Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Preparation and Characterization of Poly-L Lactide-Natural Silica Composites(2023) Şirvanlıoğlu, Berna; Tıhmınlıoğlu, FundaTissue engineering research has been primarily focused on the development of customizable 3D scaffolds capable of promoting natural tissue regeneration while providing robust structural support. Synthetic polymer-based composites have garnered significant attention in recent years for biocompatibility and biodegradability, particularly in hard tissue engineering. In this study, we have chosen to combine the synthetic polymer PLA with natural silica as Diatomaceous earth for creating a customizable biomaterial tailored for bone tissue engineering applications. To create the PLA-Diatom composites, we employed melt mixing and hot-press methods, using two different types of diatoms: calcinated and raw diatoms. To enhance the compatibility of PLA, PEG and PEG/POSS were introduced as plasticizers/compatibilizers. Various concentrations of these plasticizers and reinforcing agents were meticulously applied to the PLA matrix to fine-tune the properties of the PLA biomaterial. Our comprehensive characterization involved SEM for morphology, mechanical testing, rheological analysis, AFM for roughness, contact angle analysis for surface wettability, swelling property, and FTIR for chemical structure. Our findings revealed that 3% diatom addition into PLA significantly improved tensile strength (32,72±0,27 for PLA and 51,51±4,15 for calcinated to 55,33±0,97 MPa for raw diatom), slight decrease in modulus (2277±45,65 for PLA to 2183,11 MPa for calcinated and 2246,43±24,19 for raw diatom), and reduced strain with higher diatom concentrations. Rheological analysis indicated a shift towards more liquid-like behaviour in PLA-Diatom composites, further enhanced by plasticizers, ensuring stable viscosities. Surface roughness increased with pure and plasticized PLA with diatom application. Surface wettability and water uptake capacity improved significantly compared to pure PLAMaster Thesis Manufacturing of Starch-Based Bioplastic From Waste Potato Starch by Extrusion and Energy Analysis of the Production(2023) Tıhmınlıoğlu, Funda; Gökyıldız, Yasemin; Alsoy Altınkaya, Sacide; Altınkaya, Sacide; Tıhmınlıoğlu, FundaPlastic materials are an essential part of our daily lives and annual plastic production is higher than 380 million tons with a 4% annual increasing rate. Since the 1950s, 8.3 billion tons of plastic have been produced, 9% of these plastics have been recycled, 12% have been incinerated and the rest 79% have been dumped to landfills. Therefore, the development of biodegradable polymers obtained from renewable raw materials has become a priority to reduce the environmental impact and dependency on fossil resources. Thermoplastic starch (TPS) is a starch-based bioplastic obtained by the disruption of the starch granules with thermal and mechanical forces in the presence of plasticizer. In this thesis, production of TPS from residual potato starch by extrusion was investigated. The extrusion trials were conducted in a single-screw extruder. Glycerol was selected as plasticizer and added to starch with 20, 30 and 40 wt.%. Extrusion temperature profiles were 50-90oC, 60-90oC and 70-90oC. The pretreatment conditions for the residual starch were drying to 10 wt.% moisture content and sieving with 131μm mesh size. Specific mechanical energy values ranged between 7.89 kWhkg-1 and 43.27 kWhkg-1. The optimum product formation was selected according to processability with lower energy consumption and mechanical properties as TPS303 which has 30 wt.% glycerol content and processed between 70-90oC. Specific mechanical energy consumption for TPS303 was found to be 23.78 kWhkg-1. The mechanical properties of TPS303 were 4.48 MPa tensile strength, 59.74 MPa Young's modulus and 57.33% elongation at break. Consequently, residual potato starch was found to be a promising raw material for thermoplastic starch production with proper pretreatment.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 Surface Modification of Chitosan Films/Meshes for Biomaterial Applications(Izmir Institute of Technology, 2019) Işıklı, Berçin; Tıhmınlıoğlu, FundaModification of surface of biomaterials is a great interest for many years due to first contact of surface of materials with the biological fluids. This thesis aims to investigate surface modification effect on the chemical, surface wettability, protein adsorption as well biodegradability properties of dense chitosan (Ch) and asymmetric chitosan films (ACh). The surfaces of chitosan dense and asymmetric films were modified by ion implantation technique using carbon and carbon-nitrogen hybrid ions at a fluence of 1x1015 ions/cm2 and ion energy of 20kV. Chemical compositions of the film surfaces were analyzed by Fourier transform infrared spectroscopy (FTIR-ATR). Surface hydrophobicity measurements were conducted by static contact angle measurements. Protein adsorption on unmodified and modified surfaces on films was investigated as a function of time at various pH conditions. After ion implantation on chitosan films, both C and C-Nitrogen ion implantation, the surfaces become rougher