A simulation approach to understanding the masticatory process

An analysis of the reduction of food particle sizes during human mastication is presented in terms of the probability of a particle being broken (selection function) and the distribution of fragment sizes produced when it fails (breakage function). Both selection and breakage functions are defined and a general equation produced. Several feasible behaviours for these two variables that have been suggested in the literature are modelled by computer simulation and the results are compared to published breakdown patterns. The conclusions are that selection and breakage functions probably behave very simply with respect to particle size, and that these behaviours could be deduced from an analysis of food particle size distributions and the rate at which particle sizes are reduced per chew.     

A model of protein-colloidal gold interactions

We prepared homogeneous populations of colloidal gold particles of various sizes. These were analyzed for size distribution and number of particles per unit volume. On exposure to increasing concentrations of insulin, myoglobin, protein A, peroxidase, serum albumin, galactosylated serum albumin, lactoferrin, transferrin, catalase, low-density lipoprotein, ferritin, and polymeric IgA, protein binding was a saturable process. Using serum albumin, we verified that a reversible equilibrium was reached within 15 minutes. Scatchard analysis of the interactions between all of these proteins and the gold particles resulted in a single component, linear relation. For a given particle size, the number of binding sites for various proteins was inversely proportional to their molecular weight. Conversely, when the size of particles was varied, the number of binding sites was directly proportional to the average area of each gold particle. All results are compatible with a monomolecular shell of protein surrounding the particle at saturation, the binding capacity being inversely proportional to the projection area of the protein. We present direct morphological evidence for this model. The affinity of the various proteins for the colloid also increased with molecular weight, and was not related to the protein isoelectric point. For globular proteins, the monomolecular shell model makes possible prediction of the number of molecules that will saturate a gold particle, if the average diameter of the gold particles and the molecular weight of the protein are known.     

Postingestive selection in the sea scallop, Placopecten magellanicus (Gmelin): the role of particle size and density

Suspension-feeding bivalves can influence the energy value of their food supply by particle selection at various stages from particle clearance to production of feces. Previous workers have found that some bivalve species (Mercenaria mercenaria, Mytilus edulis) are capable of postingestive selection within the stomach. Few studies, however, have attempted to isolate the factors that influence postingestive selection. In this study, we examined the ability of the sea scallop Placopecten magellanicus to select particles within the stomach on the basis of physical properties. Scallops were presented with a mixture of three sizes of beads (5, 10 and 20 μm) or with a mixture of beads of different densities (1.05 g ml(-1) and 2.5 g ml(-1)). We demonstrate that P. magellanicus can distinguish between particles of different sizes and densities, retaining larger particles (20 μm) longer than smaller ones (5 μm) and lighter particles longer than denser ones. This ability to reject small, dense particles may benefit the scallop by reducing the amount of energy expended attempting to digest poor quality particles such as silt. This paper presents the first quantitative analysis of the effect of particle size and density on particle processing within intact bivalves.     

Interactions between protein-gold complexes and cell surfaces: a method for precise quantitation

We have developed a rapid and precise electron microscope technique for the quantitation of gold particles in suspension using latex microspheres as a reference (EM latex technique). This technique allowed us to determine the specific absorption of colloidal gold at its absorption maximum (520 nm) and the average number of ligands ([125I]IgG) bound to one gold particle. On the basis of these values important binding characteristics of protein-gold complexes to cell surfaces were analyzed in a model system consisting of Staphylococcus aureus with protein A on the cell wall as a specific binding site for IgG-Au. Our observations showed that the number of binding sites represented by one IgG-gold complex depended primarily on the particle size, with one 20-nm IgG-Au corresponding to 15 and one 6-nm IgG-Au to 2.5 binding sites. Hence, the efficiency of binding of IgG-Au complexes increased with decreasing gold particle size. Saturation of binding sites, however, was not achieved. The technique also made possible the determination of the affinity between IgG-Au complexes and the cell surface; this affinity can either be regarded as a characteristic of the ligand IgG or of the gold particle. We observed that the affinity of IgG decreased with the size of the gold particles to which IgG was bound, whereas the affinity of the entire gold particle increased with particle size. The EM latex technique for quantitation of gold particles extends the general use of protein-gold complexes to the quantitative characterization of their interaction with cell surface constituents.     

