Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis The effects of photobioreactor average shear rate on chitin nanofiber production characteristics of the diatom cyclotella cryptica(01. Izmir Institute of Technology, 2024) Ağaoğlu, Cemre; Özkan, Altan; Yılmaz, Benay UzerKitin biyomedikal uygulamalar açsıından çok yüksek potansiyelli doğal bir biyopolimerdir. Halihazırda, ticari kitin üretiminin çoğunluğu deniz ürünleri endüstrisi tarafından işlenen kabuklu deniz canlılarının atıkları kullanılarak yapılmaktadır. Diatom cinslerinden Cyclotella ve Thalassiosira kitin nanofiberlerini direkt olarak hücre duvarları üzerinde bulunan fultoportula adı verilen açıklıklardan dış ortama sentezleyebildikleri için kitin hasatı için sert ektraksiyon koşulları uygulanması gerekliliğini ortadan kaldırmaktadır. Bu çalışmada, Cyclotella cryptica CCMP 333 hücrelerinin kitin üretkenliğinin kabarcık kolon fotobiyoreaktörün havalandırma hızındaki farklılıktan kaynaklı maruz kaldıkları hidrolik kesme kuvvetinden nasıl etkilendiği iki aşamalı bir kültivasyon protokolü (birinci aşamada 0,020 mM silikon takviyesini müteakiben ikinci aşamada 1,80 mM silikon takviyesi) uygulanarak araştırılmıştır. Hücrelerin silikon starvasyonuna maruz bırakıldığı birinci aşamada havalandırma hızı 0,5 vvm olarak sabit tutulmuştur, 1,80 mM silikon takviyesinin ardından havalandırma hızlarının 0,25 vvm, 1 vvm ve 1,5 vvm olarak değiştirildiği 3 ayrı fotobiyoreaktör düzeneği kurulmuştur. Bu çalışma kapsamında ulaşılan maksimum kitin üretkenliği 852 mg/L olmuştur ve bu konsantrasyona silikon starvasyon aşamasında 0,5 vvm ile havalandırılan ve ardından 1,8 mM silikon takviyesi ile eş zamanlı olarak havalandırma hızının 1 vvm olarak değiştirildiği deney grubunda saptanmıştır. Cyclotella cryptica CCMP 333 hücre süspansiyonlarında serbest olarak ve hücreye bağlı olarak buluna kitin konsantrasyonları durağan faz sürecinde toplanan numuneler kullanılarak belirlenmiştir. Hücreye bağlı kitin nanofiberlerin konsantrasyonu ile havalandırma akış hızları arasında ters orantı olduğuna dair elde edilen sonuçlar büyük ölçekli diatom üretim tesislerinde hasatlanacak kitin nanofiberi miktarının maksimizasyonu için geliştirilecek stratejilere katkı sağlayacaktır.Master Thesis Recovery of Lithium From Aqueous System Using Manganese Oxide Adsorbent With Developed Electrospun Mat Substrate(01. Izmir Institute of Technology, 2023) Akgün, Berk; Ebil, Özgenç; Demir, Mustafa MuammerLithium is used in many fields due to its high energy density and unique electrochemical properties. Recently, there has been a strong increase in demand for lithium, so the extraction of lithium from natural water resources has become a remarkable research topic. One of the most effective methods of separating lithium from natural water sources is adsorption using lithium ion-sieve adsorbents. However, the powdered nature of the adsorbents makes them challenging to process and less recyclable. Recent studies have focused on developing adsorbents using different polymeric materials as substrates or binders. In the thesis, as a new approach, flexible and free-standing polyurethane electrospun mat substrates were produced and combined with λ-MnO2 to extract lithium from aqueous systems, and their lithium removal performance was investigated. After the fabricated mats and λ-MnO2 powder were characterized, the deposition process was performed, and filtration studies were carried out in synthetic lithium solution. Optimum conditions for lithium removal were found as an adsorbent amount of 200 mg, and 200 ppm initial [Li+], and pH 12. In addition, lithium removal performances have been improved by stacking mats and multi-stage filtration processes. Lithium removal reached 76.6% when a 400 ppm lithium solution and an 8-step filtration were used. Lithium removal experiments were performed with salt-lake brine containing high concentrations of various ions and showed that these ions reduced the lithium removal. In the study, PU electrospun mats for λ-MnO2 powder were found to be a promising substrate for lithium removal from aqueous systems.Master Thesis Improving Mechanical Properties of Adhesive Joints in Carbon Fiber Reinforced Polymer Composites by Incorporation of Graphene Added