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At least 865 records · Page 48Linked to original sources

PubMed2004

Measurement of particle size distribution in mammalian cells in vitro by use of polarized light spectroscopy.

We demonstrate the feasibility of measuring the particle size distribution (PSD) of internal cell structures in vitro. We use polarized light spectroscopy to probe the internal morphology of mammalian breast cancer (MCF7) and cervical cancer (Siha) cells. We find that graphing the least-squared error versus the scatterer size provides insight into cell scattering. A nonlinear optimization scheme is used to determine the PSD iteratively. The results suggest that 2-microm particles (possibly the mitochondria) contribute most to the scattering. Other subcellular structures, such as the nucleoli and the nucleus, may also contribute significantly. We reconstruct the PSD of the mitochondria, as verified by optical microscopy. We also demonstrate the angle dependence of the PSD.

Breast Neoplasms↗

PubMed2003

The effect of particle size on the leaching of Scirpus cubensis Poepp & Kunth.

An investigation was made on the effects of detritus particle size on leaching rates in organic matter, and the associated environmental changes caused by detritus re-cycling in an oxbow lake (Lagoa do Infernão). Experiments were conducted during the decay of an aquatic macrophyte specie, S. cubensis, which in turn led to the formation of colored compounds. The S. cubensis were collected from the Lagoa do Infernão and taken to the laboratory where they were washed, dried, and fractionated using a sieve pedological set. The detritus was classified into six groups according to size, viz. 100, 10, 1.13, 0.78, 0.61, and 0.25 mm. Overall, the fragmentation process tended to increase the detritus fraction to be dissolved and to decrease the leaching rates owing to the possible dissolution of refracting matter. Fragmentation also caused the amount of colored compounds to increase and appeared to favor dissolved electrolyte release. Finally, in Lagoa do Infernão fragmentation is probably mediated by the metabolic action of benthic communities.

Cyperaceae↗

PubMed2004

Particle size distributions of inert spheres and pelletized pharmaceutical products by image analysis.

Image analysis was used to measure particle size distributions (PSDs) of ensembles of 425 to 1400 microm-size materials. Repeatability of a measurement, suitable sample sizes, and methods of sampling were assessed. Two lots of inert spheres were compared prior to drug layering in a Glatt GPCG-5 rotor. The differences in PSD in the starting materials were reflected in the rotor-granulated products. Such detailed information was not available from sieving with U.S. standard wire mesh sieves. The products from the rotor process were polymer-coated in a Wurster process in a Glatt GPCG-3, 4-in. Wurster. The resolution of the technique was sufficient to measure differences in diameter equating to 4-microm coat thickness, which resulted from applying 2% polymer coat weight. The utility of the technique for monitoring commercial scale processes was demonstrated by measuring diameter after layering drug onto nonpareils in a Glatt RG-150 rotor, and by measuring the diameter after application of a polymer solution in a Glatt 46-in. Wurster coating process. The similarity of samples removed from the sample port in situ and samples from the batch suggested that processes in the fluid bed are intensively mixed and inherently random.

Chemistry, Pharmaceutical↗

PubMed2005

Effects of particle size, ash content, and processing pressure on the bioavailability of phosphorus in meat and bone meal for swine.

