Home About us Contact
|
Home About us Contact | ||
|
|
||
Mechanical Strength (mechanical + strength)
Kinds of Mechanical Strength Selected AbstractsA Novel Hydrogel with High Mechanical Strength: A Macromolecular Microsphere Composite Hydrogel,ADVANCED MATERIALS, Issue 12 2007T. Huang A novel hydrogel with a new, well- defined network structure is prepared through a two-step method in which the radiation-peroxidized macromolecular microspheres act as both initiators and crosslinkers. The macromolecular microsphere composite hydrogel (see figure) can effectively dissipate applied mechanical stress and has extremely high mechanical strength. Some of the hydrogels can nearly completely recover their original shapes, even after an extremely high strain (99.7%) in compression tests. [source] Improving the Processing Ability and Mechanical Strength of Starch/Poly(vinyl alcohol) Blends through Plasma and Acid ModificationMACROMOLECULAR SYMPOSIA, Issue 1 2008Sung-Yeng Yang Abstract Summary: In this study, maleic anhydride (MA), and citric acid (CA) used as the processing additive and plasma treatment to improve the processing ability and mechanical strength of biodegradable starch/poly (vinyl alcohol) (PVA) blends were studied. The melt flow index (MFI) of starch/ glycerol/PVA (300g/60g/80g) blend was increased from 2.3g/10min to 32.7g/10min by adding 3g of MA and to 130 g/10min by adding MA and plasma treatment. The tensile strength of starch/glycerol/PVA blend increased from 3.48 to 6.21 MPa by adding 1.5g of MA and 1.5g of CA, while it increased to 6.26 MPa by plasma treatment. Esterification reaction which was evidenced by FTIR has been showed to improve the compatibility between starch and PVA when MA was dissolved into glycerol and glycerol grafted onto plasma pretreatment PVA. Thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) imaging were used to study the morphology of extruded blends. [source] Mechanical strength of laser-welded cobalt,chromium alloyJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 2 2004N. Baba Abstract The purpose of this study was to investigate the effect of the output energy of laserwelding and welding methods on the joint strength of cobalt-chromium (Co-Cr) alloy. Twotypes of cast Co-Cr plates were prepared, and transverse sections were made at the center ofthe plate. The cut surfaces were butted against one another, and the joints welded with alaser-welding machine at several levels of output energy with the use of two methods. Thefracture force required to break specimens was determined by means of tensile testing. For the0.5-mm-thick specimens, the force required to break the 0.5-mm laser-welded specimens atcurrents of 270 and 300 A was not statistically different (p > 0.05) from the results for thenonwelded control specimens. The force required to break the 1.0-mm specimens double-weldedat a current of 270 A was the highest value among the 1.0-mm laser-welded specimens. The results suggested that laser welding under the appropriate conditions improved the jointstrength of cobalt- chromium alloy. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 69B: 121,124, 2004 [source] Cell removal with supercritical carbon dioxide for acellular artificial tissueJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 6 2008K. Sawada Abstract BACKGROUND: The objective of this work was to decellularize artificial tissue without using surfactant solutions. For this purpose, supercritical carbon dioxide was used as the extraction medium. RESULTS: Supercritical carbon dioxide containing a small amount of entrainer was a suitable medium to extract both cell nuclei and cell membranes from artificial tissue. Under gentle extraction conditions (15 MPa, 37 °C), cell nuclei were satisfactorily extracted from tissue within 1 h. In contrast, the efficiency of phospholipid removal depended strongly on the transfer rate of carbon dioxide in the interior of the tissue. Mechanical strength of tissue was not decreased even with prolonged treatment. CONCLUSION: Acellular artificial tissues could be prepared quickly by treatment with a carbon dioxide/entrainer system. The prepared acellular tissue could be obtained in absolutely dry condition. This is advantageous from the viewpoint of long-term preservation without putrefaction and contamination. Copyright © 2008 Society of Chemical Industry [source] Degradation of repaired denture base materials in simulated oral fluidJOURNAL OF ORAL REHABILITATION, Issue 3 2000C.-T. Lin This in vitro study evaluates the degradation of repaired denture bases upon immersion in a simulated oral fluid. Denture base materials (Luciton 199®), after being repaired by Repair Material® and Triad®, using three different joint surface designs (butt, round and 45 ° bevel), were immersed onto 99·5 vol.