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Aggregate Size (aggregate + size)
Selected AbstractsOn-line Determination of Aggregate Size and Morphology in SuspensionsPARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 3 2004Frédéric Gruy Abstract Information concerning the aggregation state of fine solid particles is an important element for process control and monitoring of product quality in many applications of industrial slurries. This work deals with the application of different in-line methods to the characterization of silica aggregate size and morphology. All of these methods exploit turbidity signals, obtained by various means including: from analysis of turbidity fluctuations in homogeneous suspension and from overall turbidity decrease during particle settling. This work also presents the opportunity to report progress in morphological and optical models of small aggregates. As a result of these models, the morphological characteristics of the aggregates along with the number of their constituting particles are derived from experimental results. Similarities between the different methods are examined and discussed. [source] Effect of flow field heterogeneity in coagulators on aggregate size and structureAICHE JOURNAL, Issue 10 2010Lyonel Ehrl Abstract Aggregate size and structure were investigated under turbulent conditions in stirred tank (ST) and Taylor,Couette-type (TC-type) devices. Root-mean-square radius of gyration, ,Rg,, and zero-angle intensity of scattered light, I(0), were acquired as a function of stirring intensity, characterized by an experimentally obtained average hydrodynamic stress, ,,,exp, determined by torque measurements. Evaluating aggregate images revealed that aggregate structure and shape are independent of the device type. However, in TC-type devices, the aggregates grow to three to four times larger sizes than inside ST, although the same ,,,exp was used in both coagulators. As confirmed by computational fluid dynamics, this can be attributed to the differences in the maximum hydrodynamic stress in ST compared with those in TC-type devices. In contrast, the power-law scaling of ,Rg, and I(0) with ,,,exp is preserved for all investigated devices, with an exponent approximately equal to ,0.5 and ,0.7, respectively. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source] Three-Dimensional Culture Environments Enhance Osteoblast DifferentiationJOURNAL OF PROSTHODONTICS, Issue 7 2008Jessica Boehrs BS Abstract Purpose: In previous work from our laboratory, we demonstrated that the three-dimensional (3D) cell cultures developed in simulated microgravity environments enhanced osseous-like aggregate formation and accelerated preosteoblast cell differentiation. Thus, as described here, we hypothesize that aggregate formation and mineralization would occur with fewer than 10 × 106 cells as previously described. Materials and Methods: Human preosteoblastic cells were cultured at different concentrations in a rotary wall vessel to simulate microgravity for 7 days. Aggregate size was assessed, and mineralization and collagen expression detected using Von Kossa and Masson Trichrome staining. Scanning electron microscopy was used for structural and elemental analysis. Immunohistochemistry was used to detect expression of the osteogenic markers BSPII and osteopontin (OP). Results: Size and calcium expression were dependent upon cultured cell number (p < 0.01). Calcium and collagen expression were detected throughout the aggregate, but organization was independent of cell number. Aggregates had similar microscopic structural patterns demonstrating organized development. Presence of BSPII and OP showed that the aggregates share common differentiation proteins with in vivo bone formation. Conclusions: These results may lead to novel bone engineering techniques associated with dental treatment. [source] Facile Functionalization and Phase Reduction Route of Magnetic Iron Oxide Nanoparticles for Conjugation of Matrix Metalloproteinase,ADVANCED ENGINEERING MATERIALS, Issue 6 2010Dan Li Abstract A protocol for the simultaneous functionalization and phase reduction route of iron oxide magnetic nanoparticles (MNPs) and its further bioconjugation is presented. It was found that surface functionalization of maghemite (,-Fe2O3) nanoparticles with mercaptopropyltrimethoxysilane (MPTMS) under anoxic environment at above 80,°C promotes in situ conversion to magnetite (Fe3O4). Full conversion to Fe3O4, as probed by Mössbauer spectroscopy, with accompanied increase in the composite saturation magnetization, was achieved at 120,°C. By controlling the MPTMS concentration, the resultant silane-MNPs morphology can be tuned from having homogeneous thin layer (<1,nm) to thick continuous silane with embedded MNP multicores. Likewise the amount of surface distal thiol moieties was dependent on the silanization conditions. The density of distal thiols (i.e., amount of thiol per surface area) and resultant aggregate size have direct impact on the attachment, as well as the activity and reusability of the conjugated matrix metalloproteinase (MMP-2, using sulfo-SMCC as crosslinker). The work has important implication