Meat and bone meal (MBM), when supplemented with tryptophan, is an excellent protein source for pigs. It is also a rich source of Ca and P, but some research has suggested that the bioavailability of P is variable. Three experiments were conducted to determine whether particle size, ash content, or processing pressure of MBM influences the bioavailability of P. Each experiment involved six replications of six treatments with individually penned pigs initially averaging 13 to 17 kg of BW. A low-P basal diet was fed with or without 0.1 or 0.2% added P (as-fed basis) from monosodium phosphate (MSP) or with three types of MBM added at levels that supplied 0.2% P (as-fed basis). The Ca level was 0.70%, and the lysine level was 0.95% in all diets. Pigs were allowed to consume their diets (meal form) on an ad libitum basis. At the end of the study, pigs were killed, and femurs and third and fourth metacarpals and metatarsals were removed for determination of breaking strength and ash content. Bone traits were regressed on added P intake for each P source, and slope-ratio procedures were used to estimate the bioavailability of P in MBM relative to that in MSP. In Exp. 1, a blended source of MBM ground to three particle sizes (amount that passed through 6-, 8-, or 12-mesh screens) was evaluated. In Exp. 2, low-ash MBM of porcine origin, high-ash MBM of bovine origin, and a 1:1 blend of the two sources were assessed. In Exp. 3, normally processed MBM was subjected to an additional 2.1 and 4.2 kg/cm2 of pressure for 20 min to determine whether excessive heat treatment would influence the bioavailability of P. Fineness of grind of MBM or processing pressure did not influence the relative bioavailability of P in this study; however, ash content of MBM affected P bioavailability. The relative availability of P in low-ash MBM of porcine origin (with composition typical of meat meal) was approximately 15 percentage units less than that in high-ash MBM of bovine origin. Overall, the bioavailability of P in MBM, relative to that in MSP, averaged 85%.

Animal Feed↗

PubMed2005

An analytical model for the dissolution of different particle size samples of Bioglass in TRIS-buffered solution.

We analyzed the early stages of reactivity of three different particle size samples of Bioglass 45S5 and a bulk sample in TRIS-buffered solution at pH 8. Ion release, measured with ion-coupled plasma emission spectroscopy, and pH variations are reported. It was demonstrated that differences in the initial surface area influence the increase in pH, the rate of elemental release, and the rate of calcium phosphate reprecipitation. In particular, a thicker Ca/P layer was obtained on larger particles. The equilibrium value of Si in solution was independent of sample form and amount of sample dissolved, and was always close to the value observed when bulk silica is dissolved at pH 8. An analytical model is proposed for cation release, based on a two-step mechanism. It was found that the early stage of dissolution was nearly diffusion controlled for larger particles and bulk samples. The second stage was similar to a first-order homogeneous dissolution. The influence of sample surface area/solution volume ratio seemed to be more complex than that proposed in the early works presented in the literature. It is suggested that variation of surface area has a significant impact on the course of the dissolution.

Biocompatible Materials↗

PubMed1989

Fat emulsion particle size: influence on the clearance rate and the tissue lipolytic activity.

In lipid emulsions for parenteral use the mean particle diameter of the droplets in the 20% emulsions is larger than in the 10% emulsions. In long-chain triglyceride emulsions it is greater than in medium-chain triglyceride emulsions. As the particle diameter decreases, the total interfacial area increases, as does the lipoprotein lipase (LPL) and hepatic lipase (HL) activity. For a given quantity of triglycerides and phospholipids the lipolytic activity is proportional to the total interfacial area. A doubling of the phospholipid concentration is accompanied by a small reduction in the activity of both enzymes. In going from long-chain to medium-chain triglycerides, there is an acceleration in the clearance rate of infused lipid. For a similar emulsion, the clearance rate decreases as the particle size decreases. It seems plausible that the larger the mean droplet diameter, the greater the participation of the reticuloendothelial system in the clearance.

Animals↗

PubMed2004

Mechanical properties of glass-ceramic A-W-polyethylene composites: effect of filler content and particle size.

Composites which comprise a bioactive filler and ductile polymer matrix are desirable as implant materials since both their biological and mechanical properties can be tailored for a given application. In the present study three-point bending was used to characterise biomedical materials composed of glass-ceramic apatite-wollastonite (A-W) particulate reinforced polyethylene (PE) (denoted as AWPEX). The effects of filler volume fraction, varied from 10 to 50 vol%, and average particle size, 4.4 and 6.7 microm, on the bending strength, yield strength, mode of fracture, Young's modulus and strain to failure were investigated. HAPEX, a commercially used composite of hydroxyapatite and polyethylene, with a 40 vol% filler content, was used for comparison. Increasing the filler content caused an increase in Young's modulus, yield strength and bending strength, and a decreased strain to failure. When filler particle size was increased, the Young's modulus, yield and bending strengths were found to be slightly reduced. A transition in fracture behaviour from ductile to brittle behaviour was observed in samples containing between 30 and 40 vol% filler.

