SEARCH · PubMed Health

Results for “Particle Size”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 667 records · Page 37Linked to original sources

PubMed2006

Addition of pectin and soy soluble polysaccharide affects the particle size distribution of casein suspensions prepared from acidified skim milk.

Pectins are negatively charged polysaccharides employed as stabilizers in acidified milk dispersions, where caseins aggregate because of the low pH and serum separation needs to be prevented. The objective of this research was to study the effect of charge on the stabilizing functionality of the polysaccharide in acid milk drinks. Unstandardized pectins with various charges (as degree of esterification, DE) as well as soybean soluble polysaccharide (SSPS) were tested for their stabilizing behavior as a function of pH and concentration. Skim milk was acidified by glucono-delta-lactone and then homogenized in the presence of polysaccharide at different pH values (in the range from 4.2 to 3.0). Measurements of particle size distribution demonstrated that pectins with a DE of 71.4, 68.6, and 67.4 stabilized milk at pH > 4.0. Pectins with a lower DE (63.9%) needed a higher concentration (0.4%) at the same pH to show a monomodal distribution of particle sizes. Pectins with lower DE (<50%) did not stabilize the dispersions. Although this difference in behavior was attributed mainly to the pectin charge, the efficiency in stabilizing the casein dispersion decreased with decreasing pectin size. For example, the high methoxyl pectin (HMP) with 63.9 DE was smaller in size than the HMPs with a higher charge. Pectins showed a pH-dependent stabilization effect, as at pH < 4.0 the dispersions contained aggregates. When SSPS was used to stabilize acid milk, at pH < 4.0, it showed a better stabilization behavior than HMP. When SSPS and pectin were used in combination, the particle size distribution of the acid milk dispersion was pH-dependent, and results were similar to those for samples containing pectin alone. This suggested that in the mixture, pectin dominated the behavior over SSPS, even when an excess of SSPS was added to the dispersions before homogenization.

Animals↗

PubMed1982

Segmental replacement of the femur in baboons with fiber metal implants and autologous bone grafts of different particle size.

A study was made of bone ingrowth into fiber metal composite prostheses used to replace large segments of the femur in baboons. Bone grafts of two different types were used to cover the segment: chips of bone with large particle size and ground bone with a smaller particle size. The prosthetic segment was bridged by bone at 3 and 6 months in all cases irrespective of the structure of the transplant. In animals sacrificed at 6 months bone ingrowth occurred, with a marked difference between specimens with the two different grafts. In the ground bone specimens ingrowth occurred over the total surface area, and bone penetrated deep into the composite. With the chip grafts ingrowth was more irregular occurring only in some areas and it was always superficial. The difference is believed to be due to the improved contact between the fiber metal surface and the transplant. The lesser bulk of the ground transplant is advantageous when the soft tissue cover of the bone is thin.

Alloys↗

PubMed1980

Particle size distribution of hydrocyanic acid in gari, a cassava-based product.

A reciprocal relationship was observed between the cyanide content of gari and particle size. Hydrocyanic acid (HCN) content was positively correlated (r = 0.62) with sugar content but the correlation with starch content was poor (r = 0.33). From both the nutritional and toxicological standpoints, it would appear that larger particles size in gari is beneficial.

Food Analysis↗

PubMed2002

Particle size effect on structure and properties of dispersed Pd-containing dental amalgam.

Focus of the study is to evaluate the effect of dispersant particle size on the structure and various properties of spherical matrix, irregular dispersant admixed type Pd amalgams. The results indicate that amalgams prepared from smaller dispersant particles have a shorter setting time (faster amalgamation reaction), smaller setting expansion, higher eta' content and lower early stage gamma2 content. Smaller dispersant particles also lead to a slightly higher compressive strength, lower creep value, more cathodic corrosion potential and less early stage mercury vapor release. The particle size effect on corrosion current density and chemical composition of gamma1 phase in aged amalgam is less significant.

Corrosion↗

PubMed2006

Effect of physical state and particle size distribution on dissolution enhancement of nimodipine/PEG solid dispersions prepared by melt mixing and solvent evaporation.

