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Materials, Volume 3, Issue 4 (April 2010), Pages 2196-2946

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Research

Jump to: Review

Open AccessArticle Versatile Biodegradable Poly(ester amide)s Derived from α-Amino Acids for Vascular Tissue Engineering
Materials 2010, 3(4), 2346-2368; doi:10.3390/ma3042346
Received: 4 January 2010 / Revised: 6 March 2010 / Accepted: 16 March 2010 / Published: 26 March 2010
Cited by 29 | PDF Full-text (3735 KB) | HTML Full-text | XML Full-text
Abstract
Biodegradable poly(ester amide) (PEA) biomaterials derived from α-amino acids, diols, and diacids are promising materials for biomedical applications such as tissue engineering and drug delivery because of their optimized properties and susceptibility for either hydrolytic or enzymatic degradation. The objective of this [...] Read more.
Biodegradable poly(ester amide) (PEA) biomaterials derived from α-amino acids, diols, and diacids are promising materials for biomedical applications such as tissue engineering and drug delivery because of their optimized properties and susceptibility for either hydrolytic or enzymatic degradation. The objective of this work was to synthesize and characterize biodegradable PEAs based on the α-amino acids L-phenylalanine and L-methionine. Four different PEAs were prepared using 1,4-butanediol, 1,6-hexanediol, and sebacic acid by interfacial polymerization. High molecular weight PEAs with narrow polydispersity indices and excellent film-forming properties were obtained. The incubation of these PEAs in PBS and chymotrypsin indicated that the polymers are biodegradable. Human coronary artery smooth muscle cells were cultured on PEA films for 48 h and the results showed a well-spread morphology. Porous 3D scaffolds fabricated from these PEAs were found to have excellent porosities indicating the utility of these polymers for vascular tissue engineering. Full article
(This article belongs to the Special Issue Advances in Biomaterials)
Open AccessArticle Generation of Type I Collagen Gradient in Polyacrylamide Hydrogels by a Simple Diffusion-Controlled Hydrolysis of Amide Groups
Materials 2010, 3(4), 2393-2404; doi:10.3390/ma3042393
Received: 2 February 2010 / Revised: 2 March 2010 / Accepted: 25 March 2010 / Published: 26 March 2010
Cited by 6 | PDF Full-text (752 KB) | HTML Full-text | XML Full-text
Abstract
The objective of this study is to develop an easy and simple diffusion-controlled fabrication technique to generate the concentration gradient of biomolecules in hydrogels. Polyacrylamide (PAAm) hydrogels with a concentration gradient of type I collagen were prepared to evaluate the cell adhesion. [...] Read more.
The objective of this study is to develop an easy and simple diffusion-controlled fabrication technique to generate the concentration gradient of biomolecules in hydrogels. Polyacrylamide (PAAm) hydrogels with a concentration gradient of type I collagen were prepared to evaluate the cell adhesion. The PAAm hydrogel was exposed to a gradient concentration of sodium hydroxide (NaOH) solution at 52 °C to generate that of carboxyl groups in the hydrogel. The carboxyl groups generated were chemically coupled with the amino groups of type I collagen to prepare the hydrogel with a concentration gradient of collagen immobilized. The attachment of L929 fibroblasts was evaluated for the collagen-immobilized hydrogel prepared. The amount gradient of carboxyl groups in the hydrogel increased with an increase in the NaOH concentration while the carboxyl groups gradient enabled to generate a gradient of collagen immobilized in the hydrogel. On the other hand, the number of fibroblasts adhered depended on the amount of collagen immobilized. These findings indicate that the adhesion behavior of cells is modified by the concentration gradient of biomolecule in the three-dimensional scaffold of cells. Full article
(This article belongs to the Special Issue Advances in Biomaterials)
Open AccessArticle Spectroscopy and 1μm Luminescence by Visible Quantum Cutting in Pr3+-Yb3+ Codoped Glass
Materials 2010, 3(4), 2405-2411; doi:10.3390/ma3042405
Received: 28 December 2009 / Revised: 25 January 2010 / Accepted: 25 March 2010 / Published: 29 March 2010
Cited by 10 | PDF Full-text (276 KB) | HTML Full-text | XML Full-text
Abstract
The quantum cutting phenomenon of a blue photon into two infrared photons is reported in glass codoped with Pr3+-Yb3+ ions. Oxyfluoride glass with compositions of 32SrF2-0.1PrF3-2.9YbF3-42SiO2-23Al2O3 were prepared, [...] Read more.
The quantum cutting phenomenon of a blue photon into two infrared photons is reported in glass codoped with Pr3+-Yb3+ ions. Oxyfluoride glass with compositions of 32SrF2-0.1PrF3-2.9YbF3-42SiO2-23Al2O3 were prepared, and photoluminescence properties in the range from visible to near-infrared were investigated. Evidence of several energy transfers, such as (Pr3+:3P01G4)→(Yb3+:2F5/22F7/2) and (Pr3+:1D23F4, 3F3)→(Yb3+:2F5/22F7/2), were demonstrated in the Pr3+-Yb3+ co-doped glass. By comparing excitation spectrum of the Yb3+ emission with absorption spectrum of Pr3+, we obtain direct evidence of quantum cutting by excitation to Pr3+:3PJ levels at 420 ~ 490 nm. Full article
(This article belongs to the Special Issue Luminescent Materials)
Open AccessArticle New Element Organic Frameworks Based on Sn, Sb, and Bi, with Permanent Porosity and High Catalytic Activity
Materials 2010, 3(4), 2447-2462; doi:10.3390/ma3042447
Received: 31 January 2010 / Accepted: 25 March 2010 / Published: 30 March 2010
Cited by 23 | PDF Full-text (452 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
We present new element organic frameworks based on Sn, Sb and Bi atoms connected via organic linkers by element-carbon bonds. The open frameworks are characterized by specific surface areas (BET) of up to 445 m2 g-1 and a good stability [...] Read more.