to the field of magneto-chemotherapeutics, where spatial control of conjugated active biomolecules under magnetic field and T2 -weighted MRI contrast can be achieved simultaneously. [source] Initial cultivation of a temperate-region soil immediately accelerates aggregate turnover and CO2 and N2O fluxesGLOBAL CHANGE BIOLOGY, Issue 8 2006A. STUART GRANDY Abstract The immediate effects of tillage on protected soil C and N pools and on trace gas emissions from soils at precultivation levels of native C remain largely unknown. We measured the response to cultivation of CO2 and N2O emissions and associated environmental factors in a previously uncultivated U.S. Midwest Alfisol with C concentrations that were indistinguishable from those in adjacent late successional forests on the same soil type (3.2%). Within 2 days of initial cultivation in 2002, tillage significantly (P=0.001, n=4) increased CO2 fluxes from 91 to 196 mg CO2 -C m,2 h,1 and within the first 30 days higher fluxes because of cultivation were responsible for losses of 85 g CO2 -C m,2. Additional daily C losses were sustained during a second and third year of cultivation of the same plots at rates of 1.9 and 1.0 g C m,2 day,1, respectively. Associated with the CO2 responses were increased soil temperature, substantially reduced soil aggregate size (mean weight diameter decreased 35% within 60 days), and a reduction in the proportion of intraaggregate, physically protected light fraction organic matter. Nitrous oxide fluxes in cultivated plots increased 7.7-fold in 2002, 3.1-fold in 2003, and 6.7-fold in 2004 and were associated with increased soil NO3, concentrations, which approached 15 ,g N g,1. Decreased plant N uptake immediately after tillage, plus increased mineralization rates and fivefold greater nitrifier enzyme activity, likely contributed to increased NO3, concentrations. Our results demonstrate that initial cultivation of a soil at precultivation levels of native soil C immediately destabilizes physical and microbial processes related to C and N retention in soils and accelerates trace gas fluxes. Policies designed to promote long-term C sequestration may thus need to protect soils from even occasional cultivation in order to preserve sequestered C. [source] Measurements of rain splash on bench terraces in a humid tropical steepland environmentHYDROLOGICAL PROCESSES, Issue 3 2003A. I. J. M. Van Dijk Abstract Soil loss continues to threaten Java's predominantly bench-terraced volcanic uplands. Sediment transport processes on back-sloping terraces with well-aggregated clay-rich oxisols in West Java were studied using two different techniques. Splash on bare, cropped, or mulched sub-horizontal (2,3°) terrace beds was studied using splash cups of different sizes, whereas transport of sediment on the predominantly bare and steep (30,40/deg ) terrace risers was measured using a novel device combining a Gerlach-type trough with a splash box to enable the separate measurement of transport by wash and splash processes. Measurements were made during two consecutive rainy seasons. The results were interpreted using a recently developed splash distribution theory and related to effective rainfall erosive energy. Splash transportability (i.e. transport per unit contour length and unit erosive energy) on the terrace risers was more than an order of magnitude greater than on bare terrace beds (0·39,0·57 versus 0·013,0·016 g m J,1). This was caused primarily by a greater average splash distance on the short, steep risers (>11 cm versus c. 1 cm on the beds). Splashed amounts were reduced by the gradual formation of a protective ,pavement' of coarser aggregates, in particular on the terrace beds. Soil aggregate size exhibited an inverse relationship with detachability (i.e. detachment per unit area and unit erosive energy) and average splash length, and therefore also with transportability, as did the degree of canopy and mulch cover. On the terrace risers, splash-creep and gravitational processes transported an additional 6,50% of measured rain splash, whereas transport by wash played a marginal role. Copyright © 2002 John Wiley & Sons, Ltd. [source] Increased strength of erythrocyte aggregates in blood of patients with inflammatory bowel diseaseINFLAMMATORY BOWEL DISEASES, Issue 5 2009Nitsan Maharshak MD Abstract Background: Increased strength of red blood cell (RBC) aggregates are present during the acute inflammatory response and contribute to erythrocyte aggregation and may lead to microvascular dysfunction. Inflammatory bowel diseases (IBDs) are characterized by damage to the bowel wall. This damage may be at least partially attributed to microvascular ischemia caused by enhanced erythrocyte aggregation. The aim of this study was to evaluate the strength of RBC aggregates in the blood of patients with IBD. Methods: The strengths of RBC aggregates were characterized by integrative RBC aggregation parameters, determined by measuring of RBC aggregation as a function of shear stress. The results are represented as the area under the curve (AUC) of aggregate size plotted against shear stress. For each patient, dynamic aggregation and disaggregation of RBC were