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At least 1,765 records · Page 98Linked to original sources
PubMed2000

Crystalloid or colloid resuscitation of uncontrolled hemorrhagic shock after moderate splenic injury.

Using a standardized moderate splenic injury (MSI) model of uncontrolled hemorrhagic shock, we studied the effect of vigorous crystalloid or colloid fluid resuscitation on the hemodynamic response and survival time in rats. The animals were randomized into 6 groups: group 1 (n = 8) sham-operated, group 2 (n = 10) MSI untreated, group 3 (n = 10) MSI treated with 41.5 mL/kg Ringer's lactate (large-volume Ringer's lactate [LVRL]), group 4 (n = 10) MSI treated with 5 mL/kg 7.5% NaCl (hypertonic saline [HTS]), group 5 (n = 10) MSI treated with 7.5 mL/kg hydroxyethyl starch (HES-7.5), group 6 (n = 10) MSI treated with 15 mL/kg hydroxyethyl starch (HES-15). After MSI, mean arterial pressure (MAP) in group 2 decreased from 105.0+/-5.6 to 64.0+/-12.7 mmHg (P < 0.001) after 60 min. Mean survival time was 157.4+/-28.9 min, and total blood loss was 24.0+/-5.4% of blood volume. LVRL infusion resulted in an early rise in MAP from 75.2+/-8.7 to 96.7+/-9.0 mmHg (P < 0.01), which then rapidly dropped to 43.0+/-9.7 mmHg (P < 0.001) after 60 min. The mean survival time was 140.7+/-22.3 min, and total blood loss was 41.4+/-4.8% (P < 0.05). Total blood loss following HTS infusion was 24.7+/-3.7%, and mean survival time was 177.5+/-18.9 min. HES-7.5 infusion was followed by bleeding of 25.6+/-5.1%, and mean survival time was 181+/-16.1. HES-15 infusion resulted in an increase in blood loss to 48.2+/-7.3% (P < 0.05), and mean survival time of 133.0+/-27.7 min. Large-volume Ringer's lactate (LVRL) or hydroxyethyl starch (HES-15) infusion in uncontrolled hemorrhagic shock after moderate splenic injury resulted in a significant increase in intra-abdominal bleeding, but survival time remained unchanged compared with untreated, small-volume HTS-, or HES-7.5-treated animals. The hemodynamic response to large-volume crystalloid or colloid infusion was similar to moderate large-vessel injury.

Animals↗
PubMed2003

Crystalloids and colloids in trauma resuscitation: a brief overview of the current debate.

BACKGROUND: Controversy regarding crystalloids or colloids for resuscitation has existed for over five decades, and large numbers of clinical trials have failed to resolve the controversy. In fact, the limitations of these studies have intensified the debate. This overview aims to revisit the debate of fluid resuscitation in trauma patients by critically appraising the meta-analyses on the subject. METHODS: This study was a critical analysis of six meta-analyses found by MEDLINE search. RESULTS: Overall, the choice of fluid may have a small or no effect on mortality. In trauma, the use of colloids is associated with a trend toward increased mortality. CONCLUSION: There is an urgent need for well-designed clinical trials. Because of many limitations, meta-analysis should be interpreted with caution, possibly as hypothesis generating. However, even considering all weaknesses and nuances of interpretation, the meta-analyses reviewed suggest that trauma patients should continue to be resuscitated with crystalloids.

Attitude of Health Personnel↗
PubMed2003

Dynamics of weakly aggregated colloidal particles.

We discuss the behaviour of the dynamics of colloidal particles with a weak attractive interparticle interaction that is induced through the addition of polymer to the solvent. We briefly review the description of their behaviour in terms of the jamming phase diagram, which parametrized the fluid-to-solid transition due to changes in volume fraction, attractive energy or applied stress. We focus on a discussion of ageing of the solid gels formed by these colloid-polymer mixtures. They exhibit a delayed collapse induced by gravity. The time evolution of the height of the sediment exhibits an unexpected scaling behaviour, suggesting a universal nature to this delayed collapse. We complement these measurements of the scaling of the collapse with microscopic investigations of the evolution of the structure of the network using confocal microscopy. These results provide new insight into the origin of this ageing behaviour.

Colloids↗
PubMed1999

Linear viscoelasticity of hard sphere colloidal crystals from resonance detected with dynamic light scattering.

