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Composite Materials (composite + material)
Selected AbstractsCharacterization of a Novel Fiber Composite Material for Mechanotransduction Research of Fibrous Connective TissuesADVANCED FUNCTIONAL MATERIALS, Issue 5 2010Hazel R. C. Screen Abstract Mechanotransduction is the fundamental process by which cells detect and respond to their mechanical environment, and is critical for tissue homeostasis. Understanding mechanotransduction mechanisms will provide insights into disease processes and injuries, and may support novel tissue engineering research. Although there has been extensive research in mechanotransduction, many pathways remain unclear, due to the complexity of the signaling mechanisms and loading environments involved. This study describes the development of a novel hydrogel-based fiber composite material for investigating mechanotransduction in fibrous tissues. By encapsulating poly(2-hydroxyethyl methacrylate) rods in a bulk poly(ethylene glycol) matrix, it aims to create a micromechanical environment more representative of that seen in vivo. Results demonstrated that collagen-coated rods enable localized cell attachment, and cells are successfully cultured for one week within the composite. Mechanical analysis of the composite indicates that gross mechanical properties and local strain environments could be manipulated by altering the fabrication process. Allowing diffusion between the rods and surrounding matrix creates an interpenetrating network whereby the relationships between shear and tension are altered. Increasing diffusion enhances the shear bond strength between rods and matrix and the levels of local tension along the rods. Preliminary investigation into fibroblast mechanotransduction illustrates that the fiber composite upregulates collagen I expression, the main protein in fibrous tissues, in response to cyclic tensile strains when compared to less complex 2D and 3D environments. In summary, the ability to create and manipulate a strain environment surrounding the fibers, where combined tensile and shear forces uniquely impact cell functions, is demonstrated. [source] Influence of Structural Principles on the Mechanics of a Biological Fiber-Based Composite Material with Hierarchical Organization: The Exoskeleton of the Lobster Homarus americanusADVANCED MATERIALS, Issue 4 2009Helge-Otto Fabritius Abstract The cuticle of the lobster Homarus americanus is a nanocomposite, such as most structural biological materials. It consists of a matrix of chitin-protein fibers associated with various amounts of crystalline and amorphous calcium carbonate in the rigid parts of the body, and is organized hierarchically at all length scales. One prominent design principle found in the hierarchical structure of such biological fibrous composite materials is the twisted plywood structure. In the lobster cuticle, it is formed by superimposing and gradually rotating planes of parallel aligned chitin-protein fibers. To adjust the mechanical properties to the requirements on the macroscopic level, the spatial arrangement and the grade of mineralization of the fibers can be modified. A second design principle of lobster cuticle is its honeycomb-like structure, generated by the well-developed pore canal system, whose twisted ribbon-shaped canals penetrate the cuticle perpendicular to its surface. Due to the hierarchical structure, the mechanical properties of the lobster cuticle have to be investigated at different length scales, which is essential for the understanding of the structure,mechanical function relations of mineralized tissues (e.g., potentially also bone and teeth). In order to investigate the influence of the structural principles on the mechanical properties on the macroscopic scale miniaturized tensile, compression, and shear tests were carried out to obtain integral mechanical data. Characterization of the microstructure included scanning electron microscopy (SEM) combined with energy dispersive X-ray (EDX) measurements. [source] Composite Material for Simultaneous and Contactless Luminescent Sensing and Imaging of Oxygen and Carbon Dioxide,ADVANCED MATERIALS, Issue 12 2006M. Borisov "Seeing" oxygen and carbon dioxide: A sensor material is described that enables simultaneous imaging and monitoring of carbon dioxide and oxygen (see figure). It relies on the measurement of the phase shift of the luminescence decay time of a material composed of microbead-contained indicators (with well-separated excitation and emission wavelengths) and polymers with excellent permeation selectivities as well as favorable optical and adhesive properties. [source] Developments in Failure and Damage Modeling for UD, 2D, and 3D Composite