recorded and analyzed according to the RBC aggregate size distribution at the different shear stresses. Aggregation indices were correlated with disease activity and inflammatory biomarkers. Results: We examined 53 IBD patients and 63 controls. IBD patients had significantly elevated concentrations of inflammation-sensitive proteins and aggregation parameters. The strength of large aggregates, represented by AUC for large fraction aggregates, among patients (15.2 ± 18.6) was double that of controls (7 ± 10.9) (P = 0.006). The strength of large aggregates correlated with disease activity (r = 0.340; P < 0.001) with concentration of fibrinogen (r = 0.575; P < 0.001) and with concentration of high sensitivity C-reactive protein (r = 0.386; P < 0.001). Conclusions: The strength of RBC aggregates is increased in patients with IBD and correlates with the intensity of the acute phase response. This could contribute to bowel damage in these diseases. (Inflamm Bowel Dis 2009) [source] Effect of flow field heterogeneity in coagulators on aggregate size and structureAICHE JOURNAL, Issue 10 2010Lyonel Ehrl Abstract Aggregate size and structure were investigated under turbulent conditions in stirred tank (ST) and Taylor,Couette-type (TC-type) devices. Root-mean-square radius of gyration, ,Rg,, and zero-angle intensity of scattered light, I(0), were acquired as a function of stirring intensity, characterized by an experimentally obtained average hydrodynamic stress, ,,,exp, determined by torque measurements. Evaluating aggregate images revealed that aggregate structure and shape are independent of the device type. However, in TC-type devices, the aggregates grow to three to four times larger sizes than inside ST, although the same ,,,exp was used in both coagulators. As confirmed by computational fluid dynamics, this can be attributed to the differences in the maximum hydrodynamic stress in ST compared with those in TC-type devices. In contrast, the power-law scaling of ,Rg, and I(0) with ,,,exp is preserved for all investigated devices, with an exponent approximately equal to ,0.5 and ,0.7, respectively. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source] Polymer flocculation of calcite: Experimental results from turbulent pipe flowAICHE JOURNAL, Issue 4 2006Alex R. Heath Abstract The kinetics of aggregation/breakage of calcite particles flocculated with a high-molecular-weight polymer flocculant has been studied in turbulent pipe flow. The mean flocculation residence time was varied by changing the length of pipe between the flocculant injection point and the in-stream particle-sizing probe (Lasentec FBRM). A variety of pipe sizes and flow rates were used to produce a range of mean fluid shear rates. The mean shear rate was calculated from the pressure drop along the pipe reactor, as measured by manometer, and was found to vary markedly as a function of both the solid fraction and aggregate size. Increased fluid shear increased the initial mixing and aggregation rates, but ultimately lead to a reduced final aggregate size due to increased aggregate breakage. Several other process variables were also studied, with the aggregate size increased with flocculant dosage and primary particle size, but reduced at higher solid fraction. © 2005 American Institute of Chemical Engineers AIChE J, 2006 [source] Controlling particle size during anatase precipitationAICHE JOURNAL, Issue 9 2001Sekhar Sathyamoorthy Titanium dioxide particles in the form of anatase are precipitated from concentrated titanyl sulfate solution in the sulfate process, which are then recovered by a filtration process downstream of the precipitation stage. A previous study by Sathyamoorthy et al. showed that the final anatase particles are aggregates (1-2 ,m) consisting of numerous crystals (7,8 nm) arranged in primary agglomerates (60,100 nm). Pigment quality is determined by crystal and primary agglomerate size. One way of improving filtration rate is by the formation of larger aggregates, while maintaining the crystal and primary agglomerate size at optimum values. In a new seeding procedure proposed, the controlled inoculation of seeds used in industry is combined with a new type of seed (Large Seeds). The new seeding procedure has the potential to increase downstream filtration efficiency by increasing aggregate size, while maintaining crystal and primary agglomerate sizes close to the values correctly obtained in industry. High yield in the precipitation process is also maintained. [source] Effect of water and nitrogen management on aggregate size and carbon enrichment of soil in rice-wheat cropping system,JOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 2 2004Rojalin Tripathy Abstract A study was carried out on a silty clay loam soil (Typic Haplustept) to evaluate the effect of farmyard manure (FYM) vis-à-vis fertilizer and irrigation application on the soil organic C content and soil structure. The fertilizer treatments comprised of eight different combinations of N and FYM and three water regimes. The results indicated that the application of FYM and increasing N rate increased soil organic carbon (SOC) content. Addition of FYM also increased the percentage