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PubMed2007

Reconstruction of particle-size distributions from light-scattering patterns using three inversion methods.

By means of a numerical study we show particle-size distributions retrieved with the Chin-Shifrin, Phillips-Twomey, and singular value decomposition methods. Synthesized intensity data are generated using Mie theory, corresponding to unimodal normal, gamma, and lognormal distributions of spherical particles, covering the size parameter range from 1 to 250. Our results show the advantages and disadvantages of each method, as well as the range of applicability for the Fraunhofer approximation as compared to rigorous Mie theory.

Journal Article↗

PubMed1968

Particle size distribution of Serratia marcescens aerosols created during common laboratory procedures and simulated laboratory accidents.

Andersen air samplers were used to determine the particle size distribution of Serratia marcescens aerosols created during several common laboratory procedures and simulated laboratory accidents. Over 1,600 viable particles per cubic foot of air sampled were aerosolized during blending operations. More than 98% of these particles were less than 5 mu in size. In contrast, 80% of the viable particles aerosolized by handling lyophilized cultures were larger than 5 mu. Harvesting infected eggs, sonic treatment, centrifugation, mixing cultures, and dropping infectious material produced aerosols composed primarily of particles in the 1.0- to 7.5-mu size range.

Accidents↗

PubMed2004

Electrophoretic microrheology of a dilute lamellar phase: relaxation mechanisms in frequency-dependent mobility of nanometer-sized particles between soft membranes.

Viscoelastic properties of complex fluids in the microscopic scale can be studied by measuring the transport properties of small, embedded probe particles. We have measured the complex electrophoretic mobility micro*(omega) of nanometer-sized particles dispersed in a lyotropic lamellar phase, which shows two relaxation processes at approximately 1 kHz (high frequency relaxation, HF) and 1 Hz (low frequency relaxation, LF). It is shown quantitatively that these processes are caused by the trapping of particles within two local structures of characteristic size in the lamellar phase: the interbilayer distance and the persistence length. The origin of observed relaxations is further investigated and augmented in this study with data obtained by two other complementary methods, dielectric spectroscopy and the direct observation of fluorescently labelled probe particles under an optical microscope. It is shown that the local distortion field of the lamellar phase is induced by the extra steric interaction involving the collision of a colloidal particle with the membrane. The resulting distortion field hinders the Brownian motion of colloidal particles parallel to the membranes (not vertical), and causes the observed HF relaxation. On the other hand, the origin of LF relaxation is presumably a result of the defects in the lamellar structure. Since the results of this study show that the transport property is strongly influenced by microscopic environments, this method is referred to as electrophoretic microrheology.

Colloids↗

PubMed2007

Effect of particle size of an amorphous calcium phosphate filler on the mechanical strength and ion release of polymeric composites.

The random clustering of amorphous calcium phosphate (ACP) particles within resin matrices is thought to diminish the strength of their polymerized composites. The objective of this study was to elucidate the effect of ball-milling on the particle size distribution (PSD) of ACP fillers and assess if improved dispersion of milled ACP in methacrylate resin sufficiently enhanced filler/matrix interactions to result in improved biaxial flexure strength (BFS), without compromising the remineralizing potential of the composites. Unmilled and wet-milled zirconia-hybridized ACP (Zr-ACP) fillers were characterized by PSD analysis, X-ray diffraction, thermogravimetric and chemical analysis, infrared spectroscopy, and scanning electron microscopy. Composite specimens made from a photoactivated, ternary methacrylate resin admixed with a mass fraction of 40% of un-milled or milled Zr-ACP were evaluated for the BFS (dry and wet) and for the release of calcium and phosphate ions into saline solutions. While having no apparent effect on the structure, composition, and morphology/topology of the fillers, milling significantly reduced the average size of Zr-ACP particulates (median diameter, d(m) = 0.9 +/- 0.2 microm) and the spread of their PSD. Better dispersion of milled Zr-ACP in the resins resulted in the improved BFS of the composites, even after aqueous soaking, and also gave a satisfactory ion release profile. The demonstrated improvement in the mechanical stability of anti-demineralizing/remineralizing ACP composites based on milled Zr-ACP filler may be beneficial in potentially extending their dental utility.

Calcium Phosphates↗

PubMed1993

Effects of forage species and particle size on bacterial cellulolytic activity and colonization in situ.

