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Pore Network (pore + network)
Selected AbstractsPolymer Scaffolds for Small-Diameter Vascular Tissue EngineeringADVANCED FUNCTIONAL MATERIALS, Issue 17 2010Haiyun Ma Abstract To better engineer small-diameter blood vessels, a few types of novel scaffolds are fabricated from biodegradable poly(L -lactic acid) (PLLA) by means of thermally induced phase-separation (TIPS) techniques. By utilizing the differences in thermal conductivities of the mold materials and using benzene as the solvent scaffolds with oriented gradient microtubular structures in the axial or radial direction can be created. The porosity, tubular size, and the orientational direction of the microtubules can be controlled by the polymer concentration, the TIPS temperature, and by utilizing materials of different thermal conductivities. These gradient microtubular structures facilitate cell seeding and mass transfer for cell growth and function. Nanofibrous scaffolds with an oriented and interconnected microtubular pore network are also developed by a one-step TIPS method using a benzene/tetrahydrofuran mixture as the solvent without the need for porogen materials. The structural features of such scaffolds can be conveniently adjusted by varying the solvent ratio, phase-separation temperature, and polymer concentration to mimic the nanofibrous features of an extracellular matrix. These scaffolds were fabricated for the tissue engineering of small-diameter blood vessels by utilizing their advantageous structural features to facilitate blood-vessel regeneration. [source] In situ SAXS studies of the morphological changes of an alumina,zirconia,silicate ceramic during its formationJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 4 2006Rudolf Winter Small-angle X-ray scattering is used at two energies, one either side of the zirconium K -edge, to probe the in situ formation of an alumina,zirconia,silicate ceramic. The use of energies either side of the edge allows the decomposition of information regarding the scattering from the zirconia particles from that of the glass matrix. Porod slope data show how the nanoparticles progress from being relatively isolated particles to becoming agglomerates as the pore network in the glass collapses. The shape of the agglomerates resembles the pore network of the glass at low temperature. The Guinier radii of the particles show the growth of the agglomerates past the Littleton softening point, whilst still resolving the primary particles. [source] APPLICATION OF DISCRETE MODELING APPROACH TO FLUIDIZED BED YEAST DRYINGJOURNAL OF FOOD PROCESS ENGINEERING, Issue 2010F. DEBASTE ABSTRACT Yeast drying is widely used to ease transport and conservation. In this work, baker's yeast drying in fluidized bed is modeled using a pore network model. Classical balanced equations at the reactor scale are coupled with the pore network for the grain, which takes into account diffusion in the gas phase, transport by liquid film in partially saturated region and pressure gradient effects in the liquid phase. The porous structure to be applied in the model is obtained using environmental scanning electron microscopy. Simulations are validated on a thermogravimetric analysis experiment. The model is then applied to fluidized bed drying for which experimental results obtained on a laboratory pilot are available. Finally, the model results are compared to those of a simplified receding front model. PRACTICAL APPLICATIONS The presented model allows simulation of Saccharomyces cerevisiae fluidized bed drying. Taking into account transport phenomena in the grain offers the opportunity to predict drying rate without the use of a desorption isotherm. Moreover, the model predicts roughly the critical humidity. Therefore, the model can be used for scale-up, design and optimization of dryer including the effect of changes in yeast granulation. [source] Optimal bimodal pore networks for heterogeneous catalysisAICHE JOURNAL, Issue 4 2004Stefan Gheorghiu Abstract A practical problem in the rational design of a heterogeneous catalyst is to optimize its structure at all scales. By optimizing the large-pore network of a bimodal porous catalyst with a given nanoporosity (for example, zeolite or mesoporous catalyst) for the yield of diffusion-limited first-order reactions, it is found that catalysts typically benefit from a hierarchical pore network with a broad pore-size distribution. When comparing the performance of the optimal structures to that of self-similar, fractal-like pore hierarchies, it is found that the latter can be made to have the same effectiveness factor as the optimal ones, suggesting that fractal-like catalysts operate very near optimality, even if their structure is considerably different from that of the true optima. This is useful, because fractal-like structures have the advantage of being organized in a modular, natural way, potentially easy to reproduce by templating. © 2004 American Institute of Chemical Engineers AIChE