of large sized water stable aggregates (> 5,mm) and reduced the percentage of smaller size aggregates. This was reflected in an increase in the mean weight diameter (MWD) and improved soil structure. The organic carbon content in macroaggregates (> 1,mm) was greater compared to microaggregates, and it declined with decrease in size of microaggregates. This difference in organic C content between macro- and microaggregates was more with higher N dose and FYM treated plots. The effect of residual FYM on MWD and organic C content of the soil after wheat harvest was not significant. The effect was less in deeper layers compared to surface layers of the soil. MWD was significantly correlated with the SOC content for the top two layers. [source] Preparation of Highly Dispersed Ultrafine Barium Titanate Powder by Using Microbial-Derived SurfactantJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2003Hidehiro Kamiya To uniformly disperse ultrafine BaTiO3 particles with a stoichiometric composition and several tens of nanometers in diameter to primary particles during the sol,gel synthesis process, a new aqueous surfactant with a high hydrophilic group density and special cis-structure was prepared from a microbial product and added to solution before the sol,gel synthesis reaction. Because of the rapid formation of large and porous aggregates which were 30,50 ,m in diameter in suspension without addition of this unique structural surfactant, the prepared ultrafine BaTiO3 particles caused rapid sedimentation in suspension. The addition of the surfactant in the range of 7.1 wt% for the synthesized BaTiO3 particles made it possible to decrease the size of the aggregates in suspension as well as the sedimentation velocity while maintaining the stoichiometric composition. The optimum additive content to obtain the minimum aggregate size of about 100,200 nm in diameter and the highest dispersion stability in suspension while maintaining the stoichiometric composition of prepared ultrafine BaTiO3 particles without other phases was determined at about 7.1 wt%. Because the excess addition of this surfactant at more than 8.5 wt% inhibited the uniform synthesis of BaTiO3 particles, an amorphous phase with a highly specific surface area and a BaCO3 phase formed in the synthesized particles. [source] A new bone vascular perfusion compound for the simultaneous analysis of bone and vasculatureMICROSCOPY RESEARCH AND TECHNIQUE, Issue 7 2010Krista L. Sider Abstract Bone is a highly vascular tissue, which plays an important role in bone development and healing. The ability to analyze both the bone and vasculature simultaneously can enhance the understanding of wound healing, development, and disease in bone. At present, analysis methods are limited in their ability to allow for this simultaneous analysis of bone and bone vasculature in three dimensions, without using the most recent dual-energy computed tomography (CT) techniques. In this study, we present a new barium sulfate (BaSO4) radiopaque vascular perfusion compound for performing postmortem microangiography with single-beam microcomputed tomography (microCT), which allows for such simultaneous analysis. This compound differs from currently available contrast mediums due to (1) the high weight-to-volume ratio of BaSO4 achieved, (2) small BaSO4 aggregate size (<5 ,m), (3) minimal additives, and (4) its miscibility with blood and saline. Most notably, it achieves a radiodensity of 2.4× that of cortical bone, with high perfusion of both the arterial and venous systems and the intervening capillary bed, resulting in an in vivo radiodensity that ranges from that of bone to titanium. Our results, verified using a rat femoral gap-healing model, show that the compound is uniquely suited to high-contrast imaging of the vasculature in the presence of undecalcified bone, with a versatility to be used in other tissues. Microsc. Res. Tech., 2010. © 2009 Wiley-Liss, Inc. [source] Gd(III)-EPTPAC16, a new self-assembling potential liver MRI contrast agent: in vitro characterization and in vivo animal imaging studies,NMR IN BIOMEDICINE, Issue 4 2008Suzana Torres Abstract The recently reported amphiphilic chelate, [Gd(EPTPAC16)(H2O)]2,, forms supramolecular aggregates in aqueous solution by self-assembly of the monomers with a relaxometrically determined critical micellar concentration (CMC) of 0.34,mM. The effect of sonication on the aggregate size was characterized by dynamic light scattering and relaxometry, indicating the presence of premicellar aggregates and an overall decrease in aggregate size and polydispersity upon sonication, slightly below the CMC. {[153Sm](EPTPAC16)(H2O)}2, radiotracer was evaluated in vivo from , scintigraphy and biodistribution in Wistar rats. It was found to depend strongly on the sample concentration, below or above the CMC, and its sonication, in a way that correlates with the effect of the same factors on the size of the aggregates formed in solution. Below CMC, the very large aggregates of the [153Sm]3+ -labeled chelate were persistently and mainly taken up by the lungs, and also by the macrophage-rich liver and spleen. Sonication of this solution led to loss of