We present new element organic frameworks based on Sn, Sb and Bi atoms connected via organic linkers by element-carbon bonds. The open frameworks are characterized by specific surface areas (BET) of up to 445 m2 g-1 and a good stability under ambient conditions resulting from a highly hydrophobic inner surface. They show good performance as heterogeneous catalysts in the cyanosylilation of benzaldehyde as a test reaction. Due to their catalytic activity, this class of materials might be able to replace common homogeneous element-organic and often highly toxic catalysts especially in the food industry. Full article
(This article belongs to the Special Issue Organometallic Compounds)
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Open AccessArticle Low Velocity Impact Behavior of Glass Filled Fiber-Reinforced Thermoplastic Engine Components
Materials 2010, 3(4), 2463-2473; doi:10.3390/ma3042463
Received: 19 February 2010 / Revised: 19 March 2010 / Accepted: 25 March 2010 / Published: 31 March 2010
Cited by 8 | PDF Full-text (711 KB) | HTML Full-text | XML Full-text
Abstract
This paper concerns automotive parts located underneath the engine and in particular the engine oil pan. Classically made of stamped steel or cast aluminum, new developments have allowed the manufacture oil pans with polyamide 66 reinforced by 35% weight of short glass [...] Read more.
This paper concerns automotive parts located underneath the engine and in particular the engine oil pan. Classically made of stamped steel or cast aluminum, new developments have allowed the manufacture oil pans with polyamide 66 reinforced by 35% weight of short glass fiber. However, polyamides have some limitations and the most significant is their response to localized impact loading. The nature of the impact considered here is of a typical stone collected from the road and projected into the oil pan. Low velocity impact investigations were carried out using a gas gun and drop weight tower. The study shows that the design of the oil pan has a significant contribution in the shock absorption. In addition to the material properties, the geometry and the ribbing both cleverly combined, increase the impact resistance of the component significantly. Areas of oil pan design improvement have been identified and conclusions drawn. Full article
(This article belongs to the Special Issue Composite Materials)
Open AccessArticle Layer-Inversion Zones in Angular Distributions of Luminescence and Absorption Properties in Biaxial Crystals
Materials 2010, 3(4), 2474-2482; doi:10.3390/ma3042474
Received: 13 January 2010 / Accepted: 29 March 2010 / Published: 31 March 2010
Cited by 3 | PDF Full-text (421 KB) | HTML Full-text | XML Full-text
Abstract
We numerically depict the complete angular distributions of luminescence and absorption properties in biaxial media, by calculating the imaginary part of the optical index for all directions of propagation. Our simulations show a double-layer surface with specific topology and symmetry properties that [...] Read more.
We numerically depict the complete angular distributions of luminescence and absorption properties in biaxial media, by calculating the imaginary part of the optical index for all directions of propagation. Our simulations show a double-layer surface with specific topology and symmetry properties that greatly differ from those of the refractive index surface. Our calculations show that the two layers intersect and inverse themselves along continuous loci related to polarization-independent luminescence or absorption properties. Specificities related to the orthorhombic, monoclinic and triclinic biaxial crystal systems are discussed. Such theoretical developments should be considered to fully exploit innovating luminescent materials. Full article
(This article belongs to the Special Issue Luminescent Materials)
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Open AccessArticle Synthesis of Green-Emitting (La,Gd)OBr:Tb3+ Phosphors
Materials 2010, 3(4), 2506-2515; doi:10.3390/ma3042506
Received: 29 December 2009 / Revised: 12 March 2010 / Accepted: 31 March 2010 / Published: 1 April 2010
Cited by 11 | PDF Full-text (347 KB) | HTML Full-text | XML Full-text
Abstract
Green-emitting phosphors based on lanthanum-gadolinium oxybromide were synthesized in a single phase form by the conventional solid state reaction method, and photoluminescence properties of them were characterized. The excitation peak wavelength of (La1-xGdx)OBr:Tb3+ shifted to the [...] Read more.
Green-emitting phosphors based on lanthanum-gadolinium oxybromide were synthesized in a single phase form by the conventional solid state reaction method, and photoluminescence properties of them were characterized. The excitation peak wavelength of (La1-xGdx)OBr:Tb3+ shifted to the shorter wavelength side with the increase in the crystal field around the Tb3+ ions by doping Gd3+ ions into the La3+ site, and, as a result, the green emission intensity was successfully enhanced. The maximum emission intensity was obtained for (La0.95Gd0.05)OBr:5%Tb3+, where the relative emission intensity was 45% of that of a commercial green-emitting LaPO4:Ce3+,Tb3+ phosphor. Full article
(This article belongs to the Special Issue Luminescent Materials)
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Open AccessArticle The Variety of Carbon-Metal Bonds inside Cu-ZSM-5 Zeolites: A Density Functional Theory Study
Materials 2010, 3(4), 2516-2535; doi:10.3390/ma3042516
Received: 31 January 2010 / Revised: 29 March 2010 / Accepted: 1 April 2010 / Published: 5 April 2010
Cited by 10 | PDF Full-text (1036 KB) | HTML Full-text | XML Full-text
Abstract
Large-scale density functional theory calculations (DFT) found various types of binding of an unsaturated hydrocarbon (C2H2 and C2H4) to a ZSM-5 zeolite extraframework copper cation. We employed the DFT calculations based on the B3LYP functional [...] Read more.
