The Experts below are selected from a list of 240 Experts worldwide ranked by ideXlab platform
B J Ballermann - One of the best experts on this subject based on the ideXlab platform.
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Shear stress-conditioned, endothelial cell-seeded vascular grafts: Improved cell adherence in response to in vitro shear stress
Surgery, 1995Co-Authors: B J BallermannAbstract:Background . Prosthetic vascular grafts with adherent endothelial cell monolayers may prove useful for small-caliber vessel bypass. However, endothelial cells adhere poorly to prosthetic graft material, and they are stripped when exposed to in vivo shear stress. This study sought to determine whether in vitro shear stress conditioning improves endothelial cell adhesion and decreases thrombogenicity of endothelial cell-seeded grafts. Methods . The lumens of 1.5 mm (inside diameter) spun Polyurethane Polymer vascular grafts were seeded with bovine aortic endothelial cells and cultured in vitro for 6 days with or without continuous laminar shear stress, first at 1 to 2 dynes/cm 2 for 3 days, then at approximately 25 dynes/cm 2 for 3 days. Grafts preconditioned by shear stress and the static control grafts were then exposed to arterial shear stress at 25 dynes/cm 2 for 25 seconds. The number of dislodged cells was counted, and the grafts were examined by light and scanning electron microscopy. Whole blood clotting time in the grafts was also determined. Results . Exposure of grafts to acute shear stress dislodged 1.35×10 6 ±0.44×10 6 cells from static grafts compared with 1.05×10 4 ±0.16×10 4 cells from grafts preconditioned by shear stress. By light and electron microscopy an intact endothelial monolayer was observed to cover the lumen of shear stress-conditioned grafts, whereas few cells remained on the luminal surface of grafts not previously exposed to shear stress. The clotting time in shear stress-conditioned grafts was significantly prolonged in relation to grafts not exposed to shear stress. Conclusions . These findings show that endothelial cell adhesion and retention on vascular grafts in vitro is markedly enhanced by preconditioning the seeded endothelial cell monolayer with long-term shear stress. Consequently, vascular grafts containing shear stress-conditioned endothelial monolayers are less thrombogenic in vitro than small-caliber vascular grafts without intact endothelial cell monolayers.
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Shear stress-conditioned, endothelial cell-seeded vascular grafts: Improved cell adherence in response to in vitro shear stress
Surgery, 1995Co-Authors: B J BallermannAbstract:Background . Prosthetic vascular grafts with adherent endothelial cell monolayers may prove useful for small-caliber vessel bypass. However, endothelial cells adhere poorly to prosthetic graft material, and they are stripped when exposed to in vivo shear stress. This study sought to determine whether in vitro shear stress conditioning improves endothelial cell adhesion and decreases thrombogenicity of endothelial cell-seeded grafts. Methods . The lumens of 1.5 mm (inside diameter) spun Polyurethane Polymer vascular grafts were seeded with bovine aortic endothelial cells and cultured in vitro for 6 days with or without continuous laminar shear stress, first at 1 to 2 dynes/cm 2 for 3 days, then at approximately 25 dynes/cm 2 for 3 days. Grafts preconditioned by shear stress and the static control grafts were then exposed to arterial shear stress at 25 dynes/cm 2 for 25 seconds. The number of dislodged cells was counted, and the grafts were examined by light and scanning electron microscopy. Whole blood clotting time in the grafts was also determined. Results . Exposure of grafts to acute shear stress dislodged 1.35×10 6 ±0.44×10 6 cells from static grafts compared with 1.05×10 4 ±0.16×10 4 cells from grafts preconditioned by shear stress. By light and electron microscopy an intact endothelial monolayer was observed to cover the lumen of shear stress-conditioned grafts, whereas few cells remained on the luminal surface of grafts not previously exposed to shear stress. The clotting time in shear stress-conditioned grafts was significantly prolonged in relation to grafts not exposed to shear stress. Conclusions . These findings show that endothelial cell adhesion and retention on vascular grafts in vitro is markedly enhanced by preconditioning the seeded endothelial cell monolayer with long-term shear stress. Consequently, vascular grafts containing shear stress-conditioned endothelial monolayers are less thrombogenic in vitro than small-caliber vascular grafts without intact endothelial cell monolayers.
Simin Nazari - One of the best experts on this subject based on the ideXlab platform.
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β-cyclodextrin-Polyurethane Polymer: A neutral and eco-friendly heterogeneous catalyst for the one-pot synthesis of 1,4-dihydropyridine and polyhydroquinolien derivatives via Hantzsch reaction under solvent-free conditions
Journal of the Serbian Chemical Society, 2014Co-Authors: Ali Reza Kiasat, Simin Nazari, Jamal DavarpanahAbstract:An efficient synthesis of 1,4-dihydropyridine and polyhydroquinoline derivatives using a β-cyclodextrin-Polyurethane Polymer (β-CDPU) as a sta- tionary micro-vessel and neutral heterogeneous catalyst via a four component coupling of aldehydes, β-ketoester (2 mol) and ammonium acetate under sol- vent-free conditions is described. Compared with the classical Hantzsch reac- tion, this new method has the advantages of good yield, short reaction time and methodological simplicity. β-CDPU was proved to be an efficient heterogene- ous catalyst that could be easily handled and removed from the reaction mix- ture by simple filtration, and also recovered and reused without loss of reac- tivity.
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magnetic nanoparticles grafted with β cyclodextrin Polyurethane Polymer as a novel nanomagnetic Polymer brush catalyst for nucleophilic substitution reactions of benzyl halides in water
Journal of Molecular Catalysis A-chemical, 2012Co-Authors: Ali Reza Kiasat, Simin NazariAbstract:Abstract The Polymer coated magnetic nanoparticles has gained significant attention for potential applications in biomedicine, separations, and magnetic storage. In this study, β-cyclodextrin–Polyurethane Polymer coated Fe 3 O 4 magnetic nanoparticle as a novel class of hybrid organic/inorganic molecular catalyst was successfully prepared and evaluated as solid–liquid phase-transfer catalyst and molecular host system for nucleophilic substitution reactions. The nanocomposite has demonstrated the ability to catalytic the nucleophilic substitution reaction of benzyl halides with thiocyanate, azide, cyanide and acetate anions in water. No evidence for the formation of by-products for example isothiocyanate or alcohol was observed and the products obtained in pure form without further purification. The nanomagnetic Polymer brush catalyst was easily removed from solution via application of a magnetic field, allowing straightforward recovery and reuse. Results obtained from scanning electron microscopy (SEM) and vibrating sample magnetometery (VSM) show that the synthesized magnetic nanocomposite are superparamagnetic with a mean diameter of 59 nm. The grafting of β-cyclodextrin–Polyurethane Polymer to Fe 3 O 4 magnetic nanoparticle is confirmed by Fourier transform infrared spectroscopy (FT-IR).
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Magnetic nanoparticles grafted with β-cyclodextrin–Polyurethane Polymer as a novel nanomagnetic Polymer brush catalyst for nucleophilic substitution reactions of benzyl halides in water
Journal of Molecular Catalysis A: Chemical, 2012Co-Authors: Ali Reza Kiasat, Simin NazariAbstract:Abstract The Polymer coated magnetic nanoparticles has gained significant attention for potential applications in biomedicine, separations, and magnetic storage. In this study, β-cyclodextrin–Polyurethane Polymer coated Fe 3 O 4 magnetic nanoparticle as a novel class of hybrid organic/inorganic molecular catalyst was successfully prepared and evaluated as solid–liquid phase-transfer catalyst and molecular host system for nucleophilic substitution reactions. The nanocomposite has demonstrated the ability to catalytic the nucleophilic substitution reaction of benzyl halides with thiocyanate, azide, cyanide and acetate anions in water. No evidence for the formation of by-products for example isothiocyanate or alcohol was observed and the products obtained in pure form without further purification. The nanomagnetic Polymer brush catalyst was easily removed from solution via application of a magnetic field, allowing straightforward recovery and reuse. Results obtained from scanning electron microscopy (SEM) and vibrating sample magnetometery (VSM) show that the synthesized magnetic nanocomposite are superparamagnetic with a mean diameter of 59 nm. The grafting of β-cyclodextrin–Polyurethane Polymer to Fe 3 O 4 magnetic nanoparticle is confirmed by Fourier transform infrared spectroscopy (FT-IR).
Chukwunonso Peter Okoli - One of the best experts on this subject based on the ideXlab platform.
