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Materials, Volume 4, Issue 8 (August 2011), Pages 1333-1518

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Research

Jump to: Review

Open AccessArticle Resonant Mode Reduction in Radiofrequency Volume Coils for Ultrahigh Field Magnetic Resonance Imaging
Materials 2011, 4(8), 1333-1344; doi:10.3390/ma4081333
Received: 13 July 2011 / Revised: 21 July 2011 / Accepted: 25 July 2011 / Published: 28 July 2011
Cited by 6 | PDF Full-text (1167 KB) | HTML Full-text | XML Full-text
Abstract
In a multimodal volume coil, only one mode can generate homogeneous Radiofrequency (RF) field for Magnetic Resonance Imaging. The existence of other modes may increase the volume coil design difficulties and potentially decreases coil performance. In this study, we introduce common-mode resonator [...] Read more.
In a multimodal volume coil, only one mode can generate homogeneous Radiofrequency (RF) field for Magnetic Resonance Imaging. The existence of other modes may increase the volume coil design difficulties and potentially decreases coil performance. In this study, we introduce common-mode resonator technique to high and ultrahigh field volume coil designs to reduce the resonant mode while maintain the homogeneity of the RF field. To investigate the design method, the common-mode resonator was realized by using a microstrip line which was split along the central to become a pair of parallel transmission lines within which common-mode currents exist. Eight common-mode resonators were placed equidistantly along the circumference of a low loss dielectric cylinder to form a volume coil. Theoretical analysis and comparison between the 16-strut common-mode volume coil and a conventional 16-strut volume coil in terms of RF field homogeneity and efficiency was performed using Finite-Difference Time-Domain (FDTD) method at 298.2 MHz. MR imaging experiments were performed by using a prototype of the common-mode volume coil on a whole body 7 Tesla scanner. FDTD simulation results showed the reduced number of resonant modes of the common-mode volume coil over the conventional volume coil, while the RF field homogeneity of the two type volume coils was kept at the same level. MR imaging of a water phantom and a kiwi fruit showing the feasibility of the proposed method for simplifying the volume coil design is also presented. Full article
(This article belongs to the Special Issue High Field Magnetic Resonance Methods and Materials)
Open AccessArticle Uniaxial Tension Test of Slender Reinforced Early Age Concrete Members
Materials 2011, 4(8), 1345-1359; doi:10.3390/ma4081345
Received: 21 June 2011 / Revised: 21 July 2011 / Accepted: 27 July 2011 / Published: 2 August 2011
Cited by 6 | PDF Full-text (330 KB) | HTML Full-text | XML Full-text
Abstract
The present study aims to obtain the tensile properties of early age concrete based on a uniaxial tension test employing RC slender members. First, the paper shows that concrete strain is equal to the strain of rebar at the mid-span of the [...] Read more.
The present study aims to obtain the tensile properties of early age concrete based on a uniaxial tension test employing RC slender members. First, the paper shows that concrete strain is equal to the strain of rebar at the mid-span of the RC member. The tensile Young’s modulus and the strain capacity of early age concrete are estimated using strain measurements. The experiment indicated that the tensile Young’s modulus at an early age is higher than the compressive modulus. This observation was similar to one found in a previous investigation which used a direct tension test of early age concrete. Moreover, the paper describes how an empirical equation for mature concrete can be applied to the relation between uniaxial tensile strength and splitting tensile strength even in early age concrete. Based on a uniaxial tension test, the paper proposes an empirical equation for the relationship between standard bond stresses and relative slip. Full article
(This article belongs to the Special Issue Construction Materials)
Open AccessArticle Osteoinductivity Assessment of BMP-2 Loaded Composite Chitosan-Nano-Hydroxyapatite Scaffolds in a Rat Muscle Pouch
Materials 2011, 4(8), 1360-1374; doi:10.3390/ma4081360
Received: 30 June 2011 / Revised: 16 July 2011 / Accepted: 27 July 2011 / Published: 2 August 2011
Cited by 8 | PDF Full-text (978 KB) | HTML Full-text | XML Full-text
Abstract
The objective of this study was to evaluate the osteoinductivity of composite chitosan-nano-hydroxyapatite scaffolds in a rat muscle pouch model. Previous in vitro characterization demonstrated the ability of the scaffolds to promote bone regeneration and as a carrier for local delivery of [...] Read more.
