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At least 1,081 records · Page 60Linked to original sources

PubMed2003

No association between micrometer-sized particles in human cerebrospinal fluid and schizophrenia.

The pathogenetic processes underlying schizophrenia are unknown, but the organic changes observed in the brain tissue of schizophrenic patients suggest the possibility of findings also in the cerebrospinal fluid (CSF) of patients suffering from this disorder. In a recently published study micrometer-sized spherical particles in CSF were isolated from significantly more schizophrenic patients compared to controls. The functional importance of these particles is unknown, but if replicated in independent study samples they could function as trait markers and spur further investigations. We analyzed CSF samples from five patients with a diagnosis of schizophrenia, nine patients with chronic pain syndrome and six healthy controls with scanning electron microscopy in accordance with the protocol described in the original report. Similar particles were identified as in the previous study, but they were not associated with disease status (P=1.00). It cannot be excluded that these divergent results are due to methodological differences, but presently the most parsimonious explanation would be that the original finding was a false positive result. More investigation is needed to clarify the source and relevance of these particles.

Adult↗

PubMed1998

Preparative application of commercial automated gel electrophoresis apparatus to subcellular-sized particles: sequential isolations, fractions re-run, sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis, yield and purity.

The analytical and preparative potential of automated gel electrophoresis apparatus with intermittent fluorescence scanning of the migration path, the HPGE-1000 apparatus (LabIntelligence, Belmont, CA) was further developed in application to subcellular-sized particles. Resolution between two rat liver microsome components in agarose (MetaPhor) gel electrophoresis was found to increase with decreasing agarose concentration to 0.04%. It was less, even in an agarose solution at that low concentration, than that in laterally aggregated 4% polyacrylamide gel. The three components of the microsomal preparation were sequentially isolated from 0.6 and 0.8% agarose gel electropherograms. One fraction when re-electrophoresed was found to exhibit the original mobility and did not give rise to the other components. Yields of each component were near-quantitative after one or two electroelution steps. Based on protein content, no impurities could be detected in two of the microsome fractions; the third fraction contained 2% of nonmicrosome impurity. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) patterns of all three microsome fractions were indistinguishable from one another and from that of the unfractionated microsome preparation.

Animals↗

PubMed2001

Theoretical and experimental study of the influence of the particle size distribution on acoustic wave properties of strongly inhomogeneous media.

The ultrasonic method is particularly suitable to characterize diffusive media, as acoustic properties (velocity and attenuation) are related to the properties and concentrations of the homogeneous phase and scatterers. Thus, ultrasonic characterization can be useful in the study of sedimentation or flocculation processes, in concentration measurements, and granulometry evaluation. Many models have been developed for media where particles are very small compared to the incident wavelength. When the diameter of the particles is close to the wavelength, multiple-scattering theories have to be used to describe the propagation of waves. In this paper, the case where the ratio of wavelength to scatterer size is around unity is studied. First, the particle size distribution is taken into account in two types of multiple-scattering theories based on the effective field approximation or on the quasicrystalline approximation and theoretical results are produced. The T-matrix formalism has been used to calculate the amplitude of the wave scattered by a single sphere. The calculation of the complex wave number in the effective medium has been implemented, using in particular the Percus-Yevick equation as a spatial pair-correlation function between scatterers, and a normal particle-size distribution. The influence of these parameters is discussed. Finally, attenuation and phase velocity measurements are performed in moving suspensions of acrylic spheres in ethylene glycol, at various concentrations and for different particle-size distributions. A good agreement between the theoretical results and the measurements is found for both velocity and attenuation. These results show that the size distribution is a critical parameter to understand velocity and attenuation behavior as function of frequency and volume fraction.

Journal Article↗

PubMedDate not supplied

Generation of equally sized particle plaques using solid-liquid suspensions.

A device is presented for the generation of equally sized plaques of sensitive particles in a 96-well format. The resulting particle plaques can be used for the measurement of adsorption isotherms and uptake kinetics in protein chromatography or for immobilization reactions. The particle plaques are formed from suspensions with a vacuum device that is designed as a reusable sandwich module. The particles are retained by a mesh while the solvent is removed by the vacuum. As most particles used for protein chromatography are sensitive to mechanical stress and dehydration, the vacuum device is gentle enough to allow the use of these particles, thus eliminating the uncertainty of slurry preparation and pipetting. Apparatus characteristics and preparation procedures are described precisely. The physical intactness of the particles after the preparation procedure is proved by microscopic analysis. Data on the uniformity of the obtained resin plaques with respect to the reproducibility of their adsorption performance is given. Finally, adsorption isothermal and kinetic data of BSA on an ordinary HIC system obtained by high-throughput measurements are shown as an application example.

