Browsing by Subject "Biomimetics."

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Open Access
Biomimetic self-assembled peptide nanofibers for bone regeneration
(2012) Kocabey, Samet
Self-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.
Open Access
Programming microenvironmental signals with bioactive peptide amphiphiles for skeletal and cardiac myogenesis
(2014) Garip, İmmihan Ceren
The extracellular matrix (ECM) is crucial for the coordination and regulation of various cellular processes, including cell adhesion, recruitment, differentiation and death. ECM components structurally support tissue function and regeneration by acting as a substrate for cell migration and differentiation. In addition, by facilitating the fine localization of signals within their structural framework, these components activate receptors on the cell membrane for the initiation of signal transduction cascades. As such, cell-matrix interactions and matrix-associated signals are important for the normal functioning of cells, as well as for natural or artificially assisted tissue regeneration. In keeping with this ECM-centric approach, we designed and synthesized peptide amphiphiles with bioactive epitopes to resemble the native microenvironment of muscle tissue and to examined their potential in the induction of progenitor cell differentiation into skeletal myotubes and cardiac myocytes. The formation of skeletal myotubes was promoted through the use of basal laminamimetic peptide nanofibers inspired by the chemical structures of laminin and fibronectin, two proteins strongly represented in the skeletal muscle extracellular matrix. We demonstrated that our basal lamina mimetic peptide nanofiber system actively interacts with the cells it contains and enhances their differentiation within 3 days. Morphological analysis and immunocytochemical stainings indicated the formation of differentiated myotubes.We also designed glycosaminoglycan-mimetic peptide amphiphiles to mimic the glycosaminoglycans found in the myocardium. Glycosaminoglycans have been reported to play substantial roles in growth factor binding and the induction of angiogenesis, and their mimicry through peptide amphiphile nanofibers is promising as a combined approach for generating multifunctional cardiovascular tissue engineering scaffolds. We demonstrated that peptide nanofibers enhance the adhesion of cells to the surface and induce cardiac myoblast cells to differentiate into cardiomyocytes through both gene expression analysis and immunostainings. In summary, myogenic platforms were developed by programming signal rich environment from self-assembled peptide nanofibers inspired from the components of the ECM to induce the differentiation of cells. These bioactive nanofiber systems serve as promising platforms for muscle tissue engineering applications.
Open Access
Self-assembled peptide template directed synthesis of one-dimensional inorganic nanostructures and their applications
(2012) Acar, Handan
Engineering at the nano scale has been an active area of science and technology over the last decade. Inspired by nature, synthesis of functional inorganic materials using synthetic organic templates constitutes the theme of this thesis. Developing organic template directed synthesis approach for inorganic nanomaterial synthesis was aimed. For this purpose, an amyloid like peptide sequence which is capable of self-assembling into nanofibers in convenient conditions was designed and decorated with functional groups showing relatively high affinity to special inorganic ions, which are presented at the periphery of the one-dimensional peptide nanofiber. These chemical groups facilitated the deposition of targeted inorganic monomers onto the nanofibers yielding one-dimensional organic-inorganic core-shell nanostructures. The physical and chemical properties of the synthesized peptide nanofibers and inorganic nanostructures were characterized using both qualitative and quantitative methods. First, silica nanotubes were obtained by silica mineralization around these peptide nanofiber templates for the construction of sensors for explosives. The fluorescence dye was used to coat the silica nanotubes to detect explosive vapor. The surface of the silica nanotubes were porous enough to adsorb more dye compared to the silica nanoparticles and silica film, and causes faster fluorescence quenching in the presence of explosives like trinitrotoluene and dinitrotoluene. The silica nanotubes which synthesized with this peptide nanofiber templates can be used in catalysis and sensors in which high surface area is advantageous. In the second part of the thesis, titanium dioxide nanotubes were obtained from titania mineralization. They are wellknown with their fascinating properties as a result of the one-dimensional nanostructure, such as more efficient electron transfer and less electron-hole recombination. The sufficient photoactivity of titanium dioxide makes them suitable materials for Dye-Sensitized Solar-Cell construction. It is demonstrated that the peptide nanofiber templated titanium dioxide nanotubes have more than two times more efficiency compared to template-free synthesized titanium dioxide particles. Finally, designed peptide sequence was conducted to a multi-step seeding mediated growth method for gold mineralization around peptide nanofibers. The gold-peptide hybrid nanostructures with different packing characteristics and sizes were synthesized and fully characterized. Further, it was demonstrated that the dry film of these nanostructures showed a resistive switching dominant conductivity, due to the nanogaps in between gold nanoparticles as a result of particle alignment driven by the peptide nanofiber. The results obtained in this thesis encourage use of a new “bottom-up” synthesis approach. Specially designed peptides with desired properties and functional groups were synthesized and peptide nanofibers formed were further used as templates for inorganic mineralization. Not only it is possible to synthesis high amount of nanostructure with this approach, but also formed one-dimensional nanostructures show advance functionalities used in several applications as a part of the thesis scope. This methodology is suitable for many metals and metal oxide based applications.