% ethanol/water solution (with similar solubility parameter) for various amounts of time (0,72 h). The flexural loads of the six combination of groups were measured by the three-point bending tests using a universal testing machine. Acoustic emission (AE) during sample fracturing were processed using the MISTRA 2001 system. The fracture pattern and surface details of the interface were examined with a scanning electronic microscope (SEM). Data were analysed using three-way anova and Tukey LSD tests. SEM micrographs of the fracture interface were used to differentiate the fracture mode. The flexural loads (2·72±0·51 Kgf) of the round joint specimens were significantly higher (P<0·05) than those (butt: 1·66±0·38 Kgf, 45 ° bevel: 1·93±0·41 Kgf) of the other two designs. This corresponds to the microscopic examination in which more cohesive failure mode was found for the round joint group after storage. The flexural loads (2·54±0·39 Kgf) of the specimens repaired with Triad® were significantly higher (P<0·05) than those (1·59±0·40 Kgf) of specimens repaired with Repair Material®. Significant progressive reduction of the flexural load and/or AE signals of the specimens was noted in proportion to the length of time of the immersion in the simulated oral fluid. Mechanical strength of a denture base repaired with a round joint design and light-cured material is significantly higher after immersion in simulated oral fluid. [source] Core-Shell Nanoblends from Soy Protein/Polystyrene by Emulsion PolymerizationMACROMOLECULAR MATERIALS & ENGINEERING, Issue 8 2008Dagang Liu Abstract Novel soy protein/polystyrene nanoblends with core-shell structures were successfully prepared by introducing nano-sized PS into soy protein through emulsion polymerization. The nanoblends showed core-shell structures, with the core being of PS and the shell of sodium dodecane sulfonate and soy protein polypeptides, when investigated by electron microscopy. Nanoblends containing high levels of PS (>30%) exhibited characteristic infrared spectrum bands, X-ray diffraction peak, and glass transition, since PS microsphere aggregated to form independent PS domains. Mechanical strength and water resistance were effectively improved by introducing PS. An effective structure-performance relationship was thereby established to describe the nanoblends. [source] Photopolymerization of alicyclic methacrylate hydrogels for controlled releasePOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 7 2009Jing Han Abstract Alicyclic hydroxy methacrylate monomer, o -hydroxycyclohexyl methacrylate (HCMA), was synthesized and characterized by Fourier transformed infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance spectroscopy (1H-NMR). Photopolymerization kinetics of HCMA was investigated via real-time infrared spectroscopy (RT-IR). Polymeric network hydrogels based on hydroxyethyl methacrylate (HEMA) and HCMA were prepared by using the photopolymerization technique. Mechanical strength, swelling characteristic, and controlled release behavior of hydrogels with various feed compositions were studied. Poly(HEMA-co-HCMA) hydrogel had higher storage modulus than that of poly(HEMA) hydrogel as investigated by dynamic mechanical analysis (DMA). Acid orange 8 was used as a model drug for the investigation of drug release behavior of copolymeric hydrogels. Results indicated that increase in HCMA ratio in hydrogel composition could reduce the swelling rate and prolong the release time. Scanning electron microscopy (SEM) was also utilized to study the surface morphology of hydrogels, and the results indicated that HCMA content influenced pore diameter on the hydrogel surface. Copyright © 2008 John Wiley & Sons, Ltd. [source] The influence of metallic substitution on the physical properties of manganese mercury thiyocyanate crystalsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 3 2007G. P. Joseph Abstract Good optical grade single crystals of pure, Cd2+ and Mg2+ doped Manganese Mercury Thiyocyanate (MMTC) crystals are grown by slow solvent evaporation technique at room temperature. Single crystal XRD studies reveal that the incorporation of metallic dopants has not changed the structure of the parent crystal. The SHG efficiencies of the pure and doped samples of MMTC are measured by Kurtz Perry powder method and the results are compared with urea. It is evident from microhardness study that the presence of dopants has increased the mechanical strength of MMTC crystal. The TG/DTG studies confirm that the thermal decomposition temperatures of pure (353°C), Mg2+ doped (363°C) and Cd2+ doped (365°C) MMTC are relatively high when compared to other NLO crystals of the same family. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Pharmacologic profile of zoledronic acid: A highly potent inhibitor of bone resorptionDRUG DEVELOPMENT RESEARCH, Issue 4 2002Jonathan R. Green Abstract Bisphosphonates are effective in treating benign and malignant skeletal diseases characterized by enhanced osteoclastic bone resorption (i.e., osteoporosis, Paget's disease, tumor-induced osteolysis). The nitrogen-containing bisphosphonate pamidronate is currently the standard treatment for hypercalcemia of malignancy (HCM) and skeletal complications of bone metastases. Zoledronic acid, a novel nitrogen-containing bisphosphonate with an imidazole substituent, has demonstrated more potent inhibition of osteoclast-mediated bone resorption than all other bisphosphonates, including pamidronate, in both in vitro and