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At least 631 records · Page 35Linked to original sources
PubMed2002

Adult-onset facial colloid milium successfully treated with the long-pulsed Er:YAG laser.

BACKGROUND: Adult colloid milium is a rare cutaneous deposition disorder that frequently involves areas of chronic sun exposure, especially the face and dorsal hands. Attempts to remove these lesions are generally unsuccessful, but dermabrasion has been reported to be effective. OBJECTIVE: To present an effective therapeutic alternative to dermabrasion for facial colloid milium. METHODS: A 41-year-old man with extensive facial colloid milium underwent full-face resurfacing with a long-pulsed Er:YAG laser (9.8 J/cm2, 5 mm spot, 10-msec pulse duration). Additional passes were performed over the areas of dense colloid milium to achieve approximately 80% ablation of lesions.results. At the 7-month follow-up there was no scarring, textural changes, dyspigmentation, or clinical evidence of recurrence. CONCLUSION: Long-pulsed Er:YAG laser should be considered an effective alternative to dermabrasion for facial colloid milium.

Adult↗
PubMed2004

Interactions between colloidal particles in polymer solutions: A density functional theory study.

We present a density functional theory study of colloidal interactions in a concentrated polymer solution. The colloids are modeled as hard spheres and polymers are modeled as freely jointed tangent hard sphere chains. Our theoretical results for the polymer-mediated mean force between two dilute colloids are compared with recent simulation data for this model. Theory is shown to be in good agreement with simulation. We compute the colloid-colloid potential of mean force and the second virial coefficient, and analyze the behavior of these quantities as a function of the polymer solution density, the polymer chain length, and the colloid/polymer bead size ratio.

Journal Article↗
PubMed2005

Combining molecular dynamics with Lattice Boltzmann: a hybrid method for the simulation of (charged) colloidal systems.

We present a hybrid method for the simulation of colloidal systems that combines molecular dynamics (MD) with the Lattice Boltzmann (LB) scheme. The LB method is used as a model for the solvent in order to take into account the hydrodynamic mass and momentum transport through the solvent. The colloidal particles are propagated via MD and they are coupled to the LB fluid by viscous forces. With respect to the LB fluid, the colloids are represented by uniformly distributed points on a sphere. Each such point [with a velocity V(r) at any off-lattice position r] is interacting with the neighboring eight LB nodes by a frictional force F = xi0(V(r)-u(r)), with xi0 being a friction coefficient and u(r) being the velocity of the fluid at the position r. Thermal fluctuations are introduced in the framework of fluctuating hydrodynamics. This coupling scheme has been proposed recently for polymer systems by Ahlrichs and Dunweg [J. Chem. Phys. 111, 8225 (1999)]. We investigate several properties of a single colloidal particle in a LB fluid, namely, the effective Stokes friction and long-time tails in the autocorrelation functions for the translational and rotational velocity. Moreover, a charged colloidal system is considered consisting of a macroion, counterions, and coions that are coupled to a LB fluid. We study the behavior of the ions in a constant electric field. In particular, an estimate of the effective charge of the macroion is yielded from the number of counterions that move with the macroion in the direction of the electric field.

Journal Article↗
PubMed2005

Mixtures of charged colloid and neutral polymer: influence of electrostatic interactions on demixing and interfacial tension.

The equilibrium phase behavior of a binary mixture of charged colloids and neutral, nonadsorbing polymers is studied within free-volume theory. A model mixture of charged hard-sphere macroions and ideal, coarse-grained, effective-sphere polymers is mapped first onto a binary hard-sphere mixture with nonadditive diameters and then onto an effective Asakura-Oosawa model [S. Asakura and F. Oosawa, J. Chem. Phys. 22, 1255 (1954)]. The effective model is defined by a single dimensionless parameter-the ratio of the polymer diameter to the effective colloid diameter. For high salt-to-counterion concentration ratios, a free-volume approximation for the free energy is used to compute the fluid phase diagram, which describes demixing into colloid-rich (liquid) and colloid-poor (vapor) phases. Increasing the range of electrostatic interactions shifts the demixing binodal toward higher polymer concentration, stabilizing the mixture. The enhanced stability is attributed to a weakening of polymer depletion-induced attraction between electrostatically repelling macroions. Comparison with predictions of density-functional theory reveals a corresponding increase in the liquid-vapor interfacial tension. The predicted trends in phase stability are consistent with observed behavior of protein-polysaccharide mixtures in food colloids.

