Kayaman-Apohan, Nilhan; Gungor, AtillaThis work involves the synthesis of novel hybrid oligomers based on a UV-curable epoxy acrylate resin (EA). The EA resin was modified with various amount of 3-isocyanatopropyl trimethoxysilane (IPTMS) coupling agent. The modification percentage of the hybrid oligomer was varied from 0 to 50 wt.%. UV-curable, hard and transparent organic-inorganic hybrid coatings were prepared on Plexiglas substrates and their characterization was performed by the analyses of various properties such as hardness, gloss, tape adhesion test and stress-strain test. Results from the mechanical measurements show that the properties of hybrid coatings improve with the increase in modification ratio. The thermal behavior of coatings was also evaluated. It is observed that the thermal stability of epoxy acrylate coatings is enhanced with incorporation of siloxane. Gas chromatography/mass spectrometry analyses showed that the initial weight loss obtained in thermogravimetric analysis is due to the degradation products of the photoinitator and the acrylic acid moiety of acrylic monomers. (c) 2006 Elsevier B.V. All rights reserved.Publication Metadata only The effect of titania content on the physical properties of polyimide/titania nanohybrid films(WILEY-BLACKWELL, 2012) DUMLUDAĞ, FATİH; Kizilkaya, Canan; Dumludag, Fatih; Karatas, Sevim; Apohan, Nilhan Kayaman; Altindal, Ahmet; Gungor, AtillaIn this study, a series of PI/TiO2 nanohybrid materials were prepared from polyamic acid of 3,3',4,4'-benzophenonetetracarboxylic dianhydride/3,3'-diaminodiphenyl sulfone, and titania precursor by the sol-gel method. The titania content in the hybrid system was varied from 0 to 5 wt %. The physical and mechanical properties of the hybrids such as refractive index, optical transmission, and tensile strength were investigated. It was determined that incorporation of titania precursor into the PI matrix improved the refractive indices and tensile modulus of the hybrid films. It was observed that the optical transmittance and tensile strength of the nanohybrids were slightly decreased with the increasing titania content. It was determined that the hybrid films might have enhanced the UV shielding properties compare to the PI films. Furhermore, the hybrid materials showed better thermal stability than the PI. SEM studies demonstrated that titania particles (1 and 3 wt %) were distributed homogeneously through the PI matrix. The effect of the titania content in the PI on DC conductivity and dielectric constant were also analyzed. For the PI film containing 5 wt % titania, activation energy value increased to 1.0 eV from the value of 0.65 eV. DC conductivity value of the films depending on titania content varied between 3.0 x 10(-11) and 1.4 x 10(-10) S/cm at room temperature. Relative dielectric constants of the films were calculated from capacitance measurements depending on frequency (40100 kHz) at different temperatures (303-360 K). The values increased with the increasing titania content. (C) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012Publication Metadata only Nonisocyanate polyurethane/silica hybrid coatings via a sol-gel route(WILEY-HINDAWI, 2012) KAYAMAN APOHAN, NİLHAN; Hosgor, Z.; Kayaman-Apohan, N.; Karatas, S.; Gungor, A.; Menceloglu, Y.Polyurethane/silica hybrids by a nonisocyanate route were prepared by reacting cyclic carbonate-modified bis(4-glycidyloxy phenyl)phenyl phosphine oxide (BGPPO), and poly(propyleneglycol)diglycidyl ether (PPG-DGE) with hexamethylene diamine. The incorporation of silica was achieved via a solgel method. The effect of silica and phosphine oxide moiety on polyurethane coating properties was studied by physical, mechanical, and thermal tests. Modulus and hardness of the coatings were enhanced by increasing the amount of silica and phosphine oxide based resin. The improvement in flame retardancy and thermal stability of nanocomposites was proved with increased char yield values and decomposition temperatures in thermogravimetric analyses. (C) 2011 Wiley Periodicals, Inc. Adv Polym Techn 31: 390400, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.20262Publication Metadata only Preparation, characterization and drug release behavior of poly(acrylic acid-co-2-hydroxyethyl methacrylate-co-2-acrylamido-2-methyl-1-propanesulfonic acid) microgels(SPRINGER, 2011) KAYAMAN APOHAN, NİLHAN; Nart, Zuhal; Kayaman-Apohan, NilhanIn this paper, Poly(acrylic acid-co-2-hydroxyethyl methacrylate-co-2-acrylamido-2-methyl-1-propanesulfonic acid (AAc-HEMA-AMPS) microgels were synthesized by using an inverse suspension polymerization technique. The increase in the AMPS content of the microgels composition caused a large increase in water uptake. The morphology of the microgels was examined by environmental scanning electron microscopy (ESEM). The AMPS containing microgels had a mean particle diameter of 10 mu m. The glass transition temperature of the microgels were examined by DSC and found that they show single Tg. Lidocaine (LD) and Methylene blue (MB) were used as model drugs for the investigation of drug release behavior of the microgels. Different drug release patterns were observed, for LD and MB loaded microgels. The release studies showed that some of the basic parameters affecting the drug release behavior of microgels were the specific and non-specific interactions between microgel and drug structure and pH of the dissolution medium. These hydrogels may be potential candidates for pH-sensitive applications.