Dilek Çökeliler

An Alternative Electrospinning Approach With Varying Electric Field for 2-D-Aligned Nanofibers

In the electrospinning process, unstructured nanofiber mats are produced by oriented fluid jets with an external electrostatic field. Electrospun fibers have wide applications for the fabrication of composite materials, tissue scaffold, and membranes. However, electrospun fiber production systems have many problems, e.g., the bending instability due to the complicated oscillations of polymer jet. In this research, parallel plate and hollow cylindrical conducting electrodes are implemented through the jet trajectory in order to investigate the possibility of controlled deposition of polymer fibers. Parallel electrodes with proper driving sources can generate the steering field for the nanofiber formation at the collector plate based on analog addressing electronics. It was shown that the modulated electric field applied through the parallel plate electrodes notably increased the deposition of the electrospun polymer fibers in a controlled fashion at the collector, which is coherent to the computer simulations. Furthermore, the finite-length hollow cylinder dampened the bending instabilities of the polymer jet which decreases the characteristic spot size of the deposited electrospun fiber to a smaller diameter.

Electrospun nanofiber reinforcement of dental composites with electromagnetic alignment approach.

Polymethylmethacrylate (PMMA) is commonly used as a base acrylic denture material with benefits of rapid and easy handling, however, when it is used in prosthetic dentistry, fracturing or cracking problems can be seen due to the relatively low strength issues. Besides, acrylic resin is the still prominent material for denture fabrication due to its handy and low cost features. Numerous proposed fillers that are used to produce PMMA composites, however electrospun polyvinylalcohol (PVA) nanofiber fillers for production of PMMA composite resins are not studied as much as the others. The other focus of the practice is to compare both mechanical properties and efficiency of aligned fibers versus non-aligned PVA nanofibers in PMMA based dental composites. Field-controlled electrospinning system is manufactured and provided good alignment in lab scale as one of contributions. Some novel auxiliary electrodes in controlled structure are augmented to obtain different patterns of alignment with a certain range of fiber diameters. Scanning electron microscopy is used for physical characterization to determine the range of fiber diameters. Non-woven fiber has no unique pattern due to chaotic nature of electrospinning process, but aligned fibers have round pattern or crossed lines. These produced fibers are structured as layer-by-layer form with different features, and these features are used in producing PMMA dental composites with different volume ratios. The maximum flexural strength figure shows that fiber load by weight of 0.25% w/w and above improves in the maximum level. As a result, mechanical properties of PMMA dental composites are improved by using PVA nanofibers as a filler, however the improvement was higher when aligned PVA nanofibers are used. The maximum values were 5.1 MPa (flexural strength), 0.8 GPa (elastic modulus), and 170 kJ/m(3) (toughness) in three-point bending test. In addition to the positive results of aligned and non-aligned nanofibers it was found that they both have a non-toxic feature.

A plasma polymerization technique to overcome cerebrospinal fluid shunt infections

Prosthetic devices, mainly shunts, are frequently used for temporary or permanent drainage of cerebrospinal fluid. The pathogenesis of shunt infection is a very important problem in modern medicine and generally this is characterized by staphylococcal adhesion to the cerebrospinal fluid shunt surfaces. In this paper, the prevention of the attachment of test microorganism Staphylococcus epidermidis on the cerebrospinal fluid shunt surfaces by 2-hydroxyethylmethacrylate (HEMA) precursor modification in the plasma polymerization system, is reported. Different plasma polymerization conditions (RF discharge power 10-20-30 W, exposure time 5-10-15 min) were employed during the surface modification. The surface chemistry and topology of unmodified and modified shunts was characterized by x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Also, static contact angle measurements were performed to state the change of surface hydrophilicity. All samples were tested in vitro with Staphylococcus epidermidis. A plasma-polymerized HEMA film (PP HEMA) was found to be an alternative simple method to decrease the microorganism attachment and create bacterial anti-fouling surfaces. The attachment of the model microorganism Staphylococcus epidermidis on the shunt surface modified by PP HEMA at 20 W and 15 min was reduced 62.3% if compared to the unmodified control surface of the shunt.

Design and Implementation of Electrospinning System

Various methods for fabricating nanoscale polymeric fibers are investigated at large, e.g. tissue engineering . Electrospinning is the most versatile process among them. Materials such as polymer, composites and metal nanofibres have been fabricated with electrospinning techniques. It is important that many parameters and post, pre-processes should be investigated thoroughly to be able to optimize the method. Characteristics of the electrostatic field, and polymer solution constitute the main design criteria. The proposed experimental setup has been implemented with newly designed high voltage power suply which can be adjusted resiliently in frequency and power amplitude.