Two ruminally cannulated Holstein heifers were used to evaluate effects of three forage species and two particle sizes in a 3 x 2 factorial arrangement on in situ fiber disappearance and carboxymethylcellulase activity (CMCase). A second objective was to compare CMCase and 15N as relative bacterial colonization markers. At time zero, 15N-enriched ammonium sulfate was dosed into the rumen. Residues in nylon bags incubated for 3, 6, 9, 12, 18, 24, 30, 36, 42, 48, 60, and 72 h were analyzed for NDF, ADF, CMCase, and 15N. Rates of NDF and ADF disappearance were faster (P < .05) for red clover (RC) than for gamagrass (GG) or orchardgrass (OG) and for forages ground to pass a 2-mm screen (P < .05) than for those ground to pass a 5-mm screen. Cumulative area under the curve (AUC) of CMCase activity was related to both NDF disappearance (r2 = .93) and 15N AUC (r2 = .99), indicating that CMCase can be used to estimate relative colonization of cellulolytic particle-associated bacteria (PAB). During the first 18 h of incubation, RC had greater (P < .05) CMCase and 15N enrichment of in situ residues than did OG or GG. The RC residues also had a greater (P < .05) ratio of CMCase activity:15N enrichment; this was presumed to indicate that, during this time, RC supported a greater total PAB population and had a greater proportion of cellulolytic PAB than did either GG or OG. Differences in the colonization rate of forage particles by cellulolytic PAB relative to total PAB may account for differences in rate of fiber digestion.

Animal Feed↗

PubMed2004

[The effect of particle size and amount of inhalation on the pulumonary function testsn in asthmatic children].

The effect of three nebulizers, Nisshou and LC plus, were compared by the particle size and amount of inhalation. The improvement of FEV1 at 15 minutes after the inhalation was significantly higher in LC plus than Nisshou (MMD: 7.43microm, 10.76microm). The amount of inhlation were compared between Nisshou with/without Y tube and LC plus nebulizer with/without LC valve system. Nisshou nebulizer with Y tube and LC plus nebulizer with LC valve systems were significantly better than that of LC plus nebulizer without LC valve system. Small loss of inhalation gave us better efficacy. The urinary excretion of disodium cromoglycate (DSCG) was highest in LC plus with LC valve system, Nisshou with Y tube and lowest in Nisshou without Y tube. The elecctric nebulizers produced better in MMD of 5microm and a smaller loss of inhalation. These results suggested that MMD less than 5microm and small loss from nebulizer are very important for inhalation therapy.

Administration, Inhalation↗

PubMed2006

Effect of the particle size of galactosylated lipoplex on hepatocyte-selective gene transfection after intraportal administration.

The purpose of this study was to examine the effect of the size of galactosylated cationic liposome (Gal-liposome)/plasmid DNA complex (Gal-lipoplex) on hepatocyte-selective gene transfection after intraportal administration. pCMV-Luc was selected as a model plasmid DNA. After intraportal administration of Gal-lipoplex to mice, the hepatic and intrahepatic gene expression was evaluated. To evaluate the effect of size, three different sizes of Gal-liposome were prepared. The mean particle sizes of Gal-lipoplex were about 141, 179, and 235 nm, respectively. The hepatic transfection efficacy was significantly enhanced by increasing the size of Gal-lipoplex. However, the gene expression in liver parenchymal cells (PC) of Gal-lipoplex of about 141 nm in size was significantly higher than that in liver non-parenchymal cells (NPC). In contrast, gene expression in PC of Gal-lipoplex of about 235 nm in size was significantly lower than that in NPC. These results highlight the importance of the Gal-lipoplex size for hepatocyte-selective gene transfer in vivo. The information in this study will be valuable for the future use, design, and development of Gal-lipoplex for in vivo applications.

Animals↗

PubMed2000

Submicron-size particles of ultrahigh molecular weight polyethylene produced via nonsolvent and temperature-induced crystallization.

Submicrometer size particles of ultrahigh molecular weight polyethylene (UHMWPE) were produced by crystallization from dilute (0.1-1.0 wt % of UHMWPE) solvent/nonsolvent emulsions. The procedure consisted of mixing a hot solution of UHMWPE in decalin or decane with a nonsolvent (tetraglyme) at approximately 160 degrees C, followed by rapid cooling of the mixture to zero or subzero temperatures. The rapid cooling causes microphase separation between the two liquids, resulting in the formation of an emulsion, which consists of microdroplets of the supercooled UHMWPE solution dispersed in tetraglyme. The consequent crystallization of the polymer in the microdroplets produces a suspension of fine crystals of UHMWPE, which can easily be isolated. The particles were characterized using scanning electron microscopy, differential scanning calorimetry, and Raman spectroscopy. Their degree of crystallinity is between that of GUR 1050 original (powder) and processed (molded) polymer. By changing the polymer concentration, solvent to nonsolvent ratio, and temperature, the size (from 0.1-1.0 microm) and shape (spheroids or rods) of the particles can be controlled. These particles may be used for immunochemical investigations and the study of the influence of UHMWPE wear debris on cell response.

