Metin Usta

BEHAVIOR AND PROPERTIES OF NEAT AND FILLED GELATINS

The purpose of this study was to determine the mechanical properties and the atomistic structures of various gelatin hydrogels as a preliminary to using these in bioengineering applications. The hydrogels were investigated as neat materials and as particulate-reinforced composites both in the as-formed state and following cross-linking with formaldehyde and/or glutaraldehyde. The compressive modulus obtained using alumina particulates as the reinforcement was found to be enhanced significantly more than expected on the basis of considering a gel matrix to be similar to a thermoplastic one. From the electron paramagnetic resonance of a Cu(2+) probe ion implanted in these materials it was determined that the variation in the compressive moduli with Bloom indices results from a gradation in the relative weightings of two discrete coordination configurations. The cross-linking led to different coordinations following the formaldehyde vs. the glutaraldehyde treatments.

Bioactivity and biocompatibility of hydroxyapatite-based bioceramic coatings on zirconium by plasma electrolytic oxidation

In the present work, hydroxyapatite (HAP)-based plasma electrolytic oxide (PEO) coatings were produced on zirconium at different current densities in a solution containing calcium acetate and β-calcium glycerophosphate by a single step. The phase structure, surface morphology, functional groups, thickness and roughness of the coatings were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), eddy current method and surface profilometer, respectively. The phases of cubic-zirconia, calcium zirconate and HAP were detected by XRD. The amount of HAP and calcium zirconate increased with increasing current density. The surface of the coatings was very porous and rough. Moreover, bioactivity and biocompatibility of the coatings were analyzed in vitro immersion simulated body fluid (SBF) and MTT (3-(4,5-dimethyl thiazol-2yl)-2,5-diphenyl tetrazolium bromide) assay, hemolysis assay and bacterial formation. The apatite-forming ability of the coatings was evaluated after immersion in SBF up to 28days. After immersion, the bioactivity of HAP-based coatings on zirconium was greater than the ones of uncoated zirconium and zirconium oxide-based surface. The bioactivity of PEO surface on zirconium was significantly improved under SBF conditions. The bacterial adhesion of the coatings decreased with increasing current density. The bacterial adhesion of the coating produced at 0.370A/cm2 was minimum compared to uncoated zirconium coated at 0.260 and 0.292A/cm2. The hemocompatibility of HAP-based surfaces was improved by PEO. The cell attachment and proliferation of the PEO coatings were better than the one of uncoated zirconium according to MTT assay results.

A tribological and biomimetic study of PI–CNT composites for cartilage replacement

This article presents an investigation into the possible matching of mechanical properties of a polyimide (PI)–carbon nanotube (CNT) composite system to natural cartilage tissue. Currently used ultrahigh molecular weight polyethylene (UHMWPE) used in total joint replacements presents certain drawbacks due to a mismatch in mechanical and tribological properties with those of a natural bone joint. Natural cartilage tissue is a composite material itself, being composed of collagen fibers, hydrophilic proteoglycan molecules, cells and other constituents. The current investigation attempts to mimic the mechanical and tribological properties of natural cartilage tissue by varying the CNT concentration in a PI matrix. Nanoindentation and pin-on-flat tribological tests were conducted for this purpose. It was found that the coefficient of friction (COF) reached a minimum at a concentration of 0.5% CNT (by volume) when articulated against Ti6Al4V alloy. When articulated against Ti6Al4V alloy in the presence of a lubricant, the minimum COF was obtained at a concentration of 0.2% CNT. The maximum penetration depth under nanoindentation varied with CNT concentration and indicated that the mechanical properties could be tailored to match that of cartilage tissue. A closer investigation into this behavior was carried out using scanning electron, transmission electron, and atomic force microscopy. It was noticed that there is good bonding between the CNTs and polyimide matrix. There was a ductile to brittle transition as the concentration of CNT was increased. Competing interactions between nanotube–matrix and nanotube–nanotube are possible reasons for the deformation and friction behavior identified.

A tribological comparison of pure and boronized chromium

Boronized metals are potential candidate materials for various industrial applications as well as for joint arthroplasty. This is due to their high hardness and corrosion resistance. In the present research, we investigated the tribological performance of boronized chromium when worn against bearing steel E52100. Pure chromium was used as a control material and tested under similar conditions. Three test conditions were used-dry sliding, with water, and with simulated body fluid (SBF). The highest coefficient of friction obtained was for chromium boride under dry sliding conditions. Water and SBF acted as lubricants and lowered the coefficient of friction. The friction coefficient for Cr and chromium boride was lowest under SBF conditions. SEM analysis showed that the wear modes were different under different test conditions. TEM analysis showed a layered-like structure of debris that could have acted as a lubricant and caused a very low friction coeffi.

Wear Behavior of Niobium Boride Coatings

Boride coatings on corrosion resistant refractory metals are potentially used as implanting materials. In this research, we investigated wear mechanisms of boride coatings on pure niobium using a pin-on-disk tribometer. Surface morphology studied using scanning electron microscope shows the compressed boride layer with indistinguishable regions such as coating intermediate transition layer and the substrate. The surface analysis after wear tests was conducted using an atomic force microscope (AFM). It was found that the boride coating underwent deformation wear, and debris formed and accumulated at both ends of the track due to adhesion.

