Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Fabrication of Colorimetric Ph Indicator Films by Electrospinning(Izmir Institute of Technology, 2022) Erez, Elif; Bayramoğlu, Beste; Eroğlu, Ahmet EminThe trend in the food packaging industry evolves towards innovative packaging materials as biosensors, which record the status of the product and can warn the consumer. The logic behind the colorimetric pH biosensor is that they provide the essential information about food visually by detecting change in pH. Anthocyanins are natural color pigments susceptible to pH change. Purple basil is rich in anthocyanins. In this study, ultrasound-assisted extraction was used for the extraction of dry purple basil. The processing conditions were optimized by response surface methodology (RSM) in terms of the total monomeric anthocyanin content and the increase in green intensity with pH. Electrospinning is a nanofiber fabrication operation used to encapsulate sensitive bioactive compounds for the production of intelligent sensing system. Polycaprolactone (PCL) films incorporating different purple basil extract (PBE) concentrations were fabricated by electrospinning procedure for the usage of colorimetric pH-indicator films as intelligent packaging. The most beadles and uniform nanofibrous mats were obtained when the spinning conditions were V=20 kV and Q=0.4 mL h-1for 10% (w v-1) PCLsolutions containing 0.4% and 0.6% (w v-1) PBE. The average fiber diameters in these films were 178.59±52.92 nm and 235.39±92.46 nm, respectively. The films gave promising results with regards to their use as colorimetric pH-indicator films. The time required to observe a visible color change (ΔE) in these films was only 4-5 s. The ΔE values between all successive pH’s were higher than 2, which is detectable by an inexperienced observer. Keywords: Anthocyanin, Purple Basil, Ultrasound-Assisted Extraction, Response Surface Methodology (RSM), Electrospinning, Colorimetric pH-indicator Films.Master Thesis A Novel Approach for Fabrication of Free-Standing Conductive Network: Pedot: Pss Based Bendable Chemo and Photoresistor(Izmir Institute of Technology, 2019) Mutlu, Mustafa Umut; Yıldız, Ümit Hakan; Demir, Mustafa MuammerElectrospinning is a simple and versatile technique for the fabrication of polymeric nanofibrous substrate with high surface to volume ratio. Besides high surface to volume ratio, their dimensional stability and flexibility make it a perfect candidate for conductive network for various sensor applications. Free-Standing conductive network can be fabricated by deposition of PEDOT:PSS or MWCNT through bendable nanofibrous substrate. As a simple example for sensor applications, the moving object has been sensed through the electrostatic interactions between fibers and object. The sensing range has been found to be 1-5 cm above the surface of fabric. By the controlled combination of conductive polymers and electrospun polymer nanofibers effective device miniaturization has been provided without loss of performance. The noncontact motion sensor platform has unique flexibility and light weight holding a potential for wearable sensor technology. For another application as a wearable electronics, the controlled combination of conductive network and light-matter interaction provides opportunities to fabricate photo-resistor exhibits broad band response 400 to 1600 nm that holding promises for ultra-thin sensors used in telecommunication. As a final example, we report the effect of gold and iron oxide nanoparticles on the selectivity and sensitivity of MWCNT or PEDOT:PSS based chemiresistor responsive to VOCs. The interplay between conductive layer by gold and iron oxide nanoparticles resulted a significant conductivity improvement that affecting selectivity which is governed by the interaction between electron-donating VOCs and NP doped conductive layer due to variation in charge carrier densities in conductive layer lattice.Master Thesis Polymer Based Extracellular Matrix Mimetics for 3d Cell Culture(Izmir Institute of Technology, 2018) Türker, Esra; Arslan Yıldız, AhuTissue engineering combines engineering principles and knowledge of life sciences to improve biological substituents. Three dimensional (3D) supporting structures, namely scaffolds obtained from biomaterials to mimic extracellular matrix (ECM) that provides suitable microenvironment for cell proliferation, migration and differentiation. In this study, poly (L-lactide-co-ε-caprolactone) (PLLCL) and collagen type I was used to fabricate scaffold by electrospinning method. In literature, collagen was often dissolved in toxic and harmful solvents that creates the major problem for cell