Adsorption↗

PubMed1995

Pharmaceutical characterization of commercially available intravenous fat emulsions: estimation of average particle size, size distribution and surface potential using photon correlation spectroscopy.

Particle profiles such as the average diameter, size distribution and dispersion, as well as the zeta potential, of commercially available intravenous fat emulsions of high-calorie nutrient fluids (6 products) and drug carriers (4 products) were examined using photon correlation spectroscopy (dynamic light scattering). Wide variations were observed in number-weighted (dn), weight-weighted (dw) and z-average diameters, and dw/dn ratios as a measure of polydispersity. Average size is not sufficient for the pharmaceutical characterization of particles and the determination of size distribution or dw/dn value is essential for more precise information. Although measuring the zeta potential of fat emulsions is of considerable value in estimating their stability on long-term storage, a medium which accurately reflects the environment of the droplets in the system of interest should be chosen when diluting the emulsion.

Absorptiometry, Photon↗

PubMed2002

Ultrafast dephasing of surface plasmon excitation in silver nanoparticles: influence of particle size, shape, and chemical surrounding.

By combination of two special methods, i.e., persistent spectral hole burning and laser assisted nanoparticle preparation, the dephasing time T2 of surface plasmon excitation in silver nanoparticles was systematically investigated. A strong dependence of T2 on the plasmon energy is found which reflects the relevance of interband damping and makes necessary a precise control of the particle shape when measuring T2. The influence of the reduced dimension on the dephasing dynamics was observed as a decrease of T2 with shrinking particle size. In addition, for silver nanoparticles on quartz substrates, a considerable amount of chemical interface damping was observed.

Journal Article↗

PubMedDate not supplied

Effectiveness of latex condoms as a barrier to human immunodeficiency virus-sized particles under conditions of simulated use.

Condoms were tested in an in vitro system simulating key physical conditions that can influence viral particle leakage through condoms during actual coitus. The system quantitatively addresses pressure, pH, temperature, surfactant properties, and anatomical geometry. A suspension of fluorescence-labeled, 110-nm polystyrene microspheres models free human immunodeficiency virus (HIV) in semen, and condom leakage is detected spectrofluorometrically. Leakage of HIV-sized particles through latex condoms was detectable (P less than 0.03) for as many as 29 of the 89 condoms tested. Worst-case condom barrier effectiveness (fluid transfer prevention), however, is shown to be at least 10(4) times better than not using a condom at all, suggesting that condom use substantially reduces but does not eliminate the risk of HIV transmission.

Contraceptive Devices, Male↗

PubMed2005

Surface properties, more than size, limiting convective distribution of virus-sized particles and viruses in the central nervous system.

OBJECT: Achieving distribution of gene-carrying vectors is a major barrier to the clinical application of gene therapy. Because of the blood-brain barrier, the distribution of genetic vectors to the central nervous system (CNS) is even more challenging than delivery to other tissues. Direct intraparenchymal microinfusion, a minimally invasive technique, uses bulk flow (convection) to distribute suspensions of macromolecules widely through the extracellular space (convection-enhanced delivery [CED]). Although acute injection into solid tissue is often used for delivery of oligonucleotides, viruses, and liposomes, and there is preliminary evidence that certain of these large particles can spread through the interstitial space of the brain by the use of convection, the use of CED for distribution of viruses in the brain has not been systematically examined. That is the goal of this study. METHODS: Investigators used a rodent model to examine the influence of size, osmolarity of buffering solutions, and surface coating on the volumetric distribution of virus-sized nanoparticles and viruses (adeno-associated viruses and adenoviruses) in the gray matter of the brain. The results demonstrate that channels in the extracellular space of gray matter in the brain are large enough to accommodate virus-sized particles and that the surface characteristics are critical determinants for distribution of viruses in the brain by convection. CONCLUSIONS: These results indicate that convective distribution can be used to distribute therapeutic viral vectors in the CNS.

Adenoviridae↗

PubMed1998

Effect of bioactive glass particle size on osseous regeneration of cancellous defects.

