Browsing by Author "Uyar, T."

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Open Access
Antibacterial electrospun poly(lactic acid) (PLA) nanofibrous webs incorporating triclosan/cyclodextrin inclusion complexes
(2013) Kayaci F.; Umu O.C.O.; Tekinay, T.; Uyar, T.
Solid triclosan/cyclodextrin inclusion complexes (TR/CD-IC) were obtained and then incorporated in poly(lactic acid) (PLA) nanofibers via electrospinning. α-CD, β-CD, and γ-CD were tested for the formation of TR/CD-IC by a coprecipitation method; however, the findings indicated that α-CD could not form an inclusion complex with TR, whereas β-CD and γ-CD successfully formed TR/CD-IC crystals, and the molar ratio of TR to CD was found to be 1:1. The structural and thermal characteristics of TR/CD-IC were investigated by 1H NMR, FTIR, XRD, DSC, and TGA studies. Then, the encapsulation of TR/β-CD-IC and TR/γ-CD-IC in PLA nanofibers was achieved. Electrospun PLA and PLA/TR nanofibers obtained for comparison were uniform, whereas the aggregates of TR/CD-IC crystals were present and distributed within the PLA fiber matrix as confirmed by SEM and XRD analyses. The antibacterial activity of these nanofibrous webs was investigated. The results indicated that PLA nanofibers incorporating TR/CD-IC showed better antibacterial activity against Staphylococcus aureus and Escherichia coli bacteria compared to PLA nanofibers containing only TR without CD-IC. Electrospun nanofibrous webs incorporating TR/CD-IC may be applicable in active food packaging due to their very high surface area and nanoporous structure as well as efficient antibacterial property. © 2013 American Chemical Society.
Open Access
Antibacterial nanofibers of pullulan/tetracycline-cyclodextrin inclusion complexes for fast-disintegrating oral drug delivery
(Elsevier Inc., 2021-12-08) Hsiung, E.; Celebioglu, A.; Chowdhury, R.; Kilic, M. E.; Durgun, Engin; Altier, C.; Uyar, T.
Tetracycline is a widely used antibiotic suffering from poor water solubility and low bioavailability. Here, hydroxypropyl-beta-cyclodextrin (HPβCD) was used to form inclusion complexes (IC) of tetracycline with 2:1 M ratio (CD:drug). Then, tetracycline-HPβCD-IC was mixed with pullulan- a non-toxic, water-soluble biopolymer - to form nanofibrous webs via electrospinning. The electrospinning of pullulan/tetracycline-HPβCD-IC was yielded into defect-free nanofibers collected in the form of a self-standing and flexible material with the loading capacity of ∼ 7.7 % (w/w). Pullulan/tetracycline nanofibers was also generated as control sample having the same drug loading. Tetracycline was found in the amorphous state in case of pullulan/tetracycline-HPβCD nanofibers due to inclusion complexation. Through inclusion complexation with HPβCD, enhanced aqueous solubility and faster release profile were provided for pullulan/tetracycline-HPβCD-IC nanofibers compared to pullulan/tetracycline one. Additionally, pullulan/tetracycline-HPβCD-IC nanofibers readily disintegrated when wetted with artificial saliva while pullulan/tetracycline nanofibers were not completely absorbed by the same simulate environment. Electrospun nanofibers showed promising antibacterial activity against both gram-positive and gram-negative bacteria. Briefly, our findings indicated that pullulan/tetracycline-HPβCD-IC nanofibers could be an attractive material as orally fast disintegrating drug delivery system for the desired antibiotic treatment thanks to its promising physicochemical and antibacterial properties.
Open Access
Bioactive surface design based on functional composite electrospun nanofibers for biomolecule immobilization and biosensor applications
(American Chemical Society, 2014-03-24) Uzun, S. D.; Kayaci, F.; Uyar, T.; Timur, S.; Toppare, L.
