Güngör Gündüz

Synthesis, characterization and osteoblastic activity of polycaprolactone nanofibers coated with biomimetic calcium phosphate

Immersion of electrospun polycaprolactone (PCL) nanofiber mats in calcium phosphate solutions similar to simulated body fluid resulted in deposition of biomimetic calcium phosphate layer on the nanofibers and thus a highly bioactive novel scaffold has been developed for bone tissue engineering. Coatings with adequate integrity, favorable chemistry and morphology were achieved in less than 6h of immersion. In the coating solutions, use of lower concentrations of phosphate sources with respect to the literature values (i.e., 3.62 vs. 10 mM) was substantiated by a thermodynamic modeling approach. Recipe concentration combinations that were away from the calculated dicalcium phosphate phase stability region resulted in micron-sized calcium phosphates with native nanostructures. While the nano/microstructure formed by the deposited calcium phosphate layer is controlled by increasing the solution pH to above 6.5 and increasing the duration of immersion experimentally, the nanostructure imposed by the dimensions of the fibers was controlled by the polymer concentration (12% w/v), applied voltage (25 kV) and capillary tip to collector distance (35 cm). The deposited coating increased quantitatively by extending the soak up to 6h. On the other hand, the porosity values attained in the scaffolds were around 87% and the biomimetic coatings did not alter the nanofiber mat porosities negatively since the deposition continued along the fibers after the first 2h. Upon confirming the non-toxic nature of the electrospun PCL nanofiber mats, the effects of different nano/microstructures formed were evaluated by the osteoblastic activity. The levels of both alkaline phosphatase activity and osteocalcin were found to be higher in the coated PCL nanofibers than in the uncoated PCL nanofibers, indicating that biomimetic calcium phosphate on PCL nanofibers supports osteoblastic differentiation.

Idarubicin-loaded folic acid conjugated magnetic nanoparticles as a targetable drug delivery system for breast cancer.

Conventional cancer chemotherapies cannot differentiate between healthy and cancer cells, and lead to severe side effects and systemic toxicity. Another major problem is the drug resistance development before or during the treatment. In the last decades, different kinds of controlled drug delivery systems have been developed to overcome these shortcomings. The studies aim targeted drug delivery to tumor site. Magnetic nanoparticles (MNP) are potentially important in cancer treatment since they can be targeted to tumor site by an externally applied magnetic field. In this study, MNPs were synthesized, covered with biocompatible polyethylene glycol (PEG) and conjugated with folic acid. Then, anti-cancer drug idarubicin was loaded onto the nanoparticles. Shape, size, crystal and chemical structures, and magnetic properties of synthesized nanoparticles were characterized. The characterization of synthesized nanoparticles was performed by dynamic light scattering (DLS), Fourier transform-infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), scanning electron microscopy (SEM) analyses. Internalization and accumulation of MNPs in MCF-7 cells were illustrated by light and confocal microscopy. Empty MNPs did not have any toxicity in the concentration ranges of 0-500μg/mL on MCF-7 cells, while drug-loaded nanoparticles led to significant toxicity in a concentration-dependent manner. Besides, idarubicin-loaded MNPs exhibited higher toxicity compared to free idarubicin. The results are promising for improvement in cancer chemotherapy.

Structure–Property Study of Waterborne Polyurethane Coatings with Different Hydrophilic Contents and Polyols

Abstract In this study, water dispersed paints were produced using polyester polyol, isophorone diisocyanate (IPDI) and hydrophilic monomers. Two sets of experiments were performed. In the first group, the effects of various proportions of the hydrophilic monomers dimethylol propionic acid (DMPA) and tartaric acid (TA) on the state of dispersion, physical, mechanical, and surface properties were investigated. The total hydrophilic content was fixed at 3.5 wt% of solids. In the second group, waterborne polyurethanes were prepared by using mixed polyols as the physical properties of waterborne polyurethanes were highly affected by the composition and the molecular chain length of the soft segment. Hence, in the second group, up to 20 wt% of polyester polyol (diol) was replaced by poly(propylene‐ethylene) copolymer polyol (triol) leading to branched polyurethanes. Only DMPA was used in this case as the ionic building block. The effects of polyester/polyether ratio on the state of dispersion, physical, mechanical, and surface properties were examined. For the first group of experiments, the increase in the amount of TA in the polymer yields coarser particle sizes and broadened particle size distributions. The increase of TA content yielded an increase in the hardness and in the contact angles with water. Upon replacing part of polyester polyol with polyether triol, higher values for average particle sizes and broadened particle size distributions were obtained. It also yielded an increase in hardness values and an increase in contact angles with water. It was found that replacing more than 15 wt% of polyester in the total polyol with polyether caused drastic changes in the state of dispersion and other properties due to a change in the internal structure. All samples showed superior impact resistance and flexibility.

Powder characteristics and microstructure of uranium dioxide and uranium dioxide-gadolinium oxide fuel

Three different fuels UO2-only, UO2-Gd203(5%), and UO2-Gd203(10%) were produced by sol-gel technique. Their powder characteristics such as flowability, BET surface area, average pore diameter, and cumulative pore volume were determined. The pore size distributions of powders, green pellets, and sintered fuels were determined by using a mercury porosimeter. The theoretical densities of sintered fuels were found to be 98.01, 95.3, and 95.9%, respectively. Their ruggedness fractal dimensions were 1.111, 1.044, and 1.042, while the fractal dimensions associated with the size distribution of grains were 1.44, 1.58, and 1.60, respectively.