The physical structure and polymorphism of nimodipine were studied by means of micro-Raman, WAXD, DSC, and SEM for cases of the pure drug and its solid dispersions in PEG 4000, prepared by both the hot-melt and solvent evaporation methods. The dissolution rates of nimodipine/PEG 4000 solid dispersions were also measured and discussed in terms of their physicochemical characteristics. Micro-Raman and WAXD revealed a significant amorphous portion of the drug in the samples prepared by the hot-melt method, and that saturation resulted in local crystallization of nimodipine forming, almost exclusively, modification I crystals (racemic compound). On the other hand, mainly modification II crystals (conglomerate) were observed in the solid dispersions prepared by the solvent evaporation method. However, in general, both drug forms may appear in the solid dispersions. SEM and HSM microscopy studies indicated that the drug particle size increased with drug content. The dissolution rates were substantially improved for nimodipine from its solid dispersions compared with the pure drug or physical mixtures. Among solid dispersions, those resulting from solvent coevaporation exhibited a little faster drug release at drug concentrations lower than 20 wt%. Drug amorphization is the main reason for this behavior. At higher drug content the dissolution rates became lower compared with the samples from melt, due to the drug crystallization in modification II, which results in higher crystallinity and increased particle size. Overall, the best results were found for low drug content, for which lower drug crystallinity and smaller particle size were observed.

Drug Compounding↗

PubMed1999

Reproducible Preparation of Silver Sols with Small Particle Size Using Borohydride Reduction: For Use as Nuclei for Preparation of Larger Particles.

Silver colloids are useful as substrates for surface enhanced Raman spectroscopy (SERS). The results are, however, seldom quantitative as the distribution of particle sizes in silver suspensions can vary from sample to sample and thus the SERS spectra can vary in intensity. Monodisperse silver sols are relatively difficult to prepare compared with gold or latex colloids as the nucleation process is difficult to control. Previous workers have used a system where small particles are formed in one process and grown in a second reaction. In this paper a simple procedure is outlined by which the small, "seed" particles (starter sols) can be prepared; this method is simpler and more reproducible than that used in the past. The process by which the sols can be grown is not discussed in detail here as it is the subject of a forthcoming publication. Copyright 1999 Academic Press.

Journal Article↗

PubMed1999

Relationship of low-density lipoprotein particle size and measures of adiposity.

OBJECTIVE: To determine if obesity measures are related to measures of low-density lipoprotein (LDL) size and LDL subfractions in a population of Mexican-Americans with high prevalence of obesity. METHODS: LDL size phenotypes, based on nondenaturing gradient gel electrophoresis and staining for cholesterol (using Sudan black B), were determined for 313 unrelated Mexican-American participants in the San Antonio Family Heart Study. LDL size measures included predominant particle diameter, median diameter (particle diameter, where half the LDL absorbance is on larger and half on smaller LDLs) and cholesterol level in various LDL subfractions. Adiposity traits included two measures of general body fatness (body-mass index (BMI) and fat mass determined with bioimpedance) and three measures of regional fat deposition (waist-to-hip ratio (WHR), waist circumference and subscapular-triceps skinfold ratio (STR)). RESULTS: Gender and diabetes were significantly associated with most LDL size measures. In addition, BMI, WHR, waist circumference and STR were significantly (P<0.05) associated with several LDL size measures. Stepwise regression analysis (including adjustment for age, gender and diabetes status) showed that in every case, the strongest adiposity correlate of LDL size, was WHR, which reflects deposition of visceral fat. If triglyceride (TG) concentration was also included in the models, no fat measure was independently correlated with LDL size, suggesting that elevation of TG, associated with increased adiposity, was more directly correlated with LDL size. Supporting this interpretation, we found that WHR was also the strongest correlate of TG among adiposity measures. Regression analysis of the LDL particle size cholesterol profile expressed in 0.1 nm increments revealed a positive correlation of WHR and LDLs in the interval 25.9-26.3 nm (P < 0.05) and a negative correlation of BMI with LDLs in the interval 27.3-28.1 nm (P < 0.05). CONCLUSION: These results suggest that different adiposity measures, reflecting different aspects of fat deposition, are related to specific LDL size intervals. We speculate that increased deposition of fat, particularly visceral fat, is associated with increased TG, which in turn is associated with decreases in LDL particle size.

Adipose Tissue↗

PubMed2007

Evaluation of the role of pores during strength testing in compacts made from different particle size fractions of sucrose.