Large-scale density functional theory calculations (DFT) found various types of binding of an unsaturated hydrocarbon (C2H2 and C2H4) to a ZSM-5 zeolite extraframework copper cation. We employed the DFT calculations based on the B3LYP functional to obtain local minima of an unsaturated hydrocarbon adsorbed on one or two copper cations embedded inside ZSM-5, and then compared their stabilization energies. The DFT results show that the stabilization energies are strongly dependent on the copper coordination environment as well as configurations of two copper cations. Consequently, the inner copper-carbon bonds are influenced substantially by a nanometer-scale cavity of ZSM-5. Full article
(This article belongs to the Special Issue Organometallic Compounds)
Open AccessArticle Low-Thermal-Conductivity (MS)1+x(TiS2)2 (M = Pb, Bi, Sn) Misfit Layer Compounds for Bulk Thermoelectric Materials
Materials 2010, 3(4), 2606-2617; doi:10.3390/ma3042606
Received: 1 January 2010 / Revised: 25 February 2010 / Accepted: 1 April 2010 / Published: 6 April 2010
Cited by 50 | PDF Full-text (1024 KB) | HTML Full-text | XML Full-text
Abstract
A series of (MS)1+x(TiS2)2 (M = Pb, Bi, Sn) misfit layer compounds are proposed as bulk thermoelectric materials. They are composed of alternating rock-salt-type MS layers and paired trigonal anti-prismatic TiS2 [...] Read more.
A series of (MS)1+x(TiS2)2 (M = Pb, Bi, Sn) misfit layer compounds are proposed as bulk thermoelectric materials. They are composed of alternating rock-salt-type MS layers and paired trigonal anti-prismatic TiS2 layers with a van der Waals gap. This naturally modulated structure shows low lattice thermal conductivity close to or even lower than the predicted minimum thermal conductivity. Measurement of sound velocities shows that the ultra-low thermal conductivity partially originates from the softening of the transverse modes of lattice wave due to weak interlayer bonding. Combined with a high power factor, the misfit layer compounds show a relatively high ZT value of 0.28~0.37 at 700 K. Full article
(This article belongs to the Special Issue Novel Thermoelectric Materials and Applications)
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Open AccessArticle Computational Study of Ferrocene-Based Molecular Frameworks with 2,5-Diethynylpyridine as a Chemical Bridge
Materials 2010, 3(4), 2668-2683; doi:10.3390/ma3042668
Received: 2 February 2010 / Revised: 13 March 2010 / Accepted: 8 April 2010 / Published: 13 April 2010
Cited by 18 | PDF Full-text (646 KB) | HTML Full-text | XML Full-text
Abstract
A computational study was carried out to examine the electronic and optical properties of the experimentally proposed ferrocene-based molecular diode that used 2,5-diethynylpyridine as a bridging unit. Density functional theory, time-dependent density functional theory, and constrained density functional theory were applied to [...] Read more.
A computational study was carried out to examine the electronic and optical properties of the experimentally proposed ferrocene-based molecular diode that used 2,5-diethynylpyridine as a bridging unit. Density functional theory, time-dependent density functional theory, and constrained density functional theory were applied to investigate various aspects of the underlying electron transfer mechanism. The results not only advance our understanding of the experimental observations, but also demonstrate the usefulness of computational approaches for the design of new electronic materials. Full article
(This article belongs to the Special Issue Organic Electronic Materials)
Open AccessArticle Gene Expression, Bacteria Viability and Survivability Following Spray Drying of Mycobacterium smegmatis
Materials 2010, 3(4), 2684-2724; doi:10.3390/ma3042684
Received: 13 January 2010 / Revised: 23 March 2010 / Accepted: 8 April 2010 / Published: 13 April 2010
Cited by 2 | PDF Full-text (284 KB) | HTML Full-text | XML Full-text
Abstract
We find that Mycobacterium smegmatis survives spray drying and retains cell viability in accelerated temperature stress (40 °C) conditions with a success rate that increases with increasing thermal, osmotic, and nutrient-restriction stresses applied to the mycobacterium prior to spray drying. M.smegmatis [...] Read more.
We find that Mycobacterium smegmatis survives spray drying and retains cell viability in accelerated temperature stress (40 °C) conditions with a success rate that increases with increasing thermal, osmotic, and nutrient-restriction stresses applied to the mycobacterium prior to spray drying. M.smegmatis that are spray dried during log growth phase, where they suffer little or no nutrient-reduction stress, survive for less than 7 days in the dry powder state at accelerated temperature stress conditions, whereas M. smegmatis that are spray dried during stationary phase, where cells do suffer nutrient reduction, survive for up to 14 days. M. smegmatis that are spray dried from stationary phase, subjected to accelerated temperature stress conditions, regrown to stationary phase, spray dried again, and resubmitted to this same process four consecutive times, display, on the fourth spray drying iteration, an approximate ten-fold increase in stability during accelerated temperature stress testing, surviving up to 105 days. Microarray tests revealed significant differences in genetic expression of M. smegmatis between log phase and stationary phase conditions, between naïve (non spray-dried) and multiply cycled dried M. smegmatis (in log and stationary phase), and between M. smegmatis in the dry powder state following a single spray drying operation and after four consecutive spray drying operations. These differences, and other phenotypical differences, point to the carotenoid biosynthetic pathway as a probable pathway contributing to bacteria survival in the spray-dried state and suggests strategies for spray drying that may lead to significantly greater room-temperature stability of mycobacteria, including mycobacterium bovis bacille Calmette-Guerin (BCG), the current TB vaccine. Full article
(This article belongs to the Special Issue Advances in Biomaterials)
Open AccessArticle Helicity Distributions of Single-Walled Carbon Nanotubes and Its Implication on the Growth Mechanism
Materials 2010, 3(4), 2725-2734; doi:10.3390/ma3042725
Received: 25 February 2010 / Revised: 10 April 2010 / Accepted: 12 April 2010 / Published: 14 April 2010
Cited by 6 | PDF Full-text (449 KB) | HTML Full-text | XML Full-text
Abstract
Single-walled nanotubes (SWNT) have attracted significant attention because of the substance’s superior crystal quality, high thermal conductivity and current carrying capacity, thus emerging as an attractive material for nanoelectrics. To optimize the selection of SWNT structures in large-scale synthesis, an understanding of [...] Read more.
