Near-wall velocities of particles suspended in shear flow and a streamwise electric field.

Particles with a diameter of ∼0.5 µm in a dilute (volume fractions φ∞  < 4 × 10-3 ) suspension assemble into highly elongated structures called "bands" under certain conditions in combined Poiseuille and electroosmotic flows in opposite directions through microchannels at particle-based Reynolds numbers Rep  < < 1. The particles are first concentrated near, then form "bands" within ∼6 µm of, the channel wall. The experiments described here examine the near-wall dynamics of individual "tracer" particles during the initial concentration, or accumulation, of particles, and the steady-state stage when the particles have formed relatively stable bands at different near-wall shear rates and electric field magnitudes. Surprisingly, the near-wall upstream particle velocities are found to be consistently greater in magnitude than the expected values based on the particles being convected by the superposition of both flows and subject to electrophoresis, which is in the same direction as the Poiseuille flow. However, the particle velocities scale linearly with the change in electric field magnitude, suggesting that the particle dynamics are dominated by linear electrokinetic phenomena. If this discrepancy with theory is only due to changes in particle electrophoresis, electrophoresis is significantly reduced to values as small as 20%-50% of the Smoluchowski relation, or well below previous model predictions, even for high particle potentials.

Observations of the near-wall accumulation of suspended particles due to shear and electroosmotic flow in opposite directions.

On the basis of previous studies, the particles in a dilute (volume fractions φ∞ < 4 × 10-3 ) suspension in combined Poiseuille and electroosmotic "counterflow" at flow Reynolds numbers Re ≤ 1 accumulate, then assemble into structures called "bands," within ∼6 µm of the channel wall. The experimental studies presented here use a small fraction of tracer particles labeled with a different fluorophore from the majority "bulk" particles to visualize the dynamics of individual particles in a φ∞ = 1.7 × 10-3  suspension. The results at two different near-wall shear rates and three electric field magnitudes E show that the near-wall particles are concentrated about 150-fold when the bands start to form, and are then concentrated about 200-fold to a maximum near-wall volume fraction of ∼0.34. The growth in the near-wall particles during this accumulation stage appears to be exponential. This near-wall particle accumulation is presumably driven by a wall-normal "lift" force. The observations of how the particles accumulate near the wall are compared with recent analyses that predict that suspended particles subject to shear flow and a dc electric field at small particle Reynolds numbers experience such a lift force. A simple model that assumes that the particles are subject to this lift force and Stokes drag suggests that the force driving particles toward the wall, of O(10-17 N), is consistent with the time scales for particle accumulation observed in the experiments.

Predictive factors of response to IVIG in pediatric immune thrombocytopenic purpura.

BACKGROUND: Immune thrombocytopenic purpura (ITP) is commonly treated with i.v. immunoglobulin (IVIG). METHODS: We retrospectively evaluated whether pretreatment clinical and laboratory finding could predict the short- and long-term response to IVIG. RESULTS: Short-term response was estimated by platelet count 2 weeks after IVIG, and long-term response was assessed on thrombocytopenia-free survival (TFS). TFS was defined as the probability of survival without treatment failure after initial IVIG, such as relapse, requirement for additional therapeutic interventions, or progressing to chronic ITP. Seventy-six patients with newly diagnosed ITP who were initially treated with IVIG were evaluated. Fifty-three patients (69.7%) were determined as responders at 2 weeks after IVIG. On multivariate analysis, age ≥23 months (P = 0.020) and platelet count <9.0 × 109 /L (P = 0.018) were considered to be unfavorable factors for short-term response. Cumulative proportion of long-term (1 year) good prognosis was estimated at 53.0% (95%CI: 40.8-65.2). On multivariate analysis of unfavorable factors for long-term response, age ≥23 months (P = 0.020) was the only significant factor. CONCLUSIONS: For new-onset ITP in patients aged >2 years, corticosteroid therapy in addition to IVIG may be considered as the initial treatment.

Lift forces on colloidal particles in combined electroosmotic and Poiseuille flow.