in vivo preclinical models. Zoledronic acid inhibited ovariectomy-induced bone loss in adult monkeys and rats, and long-term treatment prevented skeletal turnover and subsequent bone loss, reduced cortical porosity, and increased mechanical strength. Zoledronic acid also significantly inhibited bone loss associated with arthritis, bone metastases, and prosthesis loosening. The increased potency of zoledronic acid vs. pamidronate has been demonstrated clinically: zoledronic acid (4 or 8 mg iv) was superior to pamidronate (90 mg iv) in normalizing corrected serum calcium in patients with HCM. In patients with bone metastases, low doses of zoledronic acid (, 2 mg) suppressed bone resorption markers , 50% below baseline, whereas pamidronate 90 mg yielded only 20 to 30% suppression. Importantly, the increased potency of zoledronic acid is not associated with an increased incidence of local (bone) or systemic adverse events. Zoledronic acid does not impair bone mineralization and, compared with pamidronate, has a greater renal and intestinal tolerability therapeutic index. Thus, based on preclinical assays and clinical data, zoledronic acid is the most potent bisphosphonate tested to date. Given its potency and excellent safety profile, zoledronic acid is now poised to become the new standard of treatment for HCM and metastatic bone disease. Drug Dev. Res. 55:210,224, 2002. © 2002 Wiley-Liss, Inc. [source] Particle clusters in gravel-bed rivers: an experimental morphological approach to bed material transport and stability conceptsEARTH SURFACE PROCESSES AND LANDFORMS, Issue 11 2005Lea Wittenberg Abstract Structured gravel river beds clearly exert a major influence on bed stability. Indexing structural stability by field measurements of bed strength neglects the processes operating to entrain and transport bed material in different parts of each structure. This study takes a morphological approach to interpreting the critical processes, using particle tracing to determine the movement of individual cluster particles over a range of flood event magnitudes and durations. The experiment was carried out on the River South Tyne, UK; it uses flow hydrographs measured nearby and also benefits from previous studies of historical development, channel morphology and sediment transport at the same site. More than 30 clusters were monitored over a seven-month period during which clusters occupied 7,16 per cent of the bed. Threshold flows delimiting three apparently contrasting bed sediment process regimes for cluster particles are tentatively set at 100 m3 s,1 and 183 m3 s,1; durations of flow at these levels are critical for cluster development, rather than flow peak values. Wake particles are transported most easily. Flow straightening in the wandering channel planform reduces the stability of clusters, since mechanical strength is markedly reduced by this change of direction. The overall area covered by clusters between significant transport events varies little, implying a dynamic equilibrium condition. Copyright © 2005 John Wiley & Sons, Ltd. [source] Graphene Based Electrochemical Sensors and Biosensors: A ReviewELECTROANALYSIS, Issue 10 2010Yuyan Shao Abstract Graphene, emerging as a true 2-dimensional material, has received increasing attention due to its unique physicochemical properties (high surface area, excellent conductivity, high mechanical strength, and ease of functionalization and mass production). This article selectively reviews recent advances in graphene-based electrochemical sensors and biosensors. In particular, graphene for direct electrochemistry of enzyme, its electrocatalytic activity toward small biomolecules (hydrogen peroxide, NADH, dopamine, etc.), and graphene-based enzyme biosensors have been summarized in more detail; Graphene-based DNA sensing and environmental analysis have been discussed. Future perspectives in this rapidly developing field are also discussed. [source] Low-voltage electroosmosis pump for stand-alone microfluidics devicesELECTROPHORESIS, Issue 1-2 2003Yuzuru Takamura Abstract Two types of low-voltage electroosmosis pumps were developed using microfabrication technology for usage in handy or stand-alone applications of the micrototal analysis systems (,-TAS) and the lab-on-a-chip. This was done by making a thin (<,1 ,m) region in the flow path and by only applying voltages near this thin region using electrodes inserted into the flow path. The inserted electrodes must be free from bubble formation and be gas-tight in order to avoid pressure leakage. For these electrodes, Ag/AgCl or a gel salt bridge was used. For patterning the gel on the chip, a hydrophilic photopolymerization gel and a photolithographic technique were optimized for producing a gel with higher electric conductivity and higher mechanical strength. For high flow rate application, wide (33.2 mm) and thin (400 nm) pumping channels were compacted into a 1 mm×6 mm area by folding. This pump achieves an 800 Pa static pressure and a flow of 415 nL/min at 10 V. For high-pressure application, a pump was designed with the thin and thick regions in series and positive and negative electrodes were