Properties of Alumina Coating Formed by Microarc Oxidation Technique on 6061 Aluminum Alloy

Abstract In this study, thick and hard alumina coatings were produced on 6061-T6 Al alloy substrates for different oxidation times and current densities by using of microarc oxidation (MAO) technique in an alkali-silicate electrolytic solution. The influence of oxidation time and current density on the kinetics, phase composition, hardness, surface roughness and structure of the coating were investigated. It is found that the kinetics of coating mainly depends on applied current density and oxidation time. The XRD results revealed that the coatings are composed of mainly α-Al2O3, γ-Al2O3 and mullite phase. The relative ratio of harder and denser α-Al2O3 phase increases with increasing current density and oxidation time. For the same coating time, the position of maximum hardness of coatings moves away from the substrate-coating interface to the coating surface with increasing current density. The surface roughness of coating is a function of coating thickness and increases with increasing deposition time and current density. The surface micro hardness of Al 6061-T6 alloy substrate was increased up to 2200 HV hardness after the coating.

Perspectives of methods of laser monitoring of the atmosphere and sea surface

Laser monitoring (remote sensing) may be considered as the science of collecting and interpreting information about the atmosphere, earth and sea using sensors on earth, on platforms in our atmosphere (airplanes, balloons) or in space (satellites) without being in direct physical contact with them. Remote sensing by LIDARs (Light Identification Detection and Ranging) has wide applications as technique to probe the Earths atmosphere, ocean and land surfaces. LIDARs are widely used to get knowledge of spatial and temporal variations in meteorological quantities (e.g. temperature, humidity, clouds and aerosol properties) and to monitor the changes in these quantities on different timescales. Subject of the present work is quite wide. It is rather difficult to perform analysis and to provide full knowledge about existing information. In the present work, in addition to the literature data, the information will be provided also about KA-09 aerosol LIDAR developed at the Marmara Research Centre of TÜBITAK (Turkish Scientific and technological Research Council) and also about KA-14 LIDAR developed at the National Aviation Academy of Azerbaijan for remote sensing of contaminations on water surfaces taking place during oil-gas production. The main goal of this paper is to give students insight in different remote sensing instruments and techniques (including their perspectives) that are used for the derivation of meteorological quantities and obtaining the information about water surface.

The effect of high flux hemodialysis on polymeric hollow fibers used in dialyzers

High flux dialysis the first choice of therapy for hemodialysis patients within the last decade due to its clinical outcome. In this study the effect of dialysis environment on the mechanical and structural stability of high flux dialyzers containing polysulfone membranes were investigated. Dialysis sessions were performed on a certain group of patients with dialysis ages less than two years and without any other accompanying disease. Mechanical data and XRD results revealed the differences in material characteristics between virgin and used membranes obtained from polysulfone membranes. With the help of tensile tests it was shown that the mechanical properties used membranes were reduced in terms of ultimate tensile strength. XRD experiments revealed that the degree of crystallinity of the polysulfone dialysis membranes were raised. It was concluded that high flux dialyzer membranes are becoming more brittle and having more crystallinity after dialysis session. By this way the membranes are more prone to mechanical defects during dialysis. The degree of crytallinity increases under cyclic loading which resembles the changing of the pump speed or transmembrane pressure during dialysis in case of clinical situations like hypotension during dialysis. This issue is very important for dialysis centers performing reuse procedures for dialysis centers, because any damage to dialysis membranes would cause very serious clinical complications.

The Influences of Reuse Solution and the Hemodialysis Environment on the High Flux Polyamide Hollow Fiber Membranes

In order to reveal the effect of reuse solution and the hemodialysis environment on the stability of high flux polyamide hollow fiber membranes, mechanical tests, surface and X-ray diffraction studies were performed on both virgin 17S high flux polyamide hollow fiber and used-processed 17S high flux polyamide hollow fiber membranes. Used fibers were left in 4% formaldehyde solution for 14 hours and then in 5% sodium hypochloride (bleach) solution for 6 hours in order to disinfect the membrane for the reuse idea. Tensile tests performed on both virgin and used-processed fibers reveal that toughness and ductility of the used-processed fibers are lower than the virgin ones. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) studies performed on virgin and used-processed fiber visualized the morphological changes. Rough surface with defects and cracks was seen in used-processed fiber, whereas a smoother surface morphology was seen in virgin fibers. Alterations in pore morphology and the size of the pores became greater in used processed fibers. Cracks, merging of pores and also more defects were visualized in used-processed fibers. Thus, easy crack initiations and easy propagations were expected in used-processed fibers which were also confirmed by tensile test experiments. In addition to these mechanical and surface studies experiments, X-ray diffractometry studies also revealed the changes in the structure of the used-processed fibers. New or growth of the existing phases and orientations were observed in usedprocessed fibers. This study showed that dialysis environment caused structural changes on membranes which may cause clinical complications.

The Effects of Different Antiembolic Agents on the Crystallinity of Fractured Bones during the Healing Period

In order to decrease the potential clinical problems that could be caused by embolism Antiembolic agents are routinely used in orthopaedics&traumatology clinics, especially after arthroplastic operations or in case of having tumor and major trauma in order. This study was designed to evaluate the side effects of different antiembolic agents on the bone fracture healing. After experiments on animals, where “enoxaparin”, “fondaparinux” and “heparin” are used as antiembolic agents given after bone fracture, fractured and healed bones are studied by using X-Ray Diffraction technique. To reach this idea, initially, rat which was used as experimental animal was injected by different antiembolic agents. After sacrificing(with the permission of ethical committee) of animal XRD studies were performed on the bones in Material Laboratories of GYTE(Gebze Yuksek Technology Enstitusu) in order to reveal changes in the crystallinity of the bone samples.