Μm Polystyrene Particles Research Articles

An Optimized In Vitro Model of the Respiratory Tract Wall to Study Particle Cell Interactions

As a part of the respiratory tissue barrier, lung epithelial cells play an important role against the penetration of the body by inhaled particulate foreign materials. In most cell culture models, which are designed to study particle-cell interactions, the cells are immersed in medium. This does not reflect the physiological condition of lung epithelial cells which are exposed to air, separated from it only by a very thin liquid lining layer with a surfactant film at the air-liquid interface. In this study, A549 epithelial cells were grown on microporous membranes in a two chamber system. After the formation of a confluent monolayer the cells were exposed to air. The morphology of the cells and the expression of tight junction proteins were studied with confocal laser scanning and transmission electron microscopy. Air-exposed cells maintained monolayer structure for 2 days, expressed tight junctions and developed transepithelial electrical resistance. Surfactant was produced and released at the apical side of the air-exposed epithelial cells. In order to study particle-cell interactions fluorescent 1 microm polystyrene particles were sprayed over the epithelial surface. After 4 h, 8.8% of particles were found inside the epithelium. This fraction increased to 38% after 24 h. During all observations, particles were always found in the cells but never between them. In this study, we present an in vitro model of the respiratory tract wall consisting of air-exposed lung epithelial cells covered by a liquid lining layer with a surfactant film to study particle-cell interactions.

Electrospun nanofibrous filtration membrane

This paper explores the viability of developing a fibrous membrane via electrospun nanofibrous web for liquid separation and demonstrates its applicability in particulate removal. Polyvinylidene fluoride nanofibers were electrospun into membranes and characterized to relate its structural properties to membrane separation properties and performance. Characterization of these electrospun membranes revealed that they have similar properties to that of conventional microfiltration membranes. The electrospun membranes were used to separate 1, 5 and 10 μm polystyrene particles. The electrospun membranes were successful in rejecting more than 90% of the micro-particles from solution. This work opens up the avenue of exploring the use of nanofibers for more mainstream application in the separation technology as a potential membrane for pre-treatment of water prior to reverse osmosis or as pre-filters to minimize fouling and contamination prior to ultra- or nano-filtration.

Experimental and Theoretical Studies of Laser Cleaning Mechanisms for Submicrometer Particulates on Si Surfaces

Submicrometer (0.1–1 μm) polystyrene and alumina particles were removed by single-shot nanosecond 248 nm KrF laser radiation from Si wafer surfaces with or without pre-deposited thin liquid layers. Nearly complete (>90%) single-shot laser cleaning has been achieved for combinations of polystyrene and alumina particles, respectively, with 2-propanol and water used as liquid energy transfer media, while for other combinations cleaning was absent or incomplete. Time-resolved optical microscopy studies have for the first time revealed important transient microscopic interactions between these particles and Si substrates in the pre-deposited micron-thick liquid layers, resulting, in some of these cases, in significantly reduced particle-substrate coupling. The visualization results give insight into microscopic particle removal mechanisms relevant to our laser cleaning experimental conditions, which are discussed along with their theoretical analysis. Theoretical modeling has been performed to interpret these experimental results and to provide insight into microscopic particle removal mechanisms.

Particle size and surface charge affect particle uptake by human dendritic cells in an in vitro model

Current vaccine development includes optimization of antigen delivery to antigen presenting cells, such as dendritic cells (DC). Particulate systems have attracted increasing attention in the development of vaccine delivery systems. In the present study, we investigated DC uptake of model fluorescent polystyrene particles with a broad size range and variable surface properties. Localization of particles was investigated using confocal laser scanning microscopy and uptake was quantified by flow cytometry. Immature DC were generated from mononuclear cells isolated from human blood. The polystyrene particles interacted with the DC throughout the tested diameter range of 0.04–15 μm in a time- and concentration-dependent manner. The optimal particle diameter for fast and efficient acquisition by a substantial percentage of the DC was 0.5 μm and below. The surface of 1 and 0.1 μm polystyrene particles was covalently modified with different polyaminoacids/proteins, yielding particles with varying surface charge. Uptake of 1 μm particles was greatly enhanced when particles displayed a positive surface charge. In general, the present findings establish that particle diameters of 0.5 μm and below were optimal for DC uptake; however uptake of larger particles could be greatly enhanced by rendering the particle surface positive. Whether increased particle uptake is correlated with increased immune responses, remains to be established.

