Osteon-Mimetic Nanocomposite Materials For Bone Regeneration

The limitations of large bone defect regeneration has brought the focus of Bone Tissue Engineering research on fabricating three-dimensional bone-mimetic grafts that could enhance osteogenesis and vascularization. Osteons composed of apatite-deposited aligned collagen nanofiber layers are the fundamental building blocks of cortical bone. In natural cortical bone, mineralization is mediated by extracellular matrix (ECM) proteins with amino acid sequences rich in glutamic acid. This dissertation is focused on the establishment of a novel biomimetic approach to engineer scaffolds for healing large bone defects. In the first part, we investigated the effect of calcium phosphate (CaP) deposition on aligned surface-modified nanofibers (NF) with a glutamic acid peptide (GLU-NF) on osteogenic differentiation of marrow stromal cells (MSCs). In order to mimic the morphology of the bone ECM, the EEGGC peptide (GLU) with two glutamic acid residues was conjugated to a low molecular weight polylactide (PLA) macromer. The synthesized PLA-GLU polymer-peptide conjugate was blended with high molecular weight poly(lactide-co-glycolide) (PLGA) and electrospun to form GLU-NF. GLU-NF microsheets were incubated in a modified simulated body fluid (SBF) for nucleation and growth of CaP crystals on the fiber surface. To achieve a high CaP to fiber ratio, a layer-by-layer (LBL) approach was used to improve diffusion of calcium and phosphate ions inside the microsheets. Results demonstrate that surface modification of aligned synthetic NF with EEGGC peptide significantly increased nucleation and growth of CaP crystals on the fibers, leading to increased mechanical properties and osteogenic differentiation of MSCs. In addition, CaP to fiber ratios as high as 200%, which lie between those of cancellous (160%) and cortical (310%) bone, were obtained with the LBL approach. In the second part, the perforated CaP deposited NF microsheets were used to fabricate osteon-mimetic microtubes. The effect of the microtubular structure of CaP-deposited NF scaffolds on osteogenesis of MSCs and vascularization of endothelial progenitor cells (EPCs) and MSC co-cultures was investigated. It was found that microtubular scaffolds preferentially supported osteogenic and vasculogenic differentiation of MSCs and MSCs/EPCs as evidenced by elevated gene expression level of osteogenic and vasculogenic markers and enhanced calcium content, ALPase activity, and total collagen secretion. The osteon-mimetic scaffolds developed in this research are potentially useful as tissue engineered graft for regeneration of large bone defects

Material and Regenerative Properties of an Osteon-Mimetic Cortical Bone-Like Scaffold

The objective of this work was to fabricate a rigid, resorbable and osteoconductive scaffold by mimicking the hierarchical structure of the cortical bone. Aligned peptide-functionalize nanofiber microsheets were generated with calcium phosphate (CaP) content similar to that of the natural cortical bone. Next, the CaP-rich fibrous microsheets were wrapped around a microneedle to form a laminated microtube mimicking the structure of an osteon. Then, a set of the osteon-mimetic microtubes were assembled around a solid rod and the assembly was annealed to fuse the microtubes and form a shell. Next, an array of circular microholes were drilled on the outer surface of the shell to generate a cortical bone-like scaffold with an interconnected network of Haversian- and Volkmann-like microcanals. The CaP content, porosity and density of the bone-mimetic microsheets were 240 wt%, 8% and 1.9 g/ml, respectively, which were close to that of natural cortical bone. The interconnected network of microcanals in the fused microtubes increased permeability of a model protein in the scaffold. The cortical scaffold induced osteogenesis and vasculogenesis in the absence of bone morphogenetic proteins upon seeding with human mesenchymal stem cells and endothelial colony-forming cells. The localized and timed-release of morphogenetic factors significantly increased the extent of osteogenic and vasculogenic differentiation of human mesenchymal stem cells and endothelial colony-forming cells in the cortical scaffold. The cortical bone-mimetic nature of the cellular construct provided balanced rigidity, resorption rate, osteoconductivity and nutrient diffusivity to support vascularization and osteogenesis

Comparative moments: Tracing an experimental approach

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Defending future commons: the Gezi experience