The purpose of this study was to investigate the role of pores in the fracture of circular compacts and to predict compact properties and critical crack lengths. Four different particle size fractions of sucrose, ranging from 20 to 500 microm, were compressed into circular discs (i.e. flat tablets) and rectangular beam specimens of porosity between 30 and 14%. Modelling of the relationship between the tensile strength of the circular discs and the compact porosity indicated extensive fragmentation during compaction for particles in the size range of 250-500 microm, accompanied by a change in densification mechanism for very coarse particles (355-500 microm). When determining the critical stress intensity factor from rectangular single edge notched beam specimens by 3-point bending, an apparent influence of particle size on the values could be seen, whereby here the results indicated that the critical particle size for fragmentation to occur is about 20-40 microm. It was possible to predict the critical stress intensity factor of the compacts from the median pore size and the tensile strength of the circular disc specimens by interpolation of the critical crack length for propagation to occur. The results indicated that for sucrose compacts regardless of their porosity, the pores themselves acted as stress concentrators, not as sharp cracks. For sucrose compacts, crack propagation hence proceeds most likely along grain boundaries.

Materials Testing↗

PubMed2004

Particle size and temperature effect on the physical stability of PLGA nanospheres and microspheres containing Bodipy.

The purpose of this study was to investigate the effect of particle size, storage temperature, and duration of storage on the physical stability and morphology of polylactic-co-glycolic acid (PLGA) nanospheres and microspheres. PLGA nanospheres and microspheres containing the fluorescent dye, Bodipy, were prepared in varying sizes by controlling the method and degree of agitation during the emulsification phase of preparation. Mean diameters of the particles were measured by dynamic light scattering. To evaluate the effect of storage temperature and duration of storage on the extent of aggregation, nanospheres and microspheres were stored at 4 degrees C, 25 degrees C, 37 degrees C, and 50 degrees C for 6 days and then monitored using both confocal and scanning electron microscopy. The mean +/- SD diameters of PLGA particles containing Bodipy were: 266.9 +/- 2.8, 351.6 +/- 1.8, 988.8 +/- 14.1, and 1865.9 +/- 67.0 nm. The extent of aggregation of the particulate delivery system decreased as the mean diameter increased, and increased as the storage temperature increased. The maximum extent of aggregation was observed with the smallest (266 nm) nanospheres. Microspheres did not aggregate. The aggregation of nanospheres was significantly reduced by introducing an additional evaporation step during preparation, suggesting that migration of residual dichloromethane from within the nanospheres may have dissolved the PLGA on the surface. The extent of aggregation of nanospheres increased as the temperature was increased from 4 degrees C to 50 degrees C, and decreased as particle size increased. To avoid aggregation, PLGA nanospheres should be stored at 4 degrees C.

Boron Compounds↗

PubMed1993

Effects of gemfibrozil on low-density lipoprotein particle size, density distribution, and composition in patients with type II diabetes.

OBJECTIVE: To study the effects of gemfibrozil treatment on LDL particle size, density distribution, and composition in NIDDM patients. RESEARCH DESIGN AND METHODS: We performed LDL analyses on 16 NIDDM patients with stable glycemic control. They were randomly allocated to receive either gemfibrozil (n = 8) or a placebo (n = 8) for 3 mo in a double-blind study. The LDL particle size distribution and the particle diameter of the major LDL peak were measured with nondenaturing polyacrylamide gradient gel electrophoresis. The density distribution and composition of LDL were determined with the density gradient ultracentrifugation method. RESULTS: In the gemfibrozil group the mean serum TG concentration decreased by 38%, HDL cholesterol concentration increased by 10%, and LDL cholesterol concentration by 17% (P < 0.05). During gemfibrozil therapy the mean particle diameter of the major LDL peak increased from 244 to 251 A (P < 0.05), whereas in the placebo group the mean LDL particle diameter remained unchanged. We found an inverse correlation between the changes of serum TG and the particle diameters of the major LDL peak (r = 0.85, P < 0.01). Gemfibrozil produced a shift in the LDL density distribution toward lower density. The mean peak density decreased from 1.0371 to 1.0345 g/ml because of a significant rise in the light LDL concentration from 141.0 to 183.2 mg/dl (P < 0.05), whereas the concentration of dense LDL had a tendency to decrease. In the placebo group the LDL density distribution did not change. Gemfibrozil increased the CE-to-TG ratio in LDL core lipids by 27% (P < 0.05); otherwise, the LDL composition was only slightly affected. CONCLUSIONS: The results indicate gemfibrozil-induced changes in LDL properties in NIDDM patients are similar to those previously reported in nondiabetic individuals and are related to changes in serum TG level.