Biocompatible Materials↗

PubMedDate not supplied

[Distribution of subfractions of high-density lipoproteins during their separation according to hydrated density and particle size].

Distribution of high density lipoprotein (HDL) subfractions was studied by means of gradient ultracentrifugation depending on their hydration density and using electrophoresis in gradient polyacrylamide gel according to the particles size. 53 men were examined, where 43 patients were impaired with ischemic heart disease and with atherosclerosis of coronary arteries documented by angiography. In all the patients with ischemic heart disease and dislipoproteinemias distribution of the HDL particles was altered towards a decrease in amount of HDL2b particles; at the same time, loading with cholesterol of the HDL3 subfraction was lowered. The alterations in the subfraction spectrum and composition of HDL observed in the patients with the ischemia and coronary atherosclerosis appear to exhibit the atherogenous impairments in cholesterol elimination from arterial wall.

Centrifugation, Density Gradient↗

PubMed2006

Effect of particle size on the oxidizability of platinum clusters.

The catalytic properties of transition metal particles often depend crucially on their chemical environment, but so far, little is known about how the effects of the environment vary with particle size, especially for clusters consisting of only a few atoms. To gain insight into this topic, we have studied the oxygen affinity of free Pt(x) clusters as a function of cluster size (x = 1, 2, 3, 4, 5, and 10) using density functional theory (DFT) calculations (GGA-PW91). DFT-based Nosé-Hoover molecular dynamics has been used to explore the configuration space of the Pt(x)O(x) and Pt(x)O(2x) clusters, leading to the discovery of several novel Pt-oxide structures. The formation of small Pt-oxide clusters by oxidizing the corresponding Pt(x) clusters is found to be significantly more exothermic than the formation of bulk Pt-oxides from Pt metal. The exothermicity generally increases as cluster size decreases but exhibits strongly nonlinear dependence on the cluster size. The nanoclusters are also structurally distinct from the bulk oxides and prefer one- and two-dimensional chain and ringlike shapes. These findings help elucidate the oxidation behavior of Pt nanoclusters and lay the foundation for understanding the reactivity of Pt nanoclusters in oxidizing chemical environments.

Journal Article↗

PubMed2001

In vitro uptake of polystyrene microspheres: effect of particle size, cell line and cell density.

Uptake of polycation-DNA particles is the first step in achieving gene delivery with non-viral vehicles. One of the important characteristics determining uptake of DNA particles is their size. Here we have characterized the ability of several cell lines to internalise labelled polystyrene microspheres of different sizes. All the cell lines tested ingested 20-nm microspheres avidly. With larger microspheres (93, 220, 560 and 1010 nm) cell type as well as growth related differences were observed. Whereas some cell lines (HUVEC, ECV 304 and HNX 14C) took up microspheres up to 1010 nm even when the cells were confluent, others did not take up many microspheres larger than 93 nm (Hepa 1-6 and HepG2). In one cell line (KLN 205), uptake of 93-, 220- and 560-nm microspheres was avid in growing cells, but not detectable when they were confluent. In KLN 205 cells, a good correlation was found between the uptake of 560-nm microspheres and the uptake of a peptide-DNA polyplex formulation, when it was prepared under conditions leading to small particle sizes. Little correlation was found when the polyplex formulation was allowed to aggregate.

Amino Acid Sequence↗

PubMed1996

Zeta potential measurement and particle size analysis for a better understanding of urinary inhibitors of calcium oxalate crystallization.