Apatites↗

PubMed2001

ApoE polymorphism in a small Mediterranean island: relationships with plasma lipids, lipoproteins and LDL particle size.

Polymorphisms of apoE gene are able to modulate lipoprotein metabolism at different steps and to influence LDL-cholesterol (LDL-C) levels and also other lipoproteins features. Population studies documented large differences in the frequency of apoE alleles which could be even related to the prevalence of cardiovascular disease. In this study we evaluated the apoE genotypes and allele frequency in 576 subjects living in a small island in the Tyrrhenian Sea and the relative contribution of apoE polymorphism on plasma lipid and lipoprotein profile, including LDL particle size. We found a cumulative frequency of 0.073, 0.866 and 0.061 for epsilon2, epsilon3 and epsilon4 alleles respectively. Moreover epsilon3 subjects had only triglyceride levels significantly lower and LDL-C and lipoprotein (a) (Lp(a)) levels higher than epsilon2 carriers. LDL-particle size was significant smaller in epsilon2 subjects than both epsilon3 and epsilon4 carriers, but the difference disappeared when data were adjusted for triglycerides. In conclusion we have provided further evidence of a low prevalence of epsilon4 allele in a Mediterranean population which may represent a genetic protective factor of these populations. Environmental factors, such as diet, occurring in this area may have attenuated the influence of this gene on plasma lipoproteins.

Adult↗

PubMed1991

Effects of dietary glucose or fructose on the secretion rate and particle size of triglyceride-rich lipoproteins in Zucker fatty rats.

Effects of dietary carbohydrate on the secretion rate and particle size of triglyceride-rich lipoproteins were examined in Zucker fatty rats fed fructose and glucose and were compared with those of Zucker lean rats. Carbohydrates were supplied as 10% drinking solutions for 14 days. As compared with lean rats, Zucker fatty rats had hyperinsulinemia and hypertriglyceridemia associated with an increased rate of triglyceride secretion into the circulation. Feeding fructose and glucose to fatty rats produced an increase in plasma glucose levels, whereas plasma insulin concentrations did not show significant changes. Neither fructose nor glucose supplementation produced significant changes in the rate of triglyceride secretion. Despite this, plasma triglyceride concentrations in fructose-fed fatty rats were twice as high as those in glucose-fed rats or those receiving no supplementary carbohydrate. Particle diameters of lipoproteins of density between 0.96 and 1.006 were larger in fructose-fed fatty rats than in those receiving no sugar. The results suggest that feeding fructose, but not glucose, into fatty rats is associated with an impairment of triglyceride removal and a resultant increase in plasma triglyceride concentration, the latter of which is accompanied by an increase in triglyceride contents in each particle.

Animals↗

PubMed2003

[Effect of particle size distribution of dental poly (methyl methacrylate) beads on the microstructure of denture].

OBJECTIVES: To investigate the effect of particle size distribution (PSD) of dental poly (methyl methacrylate) (PMMA) beads on the microstructure of denture. METHODS: It was compared and analyzed that the porosity of three groups of spherical specimens which were made of PMMA beads with different PSD at proper polymer/monomer ratios. And the final microstructure of each group was investigated using Digital High Definition Microscope. RESULTS: With proper polymer/monomer ratio increasing, the occurrence of porosity tended to decrease. The final microstructure of denture varied with PSD of PMMA beads. CONCLUSION: By means of optimizing PSD of beads, the microstructure of denture could be improved, and the occurrence of porosity could be reduced.

Dental Materials↗

PubMed2006

Clearance of iron oxide particles in rat liver: effect of hydrated particle size and coating material on liver metabolism.