The bioactive glass known as Bioglass or Perioglass (USB) (US Biomaterials, Alachua, FL) has proven to be an effective graft material owing to the apatite layer which forms on the surface of the glass, promoting bone formation. USB particles range in size from 90 to 710 microns in diameter, as determined by optical microscopy. A similar bioactive material, BioGran (OV) (Orthovita, Malvern, PA), was developed to limit the particle size of 4555 to the range between 300 and 360 microns, as determined by sieving. The objective of this study was to histologically and biomechanically compare the 4555 bioactive glass, produced by US Biomaterials, in a wide particle range (USB) to the narrower particle range glass produced by Orthovita (OV) The grafted defects will then be compared to normal cancellous bone (NORM) of the distal femur in rabbits. Histologically, more bone was quantified at both 4 and 12 weeks within the defects filled with USB and NORM when compared to the limbs filled with OV (p < 0.05). The OV particles had greater particle axes and larger particle areas on average than the USB particles (p < 0.05). However, the particle axis and area of the two materials decreased with time at a similar rate. Biomechanically, the USB- and OV-grafted defects had comparable peak compressive load, compressive stiffness, and compressive modulus which were equivalent to normal bone.

Animals↗

PubMed2000

Comparison of the particle size distribution of heavy-duty diesel exhaust using a dilution tailpipe sampler and an in-plume sampler during on-road operation.

Originally constructed to develop gaseous emission factors for heavy-duty diesel trucks, the U.S. Environmental Protection Agency's (EPA) On-Road Diesel Emissions Characterization Facility has been modified to incorporate particle measurement instrumentation. An electrical low-pressure impactor designed to continuously measure and record size distribution data was used to monitor the particle size distribution of heavy-duty diesel truck exhaust. For this study, which involved a high-mileage (900,000 mi) truck running at full load, samples were collected by two different methods. One sample was obtained directly from the exhaust stack using an adaptation of the University of Minnesota's air-ejector-based mini-dilution sampler. The second sample was pulled from the plume just above the enclosed trailer, at a point approximately 11 m from the exhaust discharge. Typical dilution ratios of about 300:1 were obtained for both the dilution and plume sampling systems. Hundreds of particle size distributions were obtained at each sampling location. These were compared both selectively and cumulatively to evaluate the performance of the dilution system in simulating real-world exhaust plumes. The data show that, in its current residence-time configuration, the dilution system imposes a statistically significant bias toward smaller particles, with substantially more nanoparticles being collected than from the plume sample.

Air Pollution↗

PubMed2001

In vivo bone formation by human bone marrow stromal cells: effect of carrier particle size and shape.

Successful closure of bone defects in patients remains an active area of basic and clinical research. A novel and promising approach is the transplantation of human bone marrow stromal cells (BMSCs), which have been shown to possess a significant osteogenic potential. The extent and quality of bone formation by transplanted human BMSCs strongly depends on the carrier matrix with which cells are transplanted; to date, hydroxyapatite/tricalcium phosphate (HA/TCP) supports far more osteogenesis than any other matrix tested. In order to further improve the technique of BMSC transplantation, we studied whether commercially available HA/TCP particles, clinically approved as an osteoconductive material and commercially available as particles measuring 0.5-1.0 mm diameter, is an optimum matrix for promoting bone development by BMSCs. HA/TCP and HA particles of varying size were sieved into a variety of size ranges, from <0.044 mm to 1.0-2.0 mm. Transplants were formed by mixing 40 mg aliquots of particles with cultured passaged human BMSCs. They were placed in subcutaneous pockets in immunocompromised Bg-Nu-XID mice and harvested 4 or 10 weeks later. The transplants were examined histologically; the presence of bone within each transplant was evaluated using histomorphometry or blindly scored on a semiquantitative scale. Transplant morphology and the amount of new bone varied in a consistent fashion based on particle size and shape. Transplants incorporating HA/TCP particles of 0.1-0.25 mm size demonstrated the greatest bone formation at both 4 and 10 weeks; larger or smaller particles were associated with less extensive bone formation, while a size of 0.044 mm represented a threshold below which no bone formation could be observed. Flat-sided HA particles measuring 0.1-0.25 mm formed no bone. The differences in bone formation were not attributable to the differences in cell attachment among the groups. Instead, the size and spatial and structural organization of the particles within BMSC transplants appear to determine the extent of bone formation. These findings provide necessary information for the successful clinical application of BMSC transplantation techniques.

Animals↗

PubMed2006

Combining particle size distribution and isothermal calorimetry data to determine the reaction kinetics of alpha-tricalcium phosphate-water mixtures.