Materials,ADVANCED ENGINEERING MATERIALS, Issue 7 2010Lucio Raimondo This paper outlines three examples of original solutions for the modeling of three classes of composite materials, which have increasing fiber architectural complexity. Results are presented from application of a novel approach for dynamic elastic and failure modeling of UD composites, and novel failure and damage modeling approaches for 2D and 3D composites, respectively. A comparison between numerical and experimental results shows that the newly proposed strategies have excellent predictive capabilities. [source] Nanostructured Organic,Inorganic Composite Materials by Twin Polymerization of Hybrid MonomersADVANCED MATERIALS, Issue 20 2009Stefan Spange Abstract Forming two structurally different but associated polymer structures in a single step is a possible route for the production of nanostructured materials. By means of twin polymerization of specially constructed monomers consisting of two different covalently bonded building blocks (hybrid monomers), this route is realized. What is important is that two different macromolecular structures are formed from one monomer in a single process. The two polymers formed can be linear, branched, or cross-linked structures. The molecular composition of the hybrid monomer defines the degree of cross-linking of the corresponding macromolecular structures that is theoretically possible. [source] Superior-Performance Polymeric Composite Materials for High-Density Optical Data Storage,ADVANCED MATERIALS, Issue 5 2009Riccardo Castagna High-resolution holographic gratings are obtained using a combination of a multifunctional acrylate (DPHP/HA), a low-molecular-weight glass-forming liquid epoxy-aromatic resin (TPMTGE), and a UV-photoinitiator (Irgacure 819). Their optical properties (sensitivity, transparency, and optical shrinkage) are promising for high-density optical data storage applications. [source] Cellulose-Nanocomposites: Towards High Performance Composite MaterialsMACROMOLECULAR SYMPOSIA, Issue 1 2006Robert Kohler Abstract Summary: Strong cellulose fibres, e.g. flax and hemp, are increasingly used for composites. Despite substantial advantages, the tensile strength of these fibres is limited due to their complex structure and the unavoidable imperfections of the cell wall, inherent from growth or induced by processing. Essential improvements are possible by using highly crystalline cellulose fibrils ("whiskers") which can be isolated from the cell wall, thus eliminating the influence of adhesion and defects. Instead of complete fibrillation, which demands special time consuming processing, a partly fibrillation has been achieved by adapted textile finishing procedures which have the potential for mass production. By combining chemical and mechanical/hydro-mechanical treatments it is possible to produce finest fibrils with diameters from below 1 µm down to the nanometer range. The problem of fibril agglomeration during drying has been avoided by forming homogenous fibrous sheets in a wet-laid non-woven process. These sheets can be impregnated with thermosetting resins. Alternatively thermoplastic polymers can be directly integrated to form hybrid materials ready for moulding. The resulting composites show greatly enhanced mechanical properties. [source] Ionic Liquids as Versatile Precursors for Functionalized Porous Carbon and Carbon,Oxide Composite Materials by Confined Carbonization,ANGEWANDTE CHEMIE, Issue 37 2010Xiqing Wang Dr. Manche mögen's heiß: Die Thermolyse einer ionischen Flüssigkeit (IL) ergibt keine Verbrennungsrückstände, während ein Erhitzen derselben IL in einem Oxidgerüst hohe Carbonisierungsausbeuten liefert (siehe Bild). Dies ermöglicht den Einbau von Heteroatomen aus der IL in die Endprodukte zur Entwicklung funktionalisierter poröser Kohlenstoff- und Kohlenstoff-Oxid-Kompositmaterialien. [source] The Effect of Rapid High Temperature Excursions on the Moisture Absorption and Dynamic Mechanical Properties of Carbon Fibre Epoxy Composite MaterialsASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 1-2 2004G. M. Mcnally The effect of elevated temperature excursions (thermal spiking) on the moisture absorption characteristics and dynamic mechanical properties of Cycom 8 HS carbon fibre epoxy laminates was investigated. Cured laminate samples were preconditioned (65d,C, 95%R.H.) and these samples were exposed to various thermal spiking (150d,C/2min) programmes. Dynamic mechanical thermal analysis (DMTA) techniques measured the changes in glass transition temperature (Tg) storage modulus (log E') and damping (Tan , max) of the laminates as a result of exposure to these environments. The thermal spiking programme was shown to cause an increase in both the amount and