The objective of this study was to evaluate the osteoinductivity of composite chitosan-nano-hydroxyapatite scaffolds in a rat muscle pouch model. Previous in vitro characterization demonstrated the ability of the scaffolds to promote bone regeneration and as a carrier for local delivery of BMP-2. Composite microspheres were prepared using a co-precipitation method, and scaffolds were fabricated using an acid wash to adhere beads together. To determine the in vivo osteoinductivity of the scaffolds, the following groups (n = 6) were implanted into muscle pouches created in the latissimus dorsi of Sprague Dawley rats: (A) lyophilized scaffolds without rhBMP-2, (B) lyophilized scaffolds with rhBMP-2, (C) non-lyophilized scaffolds with rhBMP-2, and (D) absorbable collagen sponge with rhBMP-2 (control). Groups B, C, and D were loaded with 4 mL of a 9.0 μg/mL solution of rhBMP-2 for 48 h. The rats were sacrificed after one month and samples were analyzed for amount of residual implant material, new bone, and osteoid. Although the experimental groups displayed minimal degradation after one month, all of the scaffolds contained small amounts of woven bone and considerable amounts of osteoid. Approximately thirty percent of the open space available for tissue ingrowth in the scaffolds contained new bone or osteoid in the process of mineralization. The ability of the composite scaffolds (with and without BMP-2) to promote ectopic bone growth in vivo was demonstrated. Full article
(This article belongs to the Special Issue Carbohydrate Polymers)
Open AccessArticle Large-Scale Growth of Tubular Aragonite Whiskers through a MgCl2-Assisted Hydrothermal Process
Materials 2011, 4(8), 1375-1383; doi:10.3390/ma4081375
Received: 4 July 2011 / Revised: 29 July 2011 / Accepted: 1 August 2011 / Published: 8 August 2011
PDF Full-text (965 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, we have developed a facile MgCl2-assissted hydrothermal synthesis route to grow tubular aragonite whiskers on a large scale. The products have been characterized by powder X-ray diffraction (XRD), optical microscopy, and scanning electronic microscopy (SEM). The results [...] Read more.
In this paper, we have developed a facile MgCl2-assissted hydrothermal synthesis route to grow tubular aragonite whiskers on a large scale. The products have been characterized by powder X-ray diffraction (XRD), optical microscopy, and scanning electronic microscopy (SEM). The results show the as-grown product is pure tubular aragonite crystalline whiskers with a diameter of 5–10 mm and a length of 100–200 mm, respectively. The concentration of Mg2+ plays an important role in determining the quality and purity of the products. Furthermore, the method can be extended to fabricate CaSO4 fibers. The high quality of the product and the mild conditions used mean that the present route has good prospects for the growth of inorganic crystalline whiskers. Full article
Open AccessArticle Synthesis and Hydrolytic Degradation of Substituted Poly(DL-Lactic Acid)s
Materials 2011, 4(8), 1384-1398; doi:10.3390/ma4081384
Received: 25 May 2011 / Revised: 27 July 2011 / Accepted: 29 July 2011 / Published: 10 August 2011
Cited by 13 | PDF Full-text (1164 KB) | HTML Full-text | XML Full-text
Abstract
Non-substituted racemic poly(DL-lactic acid) (PLA) and substituted racemic poly(DL-lactic acid)s or poly(DL-2-hydroxyalkanoic acid)s with different side-chain lengths, i.e., poly(DL-2-hydroxybutanoic acid) (PBA), poly(DL-2-hydroxyhexanoic acid) (PHA), and poly(DL-2-hydroxydecanoic acid) (PDA) were synthesized by acid-catalyzed polycondensation of DL-lactic acid (LA), DL-2-hydroxybutanoic acid (BA), DL-2-hydroxyhexanoic [...] Read more.