No abstract available

Defending future commons: the Gezi experience

No abstract available

Urban renewal in Istanbul: reconfigured spaces, robotic lives

The article discusses Turkey's property-led residential redevelopment model. This entails the demolition of an existing settlement, replacing it with blocks of apartments (usually constructed on the exact same site and at a higher density), some of which are then made available to displaced residents for purchase via mortgage loans with long maturities. While the authorities promote this model of urban renewal as an innovative public housing policy, I argue that, far from being an exception to market-rate housing, the model is in fact a market-disciplinary tool. It seeks to incorporate into the formal market not just spontaneously developed and only partially regulated spaces, but also the conduct of residents living in these informal neighborhoods. The article contributes to the immense literature on urban renewal and organized struggles around the right to housing by showing that urban renewal is not simply about dispossession and displacement. In the Turkish case, urban renewal does not necessarily seek to displace poor residents (even though it often ends up doing so), rather to incorporate them into a nascent mortgage origination market. The second half of the article introduces and elaborates on a case study in Istanbul

Yersiz-yurtsuzlaşma ve kentsel mekana yeni yaklaşımlar

In contemporary debates on space, the validity of ءphysical space̕ as an indispensable category of human existence is widely questioned on the basis of the claim that the relevant interval of analysis has shifted from ءspace̕ to ءtime̕, thanks to the technological innovations enabling the speed of present-day telecommunications. The apparent primacy of mobility of أdeterritorializedؤ commodities, signs, meanings, and identities, in the contemporary society, adds new dimensions to the traumatic experience of ephemerality, in spatial and temporal categories. Through the claims declaring, the dissolution of the dichotomy between urban and rural, and redefinition of the relevant dichotomy between the ءspace of places̕ and the ءspace of flows̕ in recent theoretical efforts; we attempt to trace how the notion of ءplace̕ could be revalidated and reconstituted with reference to processes of contemporary globalization. The study examines the new paths for a constructive definition of ءplace̕, which are opened up by the crisis in locating and representing temporal and spatial categories both physically and mentally.M.Arch. - Master of Architectur

Urban pulse—(re)making space for globalization in Istanbul

This paper provides critical reflections on the urban transformation campaign launched by the Istanbul Metropolitan Municipality (IMM) as part and parcel of its ambitions to upgrade Istanbul to "world city" status. I focus on two main aspects of "urban transformation" in Istanbul: prestige mega-projects and (re)development of informal housing areas, with particular emphasis on the latter. I examine how poor residents' livelihoods are put at stake in spite of the IMM's claim that "urban transformation" is ultimately beneficial for all citizens. I conclude with the unique policy challenges that the local governments face in developing participatory models for urban renewal and regeneration in Istanbul

A Novel Technique for Fabricating Aligned Nanofibers by Using Solution Electrospinning

In this Master of Science project, a novel technique of producing aligned nanofibers has been created by using new designed apparatus. Solution electrospinning has been used for nanofibers fabrication. During solution electrospinning, when two negative (-20kV) charged wheels and a positive (+20kV) charged needle were placed in the system, aligned nanofibers were collected on the grounded aluminum collector which was located between two wheels. Polymer solutions were pumped to the system at 1.0 ml/h. As polymer, poly(lactic-co-glycolic acid) (PLGA 50/50) was dissolved in hexafluoro-2-propanol (TCI). Collected nanofibers were examined under Scanning Electron Microscope (SEM). Nanofibers were 0.7 µm in diameter and 1.5 cm in length. Besides creating aligned nanofibers by using a new designed apparatus, the other aim of this project is producing three-dimensional nanofiber structures. The reason of producing three dimensional nanofibers structure is biomimicking the structure to natural three dimensional bone structure. Furthermore, in order to make three-dimensional nanofiber structure, the collector was turned 90o after a unit time, and nanofiber arrays were printed perpendicularly on top of each other. In addition, the effects of polymer solution viscosity and applied electrical charge to the nanofibers fabrication were also evaluated

Chapter 7: ISTANBUL: FROM GECEKONDU TO ‘CRAZY’ PROJECTS

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