The combination of nanomaterials and conducting polymers attracted remarkable attention for development of new immobilization matrices for enzymes. Hereby, an efficient surface design was investigated by modifying the graphite rod electrode surfaces with one-step electrospun nylon 6,6 nanofibers or 4% (w/w) multiwalled carbon nanotubes (MWCNTs) incorporating nylon 6,6 nanofibers (nylon 6,6/4MWCNT). High-resolution transmission electron microscopy study confirmed the successful incorporation of the MWCNTs into the nanofiber matrix for nylon 6,6/4MWCNT sample. Then, these nanofibrous surfaces were coated with a conducting polymer, (poly-4-(4,7-di(thiophen-2-yl)-1H-benzo[d]imidazol-2-yl) benzaldehyde) (PBIBA) to obtain a high electroactive surface area as new functional immobilization matrices. Due to the free aldehyde groups of the polymeric structures, a model enzyme, glucose oxidase was efficiently immobilized to the modified surfaces via covalent binding. Scanning electron microscope images confirmed that the nanofibrous structures were protected after the electrodeposition step of PBIBA and a high amount of protein attachment was successfully achieved by the help of high surface to volume ratio of electroactive nanofiber matrices. The biosensors were characterized in terms of their operational and storage stabilities and kinetic parameters (K mapp and Imax). The resulting novel glucose biosensors revealed good stability and promising Imax values (10.03 and 16.67 μA for nylon 6,6/PBIBA and nylon 6,6/4MWCNT/PBIBA modified biosensors, respectively) and long shelf life (32 and 44 days for nylon 6,6/PBIBA and nylon 6,6/4MWCNT/PBIBA modified biosensors, respectively). Finally, the biosensor was tested on beverages for glucose detection. © 2014 American Chemical Society.
Open Access
Cyclodextrin-functionalized mesostructured silica nanoparticles for removal of polycyclic aromatic hydrocarbons
(Academic Press Inc., 2017) Topuz, F.; Uyar, T.
Polycyclic aromatic hydrocarbons (PAHs) are the byproducts of the incomplete combustion of carbon-based fuels, and have high affinity towards DNA strands, ultimately exerting their carcinogenic effects. They are ubiquitous environmental contaminants, and can accumulate on tissues due to their lipophilic nature. In this article, we describe a novel concept for PAH removal from aqueous solutions using cyclodextrin-functionalized mesostructured silica nanoparticles (CDMSNs) and pristine mesostructured silica nanoparticles (MSNs). The adsorption applications of MSNs are greatly restricted due to the absence of surface functional groups on such particles. In this regard, cyclodextrins can serve as ideal functional molecules with their toroidal, cone-type structure, capable of inclusion-complex formation with many hydrophobic molecules, including genotoxic PAHs. The CDMSNs were synthesized by the surfactant-templated, NaOH-catalyzed condensation reactions of tetraethyl orthosilicate (TEOS) in the presence of two different types of cyclodextrin (i.e. hydroxypropyl-β-cyclodextrin (HP-β-CD) and native β-cyclodextrin (β-CD)). The physical incorporation of CD moieties was supported by XPS, FT-IR, NMR, TGA and solid-state 13C NMR. The CDMSNs were treated with aqueous solutions of five different PAHs (e.g. pyrene, anthracene, phenanthrene, fluorene and fluoranthene). The functionalization of MSNs with cyclodextrin moieties significantly boosted the sorption capacity (q) of the MSNs up to ∼2-fold, and the q ranged between 0.3 and 1.65 mg per gram CDMSNs, of which the performance was comparable to that of the activated carbon.
Open Access
Cyclodextrin-grafted electrospun cellulose acetate nanofibers via "Click" reaction for removal of phenanthrene
(Elsevier, 2014-06-30) Çelebioğlu, A.; Demirci, S.; Uyar, T.