J, 50: 812,820, 2004 [source] AN AEOLIANITE IN THE UPPER DALAN MEMBER (KHUFF FORMATION), SOUTH PARS FIELD, IRANJOURNAL OF PETROLEUM GEOLOGY, Issue 2 2010G. Frébourg A laterally continuous, 3m thick oolitic grainstone has been studied in cores from two wells from the South Pars field (offshore Iran). This high porosity but low permeability interval occurs at the top of the gas-bearing succession in the Permian Upper Dalan Member, and is equivalent to the informally-defined K4 unit of the Khuff Formation. This interval can easily be traced between the wells and overlies high-energy marine deposits. It is composed of oomouldic, fine-grained azooic grainstones with cm-thick coarser-grained layers. Horizontal to oblique lamination or steep foresets were observed together with pinstripe lamination. Petrographic observations indicate a clean oomouldic grainstone with very thin chitonic rims associated with pedogenetic imprints as first-generation cements. Later cements include early vadose meniscus and pendant cements in coarser-grained layers and pseudophreatic cements in the finer-grained material with a tighter pore network, prior to ooid dissolution. Rhizoliths were observed in cores and thin-sections. The pedogenic imprints and the early vadose cementation, both related to emergence, as well as the presence of pinstripe lamination, suggest an aeolian depositional setting. This interval is the first aeolianite recorded within the Khuff Formation or equivalent units, and the first hydrocarbon-bearing carbonate aeolianite described in a hydrocarbon-producing unit. The discovery of aeolianites has important implications for regional sequence-stratigraphic interpretations and reservoir volume calculations. These deposits do not conform to classic subaqueous sequence stratigraphy and do not record eustatic variations in the associated marine basin. Their recognition is crucial for well-to-well correlations. [source] Measuring Permeability of Rigid Materials by a Beam-Bending Method: I, TheoryJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2000George W. Scherer When a saturated porous material is deformed, pressure gradients are created in the liquid, and the liquid flows within the pores to equilibrate the pressure. This phenomenon can be exploited to measure permeability: A rod of saturated porous material is instantaneously bent by a fixed amount, and the force required to sustain the deflection is measured as a function of time. The force decreases as the liquid flows through the pore network, and the rate of decrease depends on the permeability. This technique has been applied successfully to determine the permeability of gels, as well as their viscoelastic properties; in this paper the method is extended to ceramic materials, such as porous glass and cement paste. The theory has been modified to take account of the compressibility of the solid and liquid phases (whereas, those factors are negligible for gels). Analyses are presented for constant deflection, constant rate of deflection, and sinusoidal oscillation, where the solid phase is either purely elastic or viscoelastic, and the beam is either cylindrical or square. Experimental tests on Vycor® glass and cement paste will be presented in companion papers. [source] Loading of Bacterial Cellulose Aerogels with Bioactive Compounds by Antisolvent Precipitation with Supercritical Carbon DioxideMACROMOLECULAR SYMPOSIA, Issue 2 2010Emmerich Haimer Abstract Bacterial cellulose aerogels overcome the drawback of shrinking during preparation by drying with supercritical CO2. Thus, the pore network of these gels is fully accessible. These materials can be fully rewetted to 100% of its initial water content, without collapsing of the structure due to surface tension of the rewetting solvent. This rehydration property and the high pore volume of these material rendered bacterial cellulose aerogels very interesting as controlled release matrices. Supercritical CO2 drying, the method of choice for aerogel preparation, can simultaneously be used to precipitate solutes within the cellulose matrix and thus to load bacterial cellulose aerogels with active substances. This process, frequently termed supercritical antisolvent precipitation, is able to perform production of the actual aerogel and its loading in one single preparation step. In this work, the loading of a bacterial cellulose aerogel matrix with two model substances, namely dexpanthenol and L-ascorbic acid, and the release behavior from the matrix were studied. A mathematical release model was applied to model the interactions between the solutes and the cellulose matrix. The bacterial cellulose aerogels were easily equipped with the reagents by supercritical antisolvent precipitation. Loading isotherms as well as release kinetics indicated no specific interaction between matrix and loaded substances. Hence, loading and release can be controlled and predicted just by varying the thickness of the gel and the solute concentration in the loading bath. [source] A