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development of sustainable magnetic Polyurethane Polymer nanocomposite for abatement of tetracycline antibiotics aqueous pollution response surface methodology and adsorption dynamics
Journal of Cleaner Production, 2019Co-Authors: Chukwunonso Peter Okoli, Augustine E OfomajaAbstract:Abstract Poor surface characteristics and mechanical strength have impeded the industrial utilization of starch-based Polymers for wastewater treatment. Though miniaturization of adsorbent materials to nano-scale level, has improved the surface area of materials, nano-scale adsorbents often form stable colloidal suspension/emulsion, and thus pose separation challenges. This study was designed to develop a novel starch-based magnetic Polyurethane Polymer for removal of tetracycline antibiotics from water media. Magnetic starch was synthesized by in-situ co-precipitation of Fe2+ and Fe3+ in the presence of starch, and thereafter subjected to one-step reticulation with 4,4-methylene diphenyl diisocyanate to produce magnetic starch Polyurethane Polymer nanocomposite (MSPP). The characterization studies with FTIR, SEM, TEM, XRD, VSM, BET, and XRF indicated successful synthesis. The characterization, adsorption isotherm and pH studies indicated π-π and π-cation interaction as possible adsorption interactions. Besides optimization of desirable properties of MSPP, the RSM approach provided empirical evidence for the existence of the suggested adsorption interaction, as adsorption increased with increment in magnetite content and degree of crosslinking of the MSPP nanocomposite which were responsible for π-cation and π-π interactions, respectively. The adsorption/desorption profile of MSPP indicated multiple potential applications beyond water treatment. Aside incorporation of magnetic separation, the regenerability, cheap, and sustainable nature of starch precursor confers a comparative cost advantage to the developed Polymer. Considering its effectiveness in both simulated and real-time wastewater samples, MSPP holds great promise for commercialization of starch-based Polymer adsorbents beyond decontamination applications.
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Mechanism of dialkyl phthalates removal from aqueous solution using γ-cyclodextrin and starch based Polyurethane Polymer adsorbents.
Carbohydrate polymers, 2014Co-Authors: Chukwunonso Peter Okoli, Gregory O. Adewuyi, Qian Zhang, Paul N. Diagboya, Qingjun GuoAbstract:Phthalate esters have been known as potent endocrine disruptors and carcinogens; and their removal from water have been of considerable concern recently. In the present study, gamma-cyclodextrin Polyurethane Polymer (GPP), gamma-cyclodextrin/starch Polyurethane coPolymer (GSP), and starch Polyurethane Polymer (SPP) have been synthesized and characterized. Their adsorption efficiencies for the removal of dimethyl phthalate (DMP) and diethyl phthalate (DEP) from aqueous solutions were investigated. The characterization results showed the success of the synthesis. The isotherms were L-type, and both the Langmuir and Freundlich adsorption isotherm gave good fittings to the adsorption data. Adsorption mechanisms suggested that these adsorbents spontaneously adsorb phthalate molecules driven mainly by enthalpy change, and the adsorption process was attributed to multiple adsorbent-adsorbate interactions such as hydrogen bonding, pi-pi stacking, and pore filling. The results showed that starch and gamma-cyclodextrin Polyurethane Polymer adsorbents have excellent potential as adsorbent materials for the removal of phthalates from the contaminated water. (C) 2014 Elsevier Ltd. All rights reserved.
Meysam Banimahd - One of the best experts on this subject based on the ideXlab platform.
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reducing railway track settlement using three dimensional Polyurethane Polymer reinforcement of the ballast
Construction and Building Materials, 2013Co-Authors: Justin Kennedy, Peter Keith Woodward, Gabriela M Medero, Meysam BanimahdAbstract:Abstract This paper presents the measured settlement results of full-scale testing of unreinforced and Polymer reinforced ballast railway track under laboratory conditions, using the GRAFT I (Geopavement and Railways Accelerated Fatigue Testing) facility to show the significant reduction in track settlement that can be obtained using in-situ ballast reinforcement techniques. The measured settlement profile of each track specimen is monitored up to a maximum of 500,000 load cycles at different load levels and formation conditions, ranging from a subgrade Young’s modulus of 25–51 MPa. The results of a 3-dimensional Polyurethane ballasted track reinforcement technique called XiTRACK, at an equivalent axle load of 44.4 tonnes, are then directly compared to the unreinforced settlement profile using developed settlement models from the tests. The Polymer treated track is observed to reduce permanent track settlement by 99%, effectively giving slab-track like performance. The free draining properties of the formed GeoComposite are also highlighted. The paper concludes by presenting and commenting on, the application of the technique to real UK Switch & Crossing sites on the West Coast Main Line and at Clapham Junction. In the former case, at Points 215D, the application of the technique eliminated the need for track maintenance over the 10 year operating cycle at axle loads of 25 tonne and main line speeds of 125 mph confirming the measured laboratory observations.
