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    ?-Amylase Immobilization on P(HEMA-co-PEGMA) Hydrogels: Preparation, Characterization, and Catalytic Investigation
    (Wiley-V C H Verlag Gmbh, 2021) Dogan, Demet; Ulu, Ahmet; Sel, Evren; Koytepe, Suleyman; Ates, Burhan
    The aims of this study are to synthesize and characterize poly (2-hydroxyethyl methacrylate-co-poly (ethylene glycol) methacrylate) (P(HEMA-co-PEG500MA)) structures containing polyethylene glycol (PEG) side groups and to investigate their possible use in alpha-amylase immobilization. For this purpose, P(HEMA-co-PEG500MA) copolymer structures are synthesized by using different monomer ratios. P(HEMA-co-PEG500MA) copolymer structures are confirmed by Fourier transform infrared spectroscopy (FTIR), and elemental analysis techniques. In addition, thermal, and morphological properties of the copolymers are investigated by thermal gravimetric analysis/differential scanning calorimetry, and scanning electron microscopy (SEM). Afterward, alpha-amylase from Aspergillus oryzae is immobilized on synthesized copolymer support by using physical interactions. The success of immobilization is elucidated via FTIR, SEM, and energy dispersive X-ray spectroscopy (EDX) methods. In addition, the influences of temperature, pH, storage time, and repeated uses on the activity of free and immobilized alpha-amylase are investigated. According to the outcomes, the immobilized alpha-amylase possesses a better pH and thermal resistance than the free one. Additionally, the immobilized alpha-amylase maintains about 53% of its original activity after eight reuses and it exhibits about 50% relative activity after 28 days of storage. In conclusion, the immobilized alpha-amylase can be utilized as a potential efficient catalyst to produce maltose from the hydrolysis of starch.
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    Chemistry and engineering of brush type polymers: Perspective towards tissue engineering
    (Elsevier, 2022) Acari, Idil Karaca; Sel, Evren; Ozcan, Imren; Ates, Burhan; Koytepe, Sueleyman; Thakur, Vijay Kumar
    In tissue engineering, it is imperative to control the behaviour of cells/stem cells, such as adhesion, proliferation, propagation, motility, and differentiation for tissue regeneration. Surfaces that allow cells to behave in this way are critical as support materials in tissue engineering. Among these surfaces, brush-type polymers have an important potential for tissue engineering and biomedical applications. Brush structure and length, end groups, bonding densities, hydrophilicity, surface energy, structural flexibility, thermal stability, surface chemical reactivity, rheological and tribological properties, electron and energy transfer ability, cell binding and absorption abilities for various biological molecules of brush-type polymers were increased its importance in tissue engineering applications. In addition, thanks to these functional properties and adjustable surface properties, brush type polymers are used in different high-tech applications such as electronics, sensors, anti-fouling, catalysis, purification and energy etc. This review comprehensively highlights the use of brush-type polymers in tissue engineering applications. Considering the superior properties of brush-type polymer structures, it is believed that in the future, it will be an effective tool in structure designs containing many different biomolecules (enzymes, proteins, etc.) in the field of tissue engineering.
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    Comparative study of catalase immobilization via adsorption on P(MMA-co-PEG500MA) structures as an effective polymer support
    (Springer, 2021) Sel, Evren; Ulu, Ahmet; Ates, Burhan; Koytepe, Suleyman
    In this study, poly[methyl methacrylate-co-poly(ethylene glycol) methacrylate] (P(MMA-co-PEG500MA)) copolymers were used for catalase (CAT) immobilization. Firstly, P(MMA-co-PEG500MA) copolymers were synthesized by using different amount of methyl methacrylate (MMA) and poly(ethylene glycol) methacrylate (PEG500MA) monomers. The synthesized copolymers were characterized by different analysis techniques. Afterward, CAT enzyme was immobilized via physical adsorption method onto the P(MMA-co-PEG500MA) copolymers. P3 sample containing 1:1 (PEG500MA:MMA) monomer molar ratio was selected as model support because of exhibiting optimum surface porosity and thermal stability. A high immobilization yield (76%) was achieved under optimized conditions. The immobilized enzyme displayed improved tolerance towards pH and temperature changes. After immobilization, the optimum pH shifted from 7.5 to 7.0, whereas the optimum temperature remained unchanged at 35 degrees C. Immobilized enzyme showed good reuse potential and excellent storage stability. After 10 consecutive uses, immobilized enzyme maintained about 51.0% of its initial activity. Furthermore, free enzyme completely lost its initial activity after 4 weeks, while immobilized enzyme maintained approximately 65% of the initial activity at 25 degrees C. Approximately twofold decrease in Km was obtained which means that the affinity of enzyme to the substrate improved after immobilization. Finally, it can be concluded that the prepared P(MMA-co-PEG500MA) copolymer structure can be an ideal matrix for CAT immobilization.