Single-walled nanotubes (SWNT) have attracted significant attention because of the substance’s superior crystal quality, high thermal conductivity and current carrying capacity, thus emerging as an attractive material for nanoelectrics. To optimize the selection of SWNT structures in large-scale synthesis, an understanding of their growth mechanism is necessary. We report studies of the helicity distributions of SWNT using electron nanodiffraction. The overall statistical distribution of helicity has peaks at 0° and 30°. The peak evident at 0° was found to be a sharp local maximum, while the peak at 30° was broader. We also found that the helicity distribution varies from region to region of micrometer size. This observation indicates that local environment affects nanotube growth, resulting in different structural distributions. Full article
(This article belongs to the Special Issue Synthesis of Carbon Nanotube)
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Open AccessArticle Heat Transfer and Geometrical Analysis of Thermoelectric Converters Driven by Concentrated Solar Radiation
Materials 2010, 3(4), 2735-2752; doi:10.3390/ma3042735
Received: 2 March 2010 / Revised: 8 April 2010 / Accepted: 12 April 2010 / Published: 14 April 2010
Cited by 16 | PDF Full-text (520 KB) | HTML Full-text | XML Full-text
Abstract
A heat transfer model that couples radiation/conduction/convection heat transfer with electrical potential distribution is developed for a thermoelectric converter (TEC) subjected to concentrated solar radiation. The 4-leg TEC module consists of two pairs of p-type La1.98Sr0.02CuO4 [...] Read more.
A heat transfer model that couples radiation/conduction/convection heat transfer with electrical potential distribution is developed for a thermoelectric converter (TEC) subjected to concentrated solar radiation. The 4-leg TEC module consists of two pairs of p-type La1.98Sr0.02CuO4 and n-type CaMn0.98Nb0.02O3 legs that are sandwiched between two ceramic Al2O3 hot/cold plates and connected electrically in series and thermally in parallel. The governing equations for heat transfer and electrical potential are formulated, discretized and solved numerically by applying the finite volume (FV) method. The model is validated in terms of experimentally measured temperatures and voltages/power using a set of TEC demonstrator modules, subjected to a peak radiative flux intensity of 300 suns. The heat transfer model is then applied to examine the effect of the geometrical parameters (e.g. length/width of legs) on the solar-to-electricity energy conversion efficiency. Full article
(This article belongs to the Special Issue Novel Thermoelectric Materials and Applications)
Open AccessArticle Thermoelectric Oxide Modules (TOMs) for the Direct Conversion of Simulated Solar Radiation into Electrical Energy
Materials 2010, 3(4), 2801-2814; doi:10.3390/ma3042801
Received: 8 January 2010 / Revised: 24 March 2010 / Accepted: 12 April 2010 / Published: 15 April 2010
Cited by 19 | PDF Full-text (1205 KB) | HTML Full-text | XML Full-text
Abstract
The direct conversion of concentrated high temperature solar heat into electrical energy was demonstrated with a series of four–leg thermoelectric oxide modules (TOM). These temperature stable modules were not yet optimized for high efficiency conversion, but served as proof-of-principle for high temperature [...] Read more.
The direct conversion of concentrated high temperature solar heat into electrical energy was demonstrated with a series of four–leg thermoelectric oxide modules (TOM). These temperature stable modules were not yet optimized for high efficiency conversion, but served as proof-of-principle for high temperature conversion. They were constructed by connecting two p- (La1.98Sr0.02CuO4) and two n-type (CaMn0.98Nb0.02O3) thermoelements electrically in series and thermally in parallel. The temperature gradient ΔT was applied by a High–Flux Solar Simulator source (HFSS) which generates a spectrum similar to solar radiation. The influence of the graphite layer coated on the hot side of the Al2O3 substrate compared to the uncoated surface on ΔT, Pmax and η was studied in detail. The measurements show an almost linear temperature profile along the thermoelectric legs. The maximum output power of 88.8 mW was reached for a TOM with leg length of 5 mm at ΔT = 622 K. The highest conversion efficiency η was found for a heat flux of 4–8 W cm-2 and the dependence of η on the leg length was investigated. Full article
(This article belongs to the Special Issue Novel Thermoelectric Materials and Applications)

Review

Jump to: Research

Open AccessReview Chemical Sensors Based on Molecularly Imprinted Sol-Gel Materials
Materials 2010, 3(4), 2196-2217; doi:10.3390/ma3042196
Received: 26 November 2009 / Revised: 27 January 2010 / Accepted: 23 March 2010 / Published: 24 March 2010
Cited by 31 | PDF Full-text (547 KB) | HTML Full-text | XML Full-text
Abstract
The sol-gel technique is earning the worldwide attention of researchers in the field of material science, due to its versatility in synthesizing inorganic ceramic materials at mild conditions. High purity, homogeneity, controlled porosity, stable temperature and nanoscale structuring are the most remarkable [...] Read more.