the lung uptake. Above CMC, the metal chelate was mainly taken up by the liver, with very little uptake by the spleen and lungs. In vivo, dynamic contrast-enhanced (DCE)-MRI evaluation of the micellar [Gd(EPTPAC16)(H2O)]2, compound in Wistar rats showed a persistent hepatic positive-contrast effect in T1 -weighted images, qualitatively similar to the clinically established GdIII -based hepatobiliary-selective agents. No enhancement effect was observed in the lungs because of the scarcity of mobile protons in this organ, despite the scintigraphic evidence of significant lung retention of the [153Sm]3+ -labeled chelate at concentrations below the CMC. Copyright © 2007 John Wiley & Sons, Ltd. [source] On-line Determination of Aggregate Size and Morphology in SuspensionsPARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 3 2004Frédéric Gruy Abstract Information concerning the aggregation state of fine solid particles is an important element for process control and monitoring of product quality in many applications of industrial slurries. This work deals with the application of different in-line methods to the characterization of silica aggregate size and morphology. All of these methods exploit turbidity signals, obtained by various means including: from analysis of turbidity fluctuations in homogeneous suspension and from overall turbidity decrease during particle settling. This work also presents the opportunity to report progress in morphological and optical models of small aggregates. As a result of these models, the morphological characteristics of the aggregates along with the number of their constituting particles are derived from experimental results. Similarities between the different methods are examined and discussed. [source] Passaging Protocols for Mammalian Neural Stem Cells in Suspension BioreactorsBIOTECHNOLOGY PROGRESS, Issue 2 2002Arindom Sen Mammalian neural stem cells (NSC) offer great promise as therapeutic agents for the treatment of central nervous system disorders. As a consequence of the large numbers of cells that will be needed for drug testing and transplantation studies, it is necessary to develop protocols for the large-scale expansion of mammalian NSC. Neural stem cells and early progenitor cells can be expanded in vitro as aggregates in controlled bioreactors using carefully designed media. The first objective of this study was to determine if it is possible to maintain a population of murine neural stem and progenitor cells as aggregates in suspension culture bioreactors over extended periods of time. We discovered that serial passaging of a mixture of aggregates sizes resulted in high viabilities, high viable cell densities, and good control of aggregate diameter. When the NSC aggregates were serially subcultured three times without mechanical dissociation, a total multiplication ratio of 2.9 × 103 was achieved over a period of 12 days, whereas the aggregate size was controlled (mean diameter less than 150 ,m) below levels at which necrosis would occur. Moreover, cell densities of 1.0 × 106 cells/mL were repeatedly achieved in batch culture with viabilities exceeding 80%. The second objective was to examine the proliferative potential of single cells shed from the surface of these aggregates. We found that the single cells, when subcultured, retained the capacity to generate new aggregates, gave rise to cultures with high viable cell densities and were able to differentiate into all of the primary cell phenotypes in the central nervous system. [source] Experimental analysis of compaction of concrete and mortarINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 15 2001Nicolas Burlion Abstract Compaction of concrete is physically a collapse of the material porous microstructure. It produces plastic strains in the material and, at the same time, an increase of its bulk modulus. This paper presents two experimental techniques aimed at obtaining the hydrostatic response of concrete and mortar. The first one is a uniaxial confined compression test which is quite simple to implement and allows to reach hydrostatic pressures of about 600 MPa. The specimen size is large enough so that concrete with aggregate sizes up to 16 mm can be tested. The second one is a true hydrostatic test performed on smaller (mortar) specimens. Test results show that the hydrostatic response of the material is elasto-plastic with a stiffening effect on both the tangent and unloading bulk moduli. The magnitude of the irreversible volumetric strains depends on the initial porosity of the material. This porosity can be related in a first approximation to the water/cement ratio. A comparison of the hydrostatic responses obtained from the two testing techniques on the same material show that the hydrostatic response of cementitious materials cannot be uncoupled from the deviatoric response, as opposed to the standard assumption in constitutive relations for metal alloys. This feature should be taken into account in the development of constitutive relations for concrete subjected to high confinement pressures which are needed in the modelling of impact problems. Copyright © 2001 John Wiley & Sons, Ltd. [source] Multilevel