We present measurements of the high-frequency shear modulus and dynamic viscosity for nonaqueous hard sphere colloidal crystals both in normal and microgravity environments. All experiments were performed on a multipurpose PHaSE instrument. For the rheological measurements, we detect the resonant response to oscillatory forcing with a dynamic light scattering scheme. The resonant response for colloidal crystals formed in normal and microgravity environments was similar, indicating that the bulk rheological properties are unaffected by differing crystal structure and crystallite size within the experimental error. Our high-frequency shear modulus seems reasonable, lying close to Frenkel and Ladd's predictions [Phys. Rev. Lett. 59, 1169 (1987)] for the static modulus of hard sphere crystals. Our high-frequency dynamic viscosity, on the other hand, seems high, exceeding Shikata and Pearson [J. Rheol. 38, 601 (1994)] and van der Werff et al.'s measurements [Phys. Rev. A 39, 795 (1989)] on the high-frequency dynamic viscosity for metastable fluids. The measurements are in the linear regime for the shear modulus but may not be for the dynamic viscosity as Frith et al. [Powder Technol. 51, 27 (1987)] report that the dynamic viscosity passes through a maximum with strain amplitude.

Colloids↗
PubMed2001

Kinetics of crystallization in hard-sphere colloidal suspensions.

We propose a kinetic model for describing crystal nucleation kinetics in hard-sphere colloidal suspensions. The model captures the interplay between the enhanced thermodynamic driving force and the reduced particle diffusivity in determining crystal nucleation rates as the particle density is increased in hard-sphere suspensions. Model calculations of nucleation rates and crystal growth velocities agree quantitatively with experimental observations. The dependence of the critical cluster size on volume fraction that emerges differs qualitatively from predictions of classical theories allowing for an experimental validation of the mechanism of crystal nucleation in colloidal suspensions.

Colloids↗
PubMed2002

Diffusing wave spectroscopy and small-angle neutron scattering from concentrated colloidal suspensions.

We have studied the properties of dense colloidal suspensions with a combination of small-angle neutron scattering (SANS) and diffusing wave spectroscopy (DWS). Contrary to single light scattering, DWS provides dynamic information on length scales, from 1 to 100 nm, comparable to SANS. This offers a unique range of accessible length and time scales perfectly suited for the (noninvasive) investigation of highly concentrated systems. By this we obtain valuable information about the structural properties and the short-time diffusion of electrostatically stabilized, but strongly screened, hard-sphere-like colloidal suspensions with volume fractions up to 30%. We furthermore discuss the consequences of local structural ordering on the optical properties, such as optical density and polarization. Quantitative agreement is found when comparing transmission measurements (optical density) with parameter-free numerical calculations based on the structural characterization from SANS.

Biophysics↗
PubMed2002

Osmotic pressure of charged colloidal suspensions: a unified approach to linearized Poisson-Boltzmann theory.

We study theoretically the equation of state of a fluid suspension of charged objects (e.g., colloids, polyelectrolytes, clay platelets, etc.) dialyzed against an electrolyte solution using the cell model and linear Poisson-Boltzmann (PB) theory. From the volume derivative of the grand potential functional of linear theory we obtain two expressions for the osmotic pressure in terms of the potential or ion profiles, neither of which coincides with the expression known from nonlinear PB theory, namely, the density of microions at the cell boundary. We show that the range of validity of linearization depends strongly on the linearization point and prove that expansion about the self-consistently determined average potential is optimal in several respects. For instance, screening inside the suspension is automatically described by the actual ionic strength, resulting in the correct asymptotics at high colloid concentration. Together with the analytical solution of the linear PB equation for cell models of arbitrary dimension and electrolyte composition, explicit and very general formulas for the osmotic pressure ensue. A comparison with nonlinear PB theory is provided. Our analysis also shows that whether or not linear theory predicts a phase separation depends crucially on the precise definition of the pressure, showing that depending on the choice, an artificial phase separation in systems as important as DNA in physiological salt solution may result.

Biophysical Phenomena↗
PubMed2003

Dynamic density functional study of a driven colloidal particle in polymer solutions.

The dynamic density functional (DDF) theory and standard Brownian dynamics simulations (BDS) are used to study the drifting effects of a colloidal particle in a polymer solution, both for ideal and interacting polymers. The structure of the stationary density distributions and the total induced current are analyzed for different drifting rates. We find good agreement with the BDS, which gives support to the assumptions of the DDF theory. The qualitative aspect of the density distribution are discussed and compared to recent results for driven colloids in one-dimensional channels and to analytical expansions for the ideal solution limit.