The sol-gel technique is earning the worldwide attention of researchers in the field of material science, due to its versatility in synthesizing inorganic ceramic materials at mild conditions. High purity, homogeneity, controlled porosity, stable temperature and nanoscale structuring are the most remarkable features offered by this method for generating highly sensitive and selective matrices to incorporate analyte molecules. The crafting of sol-gel sensors through molecular imprinting has put great influence on the development of innovative chemical sensors, which can be seen from the growing number of publications in this field. The review provides a brief overview of sol-gel sensor applications, and discusses the contribution of molecular imprinting in exploring the new world of sensors. Full article
(This article belongs to the Special Issue Sol-Gel Technique)
Open AccessReview Fabrication Methods and Luminescent Properties of ZnO Materials for Light-Emitting Diodes
Materials 2010, 3(4), 2218-2259; doi:10.3390/ma3042218
Received: 15 January 2010 / Revised: 8 February 2010 / Accepted: 19 March 2010 / Published: 24 March 2010
Cited by 35 | PDF Full-text (1443 KB) | HTML Full-text | XML Full-text
Abstract
Zinc oxide (ZnO) is a potential candidate material for optoelectronic applications, especially for blue to ultraviolet light emitting devices, due to its fundamental advantages, such as direct wide band gap of 3.37 eV, large exciton binding energy of 60 meV, and high [...] Read more.
Zinc oxide (ZnO) is a potential candidate material for optoelectronic applications, especially for blue to ultraviolet light emitting devices, due to its fundamental advantages, such as direct wide band gap of 3.37 eV, large exciton binding energy of 60 meV, and high optical gain of 320 cm−1 at room temperature. Its luminescent properties have been intensively investigated for samples, in the form of bulk, thin film, or nanostructure, prepared by various methods and doped with different impurities. In this paper, we first review briefly the recent progress in this field. Then a comprehensive summary of the research carried out in our laboratory on ZnO preparation and its luminescent properties, will be presented, in which the involved samples include ZnO films and nanorods prepared with different methods and doped with n-type or p-type impurities. The results of ZnO based LEDs will also be discussed. Full article
(This article belongs to the Special Issue Luminescent Materials)
Open AccessReview Quantum Dots and Their Multimodal Applications: A Review
Materials 2010, 3(4), 2260-2345; doi:10.3390/ma3042260
Received: 5 January 2010 / Revised: 7 March 2010 / Accepted: 23 March 2010 / Published: 24 March 2010
Cited by 166 | PDF Full-text (2617 KB) | HTML Full-text | XML Full-text
Abstract
Semiconducting quantum dots, whose particle sizes are in the nanometer range, have very unusual properties. The quantum dots have band gaps that depend in a complicated fashion upon a number of factors, described in the article. Processing-structure-properties-performance relationships are reviewed for compound [...] Read more.
Semiconducting quantum dots, whose particle sizes are in the nanometer range, have very unusual properties. The quantum dots have band gaps that depend in a complicated fashion upon a number of factors, described in the article. Processing-structure-properties-performance relationships are reviewed for compound semiconducting quantum dots. Various methods for synthesizing these quantum dots are discussed, as well as their resulting properties. Quantum states and confinement of their excitons may shift their optical absorption and emission energies. Such effects are important for tuning their luminescence stimulated by photons (photoluminescence) or electric field (electroluminescence). In this article, decoupling of quantum effects on excitation and emission are described, along with the use of quantum dots as sensitizers in phosphors. In addition, we reviewed the multimodal applications of quantum dots, including in electroluminescence device, solar cell and biological imaging. Full article
(This article belongs to the Special Issue Luminescent Materials)
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Open AccessReview Towards a Guided Regeneration of Renal Tubules at a Polyester Interstitium
Materials 2010, 3(4), 2369-2392; doi:10.3390/ma3042369
Received: 16 January 2010 / Revised: 15 March 2010 / Accepted: 26 March 2010 / Published: 26 March 2010
Cited by 4 | PDF Full-text (2194 KB) | HTML Full-text | XML Full-text
Abstract
Stem/progenitor cells are promising candidates for a therapy of renal failure. However, sound knowledge about implantation and regeneration is lacking. Therefore, mechanisms leading from stem/progenitor cells into tubules are under research. Renal stem/progenitor cells were isolated from neonatal rabbit kidney and mounted [...] Read more.
Stem/progenitor cells are promising candidates for a therapy of renal failure. However, sound knowledge about implantation and regeneration is lacking. Therefore, mechanisms leading from stem/progenitor cells into tubules are under research. Renal stem/progenitor cells were isolated from neonatal rabbit kidney and mounted between layers of polyester fleece. It creates an artificial interstitium and replaces coating by extracellular matrix proteins. Tubulogenic development is induced by aldosterone. Electron microscopy illuminates growth of tubules in close vicinity to polyester fibers. Tubules contain a differentiated epithelium. The spatial extension of tubules opens a new strategy for testing morphogenic drugs and biocompatible fleece materials. Full article
(This article belongs to the Special Issue Advances in Biomaterials)
Open AccessReview Magnetic Biotransport: Analysis and Applications
Materials 2010, 3(4), 2412-2446; doi:10.3390/ma3042412
Received: 1 January 2010 / Revised: 22 February 2010 / Accepted: 25 March 2010 / Published: 30 March 2010
Cited by 22 | PDF Full-text (2854 KB) | HTML Full-text | XML Full-text
Abstract
Magnetic particles are finding increasing use in bioapplications, especially as carrier particles to transport biomaterials such as proteins, enzymes, nucleic acids and whole cells etc. Magnetic particles can be prepared with biofunctional coatings to target and label a specific biomaterial, and [...] Read more.