Filter mesh size and food particle uptake by Daphnia

Food size selection of four Daphnia, species (D. magna, D. hyalina, D. galeata, D. pulicaria) was investigated using spherical plastic beads as artificial food and with small bacteria. The size of the particles ranged from 0.1 to 35 m with special emphasis to the particle diameters between 0.1 and 1 m. In one set of experiments a mixture of differently sized particles was offered as food suspension and the selectivity of filtering was determined by comparing the size spectrum of the particles found in the gut contents with the spectrum in the food suspension. In a second series of experiments suspensions of uniformly sized particles were offered to single animals and their feeding activity was observed directly. In both types of experiments the mesh sizes of the filtering apparatus of the respective animals studied were measured after the experiments by, scanning electron microscopy. The mean sizes of the filter meshes were about 0.4–0.7 m. In all experiments the size of the particles found in the gut or those which caused high feeding activities were larger than the smallest mesh sizes of the filters. As a consequence simple mechanical sieving provides a sufficient explanation for the mechanism of particle retention of the filtering process in Daphnia. D. magna was found to feed with high efficiency on suspended freshwater bacteria, the residual species investigated showed low filtering efficiencies when bacteria were offered as food.The present study was supported by Deutscher Akademischer Austauschdients     

On the heritability of geographic range sizes

Within taxonomic groups, most species are restricted in their geographic range sizes, with only a few being widespread. The possibility that species-level selection on range sizes contributes to the characteristic form of such species-range size distributions has previously been raised. This would require that closely related species have similar range sizes, an indication of "heritability" of range sizes at the species level. Support for this view came from a positive correlation between the range sizes of closely related pairs of fossil mollusc species. We extend this analysis by considering the relationship between the geographic range sizes of 103 pairs of contemporary avian sister species. Range sizes in these sister species show no evidence of being more similar to each other than expected by chance. A reassessment of the mollusc data also suggests that the high correlation was probably overestimated because of the skewed nature of range size data. The fact that sister species tend to have similar life histories and ecologies suggests that any relationship between range sizes and biology is likely to be complicated and will be influenced by historical factors, such as mode of speciation and postspeciation range size transformations.     

Evidence for a trade-off between early growth and tooth wear in Svalbard reindeer

Ruminants depend on efficient physical degradation of forage through chewing to increase the surface area of the food particles presented to the microflora. Fossil evidence suggests that increased molar height is an adaptation for wear tolerance in dry ecosystems with sparse vegetation, but no study has shown selection pressure for hypsodonty in contemporary ruminants. We explored the relationships between particle size in rumen, tooth wear (scanned molar occlusal topography), age and body mass of female Svalbard reindeer living in an arctic desert at 78 degrees latitude on Svalbard. We predicted that (H1) if the rumen particle size is determined mainly by constraints due to tooth wear, and if tooth wear is mainly a function of age, average particle size in rumen should increase with age. From allometric relations it is known that larger individuals can survive on a lower-quality diet, we therefore predicted (H2) larger particle sizes with increases in (ln) body mass, irrespective of age and wear. Lastly, if there is a trade-off between growth and tooth wear in dry ecosystems (a selection pressure for hypsodonty), we predicted (H3) that teeth of heavier animals should be more worn than those of lighter animals of the same age. The proportion of small particles (<1.0 mm) decreased rapidly with increasing age (consistent with H1). Heavier females within an age class had more worn teeth (consistent with H3) than lighter ones. A close-to-isometric relationship between particle size and body mass suggested that heavier animals partly compensated for reduced tooth efficiency by chewing more. We provide the first evidence of a trade-off between fast early growth and wear (a somatic cost) of a senescence-related trait--the structure and height of the molar--in a wild ruminant inhabiting an arctic desert where selection pressure for increased tooth height is expected. This suggests that foraging conditions are more extreme than the environment in which the species originally evolved.     