Beta-cyclodextrin (p-CD) functionalized cellulose acetate (CA) nanofibers have been successfully prepared by combining electrospinning and "click" reaction. Initially, p-CD and electrospun CA nanofibers were modified so as to be azide-p-CD and propargyl-terminated CA nanofibers, respectively. Then, "click" reaction was performed between modified CD molecules and CA nanofibers to obtain permanent grafting of CDs onto nanofibers surface. It was observed from the SEM image that, while CA nanofibers have smooth surface, there were some irregularities and roughness at nanofibers morphology after the modification. Yet, the fibrous structure was still protected. ATR-FTIR and XPS revealed that, CD molecules were successfully grafted onto surface of CA nanofibers. The adsorption capacity of p-CD-functionalized CA (CA-CD) nanofibers was also determined by removing phenanthrene (polycyclic aromatic hydrocarbons, PAH) from its aqueous solution. Our results indicate that CA-CD nanofibers have potential to be used as molecular filters for the purpose of water purification and waste water treatment by integrating the high surface area of nanofibers with inclusion complexation property of CD molecules.
Open Access
Effect of the solvent systems on the Morphology of the Electrospun cellulose acetate Nanofibers
(Fiber Society, 2010) Çelebioğlu, A.; Uyar, T.
[No abstract available]
Open Access
Efficient ammonium removal from aquatic environments by Acinetobacter calcoaceticus STB1 immobilized on an electrospun cellulose acetate nanofibrous web
(Royal Society of Chemistry, 2013-07-09) Sarioglu, O. F.; Yasa, O.; Celebioglu, A.; Uyar, T.; Tekinay, T.
A novel biocomposite material was developed by immobilizing an ammonia-oxidizing bacterial strain, Acinetobacter calcoaceticus STB1, on an electrospun porous cellulose acetate (CA) nanofibrous web. Ammonium removal characteristics of the STB1 immobilized CA nanofibrous web were determined at varying initial ammonium concentrations, and removal rates of 100%, 98.5% and 72% were observed within 48 h for 50 mg L-1, 100 mg L-1 and 200 mg L-1 samples, respectively. Most of the ammonia is inferred to be converted into nitrogen or is accumulated as bacterial biomass, as only trace amounts of ammonium were converted into nitrite or nitrate. Reusability test results indicate that, at an initial ammonium concentration of 100 mg L-1, bacteria-immobilized CA nanofibrous webs can be reused for at least 5 cycles. SEM images of the STB1/CA nanofibrous web after five cycles of reuse and rigorous washing demonstrate that bacterial biofilms strongly adhere to nanofiber surfaces.
Open Access
Electron-phonon interaction in bulk layered graphene and its oxide in the presence of alcohols in a device: Equilibrium molecular doping
(The Royal Society of Chemistry, 2014-08-22) Vempati, S.; Celebioglu, A.; Uyar, T.
We report on electron phonon interactions in bulk layered graphene (GRA) and its oxide (GO) under bias when exposed to 1° or 2° alcohol vapors, where we have focused on the change of Raman intensity of G and D bands as a function of the bias across the device. In addition to the softening of phonons we have observed a systematic variation in the intensity for D and G bands which is directly related to guest molecules and intrinsic surface nature of GRA and GO. Although the guest molecules withdraw electrons from GRA or GO, the intrinsic nature of the host material has caused mutually contrasting behaviour in IV-characteristics, where the conductance of the former decreases while it increases for the latter. The results from IV-spectra and the intensity maps of D and G bands are juxtaposed and the changes are analyzed with respect to surface and functional group interactions. In the context of doping, it is interesting to see that under equilibrium molecular charge transfer (top-gate like), the intensity ratios of 2D and G bands are not constant in contrast to a previous study [Phys. Rev. B., 2009, 80, 165413] in which such a ratio is invariant in the field effect configuration. © the Partner Organisations 2014.
Open Access
Electrospinning of gelatin with tunable fiber morphology from round to flat/ribbon
(Elsevier, 2017) Topuz, F.; Uyar, T.