OBJECTIVES: We sought to evaluate the effect of the particle size and coating material of various iron oxide preparations on the rate of rat liver clearance. MATERIALS AND METHODS: The following iron oxide formulations were used in this study: dextran-coated ferumoxide (size = 97 nm) and ferumoxtran-10 (size = 21 nm), carboxydextran-coated SHU555A (size = 69 nm) and fractionated SHU555A (size = 12 nm), and oxidized-starch coated materials either unformulated NC100150 (size = 15 nm) or formulated NC100150 injection (size = 12 nm). All formulations were administered to 165 rats at 2 dose levels. Quantitative liver R2* values were obtained during a 63-day time period. The concentration of iron oxide particles in the liver was determined by relaxometry, and these values were used to calculate the particle half-lives in the liver. RESULTS: After the administration of a high dose of iron oxide, the half-life of iron oxide particles in rat liver was 8 days for dextran-coated materials, 10 days for carboxydextran materials, 14 days for unformulated oxidized-starch, and 29 days for formulated oxidized-starch. CONCLUSIONS: The results of the study indicate that materials with similar coating but different sizes exhibited similar rates of liver clearance. It was, therefore, concluded that the coating material significantly influences the rate of iron oxide clearance in rat liver.

Animals↗

PubMed1991

The effect of particle size reduction on the jaw gape in human mastication.

Eight subjects participated in chewing experiments to examine how the jaw gape in consecutive chewing cycles depends on the dimensions and the volume of the food bolus. Different volumes of chewing-gum and a silicone rubber (Optosil) were used. The initial particle size of Optosil was also varied. With the aid of a sieving procedure, the size distribution of Optosil particles was determined after different numbers of chewing cycles. The maximum size of a chewing-gum bolus along three orthogonal axes was determined after a random number of chewing cycles for all the volumes of chewing-gum offered. The jaw gape was measured by means of an optical motion analysis system and calibrated at the level of the first molars. The maximum jaw gape and the gape at the first fall in mandibular velocity after the onset of jaw-closing were determined for different chewing cycles from the position signal and its time derivative. For each volume of chewing gum offered to the subject, the average of the maximum gapes attained in the subsequent cycles of jaw movement was related to the characteristic height of a bolus of that volume; maximum velocity of closing appeared to occur while the antagonistic teeth were already penetrating the gum bolus. The increase in the maximum jaw gape, the gape at the velocity maximum, and the height of the gum bolus, as a function of the volume of chewing-gum, could be well-described by a power function of the volume. The exponent of the power function for both jaw gapes was only slightly smaller than the exponent obtained for the bolus height.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1991

Effect of fiber content and particle size of alfalfa silage on performance and chewing behavior.

A low NDF drought-stressed 1988 alfalfa silage (32.6% NDF) and a higher fiber 1988 alfalfa silage (46.4% NDF) were fed to lactating cows to evaluate effects on feed intake, fat test, and chewing behavior. Two groups of Holstein cows, 16 primiparous housed in tie stalls and 16 multiparous in free stalls, were assigned to diets based on parity and milk yield. The low NDF silage was fed for 6 wk in a TMR with 21.5% NDF and was compared with a TMR with 31.9% NDF. During an additional 4-wk period, one-half of each dietary group was fed a ration in which one-half of each silage was rechopped to reduce particle size. All rations contained a 1:1 ratio of forages to concentrates (DM basis) and were fed for ad libitum intake. Diets with 21.5% NDF and reduced particle size had no influence on milk fat percentage, 4% FCM yield, or plasma glucose. Cows fed these diets had reduced chewing time, due largely to decreased rumination time. Rumination and total chewing times per unit DMI and FCM also were lowest on these diets. Intake of DM on a BW basis was lowest for cows fed the low NDF rechopped silage diet. Cows fed in tie stalls had more eating bouts than those in free stalls, but total eating times were similar. Sufficient amounts of effective fiber appeared to be present in low NDF and rechopped silage diets to prevent the systemic events leading to milk fat depression but not to prevent a reduction in chewing time.

Animals↗

PubMed2004

Particle size analysis: AAPS workshop report, cosponsored by the Food and Drug Administration and the United States Pharmacopeia.

The concepts of particle engineering and dosage form design have become dominant themes in pharmaceutical manufacturing. This trend is not simply a reflection of the development of new, more sophisticated manufacturing methods of particles or dispersed systems but also recognition of the importance of quality control even in more traditional manufacturing processes. However, the diversity of particle treatments, methods of particle size analysis, expression and interpretation of data, and process applications results in complicated and sometimes confusing criteria for selection, adoption, or relevance of the available techniques.