biomimetic tubular scaffold with spatially designed nanofibers of protein/PDS® bio-blends,BIOTECHNOLOGY & BIOENGINEERING, Issue 5 2009Vinoy Thomas Abstract Electrospun tubular conduit (4,mm inner diameter) based on blends of polydioxanone (PDS II®) and proteins such as gelatin and elastin having a spatially designed trilayer structure was prepared for arterial scaffolds. SEM analysis of scaffolds showed random nanofibrous morphology and well-interconnected pore network. Due to protein blending, the fiber diameter was reduced from 800,950,nm range to 300,500,nm range. Fourier-transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) results confirmed the blended composition and crystallinity of fibers. Pure PDS scaffold under hydrated state exhibited a tensile strength of 5.61,±,0.42,MPa and a modulus of 17.11,±,1.13,MPa with a failure strain of 216.7,±,13%. The blending of PDS with elastin and gelatin has decreased the tensile properties. A trilayer tubular scaffold was fabricated by sequential electrospinning of blends of elastin/gelatin, PDS/elastin/gelatin, and PDS/gelatin (EG/PEG/PG) to mimic the complex matrix structure of native arteries. Under hydrated state, the trilayer conduit exhibited tensile properties (tensile strength of 1.77,±,0.2,MPa and elastic modulus of 5.74,±,3,MPa with a failure strain of 75.08,±,10%) comparable to those of native arteries. In vitro degradation studies for up to 30 days showed about 40% mass loss and increase in crystallinity due to the removal of proteins and "cleavage-induced crystallization" of PDS. Biotechnol. Bioeng. 2009; 104: 1025,1033. © 2009 Wiley Periodicals, Inc. [source] Designed Multifunctional Nanocomposites for Biomedical ApplicationsADVANCED FUNCTIONAL MATERIALS, Issue 10 2010Humphrey H. P. Yiu Abstract The assembly of multifunctional nanocomposite materials is demonstrated by exploiting the molecular sieving property of SBA-16 nanoporous silica and using it as a template material. The cages of the pore networks are used to host iron oxide magnetic nanoparticles, leaving a pore volume of 0.29,cm3,g,1 accessible for drug storage. This iron oxide,silica nanocomposite is then functionalized with amine groups. Finally the outside of the particle is decorated with antibodies. Since the size of many protein molecules, including that of antibodies, is too large to enter the pore system of SBA-16, the amine groups inside the pores are preserved for drug binding. This is proven using a fluorescent protein, fluorescein-isothiocyanate-labeled bovine serum albumin (FITC-BSA), with the unreacted amine groups inside the pores dyed with rhodamine B isothiocyanate (RITC). The resulting nanocomposite material offers a dual-targeting drug delivery mechanism, i.e., magnetic and antibody-targeting, while the functionalization approach is extendable to other applications, e.g., fluorescence,magnetic dual-imaging diagnosis. [source] Optimal bimodal pore networks for heterogeneous catalysisAICHE JOURNAL, Issue 4 2004Stefan Gheorghiu Abstract A practical problem in the rational design of a heterogeneous catalyst is to optimize its structure at all scales. By optimizing the large-pore network of a bimodal porous catalyst with a given nanoporosity (for example, zeolite or mesoporous catalyst) for the yield of diffusion-limited first-order reactions, it is found that catalysts typically benefit from a hierarchical pore network with a broad pore-size distribution. When comparing the performance of the optimal structures to that of self-similar, fractal-like pore hierarchies, it is found that the latter can be made to have the same effectiveness factor as the optimal ones, suggesting that fractal-like catalysts operate very near optimality, even if their structure is considerably different from that of the true optima. This is useful, because fractal-like structures have the advantage of being organized in a modular, natural way, potentially easy to reproduce by templating. © 2004 American Institute of Chemical Engineers AIChE J, 50: 812,820, 2004 [source] Micropore modification in InPPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 11 2008D. Nohavica Abstract The structural features and optical properties of microporous InP substrates used for epitaxial overgrowth of thin films have been investigated. Both crystalographically oriented (CO) and current line oriented (CLO) pore networks were created by electrochemical dissolution. Heat treatment of the InP pores converted them into microcavities maintaining the same crystallographic direction. The effect of phosphorus vapour pressure was proved to be crucial for the microcavity formation, since it influences the mass transport during heat treatment. Electron microscopy and photoluminescence experiments revealed the absence of significant extended defects, both after the pore and cavities formation. The capability of improved structural quality homo- and hetero-epitaxial overgrown films on the porous InP, was also demonstrated. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||