The electrospinning of gelatin with tunable fiber morphology from round to flat/ribbon was shown, and the detailed studies were conducted to correlate the fiber morphology with electrospinning process parameters and gelatin concentration in electrospinning solution. Particularly, variations in the applied voltage and the concentration of gelatin led to the transition of fiber shape from round to flat/ribbon. The formation of flat-shaped fibers was attributed to rapid evaporation of the solvent (formic acid) from the fiber matrix with increasing the applied voltage and gelatin concentration. On the other hand, round fibers were due to the steady evaporation of formic acid throughout the cross-section of fibers. WAXS analysis revealed that the loss of triple-helical crystalline structure in gelatin after the electrospinning process. The gelatin fibers were cross-linked through treatment with toluene 2,4-diisocyanate (TDI) in a mixed solution of acetone and pyridine, and XPS confirmed the cross-linking of the fibers over an increased carbon content on the elemental composition of the fiber surface due to the incorporated TDI moieties. Overall, this study focuses on morphological tuning of gelatin electrospun fibers towards a flat/ribbon-like structure by variation of electrospinning parameters and polymer concentration, and thus, the proposed concept can be adapted towards flattened/ribbon-like fibers of other protein-based systems by electrospinning.
Open Access
Electrospun crosslinked poly-cyclodextrin nanofibers: highly efficient molecular filtration thru host-guest inclusion complexation
(Nature Publishing Group, 2017) Celebioglu, A.; Yildiz, Z. I.; Uyar, T.
Water pollution is a serious concern for public health and environment in today's world; hence, there exists a strong demand to develop cost-effective, sustainable and eco-friendly membranes. Here, we produce a highly efficient molecular filter membrane based on bio-renewable material; cyclic oligosaccaharides known as cyclodextrins (CD). Crosslinked insoluble poly-CD nanofibers are produced by using electrospinning technique in the absence of any additional polymeric carrier. Poly-CD nanofibrous membrane exhibit significant affinity to a common class of organic pollutant (i.e. methylene blue (MB)). Remarkably, the electrospun poly-CD nanofibrous web can outdistance the commonly used filter material (i.e. activated carbon) in terms of removal capacity. The flexible and free-standing poly-CD nanofibrous membrane depicted outstanding filtration performance. We estimate of above 90% removal efficiency for highly concentrated solutions of MB pollutant (40 mg/L) under extremely high flux (3840 Lm-2h-1). Essentially, these poly-CD nanofibrous webs demonstrate quite rapid uptake of MB from liquid environment. Overall, bio-based flexible electrospun poly-CD nanofibrous membrane represents a highly efficient molecular filter for wastewater treatment.
Open Access
Electrospun functional nanofibers
(Fiber Society, 2010) Kayaci F.; Celebioglu, A.; Deniz, A.E.; Uyar, T.
[No abstract available]
Open Access
Electrospun nanowebs incorporating essential oil/cyclodextrin inclusion complexes
(Fiber Society, 2012) Kayaci, F.; Ertas, Y.; Uyar, T.
In this study, we aimed to produce functional polyvinyl alcohol (PVA) electrospun nanowebs containing essential oil; eugenol (EG), that have long-term durability and high temperature stability due to cyclodextrin (CD) inclusion complexation.
Open Access
Electrospun polyester/cyclodextrin nanofibers for entrapment of volatile organic compounds
(John Wiley & Sons, Inc., 2014-02-03) Kayaci, F.; Uyar, T.
Polyester (PET) nanofibers incorporating cyclodextrins (CD) were obtained via electrospinning. α‐CD, β‐CD, and γ‐CD were used to functionalize PET nanofibers. Bead‐free PET/CD nanofibers were obtained from lower polymer concentration indicating that the incorporation of CD in polymer solution improved the electrospinnability of the PET nanofibers. XRD studies indicated that CD were distributed into nanofiber without forming crystalline aggregates. FTIR peak shift was observed possibly due to interaction between CD and PET. TGA confirmed that initial CD loading (25%, w/w) in the polymer solution was preserved for the PET/CD nanofibers. The presence of most of CD on the surface of PET/CD nanofibers was confirmed by XPS analysis and contact angle measurement. DMA results indicated that incorporation of CD improved the mechanical property of the nanofibers. Our studies showed that PET/CD nanofibers can effectively entrap aniline vapor as a model volatile organic compound (VOC) from surrounding owing to their very large surface area and inclusion complexation capability of CD. The entrapment efficiency of aniline vapor was found to be better for PET/γ‐CD nanofibers compared to PET/α‐CD and PET/β‐CD nanofibers. Our findings suggested that electrospun PET nanofibers functionalized with CD may be used as filtering material for removal of VOC in air filtration.