Size Effects on the Uptake of Particles by Populations of Tetrahymena pyriformis Cells

Flow cytometry has been used to make direct measurements of rates of uptake of latex microspheres from dilute, monodisperse suspensions by Tetrahymena pyriformis. Measurements were made for five different sizes of microspheres, ranging from 1.09 to 6.17 μm diameter. Fractions of cells in the population that did not ingest the microspheres offered were also determined. In addition, the size distributions, as indicated by the forward angle light scattering intensity which is measured by the instrument, were determined for the whole population and for the subpopulations of cells that did and did not ingest the particles, for each particle size used. It was found that the fraction of cells that did not ingest the particles was small and independent of particle size when this was less than about 2.7 μm, but increased with particle size when particle size was increased above this value. The so-called maximum clearance rate, which can be calculated from the data, was found to increase monotonically with particle size if it were based only on those cells which actually ingested the particles offered. However, a plot of maximum clearance rate vs. particle size exhibited a maximum if the clearance rate were based on all cells present in the population.     

Getting the most out of waste: how dung beetles boost the nitrogen content in their food

The life cycle of almost all dung beetles revolve around mammalian dung, the feed on dung, look for mating partners on dung and lay eggs in the dung. We know they feed on dung, but we still do not understand how exactly they filter‐feed on the dung and which particles size range they are ingesting. The aim on this study was to investigate the filter feeding by particle selection by adult dung beetles using Scarabaeus goryi and how that improves the nutrient quality of the ingested particles. We compared the particle sizes and nutrient content of the dung with the ingested material in the foregut, hindgut and the faeces of the dung beetle. Adult dung beetles do select smaller dung particles when feeding, we found the maximum particle size for the ingested particle to be around 1400 μm. The average particle size increased through the gut length. Dung beetles also selected particles with higher nitrogen content when feeding, the nitrogen content increased from about 1.5% in the dung to just over 5% in the foregut which then decreased to the level of the unprocessed dung in the dung beetle faeces. Carbon content did not increase from the unprocessed dung to the foregut but decreased through the gut length. Feeding by particle size selection by dung beetles helps in selecting particles with higher nitrogen content to compensate for the low levels found in dung.     

Particle selection in the nauplius of Calanus pacificus

Food selection by the nauplius of Calanus pacificus is definedas the ability to ingest certain kinds of particles in behavioralpreference to others that occur simultaneously in the same environment.Using mixtures of planktonic algae and plastic beads of differentor similar sizes, the nauplii strongly selected the algal cells,consuming them almost exclusively, and at similar rates to thecontrols with only algae. In some cases, however, ingestionrates on the algae were lower than the in the controls, mainlywhen the mixture was composed of algal cells and plastic beadsof smaller sizes able to be captured by the nauplii. Selectionof algal particles was also observed when pollen grains or detrituswere used instead of the plastic beads. Selection behavior alsooccurred when mixtures of two algae of different sizes wereoffered to the nauplii, and it was dependent on the proportionand concentration of both kinds of algae in the mixture. Thepossible effect of particle production on the observed selectivepatterns is discussed.     

Grazing Rates in Euplotes mutabilis: Relationship between Particle Size and Concentration

Abstract Grazing behavior of both individual cells and populations of the marine hypotrich Euplotes mutabilis, a largely benthic ciliate that feeds on suspended particles, was studied using fluorescent latex microspheres. Microspheres of sizes 0.57-, 1.90-, 3.06-, 5.66-, and 10.0-μm diam were offered at concentrations from 10² to 10⁶ ml⁻¹. Their uptake in a ten-min period was determined. Food particles within such ranges of size and concentration are found under natural conditions. The ciliates ingested particles of all sizes offered. Uptake rates at all concentrations were dependent upon particle size, with 1.90- and 3.06-μm diam microspheres having the highest uptake rate in all cases. For all sizes, there was an increase in the percentage of feeding cells and in the uptake rate (the number of particles ingested cell⁻¹ h⁻¹), with increasing particle concentration. When uptake was expressed as the volume ingested, maximum values were obtained for 5.85-μm diam microspheres at a concentration of 10⁶ ml⁻¹. By taking a small number of large particles, present at a low concentration in the medium, a ciliate can ingest a greater biovolume than by taking a high number of small particles which are abundant in the medium. These results demonstrate that some ciliates can graze particles of a wide range of sizes. Also, its nutrition can be affected by changing ambient concentrations of different prey, both through effects on the proportion of feeding cells and through the relative food content of the particles. The data can also add to the understanding of food niche partitioning between species. At low particle concentrations, particularly, it is important to consider the behavior of individual ciliates as well as of the whole population. Received: 11 February 1997; Accepted: 21 October 1997     

