Aylin Sendemir Urkmez

Biocompatibility of plasma-treated poly(3-hydroxybutyrate-co-3-hydroxyvalerate) nanofiber mats modified by silk fibroin for bone tissue regeneration

The objective of this study was to produce biocompatible plasma-treated and silk-fibroin (SF) modified poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) nanofiber mats. The mats were plasma-treated using O2 or N2 gas to increase their hydrophilicity followed by SF immobilization for the improvement of biocompatibility. Contact angle measurements and SEM showed increased hydrophilicity and no disturbed morphology, respectively. Cell proliferation assay revealed that SF modification together with N2 plasma (PS/N2) promoted higher osteoblastic (SaOs-2) cell viability. Although, O2 plasma triggered more mineral formation on the mats, it showed poor cell viability. Consequently, the PS/N2 nanofiber mats would be a potential candidate for bone tissue engineering applications.

Synergistic role of three dimensional niche and hypoxia on conservation of cancer stem cell phenotype

Hypoxia is a pathalogical condition in which tissues are deprived of adequate oxygen supply. The hypoxia effect on tumors has a critically important role on maintenance of cancer stem cell phenotype. The aim of this study is to investigate the effects of hypoxia on cancer stem cells on three dimensional (3D) in vitro culture models. Osteosarcoma stem cells characterized by CD133 surface protein were isolated from osteosarcoma cell line (SaOS-2) by magnetic-activated cell sorting (MACS) technique. Isolated CD133(+) and CD133(-) cells were cultivated under hypoxic (1% O2) and normoxic conditions (21% O2) for 3 days. For the 3D model, bacterial cellulose scaffold was used as the culture substrate. 3D morphologies of cells were examined by scanning electron microscopy (SEM); RT-PCR and immunocytochemistry staining were used to demonstrate conservation of the cancer stem cell phenotype in 3D environment under hypoxic conditions. Cell viability was shown by MTT assay on 3. and 7. culture days. This study is seen as an introduction to develop a 3D hypoxic cancer stem cell based tumor model to study CSC behavior and tumor genesis in vitro.

In Vitro Biocompatibility and Antibacterial Activity of Electrospun Ag Doped HAp/PHBV Composite Nanofibers

The authors report herein in vitro antibacterial property and osteoblast biocompatibility of electrospun Ag doped HAp/PHBV (Ag-HAp/PHBV) composite nanofibers as an osteoconductive and antibacterial material for bone tissue engineering applications. Ag-HAp powders were synthesized and stable composite suspensions of Ag-HAp/PHBV were prepared with the aid of a cationic surfactant DTAB for the electrospinning process. Continuous and uniform composite nanofibers were generated within a diameter range of 400–900 nm. Obtained nanocomposite scaffolds provide a favorable environment for bone mineralization, SaOS-2 osteoblastic cell attachment and growth as well as they present antibacterial activity against E. coli and S. aureus bacteria without any noticeable cytotoxic effect. GRAPHICAL ABSTRACT

Investigation of central nervous system neurons under mechanical strain: An in vitro traumatic brain injury model

Effects of mechanical loading on development of central nervous system (CNS) cells and neurite extension have been recognized recently. Effects of loading are very complicated, since until a threshold, tension plays a positive role while after the threshold value, it is degenerative. The situation gets more complicated since CNS is made up of several different cell types that respond to various loads differently. There are some mechanical trauma models in the literature, but they usually employ hard and two dimensional culture substrates, which fail to mimic the natural niche of the cells. The aim of this work is to create an experimental model that can mimic the physiological habitat and normal loading conditions, and investigate the responses of CNS cells in response to different mechanical stimuli and strains, and therefore evaluate the effects of mechanical stress on cell development, neurite extension and degeneration, in order to be used in therapeutic investigations for neurodegenerative diseases. Electrospun poly-caprolactone (PCL) scaffolds were used as tissue engineering scaffolds, and B35 central nervous system neuron cell line was employed. Effects of mechanical strain on cell morphology, neurite extension and cytoskeleton, and after the threshold value, on apoptosis have been examined in morphological and molecular level.

Engineering design of in vitro mono-culture model of blood-brain barrier and investigation of methotrexate permeability on the model

Blood-brain barrier (BBB) is a control mechanism that limits the diffusion of many substances to central nervous system through blood, and governs the nutrient diffusivity. This barrier is among the main risk factors for treatment of neurodegenerative diseases, because most drugs designed are protein based, and are either blocked by BBB, or lose their bioavailability significantly. In this study, an in vitro BBB model was designed for testing therapeutics for neurodegenerative diseases, and methotrexate drug permeability was investigated. In the BBB model design step, poly-caprolactone fiber surfaces were prepared by electrospinning to be used as support membrane for cells. The fiber morphology and sizes were determined using polarizing microscopy. Human umbilical vein endothelial cells (HUVEC) and C6 glioma cells were cultured on either side of this membrane. Models proximity to in vivo models was tested by home-designed transendothelial electrical resistance measuring device; and nicotine was used as a positive control and albumin as a negative control. The effect of Methotrexate was determined indirectly by vitality test, MTT, for MCF-7 breast cancer cells seeded on the bottom of the well plates. The models proximity to models in the literature and natural blood-brain barrier was specified relatively.

Influence of processing flaws on cytotoxicity and genotoxicity of Co-Cr and Ni-Cr based dental crowns and bridges

Co-Cr and Ni-Cr based dental metal alloys are often preferred in the restoration processes inside the mouth for repairing the esthetic and functional irregularities of teeth. In this study, the cytotoxic and genotoxic effects of the possible man-made errors in the production of the dental crowns and bridges from the mentioned casting alloys in-vitro were investigated applying the test protocols according to TS EN ISO 10993 standards. As the possible man-made errors in this production, the duration of oxy-acetylene welding flame applied during the melting stage of the process and polishing time during the polishing process are determined. Their 9 different combinations are the investigated parameters of the study. Results showed that the welding flame induces toxicity in both of the alloys. In the cytotoxicity tests, as the duration of oxy-acetylene welding flame exposure increase, the negative effects on viability and morphological changes of the cells are noticed. Also increasing polishing time in the production process induces cytotoxicity and genotoxicity of these dental alloys.

Culture of central nervous system neurons on electrospun polymer fiber-covered surfaces

As the world population ages, the need for alternative therapies for neurodegenerative diseases is increasing. Neuronal tissue engineering is one of the most promising methods for creating in vitro disease models and therapies as well as regeneration of lost brain tissue due to neurodegenerative diseases. But due to inherent difficulties of culturing neurons and glia in vitro, studies in this field proceeds slowly. Our aim is to produce surfaces that nerve cells can attach and grow on in vitro. Electrospun chitosan fibers that are shown to be suitable for neurons to grow were produced in three different chemical compositions. New born hippocampal neurons and PC12 model cells were cultured on these surfaces and their interaction with the surfaces were investigated. The cells interact with electrospun fibers and these surfaces can be used for cell replacement in future clinical applications, providing new possibilities to treat human neurodegenerative diseases.