and hydrophobic having moderate wettability (����� values in the range of 72-85°) and in good agreement with FTIR-ATR data findings. It was found pH dependence of the amount of protein adsorbed on the dense chitosan films as a function of time for both un-implanted and implanted films. BSA and fibrinogen were more adsorbed on the chitosan films at pH 5. The amount of BSA and fibrinogen protein adsorption was 0.97 and 1.33 gprotein/gfilm, respectively for 60 min incubation period. Protein adsorption enhanced for C and C+N2 ion implanted samples for BSA and fibrinogen, respectively due to the hydrophobic protein surface interaction effect. In vitro degradation results showed that ACh films degrade much faster (mass loss 57 %) than Ch films (40 %) due to the porous structure at the end of 3 weeks. However, the ion implanted Ch samples degraded much slower having mass loss of 30% and 17.7% for C+N2 and C implanted samples, respectively at the end of 3 weeks compared to un-implanted Ch films as 40 %. The results are in good agreement with water sorption and surface hydrophobicity of the implanted films. This study demonstrated that surface modification, as well as structure, changes the protein sorption, wettability and biodegradation properties of the chitosan films.Master Thesis Surface Modified Halloysite Nanotubes Incorporated Polyl-Lactide Nanocomposites for Food Packaging Applications(Izmir Institute of Technology, 2019) Tüzün, Ece Zeynep; Tıhmınlıoğlu, FundaBiodegradable Poly (L-lactide) (PLA) can replace petroleum based packaging materials to solve environmental problems. PLA lacks of ductility and have moderate barrier properties. In this study, halloysite nanotubes (HNTs) possessing unique surface chemistry and tubular structure were incorporated into PLA matrix to overcome drawbacks of PLA. Firstly, HNT surface was modified with aminopropyltriethoxysilane (APTES) to enhance interfacial adhesion between HNTs and PLA matrix by decreasing the hydrophilicity of HNTs. Modified HNTs (m-HNTs) were characterized by SEM, FTIR, TGA, N2 adsorption-desorption analysis, XRD and XPS. FTIR, XRD and XPS results revealed that APTES was successfully grafted onto HNTs. The optimum pH and APTES concentration for the silanization of HNTs were determined as 3.50 and 1%, respectively. HNT/PLA and m-HNT/PLA nanocomposite films with different wt% of nanofiller loadings were prepared by solution casting. The films were characterized by FTIR, XRD, tensile test, water vapor permeation, DSC, TGA, contact angle and SEM analysis and color measurements. Better dispersion and consequently better mechanical properties were obtained with m-HNT addition compared to unmodified ones. Tensile strength at break of PLA was increased by 4.7% and 16.6% with 2 wt% HNT and m-HNT addition, respectively. m-HNT/PLA nanocomposites had better water vapor barrier properties than unmodified HNT/PLA nanocomposites while both of them improved the barrier property. Best mechanical and water vapor barrier properties were achieved with 2% modified HNT (1% APTES) containing PLA nanocomposites. Therefore, nanocomposite films produced in this study with high transparency and good barrier property can be a suitable candidate for fresh food packaging.Master Thesis Preparation and Characterization of Herbal Extract Loaded Bilayer Sponges for Wound Dressing Applications(Izmir Institute of Technology, 2019) Değer, Sibel; Tıhmınlıoğlu, FundaRecently, the use of biomaterials with natural extracts have been rapidly increasing as an alternative to antibiotic-loaded biomaterials in wound healing applications. Cissus quadrangularis (CQ) is a natural extract which has antiinflammatory, anti-bacterial and anti-fungal activities. CQ has been used as a natural therapy in India to treat many problems such as bone repair, skin infection and wound. In this thesis study, it was aimed to prepare and characterize a bilayer wound dressing consisting of CQ extract that can mimic skin structure and to investigate extract release from the wound dressing. CQ loaded chitosan nanofibers were coated on the chitosan/POSS composite sponges with the electrospinning method as a bilayer wound dressing to treat exudate wounds. The morphology and encapsulation efficiency of the extract-loaded chitosan nanofibers are optimized to achieve controlled release of the extract. Morphologies of nanofibers were observed by scanning electron microscopy (SEM) analysis. Bilayer sponges were characterized by FT-IR, swelling, porosity, mechanical properties, antimicrobial activity, and cytotoxicity analyzes. The diameters of the nanofibers were found between 77.9±4 nm and 97.4±4 nm. The water vapor permeability of the wound dressings is between 4021 and 4609 g/m2day which is found in the appropriate range for wound healing. Bilayer dressings reached 78% to 80% cumulative release at the end of fourth day and release medium showed antimicrobial activity against E. coli and S. epidermidis. Wound dressings have not shown any toxic effects on the 3T3 cell line. Consequently, the extract loaded bilayer sponges are found as potential candidates for wound dressing.Master Thesis Preparation and Characterization of Polymer Based Composite Nanospheres for Bone Infection