Many calcium phosphate bone substitutes are based on the use of alpha-tricalcium phosphate (alpha-TCP) powder. This compound has been intensively studied, but some aspects of alpha-TCP reactivity are still controversial. The goal of this study was to determine the setting kinetics of alpha-TCP based on a new approach that compared particle size distribution data to isothermal calorimetry data. Results indicated that alpha-TCP conversion is mostly controlled by surface reactions, with at later stages a diffusion-controlled mechanism. The presence of an X-ray amorphous alpha-TCP fraction in the crystalline alpha-TCP powder increased the dissolution rate threefold, without modifying the reaction mechanism.

Biocompatible Materials↗

PubMed1976

Comparison of the particle size distribution curves determined manually and automatically in an accurately calibrated Coulter Counter.

An accurately calibrated Coulter Counter, Model ZB Industrial, was used to compare the size distribution curves of seven different standard particles obtained by calculation and after the attachment of a Channelyser, Model C-1000 coupled to an XY recorder. Comparisons were made at the modes of the curves and it was found that the automatic method consistently reported the particles to be slightly larger.

Equipment and Supplies↗

PubMed1992

Effects of weight-loss by exercise and by diet on apolipoproteins A-I and A-II and the particle-size distribution of high-density lipoproteins in men.

We studied separately the effects of weight-loss by dieting or by running on apolipoprotein (apo) A-I, apo A-II, and high-density lipoprotein (HDL) subfractions in sedentary, moderately overweight men assigned at random into three groups: exercise without calorie restriction, calorie restriction without exercise, and control. The absorbance of protein-stained polyacrylamide gradient gels was used as an index of mass concentrations for five HDL subclasses that have been identified by their particle sizes: HDL3c (7.2 to 7.8 nm), HDL3b (7.8 to 8.2 nm), HDL3a (8.2 to 8.8 nm), HDL2a (8.8 to 9.7 nm), and HDL2b (9.7 to 12.9 nm). During the 1-year trial, the exercisers ran (mean +/- SD) 15.6 +/- 9.1 km/wk, and the dieters reported eating 340 +/- 71 fewer calories per day than at baseline. Total body weight and fat weight were both reduced significantly more in dieters (-7.2 +/- 4.1 and -6.2 +/- 4.1 kg, respectively) and in exercisers (-4.0 +/- 3.9 and -4.6 +/- 3.5 kg) than in controls (0.6 +/- 3.7 and -0.7 +/- 2.7 kg). As compared with mean changes in controls, exercisers and dieters each decreased HDL3b and increased HDL2b. Exercisers also significantly increased plasma apo A-I concentrations. Analysis of covariance was used to statistically adjust the mean lipoprotein changes for the effects of weight-loss. The adjustment eliminated the significant reductions in HDL3b and the significant increases in HDL2b in exercisers and dieters, and it eliminated the significant increase in apo A-I in exercisers. When adjusted, the dieters' mean changes in HDL2b had significantly decreased relative to those of both exercisers and controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMedDate not supplied

Polyvinyl alcohol foam particle sizes and concentrations injectable through microcatheters.

PURPOSE: Injection of different size ranges and concentrations of polyvinyl alcohol (PVA) foam particles was performed to determine the optimal and maximum size ranges and concentrations that may be injected reliably through microcatheters used for vascular embolization. MATERIALS AND METHODS: Eight different microcatheters were tested. Six different size ranges of PVA foam particles (three each from two manufacturers) at three different concentrations were tested with each catheter. All PVA foam particles were suspended in dilute low-osmolarity contrast material. For each size range and concentration of PVA foam particles, sixty 1-mL injections were made into each catheter tested. Continuous pressure monitoring was employed during all injections. RESULTS: For each catheter, the authors determined recommended maximum size ranges of PVA foam particles that may be injected with reasonable pressure and minimal risk of inadvertent catheter occlusion. Among the four catheters used with 0.014-0.016-inch guide wires, the authors found that PVA foam particles as large as 1,000-1,500 microm could be injected without catheter occlusion. PVA foam particles as large as 710-1,000 microm could be injected through one catheter used with 0.010-0.013-inch guide wires. Particles as small as 300-500 microm occluded the other catheter used with the same size guide wires. Both of the flow-directed microcatheters tested would allow injection of PVA foam particles as large as 355-500 microm. CONCLUSION: Given the recent proliferation of microcatheters, improved understanding of maximum PVA foam particle size ranges and concentrations that can be injected through them will help prevent inadvertent catheter occlusion during embolization. Because the authors' results are based on a simulated high-flow vascular lesion, they may not be applicable in all circumstances. Embolization of low-flow lesions, however, should not require use of the maximum possible size and concentration of PVA foam particles.

