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TUNCABOYLU, DENIZ CEYLAN

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DENIZ CEYLAN
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TUNCABOYLU
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Now showing 1 - 10 of 16
  • PublicationMetadata only
    Porous rubber cryogels: effect of the gel preparation temperature
    (2014-08-01T00:00:00Z) Oztoprak, Zeynep; Hekimoglu, Tugce; Karakutuk, Ilknur; Tuncaboylu, Deniz C.; Okay, Oğuz; TUNCABOYLU, DENIZ CEYLAN
    This paper examines the effect of the gel preparation temperature (T (prep)) on the physical properties of the rubber-based macroporous organogels prepared by solution crosslinking in benzene at subzero temperatures. Cis-polybutadiene (CBR) and styrene-butadiene rubber (SBR) were used as the rubber components, while sulfur monochloride (S2Cl2) was the crosslinker in the gel preparation. It was shown that T (prep) is an extremely important parameter to adjust the porous structure and thus, the cryogel properties. The networks formed by CBR and SBR showed an aligned porous structure with an exception of honey-comb structured porous SBR cryogels prepared at -2 A degrees C. 10(1)- to 10(2)-mu m sized regular pores of the networks caused by the benzene crystals act as a template during gelation, separated by 10-20 mu m pore walls in thickness. They exhibit fast swelling and deswelling properties as well as reversible swelling-deswelling cycles in toluene and methanol, respectively. The ability of the organogels for the removal of petroleum products from aqueous solutions was also demonstrated using diesel and crude oil as model pollutants. In addition, the reusability of the organogels and their continuous sorption capacities were checked by repeated sorption-squeezing cycles. All the tests showed that the aligned porous organogels are suitable materials for the oil spill cleanup procedures.
  • PublicationMetadata only
    Structure optimization of self-healing hydrogels formed via hydrophobic interactions
    (2012-11-09T00:00:00Z) Tuncaboylu, Deniz C.; Argun, Aslihan; Sahin, Melahat; Sari, Murat; Okay, Oğuz; TUNCABOYLU, DENIZ CEYLAN
    In an attempt to mimic self-healing functions in biological systems, we investigate here the optimum design parameters of self-healing hydrogels formed by hydrophobic associations in aqueous solutions of wormlike sodium dodecyl sulfate (SDS) micelles. n-alkyl (meth)acrylates were used as the hydrophobic comonomer (2 mol %) of acrylamide in the gel preparation. Two structural parameters are crucial for obtaining self-healing gels via hydrophobic interactions. One is the length of the alkyl side chain of the hydrophobe, and the other is the surfactant concentration. In addition, hydrophobic methacrylates generate gels with a higher healing efficiency than the corresponding acrylates due to the limited flexibility of the methacrylate backbones, leading to a greater number of non-associated hydrophobic blocks. These free blocks locating near the fracture surface of the gel samples link each other to self-heal the broken hydrogel. The physical gels without SDS are very tough due to their sacrificial bonds that are broken under force and preventing the fracture of the molecular backbone. (C) 2012 Elsevier Ltd. All rights reserved.
  • PublicationMetadata only
    Autonomic self-healing in covalently crosslinked hydrogels containing hydrophobic domains
    (2013-11-01T00:00:00Z) Tuncaboylu, Deniz C.; Argun, Aslihan; Algi, Melek Pamuk; Okay, Oğuz; TUNCABOYLU, DENIZ CEYLAN
    Self-healing hydrogels suffer from low mechanical strength due to their reversible breakable bonds which may limit their use in any stress-bearing applications. This deficiency may be improved by creating a hybrid network composed of a combination of a physical network formed via reversible crosslinks and a covalent network. Here, we prepared a series of hybrid hydrogels by the micellar copolymerization of acrylamide with 2 mol % stearyl methacrylate (C18) as a physical crosslinker and various amounts of N,N--methylenebis(acrylamide) (BAAm) as a chemical crosslinker. Rheological measurements show that the dynamic reversible crosslinks consisting of hydrophobic associations surrounded by surfactant micelles are also effective within the covalent network of the hybrid hydrogels. A significant enhancement in the compressive mechanical properties of the hybrid gels was observed with increasing BAAm content. The existence of an autonomous self-healing process was also demonstrated in hybrid gels formed at low chemical crosslinker ratios. The largest self-healing efficiency in hybrids was observed in terms of the recovered elastic modulus, which was about 80% of the original value. (C) 2013 Elsevier Ltd. All rights reserved.