Removal versus ablation in KrF dry laser cleaning of polystyrene particles from silicon

Direct absorption and melting of 0.2, 0.5 and 1.1 μm polystyrene particles on a Si substrate irradiated by 248 nm excimer laser radiation was found to contribute to their dry laser removal via a “hopping” mechanism at cleaning thresholds of 0.05, 0.1, and 0.16 J/cm2, respectively. Ablation of these particles, which starts near the beginning of substrate deceleration at fluences above 0.4–0.5 J/cm2, suppresses particle removal due to ablative recoil momentum. At fluences above a second cleaning threshold of 0.7 J/cm2 particles are completely evaporated without any visible surface damage of the Si substrate.

Three-phase material distribution measurements in a vertical flow using gamma-densitometry tomography and electrical-impedance tomography

Experiments are presented in which electrical-impedance tomography (EIT) and gamma-densitometry tomography (GDT) measurements are combined to simultaneously measure the solid, liquid, and gas radial distributions in a vertical three-phase flow. The experimental testbed is a 19.05-cm diameter bubble column in which gas is injected at the bottom and exits out the top while the liquid and solid phases recirculate. The gas phase is air and the liquid phase is deionized water with added electrolytes. For the solid phase four different particle classes are investigated: 40–100 μm and 120–200 μm glass particles ( 2.41 g/cm 3 ), and 170–260 μm and 200–700 μm polystyrene particles ( 1.04 g/cm 3 ). Superficial gas velocities of 3–30 cm/s and solid volume fractions up to 0.30 are examined. For all experimental conditions investigated, the gas distribution shows only a weak dependence on both particle size and density. The average gas volume fraction as a function of superficial gas velocity can be described to within ±0.04 by a single curve. For most cases, the solid particles appear to be uniformly dispersed in the liquid.

Microdivers to study sedimentation in polydisperse, concentrated colloidal suspensions

AbstractA small amount of polymer particles with diameters in the 100 μm range can be used as an ensemble of “microdivers” to study sedimentation velocities of polydisperse submicron particles in concentrated opaque suspensions. This tracer technique, based on Berg's (1941) diver method, is simple, measures velocities directly, and does not require underlying theory beyond conservation of momentum. It confirms that the polymer tracers reside at the position in the suspension where the suspension density corresponds to their own density. Aqueous inorganic suspensions of 250–750 nm α‐alumina particles were studied, which is electrostatically stabilized with nitric acid in water, using ∼100 μm polymethylmetacrylate and polystyrene particles as tracers. Experiments were compared with predictions by state‐of‐the‐art continuum models for multicomponent sedimentation to underpin the validity of the tracer technique.

Entrainment of fine particles from surfaces by gas jets impinging at normal incidence

This paper describes an experimental study of the removal of fine (8.3 μm) polystyrene particles from a glass substrate using a gas jet at normal impingement. In order to avoid transient effects associated with jet startup, the sample was slowly translated under a steady jet. The translating gas jet produces a long clean path that provides very good statistics for exploring the effect of jet parameters. The dependence of the spatial distribution of removal efficiency on the jet pressure ratio, the jet height, and the translation speed is examined. Clean paths greater than 16 jet diameters wide are produced with a jet pressure ratio of 7 translating at 9.0 mm/s at a dimensionless height of 10. The path width is independent of the jet height at high pressure ratios and inversely dependent on the jet translation speed. A harmonic oscillator model for particle detachment accounts for the effect of translation speed. Results suggest that the particles act as nearly-quantized shear stress sensors that provide a direct, though as yet uncalibrated, measure of the surface shear stress. Further, knowledge of the pressure required to remove 50% of the particles from the central region of the path is sufficient to predict the extent of particle removal at higher pressures.