rate of moisture absorption of the laminates. These increments were accompanied by a significant decrease in Tg, log E', and Tan , max. Scanning Electron Microscopy (SEM) analysis also showed the progressive growth of both interlaminar and translaminar micro-cracks as a result of thermal spiking. [source] Effect of prefabricated metal post-head design on the retention of various core materialsJOURNAL OF ORAL REHABILITATION, Issue 6 2000M. Zalkind Retention of various post heads to core restorative materials is an important factor in the selection of prefabricated post systems and restorative materials for the restoration of endodontically treated teeth. This study examines the retention of a post,core prefabricated system in relation to core material and post-head design. A total of 60 samples were prepared using two different post systems (ParaPost Plus® (PP) and ParaPost Unity® (PU), with amalgam, composite or glass,ionomer as one of the core materials. The samples were tested using the Instron testing machine. The PP was superior to the PU prefabricated post with respect to the retention of various core materials. Retention values in descending order of magnitude were found to be: composite, amalgam and glass,ionomer (significantly lower). The rhomboid serrated design of PP was superior in retention to the rounded smooth UP system. Composite material proved to be superior in retention, closely followed by amalgam, with glass,ionomer significantly less retentive. [source] The effect of biological studies of polyester composites filled carbon black and activated carbon from bamboo (Gigantochloa scortechinii)POLYMER COMPOSITES, Issue 1 2007H.P.S. Abdul Khalil The development of composites using various filler material increased significantly nowadays. Composite materials need to implement the biological and mechanicals impact in their life cycle. The carbon black (CB) and activated carbon (AC) from bamboo (Gigantochloa scortechinii) were used as filler in polyester composites. CB and AC were pyrolized to 700°C and activated with ZnCl2. The composites were prepared with 40% filler loading. The degradation of the composites CB and AC (mechanical properties) to the soil burial test was determined. Tensile, flexural, impact and mass changes of the buried samples were investigated. The deterioration of the samples affected by the biological attack was confirmed by SEM studies. The assessment was done after 0, 3, 6, and 12 months of the biological exposure and the results were compared with the composites filled CaCO3 (commercial filler) and cast polyester resin (as control). POLYM. COMPOS. 28:6,14, 2007. © 2007 Society of Plastics Engineers [source] An optimization procedure for the pultrusion process based on a finite element formulationPOLYMER COMPOSITES, Issue 3 2002R. M. L. Coelho Composite materials are manufactured by different processes. In all, the process variables have to be analyzed in order to obtain a part with uniform mechanical properties. In the pultrusion process, two variables are the most important: the pulling speed of resin-impregnated fibers and the temperature profile (boundary condition) imposed on the mold wall. Mathematical modeling of this process results in partial differential equations that are solved here by a detailed procedure based on the Galerkin weighted residual finite element method. The combination of the Picard and Newton-Raphson methods with an analytical Jacobian calculation proves to be robust, and a mesh adaptation procedure is presented in order to avoid integration errors during the process optimization. The two earlier-mentioned variables are optimized by the Simulated Annealing method with some constraints, such as a minimum degree of cure at the end of the process, and the resin degradation (the part temperature cannot be higher than the resin degradation temperature at any time during the whole process). Herein, the proposed objective function is an economic criterion instead of the pulling speed of resin-impregnated fibers, used in the majority of papers. [source] Direct Electrochemistry and Electrocatalysis of Hemoglobin in Lipid Film Incorporated with Room-Temperature Ionic LiquidELECTROANALYSIS, Issue 20 2008Gaiping Li Abstract A facile phospholipid/room-temperature ionic liquid (RTIL) composite material based on dimyristoylphosphatidylcholine (DMPC) and 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim]PF6) was exploited as a new matrix for immobilizing protein. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were adopted to characterize this composite film. Hemoglobin (Hb) was chosen as a model protein to investigate the composite system. UV-vis absorbance spectra showed that Hb still maintained its heme crevice integrity in this composite film. By virtue of the Hb/DMPC/[bmim]PF6 composite film-modified glassy carbon electrode (GCE), a pair of well-defined redox peaks of Hb was obtained through the direct electron transfer between protein and underlying GCE. Moreover, the reduction of O2 and H2O2 at the Hb/DMPC/[bmim]PF6 composite film-modified GCE was dramatically enhanced. [source] Carbon Nanotubes Paste Electrodes.ELECTROANALYSIS, Issue 7-8 2007A New Alternative for the Development of Electrochemical Sensors Abstract In this work we summarize the recent activities of our group regarding the analytical performance of a new composite material, the so-called carbon nanotubes paste electrode (CNTPE) obtained by dispersion of multiwall carbon nanotubes in mineral oil. The electrocatalytic properties towards different redox systems, especially those involved in important enzymatic reactions are discussed. Significant shifting in the overpotentials for the oxidation and/or reduction of hydrogen peroxide, NADH, phenol, catechol, dopamine, ascorbic acid, uric acid and hydroquinone are obtained at CNTPE in comparison with the analogous graphite paste electrode (CPE). The usefulness of the electrode as a matrix for immobilizing enzymes is also demonstrated. Highly sensitive and selective glucose quantification is accomplished even without using permselective films or redox mediators. Enzymatic biosensors obtained by incorporation of lactate oxidase, polyphenol oxidase and alcohol dehydrogenase/NAD+ within the composite material have allowed the successful quantification of lactate, phenol, dopamine, catechin and ethanol. The sensitive quantification of traces of oligonucleotides and double stranded calf thymus DNA by adsorptive stripping is reported. The confined DNA layer demonstrated to be stable either in air, acetate or phosphate buffer. The advantages of incorporating copper particles for the quantification of amino acids and albumin is also discussed. [source] Organically Modified Sol-Gel/Chitosan Composite Based Glucose BiosensorELECTROANALYSIS, Issue 7 2003Xu Chen Abstract A new type of organically modified sol-gel/chitosan composite material was developed and used for the construction of glucose biosensor. This material provided good biocompatibility and the stabilizing microenvironment around the enzyme. Ferrocene was immobilized on the surface of glassy carbon electrode as a mediator. The characteristics of the biosensor were studied by cyclic voltammetry and chronoamperometry. The effects of enzyme-loading, buffer pH, applied potential and several interferences on the response of the enzyme electrode were investigated. The simple and low-cost glucose biosensor exhibited high sensitivity and good stability. [source] Microstructural Analysis of the Reinforced Al-Cu5mgti/Tib2 5,wt % Alloy for Investment Casting Applications,ADVANCED ENGINEERING MATERIALS, Issue 6 2010Pedro Egizabal Abstract The paper describes the influence of 5,wt % titanium diboride (TiB2) particles on the microstructure of an Al-Cu alloy produced by plaster casting process. The elaboration route leads to a composite material with 1% of in situ TiB2 particles and 4% ex situ of TiB2 particles. The comparison of the reinforced alloy with the corresponding non-reinforced counterpart makes clear that the presence of TiB2 particles has a large influence in the observed microstructure. The presence of TiB2 particles decreases the grain sizes and the porosity level. It is also found that TiB2 particles play an important role in the precipitation events of Al2Cu precipitates that are formed during solidification at the TiB2/aluminum matrix interfaces. [source] Dielectric Properties of a Printed Sol,Gel Matrix Composite,ADVANCED ENGINEERING MATERIALS, Issue 5 2010Tobias Lehnert Low temperature processable materials with high dielectric constants are required for application on flexible organic substrates, for example, in printed electronics. To date, mainly organic polymers with embedded functional particles have been investigated for this purpose. For the first time, we present a printable dielectric composite material composed of ferroelectric high permittivity particles (BaTiO3) bonded by a mainly inorganic sol,gel derived network. The exemplary optimization of the properties by varying the sol,gel precursor illustrates the potential of sol,gel chemistry for printable functional materials. An operational gravure printed capacitor including printed silver electrodes is presented. The measured dielectric constants are among the highest reported in literature for low temperature cured films with moderate dissipation factors. Besides these promising dielectric properties, this composite film shows a ferroelectric response. [source] Novel TRIP-Steel/Mg-PSZ Composite,Open Cell Foam Structures for Energy AbsorptionADVANCED ENGINEERING MATERIALS, Issue 3 2010Christos G. Aneziris Porous materials have received extensive attention for energy absorption in the last years. In terms of this study austenitic TRIP-steel/Mg-PSZ composite,open cell foam structures are formed based on replicas using open-celled polyurethane foam as a skeleton with and without a supporting dense face (jacket) coating. Their compression strength as well as their specific energy absorption SEA has been registered as a function of the compressive strain. The zirconia addition has reinforced the composite material with the face coating up to a compressive strain of 50%. The stress-induced martensitic transformation of partially stabilized zirconia phases has been investigated as a function of the compressive strain by EBSD. The zirconia phase transformation is triggered already at low compressive strains below 2%. [source] Matrix Assisted Pulsed Laser Evaporation (MAPLE) of Poly(D,L lactide) (PDLLA) on Three Dimensional Bioglass® StructuresADVANCED ENGINEERING MATERIALS, Issue 8 2009Valeria Califano Matrix assisted pulsed laser evaporation (MAPLE) was used to coat Bioglass-based tissue engineering scaffolds with poly(D,L lactide). The polymer penetrated to some extent from the surface producing a graded porous composite material. This structure can be beneficial for application in osteochondral tissue engineering, where composite scaffolds are required exhibiting two distinct regions, one for cartilage integration (biopolymer) and the other one for bone contact (bioactive glass). [source] FEM-Simulation of Real and Artificial Microstructures of Mo-Si-B Alloys for Elastic Properties and Comparison with Analytical Methods,ADVANCED ENGINEERING MATERIALS, Issue 10 2007G. Biragoni Various three phase microstructures of Mo-Si-B alloys were simulated in tensile loading conditions using a 2D finite element method to predict the elastic properties of the composite material. Voronoi structures with the same areal fraction of phases as the real microstructures have been generated and simulated similarly. Also, with these Voronoi structures a variation of grain or phase sizes, respectively, was carried out for different compositions in order to study on the elastic properties of the composite. Finally, a comparison was made over the whole temperature range between the above numerical methods, classical analytical approaches and experimentally determined values for Young's modulus E, shear modulus G and Poisson's ratio ,. [source] Biomimetic Composites: Protein Localization in Silica Nanospheres Derived via Biomimetic Mineralization (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 18 2010Mater. Abstract Lysozyme-templated precipitation of silica synthesized by sol-gel chemistry produces a composite material with antimicrobial properties. This study investigates the structural properties of the composite material that allow for retention of the antimicrobial activity of lysozyme. Scanning (SEM) and transmission (TEM) electron microscopy reveal that the composite has a hierarchical structure composed of quasi-spherical structures (,450 nm diameter), which are in turn composed of closely packed spherical structures of ,8,10 nm in diameter. Using small-angle neutron scattering (SANS) with contrast variation, the scattering signatures of the lysozyme and silica within the composite were separated. It was determined that the lysozyme molecules are spatially correlated in the material and form clusters with colloidal silica particles. The size of the clusters determined by SANS agrees well with the structural architecture observed by TEM. BET analysis revealed that the surface area of the composite is relatively low (4.73 m2/g). However, after removal of the protein by heating to 200 °C, the surface area is increased by ,20%. In addition to demonstrating a well organized sol-gel synthesis which generates a functional material with antimicrobial applications, the analysis and modeling approaches described herein can be used for characterizing a wide range of mesoporous and ultrastructural materials. [source] A meso-level approach to the 3D numerical analysis of cracking and fracture of concrete materialsFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 12 2006A. CABALLERO ABSTRACT A meso-mechanical model for the numerical analysis of concrete specimens in 3D has been recently proposed. In this approach, concrete is represented as a composite material with the larger aggregates embedded in a mortar-plus-aggregates matrix. Both continuum-type components are considered linear elastic, while the possibilities of failure are provided with the systematic use of zero-thickness interface elements