inserted between them alternatively. This pump could increase the pumping pressure without increasing the supply voltage. A pump with 10-stage connections generated a pressure of 25 kPa at 10 V. [source] Novel Nanoparticle-Reinforced Metal Matrix Composites with Enhanced Mechanical PropertiesADVANCED ENGINEERING MATERIALS, Issue 8 2007C. Tjong Abstract This paper summarizes and reviews the state-of-the-art processing methods, structures and mechanical properties of the metal matrix composites reinforced with ceramic nanoparticles. The metal matrices of nanocomposites involved include aluminum and magnesium. The processing approaches for nanocomposites can be classified into ex-situ and in-situ synthesis routes. The ex-situ ceramic nanoparticles are prone to cluster during composite processing and the properties of materials are lower than the theoretical values. Despite the fact of clustering, ex-situ nanocomposites reinforced with very low loading levels of nanoparticles exhibit higher yield strength and creep resistance than their microcomposite counterparts filled with much higher particulate content. Better dispersion of ceramic nanoparticles in metal matrix can be achieved by using appropriate processing techniques. Consequently, improvements in both the mechanical strength and ductility can be obtained readily in aluminum or magnesium by adding ceramic nanoparticles. Similar beneficial enhancements in mechanical properties are observed for the nanocomposites reinforced with in-situ nanoparticles. [source] The Research Programme Contract "Precipitation": What for?ADVANCED ENGINEERING MATERIALS, Issue 12 2006The Preliminary Analysis of Needs by the Industrial Partners The predictive modelling of precipitation in steels and aluminium alloys in the solid state, based on the physical understanding of its mechanisms were the major goal of this CPR project. Wrought heat treatable aluminium alloys as well as cold and hot rolled steels are of utmost importance for applications (transportation, electrical applications, building, sport and leisure, etc.) requiring high property (e.g. mechanical strength, electrical conductivity, magnetic properties) to weight ratios. [source] Biocompatibility of Lotus-type Stainless Steel and Titanium in Alveolar BoneADVANCED ENGINEERING MATERIALS, Issue 9 2006Y. Higuchi Abstract Lotus-type porous stainless steel (SUS304L) and porous titanium were fabricated by unidirectional solidification in a mixture gas of hydrogen and argon. The porous metals which were cut into 5,mm cubes (non-dehydrogenated) and 3.4,mm,,×,5,mm cylinders (dehydrogenated) were implanted into the canine mandible alveolar bone for two, four and eight weeks for animal experiments. The changes in the tissues were observed using SEM. For porous stainless steel (cylindrical; dehydrogenated) new formation of bones was observed around the sample in two weeks without any sign of bony ingrowth into the pores. The osteogenesis was found in shallow areas in the pores in four weeks and deep in the pores in eight weeks. Porous titanium, on the other hand, showed deep ingrowth of new bones in four weeks. Our observations allowed us to expect application of the porous metals as biomaterials. They maintain mechanical strength and are lighter in weight so that it is expected to be applied for dental implants and core materials of artificial bones. [source] Novel member of the mouse desmoglein gene family: Dsg1-,EXPERIMENTAL DERMATOLOGY, Issue 1 2003L. Pulkkinen Abstract: Desmosomes are major intercellular adhesion junctions that provide stable cell,cell contacts and mechanical strength to epithelial tissues by anchoring cytokeratin intermediate filaments of adjacent cells. Desmogleins (Dsg) are transmembrane core components of the desmosomes, and belong to the cadherin supergene family of calcium-dependent adhesion molecules. Currently, there are three known isoforms of Dsgs (Dsg1, Dsg2, and Dsg3), encoded by distinct genes that are differentially expressed to determine their tissue specificity and differentiation state of epithelial cells. In this study, we cloned a novel mouse desmoglein gene sharing high homology to both mouse and human Dsg1. We propose to designate the previously published mouse Dsg1 gene as Dsg1- , and the new gene as Dsg1-,. Analysis of intron/exon organization of the Dsg1-, and Dsg1-, genes revealed significant conservation. The full-length mouse Dsg1-, cDNA contains an open reading frame of 3180 bp encoding a precursor protein of 1060 amino acids. Dsg1-, protein shares 94% and 76% identity with mouse Dsg1-, and human DSG1, respectively. RT-PCR using a multitissue cDNA panel demonstrated that while Dsg1-, mRNA was expressed in 15- to 17-day-old embryos and adult spleen and testis, Dsg1-, mRNA was detected in 17-day-old embryos only. To assess subcellular localization, a FLAG-tagged expression construct of Dsg1-, was transiently expressed in epithelial HaCaT cells. Dsg1-,-FLAG was found at the cell,cell border and was recognized by the anti-Dsg1/Dsg2 antibody DG3.10. In summary, we have cloned and characterized a novel member of the mouse desmoglein gene family, Dsg1-,. [source] Thickness-Dependent