Synthesis and characterization of waterborne and phosphorus-containing flame retardant polyurethane coatings

Phosphorus-containing flame retardant water-dispersed polyurethane coatings were produced by incorporating different amounts of a phosphorus compound onto the polyurethane main chain. The novel phosphorus containing compound (phosphorus phenyl dihydroxy) was synthesized in three steps using benzaldehyde, pentaerythritol, phenyl phosphonic dichloride, and acetic acid.The addition of phosphorus phenyl dihydroxy to the main chain of polyurethane, in which NCO/OH ratio was kept constant at 1.5 and the amount of dimethylolpropionic acid (DMPA) at 3.5 wt%, increased the hardness and abrasion resistance, but only slightly decreased the gloss values of the polyurethane paints. All the samples showed superior impact resistance and flexibility. Moreover, increasing the phosphorus content increased the char yield, and the maximum fire retardancy was reached at 1.5% P content with a limiting oxygen index (LOI) value of 29.

Extraction of strontium ions with emulsion liquid membrane technique

Abstract The aims of this study are to form a liquid membrane suitable for the extraction of strontium ions from aqueous solutions and to determine the factors influencing the stability of the membrane, the extraction efficiency and the rate of transport. The suggested membrane is composed of kerosene, Span 80 and D2EHPA. It has been observed that the extraction efficiency and the rate of transport increase with increasing ratio of emulsion to outer phase volume, stirring rate and D2EHPA concentration and decreasing pH of the inner phase. As the strontium ion concentration in the outer phase increases, the transport rate increases but the separation efficiency decreases. The maximum separation efficiency achieved in the experiments was 92%.

Highly branched and tartaric acid‐based water‐borne resins

In this study, water-borne polyurethane resins were produced using poly(propylene-ethylene) copolymer triol, toluene diisocyanate, and hydrophilic monomers, dimethylol propionic acid and tartaric acid. The hydrophilic monomers were used separately. In either case, the ratio of isocyanate functional groups to the sum of hydroxyl groups of polyol and hydrophilic monomer was kept constant. The increase in the amount of hydrophilic monomer increased the hardness of resins when used as varnish. Tartaric acid resulted in higher hardness than dimethylol propionic acid. The dispersions made by using tartaric acid had much larger particle sizes than those of dimethylol propionic acid. In another set of experiments, the samples carrying the optimum properties from the two sets were mixed with methylol urea that served as crosslinker in the baking step. The physical and mechanical properties were determined by changing the weight percentages of the two types of samples in the mixture, and by changing the methylol urea percentage of the mixture which exhibited the maximum hardness. All samples showed superior impact resistance, adhesion, and flexibility.

Flame retardant alkyd paint

In this research long oil alkyd resin, and styrenated alkyd resin were made flame retardant by the incorporation of (i) bis-pyridine bis-tribromophenoxo copper (II) complex, and (ii) polydibromo-phenylene oxide (PDBPO). The former was synthesized in the laboratory, and the second one was obtained from the decomposition of the complex. Both of these compounds exhibit very good flame retardance effect when mixed with alkyd resins. Either of the additives is physically incorporated into the resins through grinding in a pebble mill until all particulates have a size below 10 μm. An oxygen index value of 26 was achieved with about 6% by weight PDBPO, and about 2% complex addition to the resins. These additives affect the physical and the mechanical properties of the paints when introduced at an amount of 8% either complex or PDBPO. The complex did not affect the drying time of resins while PDBPO increased the drying time of styrenated alkyd resin. Leveling and sagging are not affected in either case. The hardness was increased by the complex, and was not significantly changed by PDBPO. However the impact strength was decreased by either additive. The abrasion strength of long oil alkyd resin was decreased by PDBPO, and it was increased in all other cases.

Development of new nuclear shielding materials containing vitrified colemanite and impregnated polymer

Abstract New shielding materials were developed by using vitrified colemanite in powder form in cement phase and as particles in coarse aggregate in concrete. Vitrification was done to decrease the deleterious effects of colemanite on the setting of cement and thus to increase the boron content in the shielding wall to improve thermal neutron absorption. The boron oxide content of concrete was shown to increase to 15 wt% which is about 5–6 times more than the boron oxide content of conventional nuclear reactor concrete walls. Iron chunks were partly used in coarse aggregate to compensate for the decrease in density due to vitrified colemanite, and thus the improve attenuation of gamma rays. Polymer impregnation of hardened concrete improves its mechanical and shielding properties. By using a computer shielding program it was found that the materials developed usually have better shielding properties than the conventional shielding walls.

Trace elements in Turkish tobacco determined by instrumental neutron activation analysis

The concentration of 20 trace elements in nine different brands of Turkish cigarette tobacco and in a brand of pipe tobacco and in tobacco ash has been determined by instrumental neutron activation analysis. The percent transference of elements into smoke has been estimated from the amounts remaining in the ash.