Phd Degree / Doktora
Permanent URI for this collectionhttps://hdl.handle.net/11147/2869
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Doctoral Thesis Preparation and Characterization of Polymeric Scaffolds for Nerve Tissue Engineering Applications(Izmir Institute of Technology, 2014) Büyüköz, Melda; Alsoy Altınkaya, Sacide; Erdal, Şerife EsraThe major goal in tissue engineering is to develop three-dimensional biomimetic scaffolds which can provide an optimal environment for cell adhesion, proliferation, differentiation and guide new tissue formation. In this study macroporous, nanofibrous gelatin scaffolds in the form of a disc and channeled conduit were prepared for nerve tissue engineering applications. Alginate microspheres have been integrated into the scaffolds to deliver nerve growth factor (NGF) to differentiate PC12 cells. Methods combining thermally induced phase separation technique with porogen leaching and injection molding were used to manifacture disc shaped and channeled nanofibrous scaffolds, respectively. Microcarriers loaded with NGF were fabricated by water-in-oil emulsification technique and attached in the scaffold by chemical crosslinking with carbodiimide reaction. The relationship among processing parameter, porosity, pore size, interpore connectivity and the mechanical properties were investigated. In addition release kinetics of NGF from the particles were determined and viability, proliferation and differentiation of PC12 cells in the scaffolds were evaluated. The fiber sizes of nanofibrous scaffolds were found similar to the size of natural collagen fiber bundles. In nanofibrous scaffolds, the dimensional stability and in vitro degredation rates improved when compared to solid walled scaffolds. The release rate of NGF from the particles was controlled by the alginate concentration and poly(L-lysine) coating. Integrating NGF into the nanofibrous gelatin scaffold in encapsulated form reduced amount of NGF and time required for the differentiation of PC12 compared to free NGF directly added to the cells.Doctoral Thesis Preparation, Characterization of Enzyme Immobilized Membranes and Modeling Og Their Performances(Izmir Institute of Technology, 2010) Yürekli, Yılmaz; Alsoy Altınkaya, SacideThe objective of this thesis study is to prepare active and stable urease (URE) immobilized membranes for the efficient removal of urea and to predict the performances of these membranes under pressure. Two commercially available ultrafiltration membranes namely Poly (acrylonitrile-co-sodium methallyl sulfonate) copolymer (AN69) and polyethyleneimine (PEI) deposited AN69 membranes (AN69-PEI) were used as supporting materials on which urease is immobilized by means of physical adsorption using layer-by-layer self assembly method or chemical attachment using N-ethyl-N.-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) and Nhydroxysuccinimide (NHS) coupling agents as a zero crosslinker. During physical immobilization (pH 7.4), the effect of polyelectrolyte type on the activity of immobilized urease was compared between PEI and chitosan (CHI) cationic polyelectrolytes where urease was located either on top of the polyelectrolyte layer (AN69-PEI-URE or AN69-CHI-URE) or between two polyelectrolyte layers in a sandwiched form (AN69-PEI-URE-PEI or AN69-CHI-URE-CHI). The results reveal that the amount of urease immobilized on AN69 membranes are similar and slightly higher than the amount adsorbed on the activated AN69 surface by chemical attachment (AN69-C-URE). The maximum reaction rate was observed with AN69-PEI-URE membrane while the maximum retained activity during storage time was determined with AN69-C-URE membrane. Under dynamic conditions, the hydraulic permeabilities of the commercial and urease immobilized membranes were found similar and the highest urea conversion was achieved with the AN69-PEI-URE-PEI membrane. At the end of 450 minutes of filtration under pressure, the catalytic activity of AN69-C-URE membrane was completely preserved. The mathematical model developed can correlate the experimental filtration data quite well.Doctoral Thesis Preparation and Characterization of Hemodialysis Membranes With Improved Biocompatibility Through Anticoagulant, Antioxidant and Enzyme Immobilization(Izmir Institute of Technology, 2013) Yaşar Mahlıçlı, Filiz; Alsoy Altınkaya, SacideThe objective of this thesis is to improve blood compatibility of polysulfone (PSF) based hemodialysis membranes through generating thromboresistant and/or antioxidative surfaces with biomolecule immobilization. To create a nonthrombogenic surface, support membrane was modified with layer by layer (LBL) deposition of polyethyleneimine (PEI) and alginate (ALG) and heparin (HEP) was immobilized on the outermost surface of the assembly by blending with ALG. α-lipoic acid (ALA) and superoxide dismutase (SOD)/catalase (CAT) enzyme couple were choosen to provide antioxidative properties. ALA was immobilized site-specifically to PEI deposited support membrane while SOD/CAT enzyme couple were attached both covalently and ionically on the plasma treated and PEI deposited membranes, respectively. Blending a small amount of HEP with alginate remarkably prolonged the coagulation time (APTT) of HEP free membranes. The stability of ALA under typical hemodialysis conditions was improved by immobilization, and the greatest enhancement was achieved when it was sandwiched between two PEI layers. In vitro studies showed that all ALA or SOD/CAT coated PSF membranes are capable of reducing reactive oxygen species levels in blood, furthermore, they can significantly prolong APTT. The hemocompatibility results also demonstrated that the adsorption of human plasma proteins, platelet and cell activation on all modified membranes decreased significantly compared with the unmodified PSF membranes due to the change in surface properties such as hydrophilicity, surface charge and roughness upon immobilization of the biomolecules. The modification methods proposed in this study did not change high permeability, mechanical strength and nontoxic property of the PSF membranes.