Electrospun Polymeric Nanofibers(01. Izmir Institute of Technology, 2023) Yeke, Melisa; Tanoğlu, MetinSince composites joined with mechanical fasteners cause severe delamination damage, stress concentration in the joint area, and weight increase, joining composite materials with innovative methods have recently gained more importance. These joining methods prevent delamination damage, provide a uniform distribution of stress, and do not cause considerable weight increases. However, modifying the surface of composite parts joined by innovative methods is critical. In this study, the bonding surface was modified by coating carbon/epoxy prepregs with electrospun nanofibers with 10% wt/v ratio of PA 66 and 1%, 2% and 3% wt/v ratio of rGO added. Composite parts were joined in the hot press by the secondary bonding method using 3 plies of FM 300K film adhesive. The morphological structure of nanofibers and the dispersion of rGO were analyzed by SEM. The thermal properties of nanofibers were analyzed by DSC. The contact angle measurement device was used to determine the hydrophilic and hydrophobic properties of the unmodified prepreg and nanofiber-modified prepreg surface. The most hydrophilic surface was observed on the nanofiber-coated surface with 2% rGO added. Single Lap Joints (SLJ), and Charpy Impact tests were performed to examine the mechanical properties of modified and unmodified composite plates. According to the SLJ and Charpy Impact results, an improvement of 17.89% and 30.59% was observed in carbon/epoxy composite plates whose surface was modified with 2% rGO, respectively.Master Thesis Improving Joining Performance of Composites by Electro-Spinning of Nano Fibers(01. Izmir Institute of Technology, 2021) Esenoğlu, Gözde; Tanoğlu, MetinMechanical joints traditionally used in composite materials (screws, rivets, etc.) not only increase weight but also act as a stress collector, causing serious delamination problems. At the same time, the development of alternative joining techniques has become an important issue in the composite industry due to its sensitivity to corrosion, electromagnetic properties/radar absorption properties, labor cost and adverse effects on the manufacturing process. In this master's thesis, the effects on the mechanical properties of two different prepreg composites (UD and woven) coated with polyamide 66 (PA 66) nanofibers in the joint region were investigated. In addition, the fiber structures of the produced PA66 nanofibers were investigated. The produced nanofibers were directly coated on the bond zone layer (top surface) of the carbon prepregs. The reference and nanofiber doped prepregs were cured by the hot press method, and then they were combined with the secondary bonding method using FM300K film adhesive in the hot press. Tensile, compression, bending, shear, Charpy-impact and double cantilever beam (DCB) tests were performed on the produced samples. The effect of homogeneity and areal weight density (AWD) of PA66 nanofibers on mechanical performance was investigated. The morphology and post-test deformations of the nanofibers were investigated by scanning electron microscopy (SEM). The thermal properties of PA66 nanofibers were investigated by the differential scanning calorimetry (DSC) method. By comparing the SEM images and the lap shear test results, the most efficient parameters for the mechanical performance of the composites were determined. The results showed that PA66 nanofibers produced with a 10% wt solution ratio and 10 min coating time were the most efficient on composites. The addition of PA66 nanofibers to the junction region with the electro-spinning technique has been proven to increase the junction region performance of the materials and outputs have been obtained.Master Thesis Bilayer Chitosan/Zein Based Nanofibers for Antimicrobial Wound Dressing Application(01. Izmir Institute of Technology, 2021) İskeçman, Nilsu; Tıhmınlıoğlu, FundaNowadays, modern functional wound dressings have become prominence due to their biocompatible, biodegradable, and non-toxic nature and ability to mimic ECM of skin. To enhance their mechanical and prolonged cumulative release of drugs in media, environmentally friendly inorganic nanofillers are