Properties of Relaxor-PbTiO3 Ferroelectrics for Ultrasonic TransducersADVANCED FUNCTIONAL MATERIALS, Issue 18 2010Hyeong Jae Lee Abstract The electrical properties of Pb(Mg1/3Nb2/3)O3 -PbTiO3 (PMN-PT)-based polycrystalline ceramics and single crystals were investigated as a function of scale ranging from 500 ,m to 30 ,m. Fine-grained PMN-PT ceramics exhibited comparable dielectric and piezoelectric properties to their coarse-grained counterpart in the low frequency range (<10 MHz), but offered greater mechanical strength and improved property stability with decreasing thickness, corresponding to higher operating frequencies (>40 MHz). For PMN-PT single crystals, however, the dielectric and electromechanical properties degraded with decreasing thickness, while ternary Pb(In1/2Nb1/2)O3 -Pb(Mg1/3Nb2/3)O3 -PbTiO3 (PIN-PMN-PT) exhibited minimal size-dependent behavior. The origin of property degradation of PMN-PT crystals was further studied by investigating the dielectric permittivity at high temperatures, and domain observations using optical polarized light microscopy. The results demonstrated that the thickness-dependent properties of relaxor-PT ferroelectrics are closely related to the domain size with respect to the associated macroscopic scale of the samples. [source] Dynamics of cell wall structure in Saccharomyces cerevisiaeFEMS MICROBIOLOGY REVIEWS, Issue 3 2002Frans M Klis Abstract The cell wall of Saccharomyces cerevisiae is an elastic structure that provides osmotic and physical protection and determines the shape of the cell. The inner layer of the wall is largely responsible for the mechanical strength of the wall and also provides the attachment sites for the proteins that form the outer layer of the wall. Here we find among others the sexual agglutinins and the flocculins. The outer protein layer also limits the permeability of the cell wall, thus shielding the plasma membrane from attack by foreign enzymes and membrane-perturbing compounds. The main features of the molecular organization of the yeast cell wall are now known. Importantly, the molecular composition and organization of the cell wall may vary considerably. For example, the incorporation of many cell wall proteins is temporally and spatially controlled and depends strongly on environmental conditions. Similarly, the formation of specific cell wall protein,polysaccharide complexes is strongly affected by external conditions. This points to a tight regulation of cell wall construction. Indeed, all five mitogen-activated protein kinase pathways in bakers' yeast affect the cell wall, and additional cell wall-related signaling routes have been identified. Finally, some potential targets for new antifungal compounds related to cell wall construction are discussed. [source] Glucose-Responsive Bioinorganic Nanohybrid Membrane for Self-Regulated Insulin ReleaseADVANCED FUNCTIONAL MATERIALS, Issue 9 2010Claudia R. Gordijo Abstract A bioinorganic nanohybrid glucose-responsive membrane is developed for self-regulated insulin delivery analogous to a healthy human pancreas. The application of MnO2 nanoparticles as a multifunctional component in a glucose-responsive, protein-based membrane with embedded pH-responsive hydrogel nanoparticles is proposed. The bio-nanohybrid membrane is prepared by crosslinking bovine serum albumin (BSA),MnO2 nanoparticle conjugates with glucose oxidase and catalase in the presence of poly(N -isopropyl acrylamide- co -methacrylic acid) nanoparticles. The preparation and performance of this new nanocomposite material for a glucose-responsive insulin release system is presented. The activity and stability of immobilized glucose oxidase and the morphology and mechanical properties of the membrane are investigated. The enzymatic activity is well preserved in the membranes. The use of MnO2 nanoparticles not only reinforces the mechanical strength and the porous structure of the BSA-based membrane, but enhances the long-term stability of the enzymes. The in vitro release of insulin across the membrane is modulated by changes in glucose concentration mimicking possible fluctuations of blood-glucose level in diabetic patients. A four-fold increase in insulin permeation is observed when the glucose concentration is increased from normal to hyperglycemic levels, which returns to the baseline level when the glucose concentration is reduced to a normal level. [source] High-Performance Alkaline Polymer Electrolyte for Fuel Cell ApplicationsADVANCED FUNCTIONAL MATERIALS, Issue 2 2010Jing Pan Abstract Although the proton exchange membrane fuel cell (PEMFC) has made great progress in recent decades, its commercialization has been hindered by a number of factors, among which is the total dependence on Pt-based catalysts. Alkaline polymer electrolyte fuel cells (APEFCs) have been increasingly recognized as a solution to overcome the dependence on noble metal catalysts. In principle, APEFCs combine the advantages of and alkaline fuel cell (AFC) and a PEMFC: there is no need for noble metal catalysts and they are free of carbonate precipitates that would break the waterproofing in the AFC