Substrate selection for pit making and oviposition in an antlion, Myrmeleon bore Tjeder, in terms of sand particle size

The larvae of the pit‐making antlion Myrmeleon bore Tjeder live in open sand in riverbeds with a substratum consisting of various particle sizes. We analyzed the spatial distribution of their pits in a sandy floodplain to determine their larval and adult responses to the heterogeneous substrate. The spatial distribution pattern of their pits had an aggregated distribution, and there was a significant positive correlation between pit density and the ratio of medium‐size sand particles to total weight of sand. We examined the size of sand particles selected in the larval pit‐building behavior and the oviposition behavior of the adult. Both larvae and adults selected medium‐size sand particles. The larvae of M. bore are relatively sedentary predators and rarely move great distances. Thus, the present results suggest that habitat selection by adult females is a major factor causing the aggregative distribution of the pits.     

An Intensified Vibratory Milling Process for Enhancing the Breakage Kinetics during the Preparation of Drug Nanosuspensions

As a drug-sparing approach in early development, vibratory milling has been used for the preparation of nanosuspensions of poorly water-soluble drugs. The aim of this study was to intensify this process through a systematic increase in vibration intensity and bead loading with the optimal bead size for faster production. Griseofulvin, a poorly water-soluble drug, was wet-milled using yttrium-stabilized zirconia beads with sizes ranging from 50 to 1500 μm at low power density (0.87 W/g). Then, this process was intensified with the optimal bead size by sequentially increasing vibration intensity and bead loading. Additional experiments with several bead sizes were performed at high power density (16 W/g), and the results were compared to those from wet stirred media milling. Laser diffraction, scanning electron microscopy, X-ray diffraction, differential scanning calorimetry, and dissolution tests were used for characterization. Results for the low power density indicated 800 μm as the optimal bead size which led to a median size of 545 nm with more than 10% of the drug particles greater than 1.8 μm albeit the fastest breakage. An increase in either vibration intensity or bead loading resulted in faster breakage. The most intensified process led to 90% of the particles being smaller than 300 nm. At the high power intensity, 400 μm beads were optimal, which enhanced griseofulvin dissolution significantly and signified the importance of bead size in view of the power density. Only the optimally intensified vibratory milling led to a comparable nanosuspension to that prepared by the stirred media milling.     

Do Current Standards of Practice in Canada Measure What is Relevant to Human Exposure at Contaminated Sites? I: A Discussion of Soil Particle Size and Contaminant Partitioning in Soil

Human health risk estimates for sites with contaminated soils are often based on the assumption that the bulk concentration of substances in outdoor soil samples is a reasonable predictor of exposures via incidental soil ingestion, soil particle inhalation, and dermal absorption. Most underlying conceptual models are grossly simplistic, however, when considered in light of (i) biases in the distribution of contaminants across soil particle sizes, (ii) the size range of particles in soils and dusts that is environmentally available, and (iii) factors that influence desorption from particles and uptake into humans. The available studies indicate that contaminant distribution across soil particle size fractions varies widely between different soil types and contaminant delivery mechanisms, and it cannot be assumed that higher masses of contaminants per unit mass of soil are correlated with smaller particles sizes. Soil data gathered in support of detailed human health risk assessments, therefore, should allow for the examination of distribution across particle sizes of contaminants of concern, and consider those size fractions most critical to human exposure. Soil evaluations for health risk assessments of metals/metalloids should also consider mineralogical characterization.     