preferred. Recently, halloysite nanotubes (HNTs) which is a new class of inorganic filler are using to improve mechanical properties and thanks to their tubular structure various agents encapsulated into these tubes to make drug release more controlled. In this thesis, it was aimed to fabricate and characterize bilayer wound dressing by using Zein-Vancomycin loaded HNTs nanofibers as upper layer to mimic ECM of skin and provide antibacterial protection and chitosan sponge as bottom layer to absorb the excess exudates of wound, provide gas transmission and facilitate the migration of inflammatory and fibroblast cells into the healing wounds. The morphology of nanofibers and encapsulation efficiency of HNTs are optimized to achieve similar homogeneous fiber structure with skin tissue and controlled release of Vancomycin drug. Chemical interaction between Vancomycin-HNT and Zein-HNT were characterized by FT-IR. The surface charge differences of HNTs by encapsulating drug into tubes was determined by zeta potential analysis. The weight loss percentage of nanofiber with the addition of HNTs into zein media was characterized by using thermogravimetric analysis (TGA). Bilayer sponges were characterized by SEM, FT-IR, porosity, mechanical properties, contact angle, water vapor transmission rate, swelling, degradation, cumulative drug release and their kinetics and antimicrobial activity analyzes. The diameter of drug loaded HNT-Zein nanofibers were found 202,7±0,05–225,2±0,06 nm which is in the range of native skin collagen fibril (50-500 nm) than can mimic ECM. The water vapor permeability of the wound dressings is between 2833 and 2490 g/m2day which is found in the appropriate range for wound healing. Bilayer dressings reached 78% cumulative release at the end of 14 days and the release medium showed antimicrobial activity against E. coli and for S. epidermidis. In conclusion, the developed drug-loaded bilayer mat has been found as a potential candidate for wound dressings applications to treat the chronic infections.Master Thesis Fabrication of Polymer Nanofiber / Poly (3,4 Ethylene Dioxythiophene) / Metal Particle Hybrid Composite for Volatile Organic Compound Sensing Applications(Izmir Institute of Technology, 2020) Acar, İrem; Yıldız, Ümit HakanThis study aims to produce polymer nanofiber / poly (3, 4 ethylene dioxythiophene) / metal particle hybrid composite as a bioelectronic interface for the detection of volatile organic compounds in human breath. The sensor platform consists of two layers: polymeric nanofiber structure and conductive layer. Polyurethane (PU), polycaprolactone (PCL) and poly L-lactide-co-?-caprolactone (PLLCL) were selected to form polymeric nanofibers with electrospinning. For electrospinning process, solutions of polyurethane (PU) (25wt%) in DMF, polycaprolactone (PCL) (20wt%) in DCM (4) -DMF (1) and poly L-lactide-co-?-caprolactone (PLLCL) (10wt%) in DCM (9) -DMF (1) are prepared. PU, PCL and PLLCL polymer solutions are subjected to 25 kV, 29kV and 25 kV electrical potential, respectively, to produce electrospinning fibers. Poly(3,4-ethylenedioxythiophene) (PEDOT) and multi-walled carbon nanotubes (MWCNTs) are used to produce conductive layers on PU, PCL and PLLCL polymer nanofibers. The produced sensor platforms are tested by the electrochemical station, which records the electrical current change over time. The sensing mechanism is assumed to be the adsorption of VOCs to the conductive PEDOT and CNT layer, thus blocking the electron current on the PEDOT and CNT network and causing resistance change. More clearly; swelling of the polymer structure in the sensor causes destruction in the upper layer and micro-dimensional cracks in the PEDOT and CNT network, increasing resistance to electron flow and decreasing current. Organic volatile compounds (acetone, toluene, ethanol, isopene etc.) are detected from ppm to ppb range and reproducible and reliable responses are recorded.Master Thesis Glucose Biosensor Applicatiın of Electrospun Polyvinyl Alacohol (pva) Fibers(Izmir Institute of Technology, 2016) Berber, Emine; Demir, Mustafa Muammer; Yıldız, Ümit HakanElectrospinning is a simple and versatile technique for the fabrication of polymeric nanofibrous membranes with high