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    Biosourced polymeric cryogels for future biomedical applications with remarkable antimicrobial activities and tribological properties
    (Elsevier, 2024) Gurel, Cansu Meltem; Bozbeyoglu, Naime Nur; Yardimci, Berna Kavakcioglu; Sarkaya, Koray; Mutlu, Dogukan; Akincioglu, Sitki; Dogan, Nazime Mercan
    Cryogels, known as a subclass of hydrogels, are promising biomaterials to use in various biotechnological fields. In recent years, applications of antimicrobial hydrogels with improved antimicrobial activities, high biocompatibility, and physicochemical stability have attracted attention as an alternative to using antimicrobial drugs against microbial interactions that may threaten human health, which may even result in death. In this paper, we investigated in detail the biological activities and tribological performances of the previously characterized 2hydroxyethyl methacrylate (HEMA)-based amphiphilic cryogels (PHEMA-PLinaOH) (HC series) that contain hydroxylated polymeric linoleic acid (PLinaOH) as biosource. The biocompatibilities of these cryogels were examined against human embriyonic kidney (HEK293) cell line with MTT assay and acridine orange/ethidium bromide (AO/EB) dual staining. The antimicrobial activities of the materials were extensively investigated against Staphylococcus aureus ATCC 29213 and Pseudomonas aeruginosa PA01 besides four different strains of the yeast Saccharomyces cerevisiae BY4741 by using biofilms eradication, antibiofilm activity and colony forming unit assays. Additionally, the possible morphological changes in microbial cells were evaluated by taking FESEM images. The tribological performances of the cryogels were evaluated in terms of their applicability for future biomedical applications such as artificial articular cartilage or tissue scaffold. Our results showed that while the cryogels did not show significant inhibition on HEK293 cell viability and intensive live cell population was observed after AO/EB staining, they exerted remarkable antimicrobial activities against all studied bacterial and fungal strains. The morphological deformations including the decrease in EPS density and formation of holes were recorded for bacteria and yeast cells with FESEM images, respectively. Finally, it was determined that the increase in the fatty acid ratio contributes positively to tribological properties of the cryogels. All the results indicate that these polymeric cryogels might be considered potential biomaterials for future tissue-engineering studies.
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    Dielectric properties of CdSe quantum dots-loaded cryogel for potential future electronic applications
    (Elsevier Sci Ltd, 2020) Cadirci, Musa; Sarkaya, Koray; Alli, Abdulkadir
    Cryogels are an outstanding class of materials with special and functionalized physical properties in various fields and privileges for different industrial applications. Due to unique properties of quantum dots, properties of cryogels can be engineered by adding quantum dots in. In this study, both p(HEMA)-based cryogel and CdSe QDs synthesized and characterized, separately. Then, CdSe QDs were loaded into p(HEMA) cryogels by immersing cryogel into QDs solutions. FTIR-ATR, SEM and TGA characterizations were performed to ensure that CdSe QDs penetrate p(HEMA) cryogels effectively. Dielectric properties of CdSe QDs-loaded cryogel were investigated using Electrical Impedance Spectroscopy (EIS). Real and imaginary parts of dielectric constants were decreased significantly at low frequencies in QD-loaded cryogels. While real part of impedance was increased in CdSe QDs-loaded cryogel at low frequencies. In addition, at high frequencies, those parameters were observed to be same in both cases.
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    Electrical properties of CsPbX3 (X=Cl, Br) perovskite quantum dot/poly (HEMA) cryogel nanocomposites
    (Elsevier Science Sa, 2022) Bakay, Melahat Sevgül; Sarkaya, Koray; Çadırcı, Musa
    Quantum dot-filled polymer nanocomposites are recent of interest due to the improvement of the properties and possibility of use in diverse application areas. In this study, poly(HEMA) cryogels and CsPbCl3 and CsPbBr3 perovskite quantum dots were separately synthesized and then perovskite quantum dots/cryogel nanocomposites were formed for the first time. After comprehensive characterizations of the nanocomposites, the dielectric properties of those structures were studied using impedance spectroscopy. All characterization methods revealed the effective formation of the quantum dot/cryogel nanocomposites. The real part of the dielectric components of the nanocomposites decreased concerning the pure cryogel. For the CsPbCl3 quantum dots filled nanocomposites, the imaginary part of the dielectric component and the loss tangent parameter increased almost by the factors of similar to 1.8 and similar to 2.2, respectively. On the other hand, for the CsPbBr3 quantum dots filled cryogel, the imaginary part of the dielectric component and the loss tangent parameter values decreased by the factors of similar to 2.6 and similar to 2 respectively. The large dielectric losses in the case of CsPbCl3 quantum dot-based nanocomposite were attributed to the high existence of surface traps on the surface of the CsPbCl3 quantum dots.