Granular Activated Carbon and Biological Activated Carbon Treatment of Dissolved and Sorbed Polychlorinated Biphenyls

The most widely practiced treatment method for polychlorinated biphenyls (PCBs) in aqueous wastes is activated carbon adsorption. However, the presence of particulates in aqueous wastes may affect treatment processes primarily designed to treat dissolved PCBs because PCBs tend to partition strongly to solid surfaces. In this research, bench‐scale studies were conducted to investigate the performance of granular activated carbon (GAC) and biological activated carbon (BAC) processes for treating aqueous wastes containing dissolved and sorbed PCBs. When all influent PCBs were dissolved, influent PCBs of approximately 175 μg/L were removed to approximately 0.2 μg/L in the BAC column, compared to approximately 0.8 μg/L in the GAC column. A reduction in the extent of PCB removal was observed for both GAC and BAC processes when 10 mg/L of 0.5μm polystyrene particles were added to the influent. In the presence of influent particulates, PCB removal was significantly better in the BAC column and equaled 99% compared to 62% in the GAC column. Performance differences between the GAC and BAC columns were attributed to higher particulate capture efficiency of the biological film covering the activated carbon in the BAC column. Biological activated carbon columns thus seem to offer advantages to conventional GAC processes for aqueous wastes containing either dissolved or sorbed PCBs.

Particle Retention in Airways Estimated by Unbiased Stereology and Photometry

ABSTRACT The retention pattern of 6 (μm polystyrene particles at two breathing modes was studied by unbiased stereology in hamster airways (trachea, main bronchi and intrapulmonary conducting airwa...

Laser-assisted particle removal from silicon surfaces

Abstract Laser-assisted particle removal (LAPR) is a new technique capable of removing micron and submicron scale particles from solid surfaces. In LAPR, the contaminated substrates are dosed with water vapor or other condensible gases as an energy transfer medium which preferentially adsorbs in the capillary spaces under and around the particles. The dosed substrate is then irradiated with a pulsed laser causing explosive evaporation of the energy transfer medium and propelling the particles off the substrate surface. In our experiments, LAPR was used to remove 9.5 μm Al 2 O 3 , 5 μm Al 2 O 3 , 1 μm Al 2 O 3 , and 1 μm polystyrene (PS) particles from Si substrates. Removal threshold measurements were obtained using a TEA CO 2 laser (TEM 00 mode) at wavelengths of 9.6 μm and 10.6 μm. The temperature rise in the energy transfer medium, water, was estimated at the LAPR threshold. The results suggest that superheating of the water droplet is a reasonable mechanism for LAPR. Reflection and scattering for a cw Ar + laser parallel to the substrate surface at various displacements indicated the presence of a shock wave, water vapor and ejected particles. These results are similar to time-resolved measurements of polymer ablation in which shock wave generation, propagation away from the surface at supersonic speeds and ablated particulate materials travelling at slower speeds were observed. To determine the conversion efficiency and the threshold of the shock wave, we used a self-similar approximation. The results show that we can remove particles from the surface at laser fluences significantly below the shock wave threshold.

CO2 laser assisted particle removal threshold measurements

Laser removal of particulates from solid surfaces was achieved using an energy transfer medium which preferentially adsorbs in the capillary spaces under and around the particulates on the contaminated surface. Subsequent laser irradiation causes explosive evaporation of the energy transfer medium and propels the particles off the substrate much like a small rocket engine. In our experiments, a TEA CO2 (10.6 and 9.6 μm) laser was used to remove 9.5 μm Al2O3, 5 μm Al2O3, and 1 μm polystyrene particles from Si surfaces using water as the energy transfer medium. At these wavelengths the laser energy is absorbed predominantly in the water not in the substrate. The threshold fluence for particle removal was found to follow a degenerate threshold model with measured thresholds significantly below the substrate damage threshold. The temperature rise in the energy transfer medium was estimated using energy conservation, suggesting that superheating of the adsorbed water is a reasonable mechanism for water assisted laser particle removal.

The Fate of Particles Deposited in the Intrapulmonary Conducting Airways

Inhaled particles deposited in the intrapulmonary conducting airways may be retained considerably longer than 24 hours. We studied structure and function of the 2–phase coating (gel, sol) of the wall of these airways with respect to retention and clearance of such particles. The airway surface tension was determined In vivo in sheep and horse tracheas from the spreading properties of test fluid droplets, using video bronchoscopy. Stereological analyses by light and electron microscopy were performed on hamster lungs. Immediately following inhalation, we found a number of 6 μm polystyrene particles submerged in the sol-phase and coated with surfactant. Of these particles 14% were still retained 24 hours later. The gel and sol phases were separated by a surfactant bilayer. We measured a surface tension of 31 dyn/cm in vivo, at the gel–air surface, in the trachea of sheep and horse. In vitro experiments showed that surfactant promotes the immersion of particles into the aqueous subphase. Based on our findings, we postulate, (1) that after deposition the particles are displaced into the gel–phase (initial retention) from where they may be cleared by mucociliary activity (fast clearance phase) and (2) that some particles may be further displaced into the sol–phase (prolonged retention), from where they will be cleared by airway macrophages (slow clearance phase).