An Investigation on the Effect of Polyethylene Oxide Concentration and Particle Size in Modulating Theophylline Release from Tablet Matrices

Polyethylene oxide has been researched extensively as an alternative polymer to hydroxypropyl methylcellulose (HPMC) in controlled drug delivery due to its desirable swelling properties and its availability in a number of different viscosity grades. Previous studies on HPMC have pointed out the importance of particle size on drug release, but as of yet, no studies have investigated the effect of particle size of polyethylene oxide (polyox) on drug release. The present study explored the relationship between polymer level and particle size to sustain the drug release. Tablets produced contained theophylline as their active ingredient and consisted of different polyethylene oxide particle size fractions (20–45, 45–90, 90–180 and 180–425 μm). It was shown that matrices containing smaller particle sizes of polyox produced harder tablets than when larger polyox particles were used. The release studies showed that matrices consisting of large polyox particles showed a faster release rate than matrices made from smaller particles. Molecular weight (MW) of the polymer was a key determining step in attaining sustained release, with the high MW of polyox resulting in a delayed release profile. The results showed that the effect of particle size on drug release was more detrimental when a low concentration of polyox was used. This indicates that care must be taken when low levels of polyox with different particle size fractions are used. More robust formulations could be obtained when the concentration of polyox is high. Differential scanning calorimetry (DSC) traces showed that particle size had no major effect on the thermal behaviour of polyox particles.KEY WORDS: DSC traces, particle size, polyox, sustained release, theophylline     

The interaction of high mobility proteins HMG14 and 17 with nucleosomes.

The interaction of the high mobility group proteins, HMG14 and HMG17, with nucleosome core particles has been studied. The results show that two molecules of HMG14/17 can be bound tightly but reversibly to each core particle and that their affinity for core particles is greater than their affinity for histone-free DNA of core size. Thermal denaturation and nuclease digestion studies suggest that major sites of interaction are located near the ends of the nucleosome core DNA. When nucleosome preparations from chicken erythrocyte nuclei stripped of HMG proteins are partially titrated with HMG14/17, the nucleosome-HMG complex fraction is enriched in beta-globin gene sequences.     

Immunolabeling efficiency of protein A-gold complexes

A systematic study of the adsorption of protein A on colloidal gold particles varying in size from 5-16 nm was performed at different protein concentrations. The number of protein A molecules bound per colloidal particle was evaluated and the Scatchard analysis of the adsorption parameters was applied for each size of the colloid. The binding of protein A to the colloidal gold surface exhibited the same affinity pattern for all of the particle sizes. At low concentrations of stabilizing protein, adsorption took place with high affinity (Kd 1.96-3.3 nM) and the maximum number of protein A molecules attached with this affinity correlated well with the surface of the particle. At higher concentrations of protein A, adsorption exhibited a significantly lower affinity (Kd 530-800 nM), and no saturation was recorded. Competition by albumin did not reveal a preferential removal of the "low-affinity" bound protein A molecules, contradicting the model of successive shells of stabilizing protein around the colloidal particle. The immunolabeling efficiency of conjugates having the same size of gold nucleus but carrying different numbers of protein A molecules was comparatively investigated by quantitative post-embedding immunocytochemistry. Protein A-gold formed with 5-10-nm colloids gave the highest intensity of labeling when carrying the maximum number of protein A molecules that could be adsorbed with high affinity. Overloading as well as underloading these complexes resulted in a significant decrease of their immunoreactivity. The most efficient conjugates were obtained when stabilization was performed with 6 micrograms protein A/ml gold sol of 5 and 10 nm particle diameter, and 15 micrograms protein/ml of 15-nm colloid.     