structure of reinforcing silica and carbonJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3-1 2000D.W. Schaefer Using small-angle x-ray (SAXS), neutron (SANS), x-ray diffraction and light scattering, we study the structure of colloidal silica and carbon on length scales from 4 Å < q,1 < 107 Å where q is the magnitude of the scattering vector. These materials consist of primary particles of the order of 100 Å, aggregated into micron-sized aggregates that in turn are agglomerated into 100 µ agglomerates. The diffraction data show that the primary particles in precipitated silica are composed of highly defective amorphous silica with little intermediate-range order (order on the scale of several bond distances). On the next level of morphology, primary particles arise by a complex nucleation process in which primordial nuclei briefly aggregate into rough particles that subsequently smooth out to become the seeds for the primaries. The primaries aggregate to strongly bonded clusters by a complex process involving kinetic growth, mechanical disintegration and restructuring. Finally, the small-angle scattering (SAS) data lead us to postulate that the aggregates cluster into porous, rough-surfaced, non-mass-fractal agglomerates that can be broken down to the more strongly bonded aggregates by application of shear. We find similar structure in pelletized carbon blacks. In this case we show a linear scaling relation between the primary and aggregate sizes. We attribute the scaling to mechanical processing that deforms the fractal aggregates down to the maximum size able to withstand the compaction stress. Finally, we rationalize the observed structure based on empirical optimization by filler suppliers and some recent theoretical ideas due to Witten, Rubenstein and Colby. [source] Surfactive and antibacterial activity of cetylpyridinium chloride formulations in vitro and in vivoJOURNAL OF CLINICAL PERIODONTOLOGY, Issue 6 2008Henk J. Busscher Abstract Aim: To compare effects of three cetylpyridinium chloride (CPC) formulations with and without alcohol and Tween80 on physico-chemical properties of salivary pellicles, bacterial detachment in vitro and bacterial killing in vivo. Material and Methods: Adsorption of CPC to salivary pellicles in vitro was studied using X-ray photoelectron spectroscopy and water contact angle measurements. Adhesion and detachment of a co-adhering bacterial pair was determined in vitro using a flow chamber. Killing was evaluated after live/dead staining after acute single use in vivo on 24- and 72-h-old plaques after 2-week continuous use. Results: The most pronounced effects on pellicle surface chemistry and hydrophobicity were observed after treatment with the alcohol-free formulation, while the pellicle thickness was not affected by any of the formulations. All CPC formulations detached up to 33% of the co-adhering pair from pellicle surfaces. Bacterial aggregate sizes during de novo deposition were enhanced after treatment with the alcohol-free formulation. Immediate and sustained killing in 24 and 72 h plaques after in vivo, acute single use as well as after 2-week continuous use were highest for the alcohol-free formulation. Conclusions: CPC bioavailability in a formulation without alcohol and Tween80 could be demonstrated through measures of pellicle surface properties and bacterial interactions in vitro as well as bacteriocidal actions on oral biofilms in vivo. [source] Kinetics of Formation and Physicochemical Characterization of Thermally-Induced ,-Lactoglobulin AggregatesJOURNAL OF FOOD SCIENCE, Issue 5 2010R.N. Zúñiga Abstract:, The kinetics of heat denaturation and aggregation for ,-lactoglobulin dispersions (5% w/v) were studied at 3 pHs (6, 6.4, and 6.8) and at a heating temperature of 80 °C. Protein aggregates were characterized for hydrodynamic diameter, microstructure, and molecular weight by means of dynamic light scattering, transmission electron microscopy, and polyacrylamide gel electrophoresis, respectively. Concentration of native ,-lactoglobulin decreased with holding time and with a decrease in the pH. Apparent rate constants were calculated for ,-lactoglobulin denaturation applying the general kinetic equation solved for a reaction order of 1.5. Values of the apparent reaction rate constant,k,= 7.5, 6.3 and 5.6 × 10,3 s,1 were found for pH 6, 6.4, and 6.8, respectively. Decreasing the pH of the dispersions produced higher aggregate sizes. After a holding time of 900 s, average hydrodynamic diameters for ,-lactoglobulin aggregates at pH 6, 6.4, and 6.8 were 96, 49, and 42 nm, respectively. These results were confirmed by transmission electron microscopy images, where a shift in the size and morphology of aggregates was found, from large and spherical at pH 6 to smaller and linear aggregates at pH 6.8. ,-Lactoglobulin formed disulfide-linked intermediates (dimers, trimers, tetramers) and so on) which then formed high molecular weight aggregates. From the results obtained by DLS, TEM, and SDS-PAGE a mechanism for ,-lactoglobulin aggregation was proposed. This study shows that heat treatment can be used to produce protein aggregates with different sizes and morphologies to