Non-substituted racemic poly(DL-lactic acid) (PLA) and substituted racemic poly(DL-lactic acid)s or poly(DL-2-hydroxyalkanoic acid)s with different side-chain lengths, i.e., poly(DL-2-hydroxybutanoic acid) (PBA), poly(DL-2-hydroxyhexanoic acid) (PHA), and poly(DL-2-hydroxydecanoic acid) (PDA) were synthesized by acid-catalyzed polycondensation of DL-lactic acid (LA), DL-2-hydroxybutanoic acid (BA), DL-2-hydroxyhexanoic acid (HA), and DL-2-hydroxydecanoic acid (DA), respectively. The hydrolytic degradation behavior was investigated in phosphate-buffered solution at 80 and 37 °C by gravimetry and gel permeation chromatography. It was found that the reactivity of monomers during polycondensation as monitored by the degree of polymerization (DP) decreased in the following order: LA > DA > BA > HA. The hydrolytic degradation rate traced by DP and weight loss at 80 °C decreased in the following order: PLA > PDA > PHA > PBA and that monitored by DP at 37 °C decreased in the following order: PLA > PDA > PBA > PHA. LA and PLA had the highest reactivity during polymerization and hydrolytic degradation rate, respectively, and were followed by DA and PDA. BA, HA, PBA, and PHA had the lowest reactivity during polymerization and hydrolytic degradation rate. The findings of the present study strongly suggest that inter-chain interactions play a major role in the reactivity of non-substituted and substituted LA monomers and degradation rate of the non-substituted and substituted PLA, along with steric hindrance of the side chains as can be expected. Full article
(This article belongs to the Special Issue Biodegradability of Materials in Biomedical Applications 2011)
Open AccessArticle Deacetylation of Chitosan: Material Characterization and in vitro Evaluation via Albumin Adsorption and Pre-Osteoblastic Cell Cultures
Materials 2011, 4(8), 1399-1416; doi:10.3390/ma4081399
Received: 21 July 2011 / Accepted: 5 August 2011 / Published: 12 August 2011
Cited by 29 | PDF Full-text (322 KB) | HTML Full-text | XML Full-text
Abstract
Degree of deacetylation (DDA) and molecular weight (MW) of chitosans are important to their physical and biological properties. In this study, two chitosans, HS (DDA = 73.3%) and AT (DDA = 76.8%), were deacetylated with 45% sodium hydroxide under nitrogen atmosphere at [...] Read more.
Degree of deacetylation (DDA) and molecular weight (MW) of chitosans are important to their physical and biological properties. In this study, two chitosans, HS (DDA = 73.3%) and AT (DDA = 76.8%), were deacetylated with 45% sodium hydroxide under nitrogen atmosphere at 80 °C or 90 °C for up to 120 min, to obtain two series of chitosans. The polymers produced were characterized for MW by gel permeation chromatography, DDA by titration and UV-vis methods, and crystallinity, hydrophilicity and thermal stability by X-ray diffraction, water contact angle and differential scanning calorimetry respectively. Films, made by solution casting in dilute acetic acid at ambient conditions, were evaluated for biological activity by albumin adsorption and the attachment and growth of a pre-osteoblast cell line. Chitosans with between 80–93% DDA’s (based on titration) were reproducibly obtained. Even though deacetylation under nitrogen was supposed to limit chain degradation during decetylation, MW decreased (by maximum of 37.4% of HS and 63.0% for AT) with increasing deacetylation reaction time and temperature. Crystallinity and decomposition temperature increased and water contact angles decreased with processing to increase DDA. Significantly less albumin was absorbed on films made with 93% DDA chitosans as compared with the original materials and the AT chitosans absorbed less than the HS chitosans. The cells on higher DDA chitosan films grew faster than those on lower DDA films. In conclusion, processing conditions increased DDA and influenced physicochemical and biological properties. However, additional studies are needed to unambiguously determine the influence of DDA or MW on in vitro and in vivo performance of chitosan materials for bone/implant applications. Full article
(This article belongs to the Special Issue Carbohydrate Polymers)
Figures

Open AccessArticle Preparation of Chitin Nanofibers from Mushrooms
Materials 2011, 4(8), 1417-1425; doi:10.3390/ma4081417
Received: 24 June 2011 / Revised: 3 August 2011 / Accepted: 3 August 2011 / Published: 12 August 2011
Cited by 43 | PDF Full-text (558 KB) | HTML Full-text | XML Full-text
Abstract
Chitin nanofibers were isolated from the cell walls of five different types of mushrooms by the removal of glucans, minerals, and proteins, followed by a simple grinding treatment under acidic conditions. The Chitin nanofibers thus obtained have a uniform structure and a [...] Read more.