cathode. However, the performance of most alkaline polyelectrolytes can still not fulfill the requirement of fuel cell operations. In the present work, detailed information about the synthesis and physicochemical properties of the quaternary ammonia polysulfone (QAPS), a high-performance alkaline polymer electrolyte that has been successfully applied in the authors' previous work to demonstrate an APEFC completely free from noble metal catalysts (S. Lu, J. Pan, A. Huang, L. Zhuang, J. Lu, Proc. Natl. Acad. Sci. USA2008, 105, 20611), is reported. Monitored by NMR analysis, the synthetic process of QAPS is seen to be simple and efficient. The chemical and thermal stability, as well as the mechanical strength of the synthetic QAPS membrane, are outstanding in comparison to commercial anion-exchange membranes. The ionic conductivity of QAPS at room temperature is measured to be on the order of 10,2,S cm,1. Such good mechanical and conducting performances can be attributed to the superior microstructure of the polyelectrolyte, which features interconnected ionic channels in tens of nanometers diameter, as revealed by HRTEM observations. The electrochemical behavior at the Pt/QAPS interface reveals the strong alkaline nature of this polyelectrolyte, and the preliminary fuel cell test verifies the feasibility of QAPS for fuel cell applications. [source] Proton Transport from Dendritic Helical-Pore-Incorporated PolymersomesADVANCED FUNCTIONAL MATERIALS, Issue 18 2009Anthony J. Kim Abstract The ability to add synthetic channels to polymersome (polymer vesicle) membranes could lead to novel membrane composites with unique selectivity and permeability. Proton transport through two different synthetic pores, self-assembled from either a dendritic dipeptide, (6Nf-3,4-3,5)12G2-CH2 -Boc-L-Tyr-L-Ala-OMe, or a dendritic ester, (R)-4Bp-3,4-dm8G1-COOMe, incorporated into polymersome membranes are studied. Polymersomes provide an excellent platform for studying such transport processes due to their robustness and mechanical and chemical stability compared to liposomes. It is found that the incorporated dendritic dipeptide and dendritic ester assemble into stable helical pores in the poly(ethylene oxide)-polybutadiene (PEO-PBD) polymersomes but not in the poly(2-methyloxazoline)-poly(dimethylsiloxane)-poly(2-methyl oxazoline) (PMOX-PDMS-PMOX) polymersomes. The incorporation is confirmed by circular dichroism (CD), changes in purely synthetic mechanical strength (e.g., areal expansion modulus) as assessed by micropipette aspiration, and cryo-TEM. In addition to the structural analyses, a transport measurement shows the incorporated dendritic helical pores allow facile transport of protons across the polymersome membranes after up to one month of storage. This integration of synthetic porous channels with polymersome substrates could provide a valuable tool for studying active transport processes in a composite membrane. These composites will ultimately expand the family of biologically inspired porous-membrane mimics. [source] Adhesive, Flexible, and Robust Polysaccharide Nanosheets Integrated for Tissue-Defect RepairADVANCED FUNCTIONAL MATERIALS, Issue 16 2009Toshinori Fujie Abstract Recent developments in nanotechnology have led to a method for producing free-standing polymer nanosheets as a macromolecular organization. Compared with bulk films, the large aspect ratio of such nanosheets leads to unique physical properties, such as transparency, noncovalent adhesion, and high flexibility. Here, a biomedical application of polymer nanosheets consisting of biocompatible and biodegradable polysaccharides is reported. Micro-scratch and bulge tests indicate that the nanosheets with a thickness of tens of nanometers have sufficient physical adhesiveness and mechanical strength for clinical use. A nanosheet of 75,nm thickness, a critical load of 9.1,×,104,N m,1, and an elastic modulus of 9.6,GPa is used for the minimally invasive repair of a visceral pleural defect in beagle dogs without any pleural adhesion caused by wound repair. For the first time, clinical benefits of sheet-type nano-biomaterials based on molecular organization are demonstrated, suggesting that novel therapeutic tools for overlapping tissue wounds will be possible without the need for conventional surgical interventions. [source] MEL-type Pure-Silica Zeolite Nanocrystals Prepared by an Evaporation-Assisted Two-Stage Synthesis Method as Ultra-Low- k Materials,ADVANCED FUNCTIONAL MATERIALS, Issue 12 2008Yan Liu Abstract A MEL-type pure-silica zeolite (PSZ), prepared by spin-on of nanoparticle suspensions, has been shown to be a promising ultra-low-dielectric-constant (k) material because of its high mechanical strength, hydrophobicity, and chemical stability. In our previous works, a two-stage synthesis method was used to synthesize a MEL-zeolite nanoparticle suspension, in which both nanocrystal yield and particle size of the zeolite suspension increased with increasing synthesis time. For instance, at a crystal yield of 63%, the particle size is 80,nm, which has proved to be too large because it introduces a number of problems for the spin-on