be utilized as ingredients in foods. [source] Dissimilar aggregation processes govern precipitation and gelation of human IgM cryoglobulinsJOURNAL OF MOLECULAR RECOGNITION, Issue 2 2007Vicky Vallas Abstract Cryoglobulinemia is associated with a range of diseases including rheumatoid arthritis, B-cell malignancies, and chronic viral infections. This "cold-sensitivity" condition is caused by cryoglobulins that precipitate, gel, or occasionally crystallize in the cold. Clinical manifestations vary widely in severity, depending on many factors, including the type of cryoglobulin (monoclonal or mixed immunoglobulins) and the physical nature of the aggregates (precipitate, gel, or crystal). Dynamic light scattering (DLS) was used to examine the cold-induced precipitation or gelation of two human cryoglobulins, namely, Pot IgM and Yvo IgM. The DLS assay was highly reproducible, sensitive, and had low intra-assay variations for both IgM cryoglobulins. Distinct processes were revealed to contribute to precipitation and gelation of cryoglobulins. The precipitation of Pot IgM displayed a rapid transition from solution to solid phases, with a wide distribution of aggregate sizes. In contrast, the gelation of Yvo IgM progressed gradually across a broad temperature range to produce a relatively uniform gel matrix. Initial cryoglobulin concentrations determined the kinetics and critical temperatures for both precipitation and gelation. Moreover, the Yvo IgM was observed to have a distinct relationship between concentrations and mean hydrodynamic diameters or particle sizes. Concentration-dependent effects on particle sizes were present, but not as pronounced for the Pot IgM. Precipitation and gelation of cryoglobulins were also found to be differentially responsive to changes in the aqueous environment. Our results indicate that DLS is a rapid, reliable, and sensitive method for characterizing the nature of disease-associated cryoglobulins. Copyright © 2007 John Wiley & Sons, Ltd. [source] A comparison of two methods for the isolation of free and occluded particulate organic matterJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 5 2005Angelika Kölbl Abstract Various methods exist for the isolation of particulate organic matter (POM), one of the soil-organic-matter (SOM) fractions reacting most sensitive on land-use or soil-management changes. A combination of density separation and ultrasonic treatment allows to isolate two types of POM: (1) free POM and (2) POM occluded in soil aggregates. POM fractions are closely linked to their biochemical function for the formation and stabilization of aggregates, therefore methods using different aggregate sizes may result in different POM fractions isolated. We evaluated two physical fractionation procedures to reveal whether they yield different POM fractions with respect to amount and composition, using grassland and arable soils with sandy-loam to sandy,clay-loam texture and thus low macroaggregate stability. Method I used air-dried aggregates of <2.0 mm size and a low-energy sonication for aggregate disruption, method II used field-moist aggregates <6.3 mm and a high-energy,sonication procedure for aggregate disruption. POM fractions were analyzed by elemental analysis (C, N) and CPMAS 13C-NMR spectroscopy. With both methods, about similar proportions of the SOM are isolated as free or occluded POM, respectively. The free- and occluded-POM fractions obtained with method I are also rather similar in C and N concentration and composition as shown by 13C-NMR spectroscopy. Method II isolates a free- and occluded-POM fraction with significantly different C and N concentrations. NMR spectra revealed significant differences in the chemical composition of both fractions from method II, with the occluded POM having lower amounts of O-alkyl C and higher amounts of aryl C and alkyl C than the free POM. Due to the use of larger, field-moist aggregates with minimized sample pretreatment, two distinctly different POM fractions are isolated with method II, likely to be more closely linked to their biochemical function for the formation and stabilization of aggregates. High-energy sonication as in method II also disrupts small microaggregates <63 µm and releases fine intraaggregate POM. This fraction seems to be a significant component of occluded POM, that allows a differentiation between free and occluded POM in sandy soils with significant microaggregation. It can be concluded, that microaggregation in arable soils with sandy texture is responsible for the storage of a more degraded occluded POM, that conversely supports the stabilization of fine microaggregates. Ein Vergleich zweier Methoden zur Isolierung von freier und okkludierter partikulärer organischer Substanz Partikuläres organisches Material (POM) wird im Hinblick auf die Landnutzung als sensitive Fraktion der organischen Bodensubstanz (SOM) angesehen, aber die unterschiedlichen Methoden seiner Isolierung erschweren den Vergleich zwischen verschiedenen Studien. Wir haben zwei physikalische Fraktionierungsmethoden ausgewertet, um zu zeigen, ob sie im Hinblick auf Menge und Zusammensetzung zu unterschiedlichen POM-Fraktionen führen. Hierfür