Magnetic particles are finding increasing use in bioapplications, especially as carrier particles to transport biomaterials such as proteins, enzymes, nucleic acids and whole cells etc. Magnetic particles can be prepared with biofunctional coatings to target and label a specific biomaterial, and they enable controlled manipulation of a labeled biomaterial using an external magnetic field. In this review, we discuss the use of magnetic nanoparticles as transport agents in various bioapplications. We provide an overview of the properties of magnetic nanoparticles and their functionalization for bioapplications. We discuss the basic physics and equations governing the transport of magnetic particles at the micro- and nanoscale. We present two different transport models: a classical Newtonian model for predicting the motion of individual particles, and a drift-diffusion model for predicting the behavior of a concentration of nanoparticles that takes into account Brownian motion. We review specific magnetic biotransport applications including bioseparation, drug delivery and magnetofection. We demonstrate the transport models via application to these processes. Full article
(This article belongs to the Special Issue Magnetic Nanoparticles)
Open AccessReview Current and Emerging Detoxification Therapies for Critical Care
Materials 2010, 3(4), 2483-2505; doi:10.3390/ma3042483
Received: 5 January 2010 / Revised: 3 March 2010 / Accepted: 31 March 2010 / Published: 1 April 2010
Cited by 3 | PDF Full-text (605 KB) | HTML Full-text | XML Full-text
Abstract
Toxicity resulting from prescription drugs such as tricyclic antidepressants and cardioactive steroids, as well as drugs of abuse and exposure to environmental chemicals, represents a major need for detoxification treatments. Particles and colloids, antibody fragments (Fab), and indirect treatment methods such as [...] Read more.
Toxicity resulting from prescription drugs such as tricyclic antidepressants and cardioactive steroids, as well as drugs of abuse and exposure to environmental chemicals, represents a major need for detoxification treatments. Particles and colloids, antibody fragments (Fab), and indirect treatment methods such as macroemulsions, are currently being developed or employed as detoxification therapies. Colloids, particles, and protein fragments typically mitigate toxicity by binding to the toxin and reducing its concentration in vital organs. Indirect methods such as macroemulsions and sodium bicarbonate act directly on the affected organs, rather than the toxin. In this review, key design parameters (i.e. binding affinity, biocompatibility, pharmacokinetics) are discussed for each type of detoxification treatment. In addition, some of the latest research in each area is reviewed. Full article
(This article belongs to the Special Issue Advances in Biomaterials)
Open AccessReview Persistent Luminescence in Eu2+-Doped Compounds: A Review
Materials 2010, 3(4), 2536-2566; doi:10.3390/ma3042536
Received: 17 January 2001 / Revised: 27 March 2010 / Accepted: 30 March 2010 / Published: 6 April 2010
Cited by 257 | PDF Full-text (463 KB) | HTML Full-text | XML Full-text
Abstract
In 1996, Matsuzawa et al. reported on the extremely long-lasting afterglow of SrAl2O4:Eu2+ codoped with Dy3+ ions, which was more than 10-times brighter than the previously widely used ZnS:Cu,Co. Since then, research for stable and [...] Read more.
In 1996, Matsuzawa et al. reported on the extremely long-lasting afterglow of SrAl2O4:Eu2+ codoped with Dy3+ ions, which was more than 10-times brighter than the previously widely used ZnS:Cu,Co. Since then, research for stable and efficient persistent phosphors has continuously gained popularity. However, even today - almost 15 years after the discovery of SrAl2O4:Eu2+, Dy3+ - the number of persistent luminescent materials is still relatively low. Furthermore, the mechanism behind this phenomenon is still unclear. Although most authors agree on the general features, such as the existence of long-lived trap levels, many details are still shrouded in mystery. In this review, we present an overview of the important classes of known persistent luminescent materials based on Eu2+-emission and how they were prepared, and we take a closer look at the models and mechanisms that have been suggested to explain bright afterglow in various compounds. Full article
(This article belongs to the Special Issue Luminescent Materials)
Open AccessReview Novel Materials through Non-Hydrolytic Sol-Gel Processing: Negative Thermal Expansion Oxides and Beyond
Materials 2010, 3(4), 2567-2587; doi:10.3390/ma3042567
Received: 11 January 2010 / Revised: 9 March 2010 / Accepted: 2 April 2010 / Published: 6 April 2010
Cited by 20 | PDF Full-text (497 KB) | HTML Full-text | XML Full-text
Abstract
Low temperature methods have been applied to the synthesis of many advanced materials. Non-hydrolytic sol-gel (NHSG) processes offer an elegant route to stable and metastable phases at low temperatures. Excellent atomic level homogeneity gives access to polymorphs that are difficult or impossible [...] Read more.
Low temperature methods have been applied to the synthesis of many advanced materials. Non-hydrolytic sol-gel (NHSG) processes offer an elegant route to stable and metastable phases at low temperatures. Excellent atomic level homogeneity gives access to polymorphs that are difficult or impossible to obtain by other methods. The NHSG approach is most commonly applied to the preparation of metal oxides, but can be easily extended to metal sulfides. Exploration of experimental variables allows control over product stoichiometry and crystal structure. This paper reviews the application of NHSG chemistry to the synthesis of negative thermal expansion oxides and selected metal sulfides. Full article
(This article belongs to the Special Issue Sol-Gel Technique)
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Open AccessReview Hydrophobic Modification of Layered Clays and Compatibility for Epoxy Nanocomposites
Materials 2010, 3(4), 2588-2605; doi:10.3390/ma3042588
Received: 11 February 2010 / Revised: 11 March 2010 / Accepted: 29 March 2010 / Published: 6 April 2010
Cited by 15 | PDF Full-text (987 KB) | HTML Full-text | XML Full-text
Abstract
Recent studies on the intercalation and exfoliation of layered clays with polymeric intercalating agents involving poly(oxypropylene)-amines and the particular uses for epoxy nanocomposites are reviewed. For intercalation, counter-ionic exchange reactions of clays including cationic layered silicates and anionic Al-Mg layered double hydroxide [...] Read more.