Prevention(Izmir Institute of Technology, 2018) Kımna, Ceren; Tıhmınlıoğlu, FundaCurrently, bone tissue engineering applications comprise the development of smart materials that can induce tissue regeneration meanwhile supporting the defect site of the body. Despite of the advancements, inflammation is still a serious problem that threatens human health at the post-implantation period. To overcome potential inflammations, antibiotic therapy is commonly employed in clinical trials. However, antibiotic therapy causes some side effects such as ototoxicity and nephrotoxicity, especially when applied in high doses. Therefore, local drug delivery systems play a vital role in bone disorders due to the elimination of disadvantages introduced by conventional methods. In the presented study, it was aimed to develop chitosan-based composite nanospheres as a controlled drug delivery system against bone infections. Accordingly, chitosan and montmorillonite nanoclay was homogenized with microfluidizer and electrosprayed to obtain spherical nanoparticles. The optimum electrospraying conditions were investigated using response surface methodology. Vancomycin and Gentamicin antibiotics were incorporated in the polymeric matrix to provide controlled release at the defect region to overcome inflammations after implantation. The prepared nanospheres were characterized in terms of morphology, hydrodynamic size distribution, surface charge, drug encapsulation efficiency and release profiles. The dominant drug release mechanism was determined by empirical mathematic models. Drug loaded nanospheres have been successfully produced with a size range of 180-350 nm. High encapsulation efficiency was achieved (80-95%) with a controlled drug release up to 30 days. Fickian diffusion was found as the main mechanism in drug delivery from spherical CS/MMT nanocomposites. The in vitro release medium of nanospheres showed strong antimicrobial activity against gram-positive S. aureus and gram-negative E. coli bacteria. Furthermore, it was found that the nanospheres did not show any cytotoxic effect to 3T3 and SaOS-2 cell lines. These results demonstrated that the prepared nanospheres can be a promising option for bone infection prevention.Master Thesis Preparation and Characterization of Corn Zein Coated Polypropylene (pp) Films for Food Packaging Applications(Izmir Institute of Technology, 2007) Atik, İsa Doğan; Tıhmınlıoğlu, FundaThe plasticized corn-zein coatings on polypropylene (PP) films as an alternative to multilayer packaging films consisting of non-degradable polymers were prepared to evaluate barrier, mechanical, thermal, surface and optical properties of the resulting coated film, as affected by coating formulation (solvent, corn-zein, plasticizer concentration, and plasticizer type). PP films coated with corn zein were obtained through a simple solvent casting method. Corn-zein with different amounts (5% and 15%) was dissolved in 70% and 95% aqueous ethanol solution at 50oC, respectively. Solutions of corn-zein plasticized by polyethylene glycol (PEG) and glycerol (GLY) with various levels (20% and 50%) were applied on corona-discharged-treated PP film. The resulting corn-zein coated PP films showed good appearance, flexibility and adhesion between the coating and the base film. The coated PP films showed a significant (P<0.05) increase in barrier (water and oxygen) properties and improvement in mechanical properties when coating formulation consisted of higher corn-zein content and lower amount of GLY as plasticizer. Furthermore, zein coating increased the service temperature range of the PP films, and promised good printability on the surface due to contact angle results. The statistical analysis defined that the key parameters of coating formulation that had major effect on the final properties of coated PP films as corn-zein concentration, plasticizer concentration, and plasticizer type while ethanol concentration was found to be as less effective parameter compared to others. In conclusion, corn zein coatings with appropriate formulation on PP films could have potential as an alternative to conventional synthetic coatings for food packaging applications.Master Thesis Preparation and Characterization of Corn Zein Nanocomposite Coated Polypropylene Films for Food Packaging Applications(Izmir Institute of Technology, 2010) Özçalık, Onur; Tıhmınlıoğlu, FundaFeasibility of prepared novel corn zein nanocomposite (CZNC) coated polypropylene (PP) film (CZNC-PP) structures for food packaging applications was investigated. Excellent barrier properties of corn zein nanocomposites were successfully combined with mechanically strong PP as an eco-friendly promising alternative to conventional barrier packaging systems. In this study, the effect of nano-sized layered silicate amount, type and processing of CZNC layer on the barrier, mechanical, optical and surface properties of the CZNC-PP films were investigated. Incorporation of organomodified montmorillonite (OMMT) by solution intercalation into zein coating matrix improved barrier and mechanical properties of PP films. The properties of single CZNC layers and interactions between layered silicates and zein matrix were also investigated. Fine