Browsing by Subject "Surface Modification"
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Item Open Access Biomimetic self-assembled peptide nanofibers for bone regeneration(Bilkent University, 2012) Kocabey, SametSelf-assembled peptide nanofibers are exploited in regenerative medicine applications due to their versatile, biofunctional and extracellular-matrixresembling structures. These properties provide peptide nanofibers with osteoinductive and osteoconductive behaviors for bone regeneration applications through several approaches. In this thesis, two different approaches were discussed, which were developed to induce bone regeneration and mineralization including extracellular matrix mimicking peptide nanofibers based 2-D gel formation and surface functionalization of titanium implants. For this purpose, we designed glycosaminoglycan-mimetic peptide nanofibers inspired by chemical structure of glycosaminoglycans present in the bone extracellular matrix. We demonstrated that glycosaminoglycan-mimetic peptide nanofibers interact with BMP-2, a critical growth factor for osteogenic activity. Glycosaminoglycan-mimicking ability of the peptide nanofibers and their interaction with BMP-2 promoted osteogenic activity of and mineralization by osteoblastic cells. ALP activity, Alizarin Red Staining and EDAX spectroscopy indicated efficacy of the peptide nanofibers for inducing mineralization. We also developed a hybrid osteoconductive system for titanium biomedical implants inspired by mussel adhesion mechanism in order to overcome bone tissue integration problems. For this purpose, Dopa conjugated peptide nanofiber coating was used along with bioactive peptide sequences for osteogenic activity to enhance osseointegration of titanium surface. Dopamediated immobilization of osteogenic peptide nanofibers on titanium surfaces created an osteoconductive interface between osteoblast-like cells and inhibited adhesion and viability of soft tissue forming fibroblasts compared to the uncoated titanium substrate. In summary, osteoinductive and osteoconductive self-assembled peptide nanofibers were developed to promote osteogenic activity and mineralization of osteogenic cells. These bioactive nanofibers provide a potent platform in clinical applications of bone tissue engineering.Item Open Access Biophotonic applications of ultrafast fiber lasers: from biomaterial surface modification to sub-cellular nanosurgery(Bilkent University, 2014) Erdoğan, MutluJust a year after the invention of the LASER in 1960, it was demonstrated that lasers could be used for the treatment of certain skin abnormalities. At present, lasers are extensively used in a broad range of medical treatments. After the development of femtosecond pulse lasers in the 1980s, even more exciting possibilities in a diverse range of fields have been realized. Accordingly, ultrashort pulse lasers are widely used in biological applications in recent years. In parallel to these, fiber laser systems have increasingly been utilized in a wide range of scientific and biomedical applications, since they are highly compatible systems for being employed for industrial and biomedical applications. Consequently, the aim of this Ph.D. thesis proposal is to develop compact, simpler to operate, and cost-efficient ultrafast fiber lasers with different repetition rates and pulse energies. By using such systems, we demonstrate the biophotonic applications of these lasers on two different biological research fields. As a part of this thesis study, we develop ultrafast fiber lasers and apply them in biomaterial surface modification. We demonstrate that different surfaces with micro- and nano-scale topographies can be generated at high speed, precision and repeatability. The outcomes of biomaterial surface modification with different laser parameters are compared in terms of topographical uniformity and repeatability. Additionally, a variety of topographical modifications are assessed with respect to the efficiency on cell attachment and proliferation on metal implants.As the second part of this thesis, we develop a custom-built ultrafast fiber laser-integrated microscope system for nanosurgery and tissue ablation experiments. Subsequently, we employ this system in order to make high-precision cuts onto different biological specimens ranging from the tissue level to subcellular level, such as a part of an axon or a single organelle. Finally, we improve this integrated system in a way that it becomes capable of generating optical pulses in any desired sequence possible. This is achieved by using acousto-optic modulators (AOM) and custom-developed field-programmable gate arrays (FPGA).Item Open Access Synthesis and characterisation of mesoporous transition metal ion modified silica-zirconia and silica-sulfated zirconia materials towards NOx catalysis(Bilkent University, 2006) Samarskaya, OlgaThe purpose of this work is to design and investigate mesostructured material as a potential support for the reaction of the methane with surface NOx species. Several objectives have been pursued in achievement of the goals. The first objective is to develop a facile procedure for the synthesis of mesoporous silica-zirconia mixed oxide supports that are modified with the sulphate (SO4 2-), cobalt (Co2+) and palladium (Pd2+) ions. The support with requisite catalytic properties was obtained through the adjustment of the synthetic steps and optimisation of the composition. The second objective is to explore the effect of cobalt and zirconia loading in the reaction of the NOx species with methane over the Co-, Pd-, and Co-Pd-silica-sulfated zirconia (Si-SZr). A one-pot synthesis procedure has been developed to prepare the mesoporous silica-zirconia (Si-Zr), Si-SZr supports and the supermicroporous Co(II) incorporated Si-SZr catalysts with a wide range of zirconia loadings. Introduction of the Co(II) active sites by various post-synthesis methods leads to the modification of the surface, whereas the direct (co-precipitation) techniques have provided the modification of both surface and bulk of the supports. The palladium ions were introduced by the conventional impregnation methods onto the calcined solid materials. The detailed analysis of the materials has revealed that the silica and zirconia are well mixed in the framework, whereas the cobalt and sulfate ions are uniformly dispersed on the internal surface of the silica-zirconia supports. The materials prepared in this thesis possess sufficient stability, requisite catalytic properties, as well as good Bronsted and Lewis acidity. However, the high cobalt loading renders the catalytic performance of the Pd-Si-SZr catalysts. Among the investigated catalysts, the interaction of the NOx species with the CH4 takes place at the lowest temperature over the Co-, Pd-, Co-Pd-supported zirconia rich (Zr/Si = 28) Si-SZr catalysts.