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    Investigation of tribological properties of HEMA-based cryogels as potential articular cartilage biomaterials
    (Taylor & Francis Inc, 2022) Sarkaya, Koray; Akıncıoğlu, Gülşah; Akıncıoğlu, Sıtkı
    Tribology is one of the most important issues for the repair and regeneration of living tissues in the human body, as it deals with the wear, lubrication, and friction of interrelated surfaces. Hydrogels show potential as cartilage regeneration agents due to their biocompatibility and behave similarly to the lubricating mechanisms found in cartilage tissue. Cryogels, which are included in the class of hydrogels, are more stable than hydrogels in terms of mechanical strength, and references to the tribological properties of these polymers in the literature have been minimal so far. In this study, poly(HEMA-N-vinyl formamide) (poly(HEMA-NVF) and poly(HEMA-N-vinylpyrrolidone) (poly(HEMA-NVP) cryogels with improved hydrophilic properties were synthesized with pure poly(HEMA) cryogel. The swelling properties of HEMA-based cryogels were examined under the heading of various parameters, and their physicochemical characterizations were characterized via FTIR, SEM, mercury intrusion porosimetry, elemental analysis (EDX), and TGA methods. Before investigating tribological properties, a cytotoxicity test was performed for all cryogels. Then, in line with the study's primary purpose, the tribological properties of cryogels were examined. Abrasion tests were carried out on a pin-on-disc tester linked with ASTM G99-05 standard. According to the results, the friction coefficient of poly(HEMA-NVF) and poly(HEMA-NVP) cryogels is 21.62% and 10.51% higher than poly(HEMA) cryogel, respectively. In addition, the results of abrasion and 3D surface topography images prove that the poly(HEMA-NVP) cryogel wears less and its surface is less deformed than other cryogels.
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    A Novel Benzimidazole-Based Chemosensor for Fluorometric Determination of Zinc Ions
    (Springer/Plenum Publishers, 2021) Orhan, Ersin; Ergun, Ece; Sarkaya, Koray; Ergun, Umit
    A simple and novel Schiff base chemosensor (BMHM) based on benzimidazole was synthesized. In ethanol-water (1:1, v/v) medium on varying concentrations of Zn2+ chemosensor exhibited a strong and quick turn on fluorescence response. The Zn2+ recognition was based on the Chelation-enhanced fluorescence effect. The binding constant and limit of detection for BMHM-Zn2+ complexation were estimated to be 7.99 x 104 M-1 and 0.148 mu M, respectively. The extreme fluorescent enhancement caused by Zn2+ binding in chemosensor BMHM occurred at a pH range of 6-7. The practical use of chemosensor BMHM was tested by determination of Zn2+ in real water samples and comparing the results with the data obtained using high resolution inductively coupled plasma mass spectrometry.
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    One-step preparation of poly(NIPAM-pyrrole) electroconductive composite hydrogel and its dielectric properties
    (Wiley, 2021) Sarkaya, Koray; Yildirim, Mert; Alli, Abdulkadir
    Conductive polymers and hydrogels are two of the hot prospect polymer types that are used for new stimuli responsive materials. In this study, one-step preparation of electroconductive composite hydrogels containing polypyrrole (PPy) and N-isopropylacrylamide (NIPAM) using free radical polymerization technique was achieved with N,N-methylenebisacrylamide as a crosslinker and ammonium peroxy disulphate (APS) as initiator, in mixture of water/isopropyl alcohol. The equilibrium swelling degree of the poly(NIPAM)-pyrrole) electroconductive composite hydrogel was 9.88 g of H2O/g dry polymer. According to TGA results, the thermal stability of the prepared composite poly(NIPAM-PPy) conductive hydrogel (700 degrees C) hydrogel is higher than that of pure poly(NIPAM) hydrogel (600 degrees C). Furthermore, prepared samples were characterized by FTIR, and SEM analyzes. Later, the samples were pressured into pellets so that electrical impedance spectroscopy (EIS) measurements were taken between 10 and 10 MHz at room temperature. The dielectric constant value of composite poly(NIPAM-PPy) hydrogel at 10 Hz is almost 10 times higher than that of poly(NIPAM) hydrogel. Both samples' real and imaginary parts of dielectric constant decreased with increased frequency. Samples exhibited non-Debye relaxation since experimental data fit into dielectric model of Havriliak-Negami. Moreover, low frequency data yielded d.c. conductivity of the pure and composite samples as 3.74 x 10(-11) and 1.02 x 10(-8) S/cm, respectively. Real part of impedance at low frequencies also points out similar to 10(3) times lower resistance values at 10 Hz for composite poly(NIPAM-PPy) hydrogel. Therefore, EIS results support that electroconductive composite hydrogel fabrication was achieved using free radical polymerization technique.
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    Synthesis and characterization of cryogels of p(HEMA-N-vinylformamide) and p(HEMA-N-Vinylpyrrolidone) for chemical release behaviour
    (Springer, 2021) Sarkaya, Koray; Alli, Abdulkadir
    Macroporous polymeric gels has received great attention in many fields focused on biotechnological applications. In this study, two new HEMA-based cryogel columns were synthesized. To this end, poly(HEMA-VF) and poly(HEMA-NVP) cryogels were prepared by copolymerization of 2-Hydroxyethyl methacrylate (HEMA) with N-vinylformamide (VF) and N-vinylpyrrolidone (VP) in the presence of N,N-methylenebisacrylamide (as cross-linker), then polymerization initiated by ammonium persulfate (APS) and N,N,N ',N '-tetramethylenediamine (TEMED) with free-radical polymerizations method in cryogelation conditions, respectively. p(HEMA-VF) and p(HEMA-VP) cryogels contain a continuous polymeric matrix with interconnected pores of size 2-100 mu m. Swelling behavior for these cryogels in various solvents was investigated, wherein the characterization of the cryogels is conducted via by surface area measurement (BET), Fourier transforms infrared spectroscopy (FT-IR), elemental analysis, scanning electron microscopy (SEM), Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA). As drug model compounds, Methyl Red (MR), methylene blue (MB) and methylene green (MG) were loaded into prepared cryogels and the controlled release properties of cryogel columns were examined comparatively each other. It has been shown that approximately 90% of its release from the cryogels occurred within about 2 h. In addition, MB release from p(HEMA-VF) and p(HEMA-VP) cryogels was found to be around 80% over a similar period. The proposed cryogels can be regarded as controlled release system on future biomedical applications.