Colloidal particles suspended in aqueous electrolyte solutions flowing through microchannels are subject to lift forces that repel the particles from the wall due to the voltage and pressure gradients commonly used to drive flows in microfluidic devices. There are very few studies that have considered particles subject to both an electric field and a pressure gradient, however. Evanescent-wave particle tracking velocimetry was therefore used to investigate the near-wall dynamics of a dilute suspension of 245 nm radius polystyrene particles in a monovalent electrolyte solution in Poiseuille and combined electroosmotic (EO) and Poiseuille flow through 30-µm-deep fused-silica channels. The lift force observed in Poiseuille flow, which is estimated from the near-wall particle distribution, appears to be proportional to the shear rate, a scaling consistent with hydrodynamic lift forces previously reported in field-flow fractionation studies. The estimates of the lift force observed in combined flow suggest that the force magnitude exceeds the sum of the lift forces observed in EO flow at the same electric field or in Poiseuille flow at the same shear rate. Moreover, the force magnitude appears to be proportional to the electric field magnitude and have a power law dependence on the shear rate with an exponent between 0.4 and 0.5. This unexpected scaling suggests that the repulsive lift force observed in combined electroosmotic and Poiseuille flow is a new phenomenon, distinct from previously reported electroviscous, hydrodynamic lift, or dielectrophoretic-like forces, and warrants further study.

Evanescent-wave particle velocimetry measurements of zeta-potentials in fused-silica microchannels.

The wall ζ-potential ζ(w), the potential at the shear plane of the electric double layer, depends on the properties of the BGE solution such as the valence and type of electrolyte, the pH and the ionic strength. Most of the methods estimate ζ(w) from measurements of the EOF velocity magnitude ueo , usually spatially averaged over the entire capillary. In these initial studies, evanescent-wave particle velocimetry was used to measure ueo in steady EOF for a variety of monovalent aqueous solutions to evaluate the effect of small amounts of divalent cations, as well as the pH and ionic strength of BGE solutions. In brief, the magnitude of the EOF velocity of NaCl-NaOH and borate buffer-NaOH solutions was estimated from the measured velocities of radius α = 104 nm fluorescent polystyrene particles in 33 µm fused-silica microchannels. The particle ζ-potentials were measured separately using laser-Doppler micro-electrophoresis; ζ(w) was then determined from ueo. The results suggest that evanescent-wave particle velocimetry can be used to estimate ζ(w) for a variety of BGE solutions, and that it can be used in the future to estimate local wall ζ-potential, and hence spatial variations in ζ(w).

Experimental study of the effect of external electric fields on interfacial dynamics of colloidal particles.

The interaction of colloidal particles with a planar surface (i.e., wall) in the presence of an electric field applied parallel to the planar surface is of interest in various microfluidic devices. Evanescent wave-based particle-tracking velocimetry was used to investigate the dynamics of a dilute suspension of polystyrene and silica particles (radii a = 110-463 nm) in a monovalent electrolyte solution with a Debye length of 6.8 nm driven through a microchannel by external electric fields E = 15-31 V/cm over the first 300 nm next to the channel wall. The particle velocity parallel to the wall due to electrophoresis and electroosmosis was in good agreement with the Helmholtz-Smoluchowski relation, and the hydrodynamic interactions between the wall and the particles were negligible, for all particle types. Measurements of the distribution of particles along the wall-normal coordinate, however, suggest that an additional force as great as 30 fN that repels the negatively charged particles away from the wall is induced by nonzero E. The results suggest that the magnitude of this force scales as E(2) and a(2) but is independent of the particle ζ-potential, in agreement with previous theoretical studies. However, estimates of the force assuming that the particles have a Boltzmann distribution were up to 40 times greater than the theoretical predictions, which only considered "remote" particle-wall interactions. These results are, to our knowledge, the first to observe a repulsive wall-normal force due to an applied electric field for near-wall colloidal particles.

Acoustically induced streaming flows near a model cod otolith and their potential implications for fish hearing.