Colloids↗
PubMed2004

Elastic deformation of a fluid membrane upon colloid binding.

When a colloidal particle adheres to a fluid membrane, it induces elastic deformations in the membrane which oppose its own binding. The structural and energetic aspects of this balance are investigated within the framework of a Helfrich Hamiltonian. Based on the full nonlinear shape equations for the membrane profile, a line of continuous binding transitions and a second line of discontinuous envelopment transitions are found, which meet at an unusual triple point. The regime of low tension is studied analytically using a small gradient expansion, while in the limit of large tension scaling arguments are derived which quantify the asymptotic behavior of phase boundary, degree of wrapping, and energy barrier. The maturation of animal viruses by budding is discussed as a biological example of such colloid-membrane interaction events.

Binding Sites↗
PubMed2004

Diffraction in crystalline colloidal-array photonic crystals.

We characterized the diffraction and crystal structure of a crystalline colloidal array (CCA) photonic crystal composed of 270 nm diameter polystyrene spheres which have a nearest neighbor spacing of approximately 540 nm. This CCA diffracts light in first order at approximately 1200 nm and shows strong diffraction in the visible spectral region from higher order planes. We quantitatively examined the relative diffraction intensities of the putative fcc (111), (200), (220), and (311) planes. Comparing these intensities to those calculated theoretically we find that the crystal structure is fcc with significant stacking faults. Essentially, no light transmits at the Bragg angle for the fcc (111) planes even through thin approximately 40 microm thick CCA. However, much of this light is diffusely scattered about the Bragg angle due to crystal imperfections. Significant transmission occurs from thin samples oriented at the Bragg condition for the fcc (200), (220), and (311) planes. We also observe moderately intense two-dimensional diffraction from the first few layers at the crystal surfaces. We also examined the sample thickness dependence of diffraction from CCA photonic crystals prepared from approximately 120 nm polystyrene spheres whose fcc (111) planes diffract in the visible spectral region. These experimental observations, aided by calculations based upon a simple but flexible model of light scattering from an arbitrary collection of colloidal spheres, make clear that fabrication of three-dimensional photonic band gap crystals will be challenged by crystal imperfections.

Biophysics↗
PubMed2006

Statistical mechanics of DNA-mediated colloidal aggregation.

We present a statistical mechanical model of aggregation in colloidal systems with DNA-mediated interactions. We obtain a general result for the two-particle binding energy in terms of the hybridization free energy DeltaG of DNA and two model-dependent properties: the average number of available DNA bridges and the effective DNA concentration c(eff). We calculate these parameters for a particular DNA bridging scheme. The fraction of all the n-mers, including the infinite aggregate, are shown to be universal functions of a single parameter directly related to the two-particle binding energy. We explicitly take into account the partial ergodicity of the problem resulting from the slow DNA binding-unbinding dynamics, and introduce the concept of angular localization of DNA linkers. In this way, we obtain a direct link between DNA thermodynamics and the global aggregation and melting properties in DNA-colloidal systems. The results of the theory are shown to be in quantitative agreement with two recent experiments with particles of micron and nanometer size.

Colloids↗
PubMed2001

Specific ion effects: why DLVO theory fails for biology and colloid systems.

The classical Derjaguin-Landau-Verwey-Overbeek theory that underpins colloid and surface science is shown to be flawed, especially at biological salt concentrations. This is in part because the dispersion forces acting on the ions are ignored. When these are included properly very different results are obtained. These results have substantial implications for biological and for ordinary colloid systems at moderate salt concentrations.

Algorithms↗
PubMed2005

Colloidal interactions and self-assembly using DNA hybridization.

The specific binding of complementary DNA strands has been suggested as an ideal method for directing the controlled self-assembly of microscopic objects. We report the first direct measurements of such DNA-induced interactions between colloidal microspheres, as well as the first colloidal crystals assembled using them. The interactions measured with our optical tweezer method can be modeled in detail by well-known statistical physics and chemistry, boding well for their application to directed self-assembly. The microspheres' binding dynamics, however, have a surprising power-law scaling that can significantly slow annealing and crystallization.

Colloids↗
PubMed2005

Evidence of many-particle interactions in two-dimensional charge-stabilized colloidal crystals.