Open Access
Fabrication of polymetric-metal-oxide core-shell nanofibers by electrospinning and atomic layer deposition and their photocatalytic properties
(2012) Kayacı, F.; Ozgit-Akgun, C.; Dönmez, İ.; Bıyıklı, N.; Uyar, T.
Open Access
Fluorescence from graphene oxide and the influence of ionic, π π interactions and heterointerfaces: electron or energy transfer dynamics
(Royal Society of Chemistry, 2014-08-29) Vempati, S.; Uyar, T.
2D crystals such as graphene and its oxide counterpart have sought good research attention for their application as well as fundamental interest. Especially graphene oxide (GO) is quite interesting because of its versatility and diverse application potential. However the mechanism of fluorescence from GO is under severe discussion. To explain the emission in general two interpretations were suggested, viz localization of sp2 clusters and involvement of oxygeneous functional groups. Despite this disagreement, it should be acknowledged that the heterogeneous atomic structure, synthesis dependent and uncontrollable implantation of oxygen functional groups on the basal plane make such explanations more difficult. Nevertheless, a suitable explanation enhances the applicability of the material which also enables the design of novel materials. At this juncture we believe that given the complexity in understanding the emission mechanism it would be very useful to review the literature. In this perspective we juxtapose various results related to fluorescence and influencing factors so that a conclusive interpretation may be unveiled. Apparently, the existing interpretations have largely ignored the factors such as self-rolling, byproduct formation etc. Vis-a-vis previous reviews did not discuss the interfacial charge transfer across heterostructures and the implication on the optical properties of GO or reduced graphene oxide (rGO). Such analysis would be very insightful to determine the energetic location of sub band gap states. Moreover, ionic and π-π type interactions are also considered for their influence on emission properties. Apart from these, quantum dots, covalent modifications and nonlinear optical properties of GO and rGO were discussed for completeness. Finally we made concluding remarks with outlook. © the Partner Organisations 2014.
Open Access
Functional nanofibers synthesized by electrospinning and atomic layer deposition
(2012) Ozgit-Akgun, C.; Kayacı, F.; Dönmez, İ.; Uyar, T.; Bıyıklı, N.
Open Access
Functional polymeric nanofibers via electrospinning
(2012) Uyar, T.; Kayacı, F.; Celebioglu, A.; Aytac, Z.; Ertas, Y.
Open Access
General strategy for fabrication of ordered one dimensional inorganic structures by electrospinning: structural evolution from belt to solid via hollow tubes
(Wiley-VCH Verlag GmbH & Co. KGaA, 2020-12-23) Senthamizhan, Anitha; Balusamy, Brabu; Çelebioğlu, Aslı; Uyar, T.
Super-structured hollow materials are the subject of intense research due to their attracting properties and diverse applications. Despite their significance, it still remains a crucial challenge to develop a simple and well-organized method to prepare the hollow tubes with controlled architectures. Herein, a general route to prepare structurally well-defined 1D zinc oxide (ZnO) structures by a single-spinneret electrospinning method coupled with thermal treatment is demonstrated for the first time and subsequently designated to identify high-performance materials for catalytic application. Two critical factors including tailoring the precursor amount and colloidal-stability of the precursor play critical role in tuning the structure precisely. The careful optimization of processing conditions enables chronological structural evolution from tubular to solid fiber structures composed of nanograins. These ZnO complex hollow structures showcase excellent photocatalytic performance; single nanograined wall hollow tubes manifest the high-catalytic performance over other samples with remarkable cycling stability. Benefitting from fabrication adaptability, different types of metal oxide hollow tubes are prepared that indicates the generality of the method. The proposed method postulates new insights for the development of electrospun hollow-structured fibers in a simple, cost-effective, and industrially feasible manner which holds apparent potential in many sectors.