Ali Reza Kiasat - One of the best experts on this subject based on the ideXlab platform.
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β-cyclodextrin-Polyurethane Polymer: A neutral and eco-friendly heterogeneous catalyst for the one-pot synthesis of 1,4-dihydropyridine and polyhydroquinolien derivatives via Hantzsch reaction under solvent-free conditions
Journal of the Serbian Chemical Society, 2014Co-Authors: Ali Reza Kiasat, Simin Nazari, Jamal DavarpanahAbstract:An efficient synthesis of 1,4-dihydropyridine and polyhydroquinoline derivatives using a β-cyclodextrin-Polyurethane Polymer (β-CDPU) as a sta- tionary micro-vessel and neutral heterogeneous catalyst via a four component coupling of aldehydes, β-ketoester (2 mol) and ammonium acetate under sol- vent-free conditions is described. Compared with the classical Hantzsch reac- tion, this new method has the advantages of good yield, short reaction time and methodological simplicity. β-CDPU was proved to be an efficient heterogene- ous catalyst that could be easily handled and removed from the reaction mix- ture by simple filtration, and also recovered and reused without loss of reac- tivity.
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magnetic nanoparticles grafted with β cyclodextrin Polyurethane Polymer as a novel nanomagnetic Polymer brush catalyst for nucleophilic substitution reactions of benzyl halides in water
Journal of Molecular Catalysis A-chemical, 2012Co-Authors: Ali Reza Kiasat, Simin NazariAbstract:Abstract The Polymer coated magnetic nanoparticles has gained significant attention for potential applications in biomedicine, separations, and magnetic storage. In this study, β-cyclodextrin–Polyurethane Polymer coated Fe 3 O 4 magnetic nanoparticle as a novel class of hybrid organic/inorganic molecular catalyst was successfully prepared and evaluated as solid–liquid phase-transfer catalyst and molecular host system for nucleophilic substitution reactions. The nanocomposite has demonstrated the ability to catalytic the nucleophilic substitution reaction of benzyl halides with thiocyanate, azide, cyanide and acetate anions in water. No evidence for the formation of by-products for example isothiocyanate or alcohol was observed and the products obtained in pure form without further purification. The nanomagnetic Polymer brush catalyst was easily removed from solution via application of a magnetic field, allowing straightforward recovery and reuse. Results obtained from scanning electron microscopy (SEM) and vibrating sample magnetometery (VSM) show that the synthesized magnetic nanocomposite are superparamagnetic with a mean diameter of 59 nm. The grafting of β-cyclodextrin–Polyurethane Polymer to Fe 3 O 4 magnetic nanoparticle is confirmed by Fourier transform infrared spectroscopy (FT-IR).
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Magnetic nanoparticles grafted with β-cyclodextrin–Polyurethane Polymer as a novel nanomagnetic Polymer brush catalyst for nucleophilic substitution reactions of benzyl halides in water
Journal of Molecular Catalysis A: Chemical, 2012Co-Authors: Ali Reza Kiasat, Simin NazariAbstract:Abstract The Polymer coated magnetic nanoparticles has gained significant attention for potential applications in biomedicine, separations, and magnetic storage. In this study, β-cyclodextrin–Polyurethane Polymer coated Fe 3 O 4 magnetic nanoparticle as a novel class of hybrid organic/inorganic molecular catalyst was successfully prepared and evaluated as solid–liquid phase-transfer catalyst and molecular host system for nucleophilic substitution reactions. The nanocomposite has demonstrated the ability to catalytic the nucleophilic substitution reaction of benzyl halides with thiocyanate, azide, cyanide and acetate anions in water. No evidence for the formation of by-products for example isothiocyanate or alcohol was observed and the products obtained in pure form without further purification. The nanomagnetic Polymer brush catalyst was easily removed from solution via application of a magnetic field, allowing straightforward recovery and reuse. Results obtained from scanning electron microscopy (SEM) and vibrating sample magnetometery (VSM) show that the synthesized magnetic nanocomposite are superparamagnetic with a mean diameter of 59 nm. The grafting of β-cyclodextrin–Polyurethane Polymer to Fe 3 O 4 magnetic nanoparticle is confirmed by Fourier transform infrared spectroscopy (FT-IR).