equipped with a cohesive fracture constitutive law. These elements are inserted along all potential crack planes in the mesh a priori of the analysis. In this paper, the basic features of the model are summarized, and then results of calculations are presented, which include uniaxial tension and compression loading of 14-aggregate cubical specimen along X, Y and Z axes. The results confirm the consistency of the approach with physical phenomena and well-known features of concrete behaviour, and show low scatter when different loading directions are considered. Those cases can also be considered as different specimens subjected to the same type of loading. [source] Protein Localization in Silica Nanospheres Derived via Biomimetic MineralizationADVANCED FUNCTIONAL MATERIALS, Issue 18 2010Mateus B. Cardoso Abstract Lysozyme-templated precipitation of silica synthesized by sol-gel chemistry produces a composite material with antimicrobial properties. This study investigates the structural properties of the composite material that allow for retention of the antimicrobial activity of lysozyme. Scanning (SEM) and transmission (TEM) electron microscopy reveal that the composite has a hierarchical structure composed of quasi-spherical structures (,450 nm diameter), which are in turn composed of closely packed spherical structures of ,8,10 nm in diameter. Using small-angle neutron scattering (SANS) with contrast variation, the scattering signatures of the lysozyme and silica within the composite were separated. It was determined that the lysozyme molecules are spatially correlated in the material and form clusters with colloidal silica particles. The size of the clusters determined by SANS agrees well with the structural architecture observed by TEM. BET analysis revealed that the surface area of the composite is relatively low (4.73 m2/g). However, after removal of the protein by heating to 200 °C, the surface area is increased by ,20%. In addition to demonstrating a well organized sol-gel synthesis which generates a functional material with antimicrobial applications, the analysis and modeling approaches described herein can be used for characterizing a wide range of mesoporous and ultrastructural materials. [source] Dangers relating to fires in carbon-fibre based composite materialFIRE AND MATERIALS, Issue 4 2005Tommy Hertzberg Abstract Inhalable carbon fibres have been suspected to pose similar threats to human health as asbestos fibres. It is well-known that fibres having a diameter of less than 3 µm might be inhaled and transported deep into the human respiratory system. Some composite materials use carbon fibres as structural reinforcement. These fibres do not pose any risks as such as they are firmly connected to the laminate and surrounded by a polymer matrix. Also, these fibres typically have diameters >6 µm and thus, are not inhalable. However, if the material is exposed to a fire, the carbon material might be oxidized and fractionated and thereby, inhalable fibres might be generated into the fire smoke. The capability of carbon fibre-based composite material to produce dangerous inhalable fibres from different combustion scenarios has been investigated. It was found that the risk of fires generating inhalable carbon fibres is related to the surface temperature, the oxygen level and the airflow field close to the material surface. The temperatures necessary for oxidation of the carbon fibre is so high that it is possible that only a flashover situation will pose any real danger. Other possible danger scenarios are highly intense fires (e.g. a liquid fuel fire), or situations where structural damage is part of the fire scenario. Copyright © 2005 John Wiley & Sons, Ltd. [source] Particles from fires,a screening of common materials found in buildingsFIRE AND MATERIALS, Issue 6 2003Tommy Hertzberg Abstract Small combustion generated particles are known to have a negative impact on human health and on the environment. In spite of the huge amount of particles generated locally in a fire accident, few investigations have been made on the particles from such fires. In this article, 24 different materials or products, typically found in buildings have been exposed to burning conditions in order to examine their particle generating capacity. In addition, a carbon fibre based composite material was tested in order to investigate if asbestos-resembling particles could be generated in a fire situation. The majority of the experiments were performed in the small-scale cone calorimeter, and some further data were collected in intermediate scale (SBI) and full scale (room-corner) tests. Additional testing of the composite material was made in a small-scale tubular reactor. The amount of particles and particle