To better understand urinary inhibitors of calcium oxalate crystallization, both zeta potential measurement and particle size analysis were chosen to illustrate: (1) the potential therapeutic efficacy of G872, a semi-synthetic sulfated polysaccharide, in stone prevention; and (2) the relative contribution of various urinary fractions ¿e.g., ultrafiltered urine (UFU), Tamm-Horsfall protein (THP), urinary polyanions precipitated with cetylpyridinium chloride (CPC), urinary macromolecular substances with different concentration ratios (UMS10,50,90 and UMS'10,50,90) and THP-free urine (THPFU)¿ to total urinary inhibitory activity. The results showed: (1) addition of G872 significantly enhances urinary inhibitory activity and negative zeta potential values; (2) re-addition of the CPC to UFU completely restores urinary inhibitory activity; and (3) artificial urines prepared by mixing UMS'10,50,90 from THPFU with UFU differed in inhibitory activity from that prepared by mixing UMS10,50,90 from a pooled normal urine with UFU. Based on these experimental results, the following speculations can be made: (1) normal human urines are considered to be a protective colloidal system; (2) urinary inhibitory activity originates mainly from CPC and/or UMS; (3) normal THP is a protective material to maintain urinary inhibitory activity; and (4) mutual interaction between urinary inhibitors may change the total urinary inhibitory activity.

Calcium Oxalate↗

PubMed2001

Amoxicillin-loaded polyethylcyanoacrylate nanoparticles: influence of PEG coating on the particle size, drug release rate and phagocytic uptake.

Polyethyleneglycol (PEG)-coated polyethylcyanoacrylate (PECA) nanoparticles loaded with amoxicillin were prepared and the influence of the PEG coating on the particle size, zeta potential, drug release rate and phagocytic uptake by murine macrophages was studied. Experimental results show that this colloidal drug delivery system could be useful for intravenous or oral administration. The profile of amoxicillin release from PECA nanoparticles system was studied under various conditions similar to those of some corporeal fluids. In all these experiments, amoxicillin release in the free form was studied by HPLC analysis. Experimental results showed that at pH 7.4 drug release rises when molecular weight of PEG added to polymerization medium increases; in human plasma on the contrary drug release is reduced as molecular weight of PEG rises. Phagocytosis was evaluated by incubating amoxicillin-loaded PECA nanoparticles with murine macrophages and determining the amount of phagocytized nanoparticles by dosing the amoxicillin present inside the macrophages. The results of this study showed significative differences between nanoparticles prepared in the presence or in the absence of PEG and demonstrated that the PEG coating reduces the macrophages uptake. These results suggest that nanoparticles prepared in the presence of PEG are stealth carriers, which could be an injectable colloidal system able to avoid MPS recognition after intravenous injection. Experimental data of drug release at pH 1.1 and in the presence of urease, taking into account the mucoadhesive properties of polyalkylcyanoacrylate nanoparticles and the activity of the amoxicillin versus Helicobacter pylori, suggest moreover that the colloidal drug delivery system obtained in our laboratory could be useful for the treatment of diseases caused by H. pylori by peroral administration.

Amoxicillin↗

PubMedDate not supplied

Pressure distribution using tissue conditioners on simplified edentulous ridge models. Part 2: The influence of the powder particle size and ethanol content.

The distribution of pressure changes over time at the denture periphery and the residual ridge crest were measured to evaluate the influence of powder particle size and ethanol content in liquid of tissue conditioners used for a dynamic impression technique. The study suggested that the shrinkage of tissue conditioners over time influenced the adaptation at the denture periphery when the components of tissue conditioners were varied for use as a dynamic impression material.

Dental Impression Materials↗

PubMed2002

Influence of particle size on extrapleural talc dissemination after talc slurry pleurodesis.

BACKGROUND: Cases of acute respiratory failure reported after talc pleurodesis have raised concerns about its safety. It has been speculated that this pulmonary inflammatory syndrome is secondary to the extrapleural dissemination of the talc particles. STUDY OBJECTIVES: To test the hypothesis that particle size influences extrapleural talc deposition and pleural inflammation after talc slurry pleurodesis. DESIGN: Thirty rabbits underwent pleurodesis as follows: 10 rabbits received 200 mg/kg of the talc used for human pleurodesis, normal talc (NT); 10 rabbits received 200 mg/kg of talc with particles of larger size, large talc (LT); and 10 rabbits received saline solution. Samples from the ipsilateral lung, chest wall, diaphragm, mediastinal pleura, heart, liver, spleen, and right kidney were obtained at 24 h and 7 days and processed for optic and electron microscopy and energy-dispersive x-ray analysis. RESULTS: Visceral pleural thickening was greater with NT than with LT, but no differences were observed in the macroscopic score of adhesions. There was more talc in the lungs of the rabbits that received NT than in those that received LT. Talc particles were detected in mediastinum (100%) and pericardium (20%), irrespective of the talc used. Three animals, all receiving NT, had talc particles in the liver. CONCLUSIONS: Our study shows that while both talcs were equally effective in achieving pleurodesis, the intrapleural injection of NT elicits greater pulmonary and systemic talc particle deposition than LT. Moreover, pleural inflammation was greater with NT than with LT.