Rate of movement of marker particles in the digestive tract of the rabbit.

Using small (50-100 micrometer) and large (800-1000 micrometer) polystyrene particles as a marker substance, transit through the gastrointestinal tract of the rabbit was studied during the formation of hard and soft faeces (caecotrophe). Both fractions of the marker were transported at an equal rate during soft faeces formation. During the formation of hard faeces a significantly higher amount of small particles was present in the caecum, whereas in the distal colon and rectum the number of large particles was elevated significantly.

Electrically stimulated aerosol filtration in packed beds

AbstractSince charged particles are quite mobile in an electric field, charge is often added to aerosol particles to facilitate capture; indeed, provision for such charging is an indispensable part of electrostatic precipitators. Nevertheless, calculations disclose that a very slight amount of charge may suffice when the distance the aerosol particle must travel to the collector surface is small, contrary to the usual situation. In the experiments described, here, a model aerosol containing 0.5 μm polystyrene particles passed through a radioactive charge neutralizer to deliberately reduce the charge as much as practicable and then through a packed bed under the influence of a fairly large external electric field. Filtration efficiencies approaching 100% were obtained owing to the influence of the field on small amounts of residual charge.

Aerosol particle neutralization to Boltzmann's equilibrium by a.c. corona discharge

Atomization of an aqueous suspension of 0.8 μm polystyrene particles produces highly charged aerosols. The values of the absolute mean charge unit | q| = 31 and the s.d. σ = 4.0 were obtained by charge distribution measurements. In order to neutralize the charges on aerosol particles to the values of | q| = 2.1 and σ = 2.6 given by Boltzmann's equilibrium relationship, a bipolar ion atmosphere was created by a.c. corona discharge between needle point and orifice plate electrodes. Electroneutrality of the ionic cloud was found for one value V 0, of the applied potential V, which depends upon the point-to-plate distance d, and the air velocity through the orifice v. When V < V 0 the sign of the free ion intensity was found to be negative. When V > V 0 the sign was positive. By exposing 0.8 μm aerosol charged particles to a bipolar atmosphere, the residual particle charge reflected the same behaviour as reported above. The electroneutrality was attained for V 0 = 2350 V, d = 2 mm and v = 200 m/sec. For low and higher values of V 0 the aerosol charge assumed a negative or positive value. respectively. The behaviour of the aerosol neutralization with ions created by a.c. corona is similar to the neutralization by α disintegration, where electroneutrality is attained when the source plane-to-aerosol distance corresponds to the Bragg's maximum range in air. As expected, aerosol neutralization was also attained when a bipolar atmosphere was created by two ionizers facing each other, in which the needle electrodes generated d.c. positive and negative corona discharges.

Rates of flocculation of latex particles by cationic polymers

Suspensions of 0.2 μm polystyrene particles have been flocculated with three cationic polymers differing only in molecular weight. Using a simple light scattering technique, relative rates of flocculation were obtained and optimum flocculant concentrations could be fairly dearly defined. Under given conditions the optimum concentration was independent of the molecular weight of the polymer. The rate of polymer flocculation was found to increase with decreasing ionic strength and the maximum rate observed was about twice that given by high concentrations of electrolyte or by acid. An explanation in terms of uneven charge distribution on the particles is proposed. There are indications that such studies could be extended to give information on rates of polymer adsorption and rearrangement on particle surfaces.

Do Protoplasmic Connections Function in the Phototactic Coordination of the Volvox Colony During Light Stimulation?*

SYNOPSIS. The flagellar behavior of the colonial flagellates Volvox carteri Stein and Volvox perglobator Powers was examined by placing 1.01 μm polystyrene particles in solution with swimming colonies, and photographing these particle movements. When directional light stimulation was administered to individual colonies, a cessation of flagellar activity occurred in the anterior cells of the stimulated side in both species. Since Volvox perglobator possesses prominent intercellular connections and Volvox carteri does not, the results of these experiments suggest that the connections linking colony members in some species do not function in the coordination of flagellar activity associated with light orientation behavior.