Improvement of mechanical performances by plasma polymerisation technique for composite biomaterials

In recent years, fibers are used for improving mechanical strength of acrylic-based resin which used for construction of protheses frequently. Improvement of the fiber- matrix interfase is a very important approach at redevelopment of mechanical properties. In this study, glass fibers are modified by radiofrequency (RF) plasma technique with using different monomers. Silane based monomer glisitoxypropyltrimethiloxysilane and amine based ethylenediamine (EDA)are polimerized on the glass fibers in plasma environment for application of two different approaches (hydrophobic/hydrophobic). Surface modification application is optimized with increasing power and exposure time parameters, which are used for low vacuum RF glow discharge. The change of surface properties for glass fibers are characterized by measurement of static contact angle and bending strain of fiber-acrylic composites are measured with 3 point bending device. While the cost of bending strain of the composites, which is prepared by virgin glass fibers, is 127.9±9 MPa, the maximum mechanical strength has been obtained at amine based plasma polymerization technique (150.2±4 MPa). The mechanical strenght is improved according to the working parameters that are used in silane based plasma polymerisation technique (141.2±7 MPa, power: 40W, Exposure Time: 30 min) Its proved with contact angle measurement that gaining less hydrofobic property to the surface is an appropriate approach.

Dense medium plasma technology for synthesis carbon nanomaterials

Plasma-aided nanofabrication is a rapidly expanding area of research spanning disciplines ranging from physics and chemistry of plasmas and gas discharges to solid state physics, materials science, surface science, nanoscience and nanotechnology and related engineering subject. A low-temperature nonequilibrium plasma is a favorable environment for the formation of nanoscale objects and has recently demonstrated the outstanding capability of promoting self-organization. Self-organization, defined here as simultaneous assembly and functionalization of nanostructures, or directed self-organization (when external energy drivers are applied, e.g., electric fields) can provide a very effective bottom-up nanofabrication mechanism. In addition, in order to meet the nano-manufacturing requirements, plasma research is increasingly giving attention to atmospheric plasma processes, whereby the high density promotes fast reaction rates and, therefore, the increased throughput. The possibility of producing nanostructures at atmospheric pressure has also the advantage of reduced costs of investment and maintenance due to the possibility of working without expensive vacuum equipment and without the need of process confinement. However, the generation of plasmas at atmospheric pressure has challenges and limitations that often compromise part of the advantages of atmospheric-pressure operation for nanofabrication.

Improved Bone Formation in Osteoporotic Rabbits with the Bone Morphogenetic Protein-2 (rhBMP-2) Coated Titanium Screws Which Were Coated By Using Plasma Polymerization Technique

Abstract Delaying of bone fusion in osteoporotic patients underwent spinal stabilization surgery leads to screw loosening, and this causes pseudoarticulation, mobility and fibrosis at vertebral segments. To prevent these complications, the screws coated with recombinant bone morphogenetic protein-2 (rhBMP-2) could be used. To verify this hypothesis, we coated 5 Titanium screws with rhBMP-2 using plasma polymerization method, and also used 10 uncoated screws for making comparison between coated and uncoated screws in different groups. And 15 skeletally mature white New Zealand female rabbits were assigned into three different groups: Group 1(N = 5): No osteoporosis induction and insertion of uncoated Titanium screw into right sacrum of each rabbit in group 1; group 2 (N = 5): Osteoporosis induction and insertion of uncoated Titanium screw into right sacrum of each rabbit in group 2; group 3 (N = 5) rhBMP-2 coated Titanium screw inserted into right sacrum of each rabbit in group 3. In summary, using of these coated screws provides new bone formation, but causes less fibrosis and less inflammation than uncoated screws at the interface between the coated screw and bone. Then the plasma polymerization technique provides controlled releasing of rhBMP-2 from the screw to the bone tissue in osteoporotic rabbits.

Design and implementation of radio frequency glow discharge system

Radio frequency glow discharge system is used for processing the fourth state of matter as called plasma in laboratory condition. Plasma state at room temperature is novel technique for biomedical applications especially in modification of sensor and different type of biomaterial surfaces to have proper functionality (improvement of hidrophilicity, hydrophobicity, tissue compability, blood compability etc.). In this study designs the parts of RF plasma system, RF generator, impedance matching and power source which will drive the 150 watt RF power amplifier are presented. This power which is produce by system, is applied on reference surface with the aid of electrodes. In this scope the power, which is get high frequency, is used for generating plasma at allowable value of inert gases and monomers on low pressure (10−3 Torr) and reference biomaterial surface will be modified homogeneously by this plasma generation.

The construction of biosensors with amperometric tranducers in biomedical engineering

Improving new diagnosis kit or increasing the performance of existing systems plays an important role in an application at the biomedical engineering. In this study, the production of the probe based on amperometric measurement have been achieved under the laboratory conditions. By this way some background on the main components of sensors which form the diagnostic systems will be gathered. In this study it is also aimed that this sensor will be applied as analytical device the probe with an appropriate recognation layer.