Journal Article↗
PubMed2005

Effective interactions in the colloidal suspensions from hypernetted-chain theory.

The hypernetted-chain (HNC) Ornstein-Zernike integral equations are used to determine the properties of simple models of colloidal solutions where the colloids and ions are immersed in a solvent considered as a dielectric continuum and have a size ratio equal to 80 and a charge ratio varying between 1 and 4000. At an infinite dilution of colloids, the effective interactions between colloids and ions are determined for ionic concentrations ranging from 0.001 to 0.1 mol/l and compared to those derived from the Poisson-Boltzmann theory. At finite concentrations, we discuss on the basis of the HNC results the possibility of an unambiguous definition of the effective interactions between the colloidal molecules.

Journal Article↗
PubMed2006

Anomalous potentials from inverse analyses of interfacial polydisperse attractive colloidal fluids.

This paper investigates effects of using monodisperse inverse analyses to extract particle-particle and particle-surface potentials from simulated interfacial colloidal fluids of polydisperse attractive particles. Effects of polydispersity are investigated as functions of particle concentration and attractive well depth and range for van der Waals and depletion potentials. Forward Monte Carlo simulations are used to generate particle distribution functions for polydisperse interfacial colloidal fluids from which inverted potentials are obtained using an inverse Ornstein-Zernike analysis and an inverse Monte Carlo simulation method. Attractive potentials are successfully recovered for monodisperse colloidal fluids, but polydispersity that is unaccounted for in inverse analyses produces (1) apparent softening of strong forces, (2) anomalous repulsive and attractive interactions, and (3) aphysical particle overlaps. This investigation provides insights into the role of polydispersity in altering the equilibrium structure and corresponding inverted potentials of attractive colloidal fluids near surfaces. These findings should assist the design and interpretation of optical microscopy experiments involving interfacial colloidal fluids similar to the simulated experiments reported here.

Journal Article↗
PubMed2006

Self-diffusion in submonolayer colloidal fluids near a wall.

Theoretical expressions are developed to describe self-diffusion in submonolayer colloidal fluids that require only equilibrium structural information as input. Submonolayer colloidal fluids are defined for the purpose of this work to occur when gravity confines colloids near a planar wall surface so that they behave thermodynamically as two dimensional fluids. Expressions for self-diffusion are generalized to consider different colloid and surface interaction potentials and interfacial concentrations from infinite dilution to near fluid-solid coexistence. The accuracy of these expressions is demonstrated by comparing self-diffusion coefficients predicted from Monte Carlo simulated equilibrium particle configurations with standard measures of self-diffusion evaluated from Stokesian Dynamics simulated particle trajectories. It is shown that diffusivities predicted for simulated equilibrium fluid structures via multibody hydrodynamic resistance tensors and particle distribution functions display excellent agreement with values computed from mean squared displacements and autocorrelation functions of simulated tracer particles. Results are obtained for short and long time self-diffusion both parallel and normal to underlying planar wall surfaces in fluids composed of particles having either repulsive electrostatic or attractive van der Waals interactions. The demonstrated accuracy of these expressions for self-diffusion should allow their direct application to experiments involving submonolayer colloidal fluids having a range of interaction potentials and interfacial concentrations.

Journal Article↗
PubMed2006

Three-particle correlation functions of quasi-two-dimensional one-component and binary colloid suspensions.

We report the results of experimental determinations of the triplet correlation functions of quasi-two-dimensional one-component and binary colloid suspensions in which the colloid-colloid interaction is short ranged. The suspensions studied range in density from modestly dilute to solid. The triplet correlation function of the one-component colloid system reveals extensive ordering deep in the liquid phase. At the same density the ordering of the larger diameter component in a binary colloid system is greatly diminished by a very small amount of the smaller diameter component. The possible utilization of information contained in the triplet correlation function in the theory of melting of a quasi-two-dimensional system is briefly discussed.

Journal Article↗
PubMed1994

Effects of macromolecular chelating agents on the release of 239Pu and 59Fe from rat alveolar macrophages after phagocytic uptake of 239Pu-59Fe-iron hydroxide colloid.