Recent studies on the intercalation and exfoliation of layered clays with polymeric intercalating agents involving poly(oxypropylene)-amines and the particular uses for epoxy nanocomposites are reviewed. For intercalation, counter-ionic exchange reactions of clays including cationic layered silicates and anionic Al-Mg layered double hydroxide (LDH) with polymeric organic ions afforded organoclays led to spatial interlayer expansion from 12 to 92 Å (X-ray diffraction) as well as hydrophobic property. The inorganic clays of layered structure could be modified by the poly(oxypropylene)amine-salts as the intercalating agents with molecular weights ranging from 230 to 5,000 g/mol. Furthermore, natural montmorillonite (MMT) clay could be exfoliated into thin layer silicate platelets (ca. 1 nm thickness) in one step by using polymeric types of exfoliating agents. Different lateral dimensions of MMT, synthetic fluorinated Mica and LDH clays had been cured into epoxy nanocomposites. The hydrophobic amine-salt modification resulting in high spacing of layered or exfoliation of individual clay platelets is the most important factor for gaining significant improvements of properties. In particular, these modified clays were reported to gain significant improvements such as reduced coefficient of thermal expansion (CTE), enhanced thermal stability, and hardness. The utilization of these layered clays for initiating the epoxy self-polymerization was also reported to have a unique compatibility between clay and organic resin matrix. However, the matrix domain lacks of covalently bonded crosslink and leads to the isolation of powder material. It is generally concluded that the hydrophobic expansion of the clay inter-gallery spacing is the crucial step for enhancing the compatibility and the ultimate preparation of the advanced epoxy materials. Full article
(This article belongs to the Special Issue Nanocomposites of Polymers and Inorganic Particles)
Open AccessReview A Review of the Properties and CVD Synthesis of Coiled Carbon Nanotubes
Materials 2010, 3(4), 2618-2642; doi:10.3390/ma3042618
Received: 1 March 2010 / Revised: 1 April 2010 / Accepted: 7 April 2010 / Published: 12 April 2010
Cited by 33 | PDF Full-text (1514 KB) | HTML Full-text | XML Full-text
Abstract
The CVD route for carbon nanotube production has become a popular method to make large amounts of multiwall carbon nanotubes. The structure, morphology and size of carbon materials depend critically on the catalyst preparation and deposition conditions. According to current knowledge, CVD [...] Read more.
The CVD route for carbon nanotube production has become a popular method to make large amounts of multiwall carbon nanotubes. The structure, morphology and size of carbon materials depend critically on the catalyst preparation and deposition conditions. According to current knowledge, CVD method is the only process which can produce carbon nanocoils. These nanocoils are perfect candidates for nanotechnology applications. One might indeed hope that these coils would have the extraordinary stiffness displayed by straight nanotubes. Based on theoretical studies, regular coiled nanotubes exhibit exceptional mechanical, electrical, and magnetic properties due to the combination of their peculiar helical morphology and the fascinating properties of nanotubes. In spite of its technological interest, relatively low attention has been paid to this special field. In this paper we attempt to summarize results obtained until now. Full article
(This article belongs to the Special Issue Synthesis of Carbon Nanotube)
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Open AccessReview Luminescence from Zinc Oxide Nanostructures and Polymers and their Hybrid Devices
Materials 2010, 3(4), 2643-2667; doi:10.3390/ma3042643
Received: 4 January 2010 / Revised: 15 March 2010 / Accepted: 31 March 2010 / Published: 12 April 2010
Cited by 122 | PDF Full-text (1626 KB) | HTML Full-text | XML Full-text
Abstract
Zinc oxide (ZnO) is a strong luminescent material, as are several polymers. These two materials have distinct drawbacks and advantages, and they can be combined to form nanostructures with many important applications, e.g., large-area white lighting. This paper discusses the origin of [...] Read more.
Zinc oxide (ZnO) is a strong luminescent material, as are several polymers. These two materials have distinct drawbacks and advantages, and they can be combined to form nanostructures with many important applications, e.g., large-area white lighting. This paper discusses the origin of visible emission centers in ZnO nanorods grown with different approaches. White light emitting diodes (LEDs) were fabricated by combining n-ZnO nanorods and hollow nanotubes with different p-type materials to form heterojunctions. The p-type component of the hybrids includes p-SiC, p-GaN, and polymers. We conclude by analyzing the electroluminescence of the different light emitting diodes we fabricated. The observed optical, electrical, and electro-optical characteristics of these LEDs are discussed with an emphasis on the deep level centers that cause the emission. Full article
(This article belongs to the Special Issue Luminescent Materials)
Open AccessReview Development and Evaluation of Polyvinyl Alcohol-Hydrogels as an Artificial Atrticular Cartilage for Orthopedic Implants
Materials 2010, 3(4), 2753-2771; doi:10.3390/ma3042753
Received: 9 February 2010 / Revised: 1 March 2010 / Accepted: 7 April 2010 / Published: 14 April 2010
Cited by 27 | PDF Full-text (1020 KB) | HTML Full-text | XML Full-text
Abstract
Due to its excellent biocompatibility and mechanical properties, various different applications of polyvinyl alcohol-hydrogels (PVA-H) has been attempted in many fields. In the field of orthopedic surgery, we have been engaged for long time in research on the clinical applications of PVA-H [...] Read more.
Due to its excellent biocompatibility and mechanical properties, various different applications of polyvinyl alcohol-hydrogels (PVA-H) has been attempted in many fields. In the field of orthopedic surgery, we have been engaged for long time in research on the clinical applications of PVA-H as a artificial cartilage, and have performed many basic experiments on the mechanical properties, synthesis of PVA-H, and developed orthopedic implants using PVA-H. From these studies, many applications of artificial articular cartilage, intervertbral disc and artificial meniscus etc. have been developed. This review will present the overview of the applications and recent advances of PVA-H cartilages, and discuss clinical potential of PVA-H for orthopedics implant. Full article
(This article belongs to the Special Issue Advances in Biomaterials)
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Open AccessReview Oligomers and Polymers Based on Pentacene Building Blocks
Materials 2010, 3(4), 2772-2800; doi:10.3390/ma3042772
Received: 10 February 2010 / Revised: 16 March 2010 / Accepted: 9 April 2010 / Published: 14 April 2010
Cited by 18 | PDF Full-text (1114 KB) | HTML Full-text | XML Full-text
Abstract
Functionalized pentacene derivatives continue to provide unique materials for organic semiconductor applications. Although oligomers and polymers based on pentacene building blocks remain quite rare, recent synthetic achievements have provided a number of examples with varied structural motifs. This review highlights recent work [...] Read more.