  • PublicationMetadata only
    Dynamics and Large Strain Behavior of Self-Healing Hydrogels with and without Surfactants
    (2012-02-28T00:00:00Z) Tuncaboylu, Deniz C.; Sahin, Melahat; Argun, Aslihan; Oppermann, Wilhelm; Okay, Oğuz; TUNCABOYLU, DENIZ CEYLAN
    Polyacrylamide hydrogels formed via hydrophobic interactions between stearyl groups in aqueous micellar solution of sodium dodecyl sulfate (SDS) present two faces depending on which state they are. The gels containing SDS micelles exhibit, in addition to the fast mode, a slow relaxation mode in dynamic light scattering (DLS) and time-dependent elastic moduli, indicating the temporary nature of the hydrophobic associations having lifetimes of the order of seconds to milliseconds. The gels where SDS had been removed after their preparation behave similar to chemically cross-linked ones with time-independent elastic moduli, a high degree of spatial inhomogeneity, and a single relaxation mode in DLS. Because of this drastic structural change, the physical gels are insoluble in water with a gel fraction close to unity. In surfactant containing gels, a large proportion of physical cross-links dissociate under force, but they do so reversibly, if the force is removed they reform again. The reversible disengagements of the hydrophobic units building the physical cross-links leads to a self-healing efficiency of nearly 100%, while no such healing behavior was observed after extraction of SDS due to the loss of the reversible nature of the cross-linkages.
  • PublicationMetadata only
    Microgels from microfluidic templating and photoinduced crosslinking of cinnamylidene acetic acid modified precursors
    (2017-03-01) Tuncaboylu, DENİZ CEYLAN; WISCHKE, C.; STOERMANN, F.; LENDLEIN, A.; TUNCABOYLU, DENIZ CEYLAN
    So far, a number of approaches to synthesize microgel networks have been followed, while only in few cases a detailed control of the network architecture has been possible. Here, the photoinduced [2 + 2] cycloaddition reaction of cinnamylidene acetic acid (CAA) moieties coupled to four-arm star shaped oligo (ethylene glycol) (OEG) precursors was explored for the creation of microgels with defined polymer network structures. Based on a rational solvent selection and precursor dispersion in glass-capillary microfluidics, microgels could be successfully prepared by the proposed synthesis approach. Model reactions confirmed a quantitative network formation. Therefore, compared to common radical polymerization for microgel crosslinking, CAA-dimerization may be an alternative approach particularly when well defined network structures are desired. (C) 2017 Elsevier B.V. All rights reserved.
  • PublicationMetadata only
    A multifunctional multimaterial system for on-demand protein release
    (2018-08-28) Tuncaboylu, DENİZ CEYLAN; FRIESS, Fabian; WISCHKE, Christian; LENDLEIN, Andreas; TUNCABOYLU, DENIZ CEYLAN
    In order to provide best control of the regeneration process for each individual patient, the release of protein drugs administered during surgery may need to be timely adapted and/or delayed according to the progress of healing/regeneration. This study aims to establish a multifunctional implant system for a local on-demand release, which is applicable for various types of proteins. It was hypothesized that a tubular multimaterial container kit, which hosts the protein of interest as a solution or gel formulation, would enable on-demand release if equipped with the capacity of diameter reduction upon external stimulation. Using devices from poly(epsilon-caprolactone) networks, it could be demonstrated that a shape-memory effect activated by heat or NIR light enabled on-demand tube shrinkage. The decrease of diameter of these shape-memory tubes (SMT) allowed expelling the payload as demonstrated for several proteins including SDF-1 alpha, a therapeutically relevant chemotactic protein, to achieve e.g. continuous release with a triggered add-on dosing (open tube) or an on-demand onset of bolus or sustained release (sealed tube). Considering the clinical relevance of protein factors in (stem) cell attraction to lesions and the progress in monitoring biomarkers in body fluids, such on-demand release systems may be further explored e.g. in heart, nerve, or bone regeneration in the future.
