Person: TUNCABOYLU, DENIZ CEYLAN
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Publication Metadata 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 CEYLANIn 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.Publication Metadata 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 CEYLANSelf-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.Publication Open Access Design of Biocompatible Multifunctional Hydrogels with Stearyl Methacrylate and Vinylpyrrolidone(2022-03-01T00:00:00Z) Kilic, Husna; TUNCABOYLU, Deniz Ceylan; Argun, Aslihan; ÖZTÜRK CİVELEK, DİLEK; TUNCABOYLU, DENIZ CEYLAN; ÖZTÜRK CİVELEK, DİLEKBiofunctionality and biocompatibility are essential when tissue or organs are supplemented or replaced with a polymer based material. Here, we prepared stearyl methacrylate (SM) and vinylpyrrolidone (VP) based biocompatible SM-x networks with self-healing and shape memory properties. The mole ratios were gradually changed from hydrophilic to hydrophobic units between 10 and 90% to obtain gels meeting the requirements in various potential bioapplications. In addition to having a time-dependent viscoelastic character, the mechanical properties of the gels can be controlled by the amount of SM introduced into the reaction medium. Low SM content gels cannot fully return to their initial modulus values, while the gels formed with concentrations >= 60% are completely reversible due to the dynamic hydrophobic interactions, which is also effective in the self-healing behavior. Moreover, all of the networks can completely recall their permanent shape in seconds. The viability of human skin fibroblast cells, seeded on SM-x hydrogels, closely related to the water contact angle of the structures, was found to be over 82% at all x values. In the light of the findings, the wide range of properties of SM-x gel samples may show significant potential to address needs in a variety of biomedical applications.Publication Metadata 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 CEYLANPolyacrylamide 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.Publication Metadata only Surfactant-induced healing of tough hydrogels formed via hydrophobic interactions(2014-02-01T00:00:00Z) Argun, Aslihan; Algi, Melek Pamuk; Tuncaboylu, Deniz C.; Okay, Oğuz; TUNCABOYLU, DENIZ CEYLANDifferent reversible molecular interactions have been used in the past few years to generate self-healing in synthetic hydrogels. However, self-healing hydrogels synthesized so far suffer from low mechanical strength which may limit their use in any stress-bearing applications. Here, we present a simple technique to heal mechanically strong polyacrylamide hydrogels formed via hydrophobic interactions between stearyl groups. A complete healing in the hydrogels was achieved by the treatment of the damaged areas with an aqueous solution of wormlike sodium dodecyl sulfate micelles. The micelles in the healing agent solubilize the hydrophobes in the cut surfaces, so that they easily find their partners in the other cut surface due to the hydrophobic interactions. Surfactant-induced healing produces high toughness (similar to 1 MPa) gels withstanding 150 kPa of stress at a deformation ratio of 1,100 %. The healing technique developed here is generally applicable to the physical gels formed by hydrophobic associations.