Functionalized pentacene derivatives continue to provide unique materials for organic semiconductor applications. Although oligomers and polymers based on pentacene building blocks remain quite rare, recent synthetic achievements have provided a number of examples with varied structural motifs. This review highlights recent work in this area and, when possible, contrasts the properties of defined-length pentacene oligomers to those of mono- and polymeric systems. Full article
(This article belongs to the Special Issue Conjugated Oligomers)
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Open AccessReview Sol-Gel Synthesis of Non-Silica Monolithic Materials
Materials 2010, 3(4), 2815-2833; doi:10.3390/ma3042815
Received: 15 February 2010 / Revised: 13 April 2010 / Accepted: 16 April 2010 / Published: 21 April 2010
Cited by 36 | PDF Full-text (592 KB) | HTML Full-text | XML Full-text
Abstract
Monolithic materials have become very popular because of various applications, especially within chromatography and catalysis. Large surface areas and multimodal porosities are great advantages for these applications. New sol-gel preparation methods utilizing phase separation or nanocasting have opened the possibility for preparing [...] Read more.
Monolithic materials have become very popular because of various applications, especially within chromatography and catalysis. Large surface areas and multimodal porosities are great advantages for these applications. New sol-gel preparation methods utilizing phase separation or nanocasting have opened the possibility for preparing materials of other oxides than silica. In this review, we present different synthesis methods for inorganic, non-silica monolithic materials. Some examples of application of the materials are also included. Full article
(This article belongs to the Special Issue Sol-Gel Technique)
Open AccessReview Luminescence in Sulfides: A Rich History and a Bright Future
Materials 2010, 3(4), 2834-2883; doi:10.3390/ma3042834
Received: 8 April 2010 / Accepted: 18 April 2010 / Published: 21 April 2010
Cited by 93 | PDF Full-text (1294 KB) | HTML Full-text | XML Full-text
Abstract
Sulfide-based luminescent materials have attracted a lot of attention for a wide range of photo-, cathodo- and electroluminescent applications. Upon doping with Ce3+ and Eu2+, the luminescence can be varied over the entire visible region by appropriately choosing the [...] Read more.
Sulfide-based luminescent materials have attracted a lot of attention for a wide range of photo-, cathodo- and electroluminescent applications. Upon doping with Ce3+ and Eu2+, the luminescence can be varied over the entire visible region by appropriately choosing the composition of the sulfide host. Main application areas are flat panel displays based on thin film electroluminescence, field emission displays and ZnS-based powder electroluminescence for backlights. For these applications, special attention is given to BaAl2S4:Eu, ZnS:Mn and ZnS:Cu. Recently, sulfide materials have regained interest due to their ability (in contrast to oxide materials) to provide a broad band, Eu2+-based red emission for use as a color conversion material in white-light emitting diodes (LEDs). The potential application of rare-earth doped binary alkaline-earth sulfides, like CaS and SrS, thiogallates, thioaluminates and thiosilicates as conversion phosphors is discussed. Finally, this review concludes with the size-dependent luminescence in intrinsic colloidal quantum dots like PbS and CdS, and with the luminescence in doped nanoparticles. Full article
(This article belongs to the Special Issue Luminescent Materials)
Open AccessReview Microstructure and Properties of Polypropylene/Carbon Nanotube Nanocomposites
Materials 2010, 3(4), 2884-2946; doi:10.3390/ma3042884
Received: 29 January 2010 / Revised: 4 April 2010 / Accepted: 18 April 2010 / Published: 21 April 2010
Cited by 84 | PDF Full-text (6237 KB) | HTML Full-text | XML Full-text
Abstract
In the last few years, great attention has been paid to the preparation of polypropylene (PP) nanocomposites using carbon nanotubes (CNTs) due to the tremendous enhancement of the mechanical, thermal, electrical, optical and structural properties of the pristine material. This is due [...] Read more.
In the last few years, great attention has been paid to the preparation of polypropylene (PP) nanocomposites using carbon nanotubes (CNTs) due to the tremendous enhancement of the mechanical, thermal, electrical, optical and structural properties of the pristine material. This is due to the unique combination of structural, mechanical, electrical, and thermal transport properties of CNTs. However, it is well-known that the properties of polymer-based nanocomposites strongly depend on the dispersion of nanofillers and almost all the discussed properties of PP/CNTs nanocomposites are strongly related to their microstructure. PP/CNTs nanocomposites were, mainly, prepared by melt mixing and in situ polymerization. Young’s modulus, tensile strength and storage modulus of the PP/CNTs nanocomposites can be increased with increasing CNTs content due to the reinforcement effect of CNTs inside the polymer matrix. However, above a certain CNTs content the mechanical properties are reduced due to the CNTs agglomeration. The microstructure of nanocomposites has been studied mainly by SEM and TEM techniques. Furthermore, it was found that CNTs can act as nucleating agents promoting the crystallization rates of PP and the addition of CNTs enhances all other physical properties of PP. The aim of this paper is to provide a comprehensive review of the existing literature related to PP/CNTs nanocomposite preparation methods and properties studies. Full article
(This article belongs to the Special Issue Nanocomposites of Polymers and Inorganic Particles)
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