Particle Size↗

PubMed1984

Particle size analysis of microcapsules.

To standardize the preparation of three-walled w/o/w microcapsules it was necessary to assess their particle size distribution, since they occur as both unicored and multicored types. The log-normal law, reported to be obeyed by many particulate systems, including microcapsules, was not applicable to the size data. A curve-fitting computer program using least squares minimization was used to assess the size distribution data. The models tested were the unimodal and bimodal log-normal distributions, the bimodal form being the most appropriate. Using the equations to the curves of best fit, the modal size and standard deviation of each population were estimated, and the relative percentages of unicored and multicored microcapsules could be deduced from an analysis of the bimodal curves in which they were represented as the sum of two constituent unimodal distributions.

Acacia↗

PubMed1998

Exposure to dust and its particle size distribution in California agriculture.

The aim of this study was to measure personal dust exposure levels and the dust particle size distribution during various agricultural operations in California. Personal dust exposure levels were measured with four-stage cascade impactors and respirable dust cyclones during field crop, fruit and nut farming, and dairy operations at three farms. Altogether, 103 cascade impactor measurements and 108 cyclone measurements were taken. High personal dust exposure levels were measured during various operations in particular during ground preparation operations such as land planing (geometric mean [GM] = 57.3 mg/m3, geometric standard deviation [GSD] = 2.4) and discing (GM = 98.6 mg/m3, GSD = 2.9). Dust particles were relatively large and the great majority belonged to the extrathoracic fraction. Dust levels were considerably lower when an enclosed cabin was present on the tractor; for example, during discing, dust exposure levels were reduced more than sixtyfold for the larger dust particle fraction and more than fourfold for the respirable dust fraction.

Agriculture↗

PubMed2006

Phase behavior and particle size cutoff effects in polydisperse fluids.

We report a joint simulation and theoretical study of the liquid-vapor phase behavior of a fluid in which polydispersity in the particle size couples to the strength of the interparticle interactions. Attention is focused on the case in which the particle diameters are distributed according to a fixed Schulz form with degree of polydispersity delta = 14%. The coexistence properties of this model are studied using grand canonical ensemble Monte Carlo simulations and moment free energy calculations. We obtain the cloud and shadow curves as well as the daughter phase density distributions and fractional volumes along selected isothermal dilution lines. In contrast to the case of size-independent interaction [N. B. Wilding et al., J. Chem. Phys. 121, 6887 (2004)], the cloud and shadow curves are found to be well separated, with the critical point lying significantly below the cloud curve maximum. For densities below the critical value, we observe that the phase behavior is highly sensitive to the choice of upper cutoff on the particle size distribution. We elucidate the origins of this effect in terms of extremely pronounced fractionation effects and discuss the likely appearance of new phases in the limit of very large values of the cutoff.

Journal Article↗

PubMed1991

Blood glucose, plasma insulin and sensory responses to guar-containing wheat breads: effects of molecular weight and particle size of guar gum.

The effectiveness of guar gum in reducing post-prandial blood glucose and plasma insulin levels in human subjects seems to depend mainly on its ability to increase the viscosity of digesta in the small intestine. However, the precise relationship between the rheological properties of guar gum (either in vitro or in vivo) and the changes in blood metabolites and hormones is unknown. The aim of the present study, therefore, was to investigate the effects of wheat breads containing guar gum samples varying in molecular weight (Mw) and particle size (characteristics that strongly influence the rheological properties of guar gum) on post-prandial blood glucose and plasma insulin levels in healthy subjects. The sensory qualities of breads containing guar-gum flours of different Mw were also evaluated using a hedonic scoring technique. No significant differences in the post-prandial blood glucose responses were found between the control and guar breads. However, all the guar breads elicited significant (P less than 0.05) decreases in the post-prandial rise in plasma insulin, an effect that did not appear to be influenced by large variations in Mw or particle size of guar gum. Moreover, the sensory qualities of guar bread were markedly improved by using low Mw grades of guar gum.

Adolescent↗