size distributions were measured by the use of a low-pressure impactor and particle aerodynamic diameter sizes from 30 nm to 10 ,m were measured. The results from the project show that the yield of particles generated varied significantly between materials but that the shape of mass and number size distributions were very similar for all the materials tested. The maximum amount of particles was obtained from materials that did not burn well (e.g. flame retarded materials). Well-burning materials, e.g. wood materials, tend to oxidize all available substances and thereby minimize the amount of particles in the smoke gas. It was found that asbestos-resembling particles could be produced from under-ventilated combustion of the composite material tested. Copyright © 2003 John Wiley & Sons, Ltd. [source] Characterization of a Novel Fiber Composite Material for Mechanotransduction Research of Fibrous Connective TissuesADVANCED FUNCTIONAL MATERIALS, Issue 5 2010Hazel R. C. Screen Abstract Mechanotransduction is the fundamental process by which cells detect and respond to their mechanical environment, and is critical for tissue homeostasis. Understanding mechanotransduction mechanisms will provide insights into disease processes and injuries, and may support novel tissue engineering research. Although there has been extensive research in mechanotransduction, many pathways remain unclear, due to the complexity of the signaling mechanisms and loading environments involved. This study describes the development of a novel hydrogel-based fiber composite material for investigating mechanotransduction in fibrous tissues. By encapsulating poly(2-hydroxyethyl methacrylate) rods in a bulk poly(ethylene glycol) matrix, it aims to create a micromechanical environment more representative of that seen in vivo. Results demonstrated that collagen-coated rods enable localized cell attachment, and cells are successfully cultured for one week within the composite. Mechanical analysis of the composite indicates that gross mechanical properties and local strain environments could be manipulated by altering the fabrication process. Allowing diffusion between the rods and surrounding matrix creates an interpenetrating network whereby the relationships between shear and tension are altered. Increasing diffusion enhances the shear bond strength between rods and matrix and the levels of local tension along the rods. Preliminary investigation into fibroblast mechanotransduction illustrates that the fiber composite upregulates collagen I expression, the main protein in fibrous tissues, in response to cyclic tensile strains when compared to less complex 2D and 3D environments. In summary, the ability to create and manipulate a strain environment surrounding the fibers, where combined tensile and shear forces uniquely impact cell functions, is demonstrated. [source] Enhanced Optical Properties and Opaline Self-Assembly of PPV Encapsulated in Mesoporous Silica SpheresADVANCED FUNCTIONAL MATERIALS, Issue 23 2009Timothy L. Kelly Abstract A new poly(p -phenylenevinylene) (PPV) composite material has been developed by the incorporation of insoluble PPV polymer chains in the pores of monodisperse mesoporous silica spheres through an ion-exchange and in situ polymerization method. The polymer distribution within the resultant colloidal particles is characterized by electron microscopy, energy dispersive X-ray microanalysis, powder X-ray diffraction, and nitrogen adsorption. It was found that the polymer was selectively incorporated into the mesopores of the silica host and was well distributed throughout the body of the particles. This confinement of the polymer influences the optical properties of the composite; these were examined by UV,vis and fluorescence spectroscopy and time-correlated single-photon counting. The results show a material that exhibits an extremely high fluorescence quantum yield (approaching 85%), and an improved resistance to oxidative photobleaching compared to PPV. These enhanced optical properties are further complemented by the overall processability of the colloidal material. In marked contrast to the insolubility of PPV, the material can be processed as a stable colloidal dispersion, and the individual composite spheres can be self-assembled into opaline films using the vertical deposition method. The bandgap of the opal can be engineered to overlap with the emission band of the polymer, which has significant ramifications for lasing. [source] Fabrication and Electromechanical Characterization of a Piezoelectric Structural Fiber for Multifunctional CompositesADVANCED FUNCTIONAL MATERIALS, Issue 4 2009Yirong Lin Abstract The use of piezoceramic materials for structural sensing and actuation is a fairly well