culture applications. To overcome this problem “co-spinning” methodology is utilized for the formation of non-toxic collagen-based ECM mimetic scaffold. Collagen mixed with water-soluble carrier materials which is either polyvinylpyrrolidone (PVP) or polyvinyl alcohol (PVA) and co-electrospinning is carried out with PLLCL. Fabricated scaffolds were immersed into water to remove co-spinning agent; PVA or PVP, so only PLLCL/Collagen remained. PLLCL has homogeneous fibers in a diameter of 1.312 ± 0.22μm. The contact angle of PLLCL (136.6° ± 2.6) proved hydrophobic behavior of PLLCL material. The contact angle of the scaffold decreased up to 86.7° ± 0.1 confirming that hydrophobic behavior is decreased with the addition of collagen. Also, collagen-containing scaffolds were saturated at lower amount of protein than PLLCL, PLLCL/PVA and PLLCL/PVP scaffolds. Cytotoxicity analysis of scaffolds showed that PVA containing scaffolds had lower viability than PVP containing scaffolds; so most of the cell studies were carried out with PLLCL/ Collagen scaffolds fabricated by PVP cospinning. Cell proliferation on PLLCL/Collagen scaffolds found to be more favorable than PLLCL and PLLCL/PVP scaffolds.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.Master Thesis Preparation of Electrospun Composite Fibers Based on Ps-pi-ps/Cdsxse1-x Nanoparticles(Izmir Institute of Technology, 2011) Aşkın, Görkem; Demir, Mustafa Muammer; Özçelik, SerdarPolymeric fibrous films were prepared based on polystyrene-b-polyisoprene-bpolystyrene triblock copolymer (SIS) and CdSxSe1-x nanoparticles by electrospinning process. SIS with 14 wt % Styrene (14% PS-SIS) and 22 wt % Styrene (22% PS-SIS) triblock copolymers were employed. Both of them undergo microphase separation. While the former shows cylinder-like morphology, the latter exhibits the lamellae one. CdSxSe1-x partciles were stabilized by two different surfactant molecules: i) n-trioctylphosphine oxide (TOPO) and ii) oleic acid (OA). When the particles were blended with 22% PS-SIS, particles capped with TOPO preferentially filled to PS domain whereas particles capped with OA loaded into the PI domain. Composite electrospun fibers were prepared with a diameter of 1.5 mm on average. Electrospinning parameters (potential difference, solution concentration, flow rate) were investigated on fiber morphology. The films are colorless under day light and have strong green emission under UV light.Master Thesis Investigation on Emission Features of Ttbc Aggregates in Pva Fiber Mats by Electrospinning(Izmir Institute of Technology, 2010) Özen, Bengisu; Demir, Mustafa Muammer1,1’,3,3’-tetraethyl-5,5’,6,6’ -tetrachlorobenzimidazolocarbocyanine (TTBC) is a frequently used cyanine dye that undergoes two different types of molecular aggregate (J and H-type). Dye molecules, in general, come into aggregation in ionic solutions and solid surfaces without control over the type and orientation of the resulting aggregate. In this research, we focused on electrospinning of aqueous poly(vinyl alcohol) (PVA)/TTBC solutions and investigated whether the aggregate formation could be controlled by solution and instrumental parameters of this process. Initially, TTBC was molecularly dispersed in aqueous PVA solution with a weight fraction of 0.001- 0.65 % and the precursor solution was subjected to electrospinning under electrical field ranging from 0.95-1.81 kV/cm. A stationary horizontal electrospinning set-up was used including two parallel-positioned metal strips as counter electrode. Both randomlydeposited and uniaxially aligned fibers were achieved. For the reason of comparison, reference films were prepared by spin-coating and film casting. Photoluminescence and polarized FTIR spectroscopy techniques were employed to examine spectral properties of the fibers. While H- and J-type aggregates coexist within spin-coated films and only J-aggregates exist within cast films, only H-type aggregates were observed within the fibers regardless of their alignment. A strong polarized emission was obtained from the unaxially aligned fibers due to the orientation of H-aggregates along the fibers. Consequently, electrospinning was found to be an alternative method to bring individually dispersed dye molecules into oriented H-type aggregates within submicron diameter fibers. Similar experimentation was also applied to TTBC/PS and Pyrene/Polystyrene(PS) systems to investigate aggregation behavior of dye molecules. TTBC exhibited similar behavior in PS/Dimethylformamide (DMF) system observed in PVA/H2O system. However, electrospinning has no remarkable influence on aggregation of pyrene in excimers. It slightly disassemble excimer structure.