Catheterization↗

PubMed1981

Effect of core composition and particle size of lipid emulsions on apolipoprotein transfer of plasma lipoproteins in vivo.

Lipid emulsions corresponding in size and surface composition to chylomicron and low density lipoprotein but differing in lipid core composition were injected into rats a tail vein cannula and 10 min later blood was withdrawn via the abdominal aorta. Plasma lipoproteins were isolated by ultracentrifugation and the lipid and apolipoprotein composition was determined by gas-liquid chromatography and gel electrophoresis, respectively. It was found that apolipoprotein C peptides were transferred to Sf greater than 400 particles of large diameter regardless of whether their cores contained cholesteryl esters or triacylglycerols, but not to Sf greater than 400 particles of small diameter. Apolipoprotein A-I transferred to both large and small diameter cholesteryl ester core particles but only to larger diameter triacylglycerol core particles. In contrast, apolipoprotein E became associated with small and large diameter particles regardless of core composition. In addition, all Sf greater than 400 fractions contained significant amounts of apopeptides with molecular weights greater than 45 000, which did not correspond to the common apolipoproteins. This is the first study to prove systematically the effects of lipid composition and particle size on apolipoprotein transfer in vivo.

Animals↗

PubMed1992

Effect of fibre level, particle size and adaptation period on digestibility and rate of passage as measured at the ileum and in the faeces in the adult rabbit.

The use of specific methods other than gravimetric ones to analyse fibre permitted a more precise study of the degradation of cell wall (CW) in the digestive tract. Digesta flow and rate of passage measurements have not been assessed previously in rabbits to investigate fibre digestion and fibre effects simultaneously in the proximal and in the distal segments of the tract. The effect of the level of dietary fibre on ileal and overall digestibility and rate of passage were studied by comparing semi-purified diets containing only one source of CW (dehydrated lucerne (Medicago sativa) meal) given to adult female rabbits. The effect of fibre particle size and adaptation period were also investigated. Measurements of fibre composition using both colorimetric and gas-liquid chromatographic techniques, showed that large amounts of (CW) were degraded in the caecocolic segments. Increasing dietary fibre level reduced the rate of passage but fibre degradation was increased, at the same time a lower digestive efficiency for energy in the small intestine was found. A small quantity of CW was apparently degraded before the caecum, assuming that the water-soluble fraction of CW was essentially implicated. Grinding lucerne meal through a 1 mm instead of a 3 mm screen did not improve CW digestibility in spite of a longer rate of passage in the caeco-colic segments. Adaptation to a high-fibre diet resulted in an higher digestive volume for colon and caecum, related to an improved degradation of CW. Furthermore, digestive efficiency in the small intestine appeared higher for rabbits adapted to a high-fibre diet than that for rabbits initially fed on a low-fibre diet.

Adaptation, Physiological↗

PubMed1997

Reconstituted high-density lipoproteins with a disulfide-linked apolipoprotein A-I dimer: evidence for restricted particle size heterogeneity.

The apolipoprotein A-IMilano (apoA-IM) is a molecular variant of apoA-I characterized by the Arg173-->Cys substitution, resulting in the formation of homodimers (A-IM/A-IM) and heterodimers with apoA-II. In order to examine the effects of the introduction of an interchain disulfide bridge on the lipid-binding properties of apoA-I, the present studies compare the kinetics of association of A-IM/A-IM and apoA-I with dimyristoylphosphatidylcholine (DMPC), and the structure and properties of reconstituted HDL containing palmitoyloleoylphosphatidylcholine (POPC) and either A-IM/A-IM or apoA-I. The results show that apoA-I dimerization does not affect the rate of association with DMPC. Apolipoprotein-POPC complexes instead, when analyzed by nondenaturing gradient gel electrophoresis, demonstrate that, differently from apoA-I, A-IM/A-IM forms only two species of rHDL particles despite a wide range of initial lipid to protein ratios. These two rHDL species contain one or two A-IM/A-IM molecules and have a diameter of 7.8 nm and 12.5 nm. Investigations of the A-IM/A-IM structure in these two rHDL, by circular dichroism, fluorescence, and second-derivative UV spectroscopy, suggest that the secondary and tertiary structures of A-IM/A-IM are remarkably similar in both small and large particles. These results suggest that the introduction of an interchain disulfide bridge does not affect the association of apoA-I with lipids but restricts HDL particle size heterogeneity, thus possibly affecting HDL function in lipid metabolism and atherosclerosis protection.

Apolipoprotein A-I↗