  • PublicationMetadata only
    Rheological characterization of starch gels: A biomass based sorbent for removal of polycyclic aromatic hydrocarbons (PAHs)
    (2019-06-05) Ceylan Tuncaboylu, DENİZ CEYLAN; ABDURRAHMANOĞLU, SUZAN; GAZİOĞLU, IŞIL; TUNCABOYLU, DENIZ CEYLAN; GAZİOĞLU, IŞIL
  • PublicationMetadata only
    Self-healing hydrogels formed in catanionic surfactant solutions
    (2013-01-01T00:00:00Z) Akay, Gizem; HASSAN-RAEISI, Azadeh; Tuncaboylu, Deniz C.; Orakdöğen, Nermin; ABDURRAHMANOĞLU, SUZAN; OPPERMANN, Wilhelm; Okay, Oğuz; TUNCABOYLU, DENIZ CEYLAN
    Physical gels with remarkable properties were obtained by copolymerization of acrylamide with the hydrophobic monomer stearyl methacrylate (C18) in a micellar solution of cetyltrimethylammonium bromide (CTAB) containing up to 15 mol% sodium dodecyl sulfate (SDS). The addition of SDS causes the CTAB micelles to grow and thus enables solubilization of C18. The gels exhibit time-dependent dynamic moduli, high elongation ratios at break (1800-5000%), and self-healing, as evidenced by rheological and mechanical measurements and substantiated by dynamic light scattering. As the size of the micelles in the gelation solution increases, both the degree of temporary spatial inhomogeneity and the lifetime of hydrophobic associations in the gels increase while the elongation ratio at break decreases. Although the physical gels were insoluble in water due to strong hydrophobic interactions, they could be solubilized in surfactant solutions thus providing a means of characterization of the network chains. Viscometric and rheological behaviors of polymer solutions show a substantial increase in the associativity of the network chains with rising micelle size, which results in prolonged lifetime of hydrophobic associations acting as physical cross-links in gels. The internal dynamics of self-healing gels could thus be controlled by the associativity of the network chains which in turn depends on the size of CTAB micelles.
  • PublicationMetadata only
    Dimethylacrylamide gels linked by dimethacrylate cross-linkers
    (2019-10-01T00:00:00Z) TUNCABOYLU, Deniz Ceylan; Yildirim, Tuana Seray; TUNCABOYLU, DENIZ CEYLAN
    Poly(N,N-dimethylacrylamide) (PDMA) is a water-soluble and biocompatible polymer useful in biomedical, biotechnological and pharmaceutical application areas. In this study, dimethylacrylamide (DMA) units were connected with dimethacrylate chemical cross-linkers (DMA-xl) with various chain lengths to get homogeneous, biocompatible and mechanically strong DMA hydrogels and cryogels. In the first step, the effect of the distance between the vinyl groups of the cross-linker molecules on swelling and mechanical properties was investigated. While cross-linkers bearing longer ethylene glycol units from DMA-1 to DMA-2 bond more water molecules, DMA-9-s equilibrium swelling values are the lowest, which may be due to the better movement capability of the chains with longer cross-linker units that will increase the physical interactions between the molecules and lead to the more compact structures. In the second step, cross-linker ratio was changed with a fixed dimethacrylate group. When the mol ratio of DMA-2 is decreasing step by step from the highest to lowest concentration for the gels after synthesis, the elastic modulus decreases gradually from 30 to 6 kPa, and the gels show similar mechanical behavior in the swollen state. In the last step, the amount of cross-link units on the morphology of cryogels was investigated with DMA-2 gels. The results explicitly indicated that while the mesh size of PDMA cryogels decreased with an increase in DMA-2 concentration, the mechanical stability of the gels was increased.
  • PublicationMetadata only
    Tough interpenetrating Pluronic F127/polyacrylic acid hydrogels
    (2013-05-01T00:00:00Z) Baskan, Tuba; Tuncaboylu, Deniz C.; Okay, Oğuz; TUNCABOYLU, DENIZ CEYLAN
    Tough interpenetrating polymer network (IPN) hydrogels with pH- and temperature sensitivity were prepared by crosslinking copolymerization of acrylic acid (AAc) and N,N--methylenebis(acrylamide) in 20 w/v% aqueous solutions of F127 (PEO99-PPO65-PEO99). The presence of F127 within the gel network slightly decreases the elastic modulus while the loss factor significantly increases, revealing increasing energy dissipation in IPN hydrogels. Cyclic compression tests show large mechanical hysteresis in IPN hydrogels due to the reversible formation of ionic clusters and hydrophobic associations of F127 molecules. The dissipative mechanisms created by F127 lead to the improvement in the mechanical performance of IPN hydrogels when compared to the polyacrylic acid (PAAc) gel controls. PAAc hydrogel formed at 10% AAc fractures under a compression of 0.2 MPa at 78% strain, while the corresponding IPN hydrogel sustains up to 7 MPa compressions at 98% strain, leading to an increase of toughness from 31 to 335 kJ/m(3). IPN hydrogels subjected to the heating-cooling cycles between below and above the micellization temperature of F127 show characteristic features of F127 solutions, i.e., increase of the dynamic moduli on raising the temperature, and thermal hysteresis behavior. (c) 2013 Elsevier Ltd. All rights reserved.