Chitin nanofibers were isolated from the cell walls of five different types of mushrooms by the removal of glucans, minerals, and proteins, followed by a simple grinding treatment under acidic conditions. The Chitin nanofibers thus obtained have a uniform structure and a long fiber length. The width of the nanofibers depended on the type of mushrooms and varied in the range 20 to 28 nm. The Chitin nanofibers were characterized by elemental analyses, FT-IR spectra, and X-ray diffraction profiles. The results showed that the α-chitin crystal structure was maintained and glucans remained on the nanofiber surface. Full article
(This article belongs to the Special Issue Carbohydrate Polymers)
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Open AccessArticle Low and High Field Magnetic Resonance for in Vivo Analysis of Seeds
Materials 2011, 4(8), 1426-1439; doi:10.3390/ma4081426
Received: 7 June 2011 / Revised: 4 August 2011 / Accepted: 4 August 2011 / Published: 16 August 2011
Cited by 7 | PDF Full-text (726 KB) | HTML Full-text | XML Full-text
Abstract
Low field NMR has been successfully used for the evaluation of seed composition and quality, but largely only in crop species. We show here that 1.5T NMR provides a reliable means for analysing the seed lipid fraction present in a wide range [...] Read more.
Low field NMR has been successfully used for the evaluation of seed composition and quality, but largely only in crop species. We show here that 1.5T NMR provides a reliable means for analysing the seed lipid fraction present in a wide range of species, where both the seed size and lipid concentration differed by >10 fold. Little use of high field NMR has been made in seed research to date, even though it potentially offers many opportunities for studying seed development, metabolism and storage. Here we demonstrate how 17.5T and 20T NMR can be applied to image seed structure, and analyse lipid and metabolite distribution. We suggest that further technical developments in NMR/MRI will facilitate significant advances in our understanding of seed biology. Full article
(This article belongs to the Special Issue High Field Magnetic Resonance Methods and Materials)
Open AccessArticle Simulation of Granular Flows and Pile Formation in a Flat-Bottomed Hopper and Bin, and Experimental Verification
Materials 2011, 4(8), 1440-1468; doi:10.3390/ma4081440
Received: 17 June 2011 / Revised: 11 August 2011 / Accepted: 12 August 2011 / Published: 22 August 2011
Cited by 2 | PDF Full-text (2597 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Granular flows of 200 μm particles and the pile formation in a flat-bottomed hopper and bin in the presence of air and in a vacuum were predicted based on three-dimensional numerically empirical constitutive relations using Smoothed Particle Hydrodynamics and Computational Fluid Dynamics [...] Read more.