surface to volume ratio. Besides the large surface area of the fibrous membranes, their dimensional stability and flexibility allows the immobilization of biomolecules on to the nanofiber surfaces. Therefore, electrospun nanofibers have been extensively used in enzyme electrodes. This thesis examines the glucose biosensor application of electrospun polyvinyl alcohol (PVA) nanofibers – carbon nanotube (CNT) nanocomposite membranes. By manipulating the structural design and the composition of the nanocomposite membranes, glucose sensing efficiency of the five different enzyme electrodes a) Glucose oxidase (GOx) immobilized PVA electrospun electrode, b) Glucose oxidase (GOx) immobilized PVA electrospun electrode containing multi-walled carbon nanotube (MWCNT), c) Glucose oxidase (GOx) immobilized PVA electrospun electrode containing Poly(diallyldimethylammonium chloride) (PDDA) functionalized multi-walled carbon nanotube (MWCNT) d) Glucose oxidase (GOx) immobilized PVA electrospun electrode containing Poly(diallyldimethylammonium chloride) (PDDA) functionalized single-walled carbon nanotube (SWCNT), e) Interfacially cross-linked PVA electrospun electrode containing Poly(diallyldimethylammonium chloride) (PDDA) functionalized multi-walled carbon nanotube (MWCNT) were comperatively studied. PVA electrospun nanofibers were fabricated by using electrospinning technique. Morphology and average diameter of the fibers were characterized by using Scanning Electron Microscopy (SEM). Average diameter for the neat PVA electrospun fibers were 115 nm. Carbon nanotubes were oxidatively functionalized by acid treatment and addition of functional groups after acid treatment was proved by using Raman Spectroscopy. Glucose sensing activities of the electrodes were amperometrically measured at an applied voltage -0.5 V (vs. Ag/AgCl) in 0.1M phosphate buffer solution (PBS pH 7). Glucose detection sensitivies of the electrodes were calculated as 19.6, 27.7, 67.5, 44.4, 4.0 μA mM-1cm-2 respectively.Master Thesis Development of Natural Compound-Loaded Nanofibers by Electrospinning(Izmir Institute of Technology, 2010) Balta, Ali Bora; Bayraktar, OğuzIn this study, the crude silk which is obtained from silkworm was turned into a silk solution after a serial procedure. Then, regenerated silk (foam) was obtained. The regenerated silk was dissolved in formic acid and polymer solution was prepared. After, nanofibers were produced by electrospinning. On the other hand, the content and antimicrobial activities of some plants were analyzed. Then all three forms of silk was absorbed with the olive leaf extract and extract desorption tests were done. As the first step of the study, the analyses of extracts which were obtained from four different plants were done. For this, total phenolic content and antioxidant capacity were found. In addition, minimum inhibition concentration (MIC) test and disc diffusion test were made for all extracts to Escherichia coli, Staphylococcus epidermidis, Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeruginosa bacteria and Candida albicans fungi in order to determine their antimicrobial activity. While producing nanofibers from silk polymer with electrospinning method, different parameters such as concentration, voltage and distance were examined. Morphological characterization of nanofibers was done by scanning electron microscope (SEM). According to the results, the nanofiber with an optimum value which has a suitable diameter and structure was selected. With this nanofiber, the absorption and desorption tests of natural compound were made. The results were obtained by High pressure liquid chromatography (HPLC). Same adsorption and desorption tests were done also with the microfiber silk and regenerated silk (foam). As a result, it was shown by the controlled experiments that nanofibers were better for adsorption and desorption of natural compound when compared to microfiber silk and regenerated silk. In conclusion, nano-sized silk fibroin structures can be adsorbed with natural compounds in order to gain functionality. Using this kind of biofunctional products as medical textile and wound dressing material will be more advantageous when compared to current wound dressing materials.