delamination of OMMT in zein coating was found to be responsible for the improvements in oxygen and water vapor barrier of single corn zein layers due to more tortuous path formed for permeation of oxygen and water vapor. Prepared CZNC-PP films achieved nearly 4 times reduced oxygen permeability while WVP of the films were reduced by 30% with 5 wt% OMMT content in 5.9 m corn zein coating. Meanwhile, improvements were less significant for unmodified nanoclay loadings due to the incompatibility between unmodified MMT and corn zein. Hydrophobicity of CZNC surface increased with increasing OMMT loading in accordance with WVP results. Permeation data was fitted to various phenomenological models predicting the permeability of polymer nanocomposites as a function of clay concentration and aspect ratio of nanoplatelets. While significant improvements in mechanical properties including doubled elastic modulus and 75% higher yield strength of PP films were obtained, incorporation of OMMT in CZNC layer did not change the color of CZNC-PP films significantly.Master Thesis Preparation and Characterization of Polypropylene Based Composite Films(Izmir Institute of Technology, 2001) Pehlivan, Hilal; Tıhmınlıoğlu, FundaIn the scope of this study, preparation of silver . natural zeolite reinforced polypropylene (PP) composite system possessing antibacterial properties via ion exchange process and characterization by means of different techniques (FTIR, TGA, DSC, mechanical tests, optical microscopy) were aimed. It has been established that zeolites are suitable for removing Ag ions from silver containing solutions and that silver zeolites are increasingly investigated as germicidal, bactericidal, antifungal, and antiseptic components in different compositions (Hagiwara 1990, Kawahara 2000, Klasen 2000).In the present study, prior to the ion exchange studies, water sorption behavior of PP . clinoptilolite rich natural zeolite composites was investigated, since the ion exchange process was to be conducted in aqueous media. It was observed that a hydrophobic polymer, PP attained the property of water sorption due to the porous structure of the composite films. The effective diffusivity of liquid water in the PP-zeolite composites prepared by hot press and extrusion techniques varied in the range of 0.3- 9.9 x10-10 and 0.1 - 3.3 x10-12 cm2/s, respectively. Silver loading to PP - zeolite composites was provided by means of two different methods. In Method I, PP - zeolite composite films were treated with a variety of silver ion containing solutions (5 to 50 ppm AgNO3 solution), whereas in Method II silver exchanged zeolite minerals (prepared with initial AgNO3 concentrations of 50, 500, and 5000 ppm) were molded with PP in the presence of DOP (Dioctyl Phthalate). The amounts of Ag+ loaded per gram of zeolite for initial AgNO3 concentrations of 50, 500, and 5000 ppm were determined as 4.36, 27.85, and 183.78 mg, respectively. Antibacterial activity tests against E.coli indicated that the samples obtained in Method II were superior to those prepared by Method I since the penetration of silver ions to the zeolite phase was limited by the PP phase in the case of Method I. However, the discoloring effect of silver ion was readily observed for the samples prepared by Method II as indicated by the discoloration parameters. The release of Ag+ to water was found to be negligible as reported in literature leading to long . term antibacterial activity.The thermal characterization studies showed that the addition of the zeolite increased the crystallinity of the structure acting as a nucleating agent in PP crystallization as well as retarded the degradation temperature of PP. At low silver concentrations, the zeolite behaved as a decelerating agent in PP, however at higher silver concentrations, the composites degraded at a faster rate than pure PP. Yet the activation energy values for the thermal decomposition reactions of Method II was considerably lower indicating that the decomposition has been accelerated by the presence of silver.It was found that the addition of the zeolite into the PP matrix decreased the density of pure PP (0.89 g/cm3) due to the formation of voids. However, a systematic approach was not observed with the increasing zeolite content as a consequence of the uneven zeolite distribution. On the other hand, a considerable enhancement was noticed for the tensile tested film densities changing between 0.58 - 0.78 g/cm3, which are in a better agreement with the commercially desired range (0.6 - 0.65 g/cm3) for packaging applications of PP composites. Mechanical tests indicated that the addition of the zeolite tended to decrease the yield stress values while a slight decrease was observed for Young moduli. The effect of silver on the Young Modulus values of the composites is not quite significant, however the yield stress values increased from 23.6 to 29.5 MPa with the increasing silver concentration.Consequently, of all the composite films prepared by Method II, the ones loaded with 4.36 (mg Ag+/g zeolite) containing 2, and 4 % wt zeolite were selected to be the most appropriate, considering the thermal, mechanical, and structural characteristics as well as the discoloring actions.