Osman Kilic

The Levenberg-Marquardt Neural Network model of the PEMFC's MEA

Fuel cells are electrochemically complex, nonlinear, and dynamic energy conversion systems. Due to the dynamic characteristics of the fuel cell electrical performance models are used for system evaluation. In this study, Artificial Neural Network (ANN) technique is used as the modeling tool for internal structures of the fuel cells complex electrochemical reactions. The proton exchange membrane fuel cell (PEMFC) inputs are selected as anode flow, cathode flow, and cell temperature for the proposed Levenberg-Marquardt Neural Network model (LMNN). The outputs for the PEMFC model are current and voltage parameters. The model outputs are compared with the measured values and the maximum error is around 3%. The proposed ANN model is developed with MATLAB.

Electrohydrodynamic (EHD) Bioprinting of Polycaprolactone Scaffolds

This study is combined a 3D printing and Electrohydrodynamic (EHD) methods to fabricate a 3D PCL scaffolds for tissue engineering. Various kV values were applied to the different PCL solutions to investigate the effect of the voltage on scaffolds. The morphology of 3D-EHD printed PCL scaffolds were characterized by an Optical Microscope. 10 wt.% PCL up to 3 kV was obtained best sample to use for tissue engineering scaffolds.

Microstructural and Mechanical Properties of Nano-Yttria-Oxide Doped Hydroxyapatite Composites

Nowadays hydroxyapatite (HA) bioceramics are very important because increasing traffic accidents and ageing of the population. They can be produced from synthetic or natural sources with different production methods. The biggest negative issue of HA is being very brittle and unstable under pressure. Various materials are added for restoring these weaknesses, but there is not so much studies adding nano-ingredients for restoring the mechanical properties of HA. In this study, 5-10% nano-yittria-oxide is added to bovine derived HA (BHA) and to commercial synthetic (CSHA) as a control group. Physical and mechanical properties are examined. Results show that adding of nano-ingredients are really helping to mechanical properties of HA.

3D Liquid Bioprinting of the PCL/β-TCP Scaffolds

In this present work, an original 3D bioprinting method has been developed by modifying an exceptional 3D printer. Using a composite material, bioprinting was carried out to create the ideal scaffold material to contribute regeneration of the certain amount of tissue types in humans. After bypassing the extruder and heating system of the 3D printer, instead of using solid filaments, polymer-ceramic composite was dissolved using an organic agent and bioprinting was conducted. During the bioprinting, dissolving agent was evaporated quickly and solidification process was completed. Despite of the traditional 3D printing, which benefits from the glass transition temperature of the materials, regardless of the temperature, rapid prototyping technology has been merged with controlled flow rate of the composite solution and evaporation of the solvents were adjusted meticulously for proper solidification and layer by layer bioprinting of the scaffolds.

Novel electrospun polycaprolactone/graphene oxide/Fe3O4 nanocomposites for biomedical applications

In this study, one of the most promising methods of tailoring a composite scaffold material in nano sized diameters, electrospinning method were used to produce Polycaprolactone (PCL)/Graphene Oxide (GO)/Iron(II, III) Oxide (Fe3O4) nanocomposite fibers as biocompatible scaffolds for biomedical applications. Products were analyzed by scanning electron microscopy (SEM) for morphological analysis of the electrospun nanocomposites and Fourier Transform Infrared Spectroscopy (FTIR) was used to determine functional groups of the PCL, GO, and Fe3O4 materials in the electrospun nanocomposites. For physical properties, viscosity, density, permittivity, dielectric loss and liquid and solid state alternating current conductivity, measurements were done for each nanocomposite fibers. Effects of concentration percentage of GO on permittivity, dielectric loss and AC conductivity have been analyzed by using measured and calculated data. Trend lines have been drawn for permittivity, dielectric loss and conductivity via concentration percentage of GO. The relation between ac conductivity and frequency have been studied for each concentration percentage of GO and interpretations have been done by using the obtained results.

Effects of sintering temperature on electrical properties of sheep enamel hydroxyapatite

Bioceramics, especially calcium phosphate based bioceramics, whose examples are hydroxyapatite, and calcium phosphate powders have been widely used in the biomedical engineering applications. Hydroxyapatite (HA) is one of the most promising biomaterials, which are derived from natural sources, chemical method, animal like dental enamel and corals. The influence of sintering temperature on the electrical properties (i.e. DC conductivity, AC conductivity) of samples of sintered sheep enamel (SSSE) was studied in air and in vacuum ambient at room temperature. The sheep enamel were sintered at varying temperatures between 1000°C and 1300°C. DC conductivity results revealed that while dc conductivity of the SSSE decreases with increasing the sintering temperature in air ambient the values increased with increasing the sintering temperature in vacuum ambient. AC conductivity measurements were performed in the frequency range of 40 Hz - 105 Hz. The results showed that ac conductivity values decrease with increasing the sintering temperature.

Mechanical and Physical Properties of Dentine-Glass Composites

Hydroxyapatite (HA) is one of the most widely used bioceramics to reconstruct most parts of the skeleton. HA biomaterials are nontoxic and biocompatible with bony tissues. It can be derived from natural sources like bovine bone and other original sources. Also it can be produced synthetically from reagent materials. Due to the fact that HA is not able to be used in biomedical applications cause of bear loadings. It has to be reinforced with materials such as whiskers, metallic oxides, glasses and others. In this study, sintering effects on physical and mechanical properties, such as density (gr/cm3), compression strength (MPa) and Vickers microhardness (HV) of the commercial inert glass (CIG) added human dentine HA (DHA) composite investigated. HA source material is dentine material which is obtained from extracted human teeth. After calcinations enamel and dentine parts were separated (850°C - 4 hours). DHA particles were ball milled and sieved through 100µm sieve. DHA is mixed with 5 and 10 % CIG. Then, this composite material is pressed with a steel mould and sintered in the temperature range of 1000°C to 1300°C with 100°C increments. After scanning electron microscope (SEM) and x-ray diffraction (XRD) studies, both physical and mechanical characterization for DHA – CIG composites are completed by performing density, micro and macro-mechanical test procedures, i.e., HV and compression testing. Briefly, density measurements are conducted corresponding to the Archimedes principle. HV measurements are obtained under a 200g load. Compression test is performed at a rate of 2 mm/min. Here the densest structure was obtained as 2.48 gr/cm3 at 1300°C with 5 wt.% CIG addition. The HV values are increasing with temperature (1082 HV at 1300°C with 10 wt.% CIG addition). The toughest MPa value is 118MPa with 10%CIG addition, sintered at 1300°C. Inert glass addition to dentine HA sounds promising with increasing values of microhardness and compression properties. It can be described as a very hard and a strong biomaterial.