developed practice that has found use in a wide variety of applications. However, just as advanced composites offer numerous benefits over traditional engineering materials for structural design, actuators that utilize the active properties of piezoelectric fibers can improve upon many of the limitations encountered when using monolithic piezoceramic devices. Several new piezoelectric fiber composites have been developed; however, almost all studies have implemented these devices such that they are surface-bonded patches used for sensing or actuation. This paper will introduce a novel active piezoelectric structural fiber that can be laid up in a composite material to perform sensing and actuation, in addition to providing load bearing functionality. The sensing and actuation aspects of this multifunctional material will allow composites to be designed with numerous embedded functions, including structural health monitoring, power generation, vibration sensing and control, damping, and shape control through anisotropic actuation. This effort has developed a set of manufacturing techniques to fabricate the multifunctional fiber using a SiC fiber core and a BaTiO3 piezoelectric shell. The electromechanical coupling of the fiber is characterized using an atomic force microscope for various aspect ratios and is compared to predictions made using finite element modeling in ABAQUS. The results show good agreement between the finite element analysis model and indicate that the fibers could have coupling values as high as 68% of the active constituent used. [source] A Delivery System for Self-Healing Inorganic Films,ADVANCED FUNCTIONAL MATERIALS, Issue 22 2008Harvey A. Liu Abstract Multilayer composites that utilize polymeric and brittle inorganic films are essential components for extending the lifetimes and exploiting the flexibility of many electronic devices. However, crack formation within the brittle inorganic layers that arise from defects as well as the flexing of these multilayer composite materials allows the influx of atmospheric water, a major source of device degradation. Thus, a composite material that can initiate self-healing upon the influx of environmental water through defects or stress-induced cracks would find potential applications in multilayer composite materials for permeation barriers. In the present study, the reactive metal oxide precursor TiCl4 is encapsulated within the pores of a degradable polymer, poly(lactic acid) (PLA). Electrospun PLA fibers are found to be reactive to atmospheric water leading to the hydrolysis of the degradable polymer shell and subsequent release of the reactive metal oxide precursor. Release of the reactive TiCl4 from the pores results in hydrolysis of the metal oxide precursor, forming solid titanium oxides at the surface of the fibers. The efficacy of this self-healing delivery system is also demonstrated by the integration of these reactive fibers in the polymer planarization layer, poly(methyl methacrylate), of a multilayer film, upon which an alumina barrier layer is deposited. The introduction of nanocracks in the alumina barrier layer lead to the release of the metal oxide precursor from the pores of the fibers and the formation of titanium dioxide nanoparticles within the crack and upon the thin film surface. In this study the first delivery system that may find utility for the self-healing of multilayer barrier films through the site-specific delivery of metal oxide nanoparticles through smart reactive composite fibers is established. [source] Synthesis and Characterization of a Composite Zeolite,Metglas Carbon Dioxide Sensor,ADVANCED FUNCTIONAL MATERIALS, Issue 7 2005G. Giannakopoulos Abstract The synthesis of a faujasite,Metglas composite material that can be used in gas-sensing applications is presented. A continuous faujasite film was synthesized on a Metglas magnetoelastic strip using the secondary growth method. The ability of the new composite to remotely sense carbon dioxide in a nitrogen atmosphere at room temperature over a wide range of concentrations is demonstrated by monitoring the changes in the resonance frequency of the strip. The novel sensor combines the electromagnetic properties of the magnetoelastic material with the adsorption properties of the faujasite crystals. Experiments performed over a period of a few months showed that the composite sensor remained fully operational, thus indicating its long-term stability. Furthermore, the present work demonstrates that a zeolite,Metglas composite can be used as a sensor of an analyte in a mixture as long as it adsorbs selectively larger amounts of the particular analyte than other compounds present in the mixture. [source] | |||||||||||||||||||||||||||||||||||||||||||