Electrostatic interaction in two-dimensional colloidal crystals obeying the nonlinear Poisson-Boltzmann equation is studied numerically. The force constants which are the coefficients of the energy quadratic form of the crystal are obtained. Significant discrepancy between the results of computer experiments and predictions of the harmonic crystal theory based on the idea of pairwise interaction has been detected. Two simple parameters are introduced for uniform quantitative estimation of many-particle effects and validity of the approximation of nearest-neighbor interaction. It is shown that the contribution of many-particle interaction into the total electrostatic interaction in colloidal crystals is significant for a broad range of crystal lattice constants and particles' sizes.

Colloids↗
PubMed2006

Direct numerical simulations of electrophoresis of charged colloids.

We propose a numerical method to simulate electrohydrodynamic phenomena in charged colloidal dispersions. This method enables us to compute the time evolutions of colloidal particles, ions, and host fluids simultaneously by solving Newton, advection-diffusion, and Navier-Stokes equations so that the electrohydrodynamic couplings can be fully taken into account. The electrophoretic mobilities of charged spherical particles are calculated in several situations. The comparisons with approximation theories show quantitative agreements for dilute dispersions without any empirical parameters; however, our simulation predicts notable deviations in the case of dense dispersions.

Colloids↗
PubMed2002

Flow-rate measurements and models for colloid and crystalloid flows in central and peripheral venous line infusion systems.

The resuscitation fluids, including crystalloids and colloids, were tested in an experimental module with 16-gauge central and peripheral catheters. Infusion pressures were ranged from the gravity driving 10 kPa (75 mmHg) to the pressurized driving 50 kPa (375 mmHg). The experiment results were correlated to obtain the empirical friction factors and the loss factors for the components commonly used in a fluid resuscitation system. The modified Bernoulli equation with the correlated friction factors and loss factors for the components were used to evaluate the pressure and flow relationship in the fluid resuscitation system with peripheral and central catheters. Fair agreements were observed from the comparison of the predictions of the total driving pressure and test results from water, crystalloid and colloid solutions. The modified Bernoulli equation is, therefore, applicable to evaluate the pressure-flow relationship for efficient fluid resuscitations. The coefficients of flow (F) and the square of flow (F2) for the binominal model are varied with the changes of geometry and size of the infusion components, fluid properties and the units of parameters. These coefficients for the fluids and catheters tested in this study were also listed for reference.

Blood Flow Velocity↗
PubMed2006

Nanofabrication of polymer surfaces utilizing colloidal lithography and ion etching.

In this paper, we utilize colloidal lithography based on electrostatic self-assembly of polystyrene colloidal particles onto a polymer surface as a nanoscale mask. The pattern is then transferred to the surface by ion beam etching. Each particle acts as an individual mask, resulting in an array of identical structure. Ion beam exposure etches away the unmasked surface between the particles, so the particle mask pattern can be transferred into the polymer surface. This method allows to nanofabricate bulk polymeric surfaces with systematic variation in relief, structure sizes, and aspect ratios. It is a fast, simple, and reliable method to fabricated different polymeric surfaces even on large area samples (> 1 cm2). The structural variation is achieved by use of different conditions during the self-assembly of the mask (e.g., different particles sizes) or different ion etching conditions during the pattern transfer (e.g., ion energy, ion flux, ion incident angle, etching time, gas environment).

Biocompatible Materials↗
PubMed2003

Roles of conformational stability and colloidal stability in the aggregation of recombinant human granulocyte colony-stimulating factor.

We studied the non-native aggregation of recombinant human granulocyte stimulating factor (rhGCSF) in solution conditions where native rhGCSF is both conformationally stable compared to its unfolded state and at concentrations well below its solubility limit. Aggregation of rhGCSF first involves the perturbation of its native structure to form a structurally expanded transition state, followed by assembly process to form an irreversible aggregate. The energy barriers of the two steps are reflected in the experimentally measured values of free energy of unfolding (DeltaG(unf)) and osmotic second virial coefficient (B(22)), respectively. Under solution conditions where rhGCSF conformational stability dominates (i.e., large DeltaG(unf) and negative B(22)), the first step is rate-limiting, and increasing DeltaG(unf) (e.g., by the addition of sucrose) decreases aggregation. In solutions where colloidal stability is high (i.e., large and positive B(22) values) the second step is rate-limiting, and solution conditions (e.g., low pH and low ionic strength) that increase repulsive interactions between protein molecules are effective at reducing aggregation. rhGCSF aggregation is thus controlled by both conformational stability and colloidal stability, and depending on the solution conditions, either could be rate-limiting.

Colloids↗