Determination of the size distribution of liposomes by SEC fractionation,and PCS analysis and enzymatic assay of lipid content

In this study, small liposomes obtained by high-pressure homogenization were fractionated according to their particle sizes by size exclusion chromatography (SEC). The subfractions were analyzed by photon correlation spectroscopy (PCS) as well as enzymatic phosphatidylcholine (PC) assay for their particle sizes and lipid contents, respectively. For small egg PC-liposomes, a size range of 15 nm to 60 nm was found, with 80% of the vesicles being smaller than 30 nm in size. This is in contradiction to a mean size of 85±32 nm as indicated by PCS without fractionation. The PCS technique appears to underestimate very small particles below 30 nm if (few) bigger particles are present. The PCS particle size analysis of unfractionated hydrogenated egg PC/cholesterol-liposomes (2:1, mole/mole) by PCS did not yield any significant results. On fractionation, however, a particle size range of 40 nm to 120 nm was determined in a reproducible manner. Our results indicate that the combination of size exclusion fractionation with subsequent photon correlation spectroscopic particle size analysis and enzymatic PC assay can give both more detailed and more reliable insight into the particle size distribution of small liposomes than PCS alone. Published: May 15, 2002.     

Determining the basic characteristics of aerosols suitable for studies of deposition in the respiratory tract

Studies of aerosol particle deposition in the respiratory tract requires experimental inhalation of artificial model aerosols. The paper formulates some of the most important requirements for the properties of such aerosols. Several suitable fractions were prepared as part of a research project dealing with the use of microporous polymers for diagnostic purposes. 5 fractions of the polymer designated G-gel 60 with the particle size as stated by the manufacturer, ranging from 3 to 7 micron were evaluated using a 16-channel particle dispersity analyzer HIAC/ROYCO MT 3210 with the sensor 1200 and operated by a microprocessor, the equipment being coupled to an APPLE IIe computer. G-gel 60 particles introduced into the aerosol were characterized by the parameters CMAD, MMAD and sg both numerically and graphically. The measurement procedure was found to be very sensitive with respect to all fractions in evaluating the subtile differences between different lot numbers of the aerosol. G-gel 60 fractions characterized both numerically and graphically were compared with the known aerosols from paraffin oil and atmospheric air. The equipment MT 3210 enables prompt determination of the percentages of aerosol particles distribution by size class. The authors conclude that the procedure, both in its numerical and graphical versions, is particularly suitable for the diagnosis of aerosol particles deposition in the respiratory tract, offering a new application for HIAC/ROYCO in the field of medicine. In evaluating atmospheric aerosol in exhaled air, the number of particles was found to be below that in inhaled air, the difference being dependent on the choice of investigation methods. Percentual distribution of deposited particles following one minute ventilation proved to be at its maximum, as regards atmospheric aerosol, in the 0.30-0.50 micron range. The deposition curve was similar to already published curves, being characterized by an S-shaped pattern with maximum deposition in the greater size classes. An analysis of inhaled, exhaled and deposited aerosol suggested that deposited aerosol is more polydisperse and has particles of greater sizes than inhaled aerosol. Investigation of the effect of apnoe on deposition indicated that deposition increased as a function of apnoeic pause.     

Soil Particle Heterogeneity Affects the Growth of a Rhizomatous Wetland Plant

Soil is commonly composed of particles of different sizes, and soil particle size may greatly affect the growth of plants because it affects soil physical and chemical properties. However, no study has tested the effects of soil particle heterogeneity on the growth of clonal plants. We conducted a greenhouse experiment in which individual ramets of the wetland plant Bolboschoenus planiculmis were grown in three homogeneous soil treatments with uniformly sized quartz particles (small: 0.75 mm, medium: 1.5 mm, or large: 3 mm), one homogeneous treatment with an even mixture of large and medium particles, and two heterogeneous treatments consisting of 16 or 4 patches of large and medium particles. Biomass, ramet number, rhizome length and spacer length were significantly greater in the treatment with only medium particles than in the one with only large particles. Biomass, ramet number, rhizome length and tuber number in the patchy treatments were greater in patches of medium than of large particles; this difference was more pronounced when patches were small than when they were large. Soil particle size and soil particle heterogeneity can greatly affect the growth of clonal plants. Thus, studies to test the effects of soil heterogeneity on clonal plants should distinguish the effects of nutrient heterogeneity from those of particle heterogeneity.