Apolipoproteins B↗

PubMedDate not supplied

Particle size analysis of gelatin-acacia coacervate and ethylcellulose walled microcapsules.

The Coulter counter has become one of the methods of choice for the measurement of small particle sizes. However, many colloidal walled microcapsules are prone to hydration when dispersed in the electrolyte solution used in Coulter measurements. This hydration causes the walls to swell, producing different size analyses dependent upon the time of measurement. In the present work the change in size with time was studied for microcapsules with gelatin-acacia coacervate, or ethylcellulose, walls. The former, although rendered insoluble with formalin, still hydrated; the latter were almost unaffected by water. A sample size of 30 mg was required to prevent blocking of the orifice with larger samples, or too few particles to permit measurement in smaller samples. The coacervate coated microcapsules showed a bimodal distribution, in part due to aggregate of smaller microcapsules, and this distribution changed significantly over the time of measurement. Although the peak due to larger microcapsules did not disappear, the number of large microcapsules fell significantly, most probably because of the disintegration of aggregated microcapsules. Microcapsules with ethyl cellulose walls did not show a bimodal distribution and the particle size analysis did not alter significantly with time.

Capsules↗

PubMed2002

Particle size effects on uptake of heavy metals from sewage sludge compost using natural zeolite clinoptilolite.

Land application of sewage sludge may be the least energy consuming and the most cost-effective means of sludge disposal or utilization. However, the major technical problem with land application of sludge concerns the high concentrations of heavy metals. These metals may be leached and enter the ecosystem, the food chain, and eventually the human population. This paper deals with the removal of heavy metals from sewage sludge compost using natural zeolite clinoptilolite, in respect to the particle size. The final results indicate that heavy metals can be sufficiently removed by using 25% w/w of zeolite with particle size of 3.3-4.0 mm. Pore clogging and structural damage in smaller particle sizes is probably the reason for lower uptake of metals by the latter.

Journal Article↗

PubMed1980

The effect of particle size on the osteogenic activity of composite grafts of allogeneic freeze-dried bone and autogenous marrow.

This study was carried out to determine if particle size is a factor to be considered in the evaluation of the osteogenic activity of freeze-dried bone allografts (FDBA) and, if so, whether small particles enhance or inhibit osteogenesis. Small particle FDBA (100-300 microns) plus marrow and large particle FDBA (1000-2000 microns) plus marrow were placed in plexiglass diffusion chambers secured to the femurs of six Rhesus monkeys. Control chambers contained either marrow alone or were left empty. Two animals were given injections of oxytetracycline hydrochloride at 5 and 7 weeks to obtain intravital osseous labeling. All chambers were removed after 8 weeks. Ten chambers were evaluated for new bone formation by fluorescent microscopy. The contents of 15 additional chambers were evaluated by single blind technique for presence or absence of bone resorption and ossification. The results indicated that there was significantly more new bone formation associated with small particle FDBA (100-300 microns) plus autogenous marrow than with large particle FDBA (1000-2000 microns) plus autogenous marrow. In addition, small particle FDBA (100-300 microns) plus autogenous marrow tended to display more resorption than large particle FDBA (1000-2000 microns) plus autogenous marrow. It was concluded that within the parameters of this study, small particles of FDBA enhance osteogenesis. This study also demonstrated that particle size is a variable to be considered when comparing the osteogenic potential of freeze-dried bone allografts.

Animals↗

PubMed1993

A comparison between sieving and optical scanning for the determination of particle size distributions obtained by mastication in man.