Granular flows of 200 μm particles and the pile formation in a flat-bottomed hopper and bin in the presence of air and in a vacuum were predicted based on three-dimensional numerically empirical constitutive relations using Smoothed Particle Hydrodynamics and Computational Fluid Dynamics methods. The constitutive relations for the strain rate independent stress have been obtained as the functions of the Almansi strain including the large deformation by the same method as Yuu et al. [1]. The constitutive relations cover the elastic and the plastic regions including the flow state and represent the friction mechanism of granular material. We considered the effect of air on the granular flow and pile by the two-way coupling method. The granular flow patterns, the shapes of piles and the granular flow rates in the evolution are compared with experimental data measured under the same conditions. There was good agreement between these results, which suggests that the constitutive relations and the simulation method would be applicable for predicting granular flows and pile formation with complex geometry including free surface geometry. We describe the mechanisms by which the air decreases the granular flow rate and forms the convergence granular flow below the hopper outlet. Full article
(This article belongs to the Special Issue Advances in the Dynamics of Granular Materials)
Open AccessArticle The Effect of Synovial Fluid Enzymes on the Biodegradability of Collagen and Fibrin Clots
Materials 2011, 4(8), 1469-1482; doi:10.3390/ma4081469
Received: 18 July 2011 / Revised: 5 August 2011 / Accepted: 12 August 2011 / Published: 22 August 2011
Cited by 1 | PDF Full-text (390 KB) | HTML Full-text | XML Full-text
Abstract
Recently there has been a great deal of interest in the use of biomaterials to stimulate wound healing. This is largely due to their ability to centralize high concentrations of compounds known to promote wound healing at a needed location. Joints present [...] Read more.
Recently there has been a great deal of interest in the use of biomaterials to stimulate wound healing. This is largely due to their ability to centralize high concentrations of compounds known to promote wound healing at a needed location. Joints present a unique challenge to using scaffolds because of the presence of enzymes in synovial fluid which are known to degrade materials that would be stable in other parts of the body. The hypothesis of this study was that atelocollagen scaffolds would have greater resistance to enzymatic degradation than scaffolds made of gelatin, fibrin and whole blood. To test this hypothesis, collagen and fibrin-based scaffolds were placed in matrix metallopeptidase-1 (MMP-1), elastase, and plasmin solutions at physiologic concentrations, and the degradation of each scaffold was measured at varying time points. The atelocollagen scaffolds had a significantly greater resistance to degradation by MMP-1, elastase and plasmin over the fibrin based scaffolds. The results suggest that atelocollagen-based scaffolds may provide some protection against premature degradation by synovial fluid enzymes over fibrin-based matrices. Full article
(This article belongs to the Special Issue Biodegradability of Materials in Biomedical Applications 2011)

Review

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Open AccessReview Matrices for Sensors from Inorganic, Organic, and Biological Nanocomposites
Materials 2011, 4(8), 1483-1518; doi:10.3390/ma4081483
Received: 19 May 2011 / Revised: 2 August 2011 / Accepted: 11 August 2011 / Published: 24 August 2011
Cited by 4 | PDF Full-text (1941 KB) | HTML Full-text | XML Full-text
Abstract
Matrices and sensors resulting from inorganic, organic and biological nanocomposites are presented in this overview. The term nanocomposite designates a solid combination of a matrix and of nanodimensional phases differing in properties from the matrix due to dissimilarities in structure and chemistry. [...] Read more.
Matrices and sensors resulting from inorganic, organic and biological nanocomposites are presented in this overview. The term nanocomposite designates a solid combination of a matrix and of nanodimensional phases differing in properties from the matrix due to dissimilarities in structure and chemistry. The nanoocomposites chosen for a wide variety of health and environment sensors consist of Anodic Porous Allumina and P450scc, Carbon nanotubes and Conductive Polymers, Langmuir Blodgett Films of Lipases, Laccases, Cytochromes and Rhodopsins, Three-dimensional Nanoporous Materials and Nucleic Acid Programmable Protein Arrays. Full article
(This article belongs to the Special Issue Nanocomposites of Polymers and Inorganic Particles 2011)

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