films, including large surface roughness, surface striations, and large mesopores. In the current study, the two-stage synthesis method is modified into an evaporation-assisted two-stage method by adding a solvent-evaporation process between the two thermal-treatment steps. The modified method can yield much smaller particle sizes (e.g., 14,vs. 80,nm) while maintaining the same nanocrystal yields as the two-stage synthesis. Furthermore, the nanoparticle suspensions from the evaporation-assisted two-stage synthesis show a bimodal particle size distribution. The primary nanoparticles are around 14,nm in size and are stable in the final suspension with 60% solvent evaporation. The factors that affect nanocrystal synthesis are discussed, including the concentration, pH value, and viscosity. Spin-on films prepared by using suspensions synthesized this way have no striations and improved elastic modulus (9.67,±,1.48,GPa vs. 7.82,±,1.30,GPa), as well as a similar k value (1.91,±,0.09 vs. 1.89,±,0.08) to the previous two-stage synthesized films. [source] Shaping Carbon Nanotubes and the Effects on Their Electrical and Mechanical Properties,ADVANCED FUNCTIONAL MATERIALS, Issue 11 2006S. Wang Abstract A method is developed and shown to be able to shape a carbon nanotube (CNT) into a desired morphology while maintaining its excellent electrical and mechanical properties. Single, freestanding nanotubes are bent by a scanning tunneling microscopy probe, and their morphology is fixed by electron-beam-induced deposition (inside a transmission electron microscope) of amorphous carbon on the bent area. It is shown that the mechanical strength of the bent CNT may be greatly enhanced by increasing the amount of carbon glue or the deposition area, and the electrical conduction of the nanotube shows hardly any dependence on the bending deformation or on the deposition of amorphous carbon. Our findings suggest that CNTs might be manipulated and processed as interconnections between electronic devices without much degradation in their electrical conductance, and be used in areas requiring complex morphology, such as nanometer-scale transport carriers and nanoelectromechanical systems. [source] Cover Picture: Fabrication and Electrical and Mechanical Properties of Carbon Nanotube Interconnections (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 11 2005Mater. Abstract The fabrication of carbon nanotube (CNT) structures, including simple tube,tube connections, crossed junctions, T-junctions, zigzag structures, and even nanotube networks, has been achieved by cutting and soldering CNTs using electron-beam-induced deposition of amorphous carbon (a-C), as detailed in the work of Peng and co-workers on p.,1825. These CNT structures have been constructed with a high degree of control, and it is found that the electric conductance and mechanical strength of the junctions can be improved by the deposition of a-C and by increasing the contact area of the junctions. Individual carbon nanotubes (CNTs) have been cut, manipulated, and soldered via electron-beam-induced deposition of amorphous carbon (a-C) and using a scanning tunneling microscope inside a transmission electron microscope. All CNT structures, including simple tube,tube connections, crossed junctions, T-junctions, zigzag structures, and even nanotube networks, have been successfully constructed with a high degree of control, and their electrical and mechanical properties have been measured in situ inside the transmission electron microscope. It is found that multiple CNTs may be readily soldered together with moderate junction resistance and excellent mechanical resilience and strength, and the junction resistance may be further reduced by current-induced graphitization of the deposited a-C on the junction. [source] Formation of Network and Cellular Structures by Viscoelastic Phase SeparationADVANCED MATERIALS, Issue 18 2009Hajime Tanaka Abstract Network (sponge) and cellular structures are often seen in various types of materials. Materials with such structures are generally characterized by light weight and high mechanical strength. The usefulness of such materials is highlighted, for example, by the remarkable material properties of bone tissue, which often has a highly porous structure. In artificial materials, plastic and metallic foams and breads have such structures. Here, we describe a physical principle for producing network and cellular structures using phase separation, and its potential applications to the morphological control of materials spanning from soft to hard matter. [source] Nanoindentation Studies Reveal Material Properties of VirusesADVANCED MATERIALS, Issue 10-11 2009Wouter H. Roos Abstract Over the last years, a paradigm shift has occurred from approaching viruses solely as disease-bringing agents toward regarding them as functional nanoparticles, and a perfect example of Nature's capability to self-assemble complex, multicomponent materials at the nanoscale. Viruses are now used as templates for constructing specific nanocontainers, either by changing the properties of the viruses themselves or by copying their compact, shelled