wurden Proben von Grünland- und Ackerböden verwendet. Für Methode I wurden luftgetrocknete Aggregate der Größe <2 mm verwendet, zu deren Zerstörung eine Ultraschallbehandlung mit geringem Energieeintrag eingesetzt wurde. Für Methode II wurden feldfeuchte Aggregate der Größe <6.3 mm und eine Ultraschallbehandlung mit vergleichsweise hoher Energie zur Aggregatzerstörung herangezogen. Mit beiden Methoden konnten zwei POM-Gruppen gewonnen werden: (1) freies POM und (2) in Bodenaggregaten eingeschlossenes POM. Die POM-Fraktionen wurden mittels Elementanalyse (C, N) und CPMAS- 13C-NMR,Spektroskopie untersucht. Methode I zeigte im Hinblick auf Menge und Zusammensetzung nur sehr geringe Unterschiede zwischen freien und okkludierten POM-Fraktionen. Methode II isolierte freie und okkludierte POM-Fraktionen mit signifikant unterschiedlichen C- und N-Konzentrationen. Auch die NMR-Spektren zeigten Unterschiede in der chemischen Zusammensetzung der mit Methode II gewonnenen Fraktionen, die sich in signifikant geringeren O-Alkyl-C-Gehalten bei höheren Aryl-C- und Alkyl-C-Gehalten des okkludierten POM nachweisen ließen. Die Verwendung von größeren, feldfeuchten Aggregaten und die Minimierung der Probenvorbehandlung führt zu einer besseren Differenzierung beider POM-Fraktionen, die wahrscheinlich ihre biologische Funktion besser widerspiegelt. Zusätzlich führt eine Ultraschall-Behandlung mit hohem Energieeintrag zur Zerstörung von kleinen Mikroaggregaten <63 µm und damit zur Freisetzung von feinem Intraaggregat-POM. Diese Fraktion scheint in sandigen Böden mit niedriger Makroaggregat-Stabilität aussagekräftiger zwischen freier und okkludierter POM unterscheiden zu können. Folglich ist eine an das Bodenmaterial angepasste Probenvorbehandlung und Fraktionierungsmethode entscheidend, um eine präzise Charakterisierung der POM-Fraktionen zu gewährleisten. [source] Aggregation of Fillers Blended into Random Elastomeric Networks: Theory and Comparison with ExperimentsMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 16 2006Mustafa M. Demir Abstract Summary: A theoretical model describing aggregation of filler particles in amorphous elastomers is proposed. The model is based on a counting technique originally used in genome analysis to characterize the size and distribution of overlapping segments randomly placed on a DNA molecule. In the present model, the particles are first assumed to aggregate randomly upon mixing into the elastomer and their sizes are calculated. The sizes and distributions of aggregates are also studied in the presence of attractive interparticle forces. Results of the proposed model are compared with experimental data on silica-filled end-linked poly(dimethylsiloxane) networks. Comparison of the theory and experiment shows that the random aggregation assumption where no attractive forces exist between the particles is not valid and a significant attraction between the silica particles is needed in the theory to justify the experimental data obtained using atomic force microscopy. For filler content below 1.45 vol.-%, the model agrees, qualitatively, with experiment and shows the increase in cluster size with increasing amount of filler. It also explains the increase in the dispersion of aggregate sizes with increasing amount of filler. Clustering of the primary silica particles in an imaginary volume of poly(dimethylsiloxane) network. [source] Passaging Protocols for Mammalian Neural Stem Cells in Suspension BioreactorsBIOTECHNOLOGY PROGRESS, Issue 2 2002Arindom Sen Mammalian neural stem cells (NSC) offer great promise as therapeutic agents for the treatment of central nervous system disorders. As a consequence of the large numbers of cells that will be needed for drug testing and transplantation studies, it is necessary to develop protocols for the large-scale expansion of mammalian NSC. Neural stem cells and early progenitor cells can be expanded in vitro as aggregates in controlled bioreactors using carefully designed media. The first objective of this study was to determine if it is possible to maintain a population of murine neural stem and progenitor cells as aggregates in suspension culture bioreactors over extended periods of time. We discovered that serial passaging of a mixture of aggregates sizes resulted in high viabilities, high viable cell densities, and good control of aggregate diameter. When the NSC aggregates were serially subcultured three times without mechanical dissociation, a total multiplication ratio of 2.9 × 103 was achieved over a period of 12 days, whereas the aggregate size was controlled (mean diameter less than 150 ,m) below levels at which necrosis would occur. Moreover, cell densities of 1.0 × 106 cells/mL were repeatedly achieved in batch culture with viabilities exceeding 80%. The second objective was to examine the proliferative potential of single cells shed from the surface of these aggregates. We found that the single cells, when subcultured, retained the capacity to generate new aggregates, gave rise to cultures with high viable cell densities and were able to differentiate into all of the primary cell phenotypes in the central nervous system. [source] | ||||||||||||||||||||||