Animals↗

PubMed2002

Whole-body insulin sensitivity, low-density lipoprotein (LDL) particle size, and oxidized LDL in overweight, nondiabetic men.

Insulin resistance is often accompanied by elevated plasma triglycerides (TG) and a preponderance of small, dense low-density lipoprotein (LDL) particles. However, it remains unclear whether or not insulin resistance is related to LDL particle size, independent of plasma TG. We sought to determine the strength of the relationships among these variables in a group of overweight, nondiabetic men (N = 34; body mass index [BMI], 25 to 35 kg/m(2); age, 50 to 75 years), as well as to examine the possible relation between insulin sensitivity and oxidized LDL (oxLDL). We also examined the strength of the relationships between these lipid variables and estimates of insulin sensitivity using calculated indices based on fasting insulin and glucose concentrations. Insulin sensitivity (Si) was significantly associated with total TG (r = -0.61, P <.001), very-low-density lipoprotein (VLDL)-TG (r = -0.60, P <.001), and LDL size (r =.414, P <.05). LDL size was also significantly associated with TG (r = -0.73, P <.001), VLDL-TG (r = -0.73, P <.001), high-density lipoprotein-cholesterol (HDL-C) (r = 0.65, P <.001), the quantitative insulin sensitivity check index (QUICKI) (rho = 0.46, P <.01), and the homeostatic model for the assessment of insulin resistance (HOMA-IR) (rho = -0.45, P <.01). Si was a significant predictor of LDL size, with age and BMI also independent contributors to the variance in LDL size (R(2) = 0.172). However, when TG and HDL-C were added to the model, Si was no longer a significant predictor of LDL size. The correlation between Si and oxLDL was weak, but stastically significant (rho = -0.40, P =.02). These data suggest that the relation between Si and LDL size is largely mediated by plasma TG, and that Si is only weakly related to oxLDL in overweight, nondiabetic men.

Aged↗

PubMed2000

The conformation of apolipoprotein A-I in high-density lipoproteins is influenced by core lipid composition and particle size: a surface plasmon resonance study.

Plasma high-density lipoproteins (HDL) are a heterogeneous group of particles that vary in size as well as lipid and apoprotein composition. The effect of HDL core lipid composition and particle size on apolipoprotein (apo) A-I structure was studied using surface plasmon resonance (SPR) analysis of the binding of epitope-defined monoclonal antibodies. The association and dissociation rate constants of 12 unique apo A-I-specific monoclonal antibodies for isolated plasma HDL were calculated. In addition, the association rate constants of the antibodies were determined for homogeneous preparations of spherical reconstituted HDL (rHDL) that contained apo A-I as the sole apolipoprotein and differed either in their size or in their core lipid composition. This analysis showed that lipoprotein size affected the conformation of domains dispersed throughout the apo A-I molecule, but the conformation of the central domain between residues 121 and 165 was most consistently modified. In contrast, replacement of core cholesteryl esters with triglyceride in small HDL modified almost the entire molecule, with only two key N-terminal domains of apo A-I being unaffected. This finding suggested that the central and C-terminal domains of apo A-I are in direct contact with rHDL core lipids. This immunochemical analysis has provided valuable insight into how core lipid composition and particle size affect the structure of specific domains of apo A-I on HDL.

Antibodies, Monoclonal↗

PubMed1975

Influence of particle size on rectal absorption of aspirin.

The rectal absorption of aspirin from theobroma oil suppositories was studied in seven human subjects using urinary excretion measurements. The effect of particle size on the excretion rate and cumulative amount of total salicylate excreted was demonstrated by the administration of a 600-mg dose as powdered aspirin and as aspirin disks having 0.023 as much surface as powdered aspirin. In vitro dissolution profiles of aspirin from the suppositories were studied. By the NF XIII Method II, the time required for 50% of the aspirin to dissolve from the suppository was 50 and 100 min for the powdered aspirin and the aspirin disks, respectively. In the bioavailability study, the diffusion equilibrium was attained at approximately 4-5 and 9-10 hr after the rectal administration of powdered aspirin and aspirin disks, respectively. No correlation was found between bioavailability and the dissolution profiles as determined by the USP XVIII dissolution method.

Adult↗