structure into engineered materials, which are able to encapsulate various agents. To exploit the mechanisms used by nature to create functional nanocontainers, we need to understand what their material and biomechanical properties are. Nanoindentation, a technique based on atomic force microscopy, is perfectly suited to determine these characteristics. Here, we discuss the advances this research field has achieved, exploring prokaryotic (bacteriophages) as well as eukaryotic viruses. The material properties of viral shells (capsids) and of more complex viral assemblies are analyzed and compared. We discuss the Young's modulus of capsids, the maximal forces viruses can withstand, and explore the occurrence of material fatigue in nanosize objects. Finally, the impact of internalized materials and of specific alterations to the capsid proteins on the particle's mechanical strength is analyzed. [source] Determination of rock mass strength properties by homogenizationINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 13 2001A. Pouya Abstract A method for determining fractured rock mass properties is presented here on the basis of homogenization approach. The rock mass is considered to be a heterogeneous medium composed of intact rock and of fractures. Its constitutive model is studied numerically using finite element method and assimilating the fractures to joint elements (Coste, Comportement Thermo-Hydro-Mécanique des massifs rocheux fracturés. Thèse de Doctorat, Ecole Nationale des Ponts et Chaussées, Paris, 1997). The method has been applied to a granite formation in France. Geological data on different families of fractures have been used for the statistical representation of the fractures. A mesh-generating tool for the medium with high density of fractures has been developed. The mechanical behaviour of the rock mass (elasticity, ultimate strength and hardening law) has been determined assuming linear elasticity and Mohr,Coulomb strength criterion both for the intact rock and the fractures. Evolution of the mechanical strength in different directions has been determined as a function of the mean stress, thanks to various numerical simulations. The mechanical strength appears to be anisotropic due to the preferential orientation of the fractures. The numerical results allowed us to determine an oriented strength criterion for the homogenized rock mass. A 2D constitutive law for the homogenized medium has been deduced from numerical data. A 3D extension of this model is also presented. Copyright © 2001 John Wiley & Sons, Ltd. [source] Bone-like Resorbable Silk-based Scaffolds for Load-bearing Osteoregenerative Applications,ADVANCED MATERIALS, Issue 1 2009Andrew M. Collins Hydroxyapatite/silk biocompatible composites with unprecedented mechanical strength and toughness areproduced in a new process with theintegrated mineralization of macroporous silk fibroin scaffolds. Thebiomimetic bone-like composites areabsorbable and load-bearing with compressive strength, modulus, andtoughness comparable to the mechanical tolerances of cancellous bone. [source] Zero Shrinkage of LTCC by Self-Constrained SinteringINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 5 2005Torsten Rabe Low shrinkage in x and y direction and low tolerances of shrinkage are an indispensable precondition for high-density component configuration. Therefore, zero shrinkage sintering technologies as pressure-assisted sintering and sacrificial tapes have been introduced in the low-temperature co-fired ceramics (LTCC) production by different manufacturers. Disadvantages of these methods are high costs of sintering equipment and an additional process step to remove the sacrificial tapes. In this article, newly developed self-constrained sintering methods are presented. The new technology, HeraLock®, delivers LTCC modules with a sintering shrinkage in x and y direction of less than 0.2% and with a shrinkage tolerance of ±0.02% without sacrificial layers and external pressure. Each tape is self-constrained by integration of a layer showing no shrinkage in the sintering temperature range of the LTCC. Large area metallization, integration of channels, cavities and passive electronic components are possible without waviness and camber. Self-constrained laminates are an alternative way to produce zero shrinkage LTCC. They consist of tapes sintering at different temperature intervals. Precondition for a successful production of a self-constrained LTCC laminate is the development of well-adapted material and tapes, respectively. This task is very challenging, because sintering range, high-temperature reactivity and thermal expansion coefficient have to be matched and each tape has to fulfill specific functions in the final component, which requires the tailoring of many properties as permittivity, dielectric loss, mechanical strength, and roughness. A self-constrained laminate is introduced in this article. It consists of inner tapes sintering at especially low-temperature range between 650°C and 720°C and outer tapes with an as-fired surface suitable for thin-film processes. [source] | ||||||||||||||||||||||||||||||||||||||||