Open Access
Orally fast disintegrating cyclodextrin/prednisolone inclusion-complex nanofibrous webs for potential steroid medications
(American Chemical Society, 2021-12-06) Çelebioğlu, A.; Wang, N.; Kılıç, M. E.; Durgun, Engin; Uyar, T.
Prednisolone is a widely used immunosuppressive and anti-inflammatory drug type that suffers from low aqueous solubility and bioavailability. Due to the inclusion complexation with cyclodextrins (CDs), prednisolone’s drawbacks that hinder its potential during the administration can be eliminated effectively. Here, we have early shown the electrospinning of free-standing nanofibrous webs of CD/prednisolone inclusion complexes (ICs) in the absence of a polymer matrix. In this study, hydroxypropyl-beta-CD (HPβCD) has been used to form ICs with prednisolone and generate nanofibrous webs with a drug loading capacity of ∼10% (w/w). Pullulan/prednisolone nanofibrous webs have been also fabricated as a control sample having the same drug loading (∼10%, w/w). It has been demonstrated that prednisolone has been found in an amorphous state in the HPβCD/prednisolone nanofibrous web due to inclusion complexation, while it has retained its crystal structure in the pullulan/prednisolone nanofibrous web. Therefore, the HPβCD/prednisolone IC nanofibrous web has shown a faster and enhanced release profile and superior disintegration feature in artificial saliva than the pullulan/prednisolone nanofibrous web. The complexation energy calculated using ab initio modeling displayed a more favorable interaction between HPβCD and prednisolone in the case of a molar ratio of 2:1 than 1:1 (CD: drug). Here, the HPβCD/prednisolone IC nanofibrous web has been developed without using a toxic component or solvent to dissolve drug molecules and boost drug loading in amorphous nature. The investigation of IC nanofibrous webs has been conducted to formulate a promising alternative to the orally disintegrating tablet formulation of prednisolone in the market. The nanofibrous structure and the improved physicochemical properties of prednisolone arising with the complexation might ensure a faster disintegration and onset of action against commercially available and orally disintegrating delivery systems during the desired treatment.
Open Access
Orally fast-disintegrating resveratrol/cyclodextrin nanofibrous films as a potential antioxidant dietary supplement
(American Chemical Society, 2022-03-04) Celebioglu, A.; Tekant, D; Kilic, M.E.; Tekant, D.; Durgun, Engin; Uyar, T.
Encapsulation of dietary supplements into electrospun cyclodextrin (CD) inclusion complex (IC) nanofibers can pave the way for the development of novel delivery systems with orally fast-disintegrating properties. Here, resveratrol/CD-IC nanofibrous films were fabricated using the electrospinning technique. Resveratrol is a well-known bioactive agent with its antioxidant potential, and it is commonly used in the formulation of dietary supplements. Here, the hydroxypropylated (HP-) βCD and γCD were used for both encapsulation of resveratrol and the electrospinning of free-standing nanofibrous films. SEM imaging confirmed the uniform fibrous morphology of electrospun films. The encapsulation and amorphization of resveratrol by inclusion complexation were verified using various techniques including FTIR, 1H NMR, XRD, DSC, TGA, and computational modeling. Besides the results of all these techniques, phase solubility studies also revealed the more favorable complex formation of resveratrol with HPβCD compared to HP γCD. Nanofibrous films were obtained having ∼100% loading efficiency without a loss during the process. The amorphous distribution of resveratrol and the unique properties of nanofibers ensured the fast disintegration of nanofibrous films in the saliva simulation. The enhanced solubility of resveratrol also ensured an improved antioxidant property. The polymeric resveratrol/pullulan nanofibrous film was also formed as a control sample. CD-IC nanofibrous films showed faster disintegration/dissolution, higher/faster release profile, and significantly better antioxidant potential compared to resveratrol/pullulan-based samples.