The ears of fishes are remarkable sensors for the small acoustic disturbances associated with underwater sound. For example, each ear of the Atlantic cod (Gadus morhua) has three dense bony bodies (otoliths) surrounded by fluid and tissue, and detects sounds at frequencies from 30 to 500 Hz. Atlantic cod have also been shown to localize sounds. However, how their ears perform these functions is not fully understood. Steady streaming, or time-independent, flows near a 350% scale model Atlantic cod otolith immersed in a viscous fluid were studied to determine if these fluid flows contain acoustically relevant information that could be detected by the ear's sensory hair cells. The otolith was oscillated sinusoidally at various orientations at frequencies of 8-24 Hz, corresponding to an actual frequency range of 280-830 Hz. Phase-locked particle pathline visualizations of the resulting flows give velocity, vorticity, and rate of strain fields over a single plane of this mainly two-dimensional flow. Although the streaming flows contain acoustically relevant information, the displacements due to these flows are likely too small to explain Atlantic cod hearing abilities near threshold. The results, however, may suggest a possible mechanism for detection of ultrasound in some fish species.

Quantitative evaluation of latent fingermarks with novel enhancement and illumination.

A variety of suspended silica and metal nanoparticles have been used over the last 20 years to enhance latent fingermarks. This study quantitatively evaluates enhancement of natural and sebum-enriched fingermarks from three adult subjects acquired with a consistent applied force on glass with a fingermark press using suspended commercially available polystyrene (PS) particles. Images of the enhanced fingermarks acquired with total internal reflection (TIR), or standard overhead white light (WL), illumination are compared with fingermarks enhanced with conventional methods including cyanoacrylate fuming. The different enhancement and illumination methods are quantified based on the brightness and contrast of the fingermark images, as well as the number of minutiae that can be identified and matched to those on an inked manually acquired "template" fingermark using automatic fingerprint identification system (AFIS) software. Enhanced fingermarks acquired with the press are shown to be more consistent than manually acquired fingermarks based on these metrics. The results demonstrate that TIR illumination from a large-area illuminator built in house gives enhanced fingermark images with more matched minutiae and contrast superior to that for WL illumination for all types of enhancement. "Wet-powdering" with PS particles gives fingermark images that are for the most part comparable in terms of the number of matched minutiae to fingermarks enhanced with more conventional methods, suggesting that this novel enhancement method has a performance comparable to conventional enhancement methods. Interestingly, the age of the fingermark appears to have almost no effect on this new type of enhancement; sebum-enriched fingermarks ranging in age from 12 h to 435 days appear to have statistically identical numbers of matched minutiae.

Treatment of McLeod phenotype chronic granulomatous disease with reduced-intensity conditioning and unrelated-donor umbilical cord blood transplantation.

Patients with chronic granulomatous disease (CGD) complicated by antimycotics-refractory invasive aspergillosis have an extremely poor prognosis if they cannot undergo allogeneic hematopoietic stem cell transplantation from a suitable related donor while in good clinical condition. We successfully treated a 20-year-old man with very rare McLeod phenotype CGD with reduced-intensity conditioning and unrelated-donor umbilical cord blood transplantation. We postulate that reduced-intensity conditioning-allogeneic hematopoietic stem cell transplantation is a promising therapeutic strategy for patients with CGD even if only unrelated-donor umbilical cord blood is available.

Electrokinetically driven reversible banding of colloidal particles near the wall.

Polystyrene microparticles of 0.5 µm diameter form long-lived streamwise bands within 1 µm of the wall in the combined steady electroosmotic (EO) and Poiseuille flow of a dilute particle suspension through fused-silica microchannels. The bands disappear when the electric field driving the EO flow is turned off, and the band characteristics can be changed by adjusting the flow parameters. To our knowledge, these are the first observations of near-wall particle self-assembly due to shear and steady electric fields.

Determination of the deletion breakpoints in two patients with contiguous gene syndrome encompassing CYBB gene.

X-linked chronic granulomatous disease is a primary immunodeficiency caused by mutations in CYBB. Although large deletions involving CYBB are known to cause contiguous gene syndrome (CGS), only a few patients have been studied precisely at the molecular levels. Our study determined the deletion breakpoints in two patients with CGS involving CYBB by array comparative genomic hybridization and the following PCR and DNA walking studies. The deletion size was 3.5 Mb in Patient 1 and 0.8 Mb in Patient 2. There were no homologous architectural features between the telomeric and centromeric breakpoint junctions in the deletions of either patient. However, the telomeric breakpoint of Patient 2 was embedded in a stretch of low-copy repeats and the centromeric breakpoint was also embedded in a stretch of short segments with significant sequence homology. These findings suggest the potential involvement of genome architecture in stimulating genomic rearrangements in Patient 2.