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    Polietilen glikol yan zincirli poli(metil metakrilat) yapılarının sentezi, karakterizasyonu ve uygulama alanlarının belirlenmesi
    (İnönü Üniversitesi, 2019) Sel, Evren
    Bu çalışmanın amacı özelikle biyomedikal uygulamalarda kullanım potansiyeline sahip polietilen glikol yan grupları içeren poli(metil metakrilat) yapılarının sentezi ve karakterizasyonudur. Bu polimer yapıların enzim immobilizasyonu, biyouyumlu polimerik yüzeylerin eldesi ve biyosensör uygulamaları hedeflenmiştir. Bu amaç dahilinde homo ve kopolimer yapısında, üzerinde farklı uzunluklarda polietilen glikol grupları içeren fırça tipi polimerler sentezlenmiştir. Elde edilen homo ve kopolimerler elementel analiz ve FTIR teknikleri ile kararkterize edilmişlerdir. Polimerlerin termal özellikleri TGA ve DSC termogramları ile belirlenmiştir. Sentezlenen polimerlerin morfolojik özellikleri SEM analizleri ile tespit edilmiştir. Ayrıca sentezlenen polimerlerin ilaç taşıyıcı sistem, antibakteriyel polimerik film, enzim immobilizasyon matriksi gibi biyomedikal uygulamalarda kullanılabilirliği tespit edilmiştir. Sonuç olarak sentezlenen homo ve kopolimerler yaklaşık 250°C gibi bir sıcaklığa kadar dayanabilmekte ve Tg değerleri yaklaşık 114°C ile 75°C arasında değişmektedir. Bu polimerler katalaz enzimi için uygun bir enzim taşıyıcı matrikstir. Ayrıca onların etkili polar fırça yapısı, polar yapılı antibakteriyel moleküllerin taşınması için uygundur.
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    Recent Progress and Perspectives on Polyurethane Membranes in the Development of Gas Sensors
    (Taylor & Francis Inc, 2021) Aksoy, Busra; Sel, Evren; Kuyumcu Savan, Ebru; Ates, Burhan; Koytepe, Suleyman
    In today's technology, gas sensors are of great importance in areas such as assessing environmental impacts, monitoring gas production facilities, measuring natural gas, controlling mines and gas leaks. Improving sensor sensitivity and decreasing the determination time is among the subjects that are continuously investigated. The use of polymeric membranes to make such improvements is common practice in the gas sensor field. By the development of polymeric membrane-based gas sensors and increasing the measurement sensitivity, accurate, sensitive, precise and fast measurements of toxic gases, volatile organic gases, and trace gases have been possible. Therefore, polyurethane membranes have been promising in the development of next-generation gas sensors based on membrane diffusion to ensure real-time and continuous monitoring of gases in industry and academic studies. This study aims to evaluate, compare and discuss the recent developments in the use of polyurethane membranes in existing gas detection technologies with chemical, electrical and optical measurement methods. In these measurement methods, polyurethane structures act as a selectively permeable membrane, an ideal matrix material for conductive additives or a suitable film structure for coating the conductive polymeric films. Conductive additives or conductive film structures for gas sensors play an important role in the detection of the gas structure with the change in electrical properties during the passage of gas molecules. This review has focused on important properties such as selectivity, detection time and measurement sensitivity concerning gas detection technology containing polyurethane, which has been used so far.
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    Simultaneous Electrochemical Detection of Estradiol and Testosterone Using Nickel Ferrite Oxide Doped Mesoporous Carbon Nanocomposite Modified Sensor
    (Electrochemical Soc Inc, 2020) Tanrikut, Emrullah; Ozcan, Imren; Sel, Evren; Koytepe, Sueleyman; Savan, Ebru Kuyumcu
    Estradiol levels in women are related to lung, uterine (endometrial), ovarian and breast cancers, although the exact mechanism of cancer development is not fully understood. A new cost-effective sensor was fabricated by incorporating conductive NiFe2O4 metal oxide into the electrochemical sensitive platform of mesoporous carbon (MC) derived from cotton to measure estradiol determination by electrochemical methods. A new modified GCE/NiFe2O4-MC electrode, which exhibits electrocatalytic activities, was created by dropping NiFe2O4-MC onto the glassy carbon electrode (GCE) surface using the drop casting technique to detect the electroactive estradiol molecule. Estradiol was determined electrochemically by using the square wave voltammetry technique with a detection limit of 6.88 nM in 20.0-566 nM linear range in phosphate buffer solution at pH 7.4 with this novel modified GCE/NiFe2O4-MC electrode, that has the best electron transfer rate. The simultaneous determination of estradiol in the presence of testosterone was successfully performed in 0.1 M tetrabutylammonium tetrafluoroborate supportive electrolyte solution prepared in acetonitrile, an anhydrous medium. Real sample applications were carried out to prove the applicability and precision of the novelty-produced electrode. The amount of estradiol in tablet samples was obtained satisfactorily with high recovery values by standard addition method. (C) 2020 The Electrochemical Society (ECS). Published on behalf of ECS by IOP Publishing Limited.