Mixtures of particles of different sizes, as obtained after chewing, were analysed. Coarse, medium and fine mixtures of particles of an artificial (Optosil) test food were used. Mixtures of Optosil particles of known form and size (half-cubes) were used to validate the analytical methods. The results of both methods were described by particle size distributions based on the volume of the particles. Complete agreement between methods was found for the mixtures of half-cubes. In order to determine the median particle size by volume from the results of optical scanning an assumption on the form of the chewed particles had to be made. Using the assumption that, on average, the particles resemble spheres a slight overestimate of the median particle size was obtained for scanning as compared to sieving. It can be concluded that, although different aspects of the fragmented particles are measured, sieving and optical scanning are both adequate methods for quantifying mixtures of chewed food particles and yield similar results for the degree of particle size reduction.

Calibration↗

PubMed1963

Adequate expression for average particle size of microbiological aerosols.

Attention was called to the fact that mathematical expressions exist for relating the various means commonly employed to describe the average particle size of microbiological aerosols. These include the count median diameter (CMD), the mass median diameter (MMD), the petri ratio (P(a)) size, and the settling rate (V(g)) size. It was pointed out that the diameters derived from the P(a) and V(g) are mathematically identical to the average surface-diameter (SMD), because this average is determined from the square of the diameters, a relationship which also describes the settling of particles by the Stokes equation. The useful equations are: log SMD = log CMD + 2.3026 log(2)sigma(g) and log MMD = log CMD + 6.9078 log(2)sigma(g) where sigma(g) is the standard geometric deviation, and the CMD is determined on a count basis and the MMD on a weight basis. It was suggested that the SMD is the most adequate expression for the average particle size of microbiological aerosols.

Aerosols↗

PubMed2005

Modified structural model for predicting particle size in the microemulsion and emulsion polymerization of styrene under microwave irradiation.

In this study, the microemulsion and emulsion polymerization of styrene at 70 degrees C in the presence of sodium dodecyl sulfate (SDS, surfactant) and potassium persulfate (KPS, initiator) was conducted under microwave radiation. Laser light scattering was used to characterize the resultant polystyrene latex particles formed at different polymerization stages. The influence of the initial emulsion composition, that is, the SDS, KPS, and styrene concentrations, on the final particle size led us to a simple modified structural model in which we considered the stabilization effects of both the surfactant and the ionic end groups generated from the initiator. This model extended the application of the previous Wu plot from microemulsion polymerization to emulsion polymerization. Using this model, we were not only able to control the particle size but were also able to predict the monomer concentration dependence of the number of the resultant latex particles and the effect of diluting the reaction mixture on the resultant particle size.

Journal Article↗

PubMed1997

The effect of surfactant and suspending agent concentration on the effective particle size of metered-dose inhalers.

The aim of this study was to examine the influence of the concentrations of surfactant and suspending agent on the quantity of effective particles (size < 10 microm) delivered by metered-dose inhalers. A 2-factor, 3-level, face-centred central composite design was used to construct a second-order polynomial model which describes the effect of formulation factors (suspending agent, surface-active ingredient) on the therapeutically important characteristic (effective particle size) delivered by metered-dose inhalers. Oleic acid was selected as the surface-active ingredient, and the suspending agent was anhydrous alcohol. A non-linear model demonstrated with good correlation the effect of the amounts of surfactant and suspending agent on the quantity of particles of effective size. The results obtained enable determination of the correct amount of surface-active ingredient and the optimum quantity of the suspending agent, thus enabling formulation of a therapeutically effective formulation.

Chemistry, Pharmaceutical↗

PubMed2005

The effects of particle size and surface coating on the cytotoxicity of nickel ferrite.

The safety and toxicity of nanoparticles are of growing concern despite their significant scientific interests and promising potentials in many applications. The properties of nanoparticles depend not only on the size but also the structure, microstructure and surface coating. These in turn are controlled by the synthesis and processing conditions. The dependence of cytotoxicity on particle size and on the presence of oleic acid as surfactant on nickel ferrite particles were investigated in vitro using the Neuro-2A cell line as a model. For nickel ferrite particles without oleic acid prepared by ball milling, cytotoxicity was independent of particle size within the given mass concentrations and surface areas accessible to the cells. For nickel ferrite particles coated with oleic acid prepared by the polyol method, the cytotoxicity significantly increased when one or two layers of oleic acid were deposited. Large particles (150+/-50 nm diameter) showed a higher cytotoxicity than smaller particles (10+/-3 nm diameter).

Animals↗