The chelation-mediated mobilization of 239Pu and 59Fe from rat alveolar macrophages which had engulfed 239Pu-59Fe-hydroxide colloids was studied by exposing the macrophages to diethylenetriaminepentaacetic acid and macromolecular weight forms of diethylenetriaminepentaacetic acid. The release of 239Pu and 59Fe by these macromolecular weight chelating agents and diethylenetriaminepentaacetic acid was assessed in monolayer culture and shown to be dependent upon the nature of the engulfed colloids. Whereas calcium-diethylenetriaminepentaacetic acid, aminoethylcellulose-diethylenetriaminepentaacetic acid, and aminoethylcellulose-diethylenetriaminepentaacetic acid oxidized with periodic acid (aminoethylcellulose-diethylenetriaminepentaacetic acid(I2) exhibited some effectiveness at releasing 239Pu and 59Fe from macrophages which had engulfed the low aggregative colloid, they were less effective in the release of these radionuclides from the high aggregative colloid. The efficacy of these chelating agents on the removal of radionuclides from alveolar macrophages differed between iron and plutonium, suggesting the significant difference in the dissolution and subsequent metabolism of these radionuclides in alveolar macrophages. From the similarities of the percentage increases in 239Pu mobilized from the low aggregate colloid by aminoethylcellulose-diethylenetriaminepentaacetic acid (I2) and diethylenetriaminepentaacetic acid, it would appear that both forms of diethylenetriaminepentaacetic acid could be accessing the same deposits of 239Pu; however, for 59Fe the percentage increases are quite different for the two forms of diethylenetriaminepentaacetic acid. SiO2-diethylenetriaminepentaacetic acid, an insoluble macromolecular weight chelating agent, was ineffective at releases 239Pu but was slightly effective at releasing radioiron.

Animals↗
PubMed2001

Infratentorial supracerebellar approach to the colloid cysts of the third ventricle.

OBJECTIVE: The transcallosal and the frontal transcortical approaches are the most widely used methods in surgery of third ventricle colloid cysts. However, these approaches require traction of the frontal lobe and dissection of the corpus callosum or corticotomy and involve some postoperative consequences. The rationale of the proposed method is to remove the colloid cyst by the infratentorial supracerebellar approach and the posterior wall of the third ventricle without dissection of any neural structures. METHODS: Five patients with a colloid cyst of the third ventricle were operated on by the proposed method. The first patient presented with several months' history of symptoms that included increased intracranial pressure and right-sided cerebellar signs, caused by a metastatic tumor of the right cerebellar hemisphere. The other four patients had symptoms including intracranial hypertension for an extended period of time without any other neurological deficits. In all patients, magnetic resonance imaging revealed a colloid cyst of the third ventricle without hydrocephalus. TECHNIQUE: With the infratentorial supracerebellar approach, the arachnoid of the quadrigeminal cistern is dissected. The pineal body is separated and displaced from the internal vein medially, and the posterior velum interpositum is opened. Perforation of the inferior layer of the tela choroidea just above the suprapineal recess allows opening of the third ventricle cavity. A foraminal region is exposed after a slight lateral displacement of medial surfaces of the thalamus along the third ventricle roof. CONCLUSION: The proposed approach through the infratentorial supracerebellar space and the posterior wall of the third ventricle may be used for removal of colloid cysts, especially in patients in whom the lateral ventricles are not enlarged.

Adolescent↗
PubMed2003

Sentinel node detection using 99mTc-rhenium sulphide colloid in breast cancer patients: evaluation of 1 day and 2 day protocols, and a dose-finding study.

Sentinel node (SN) biopsy is a promising replacement for standard axillary lymph node dissection for the staging of early breast cancer, and various techniques have been studied to identify SNs with dye or radioactive colloid. This study assesses the effect of the dose of radioactivity and the time before biopsy in order to set standards for the use of 99mTc-rhenium sulphide for the detection of SNs in breast cancer patients. Sixty patients with stage T1-2 N0 M0 breast cancer underwent SN biopsy, which was immediately followed by standard axillary dissection to confirm the SN results. For SN biopsy, 99mTc-rhenium colloid was injected peritumorally. A 1 day (morning injection and afternoon surgery) or 2 day (day before afternoon injection and morning surgery) protocol was applied. A dose-finding study was performed simultaneously using 7.4-37 MBq for the 1 day protocol and 37-74 MBq for the 2 day protocol. A scintigram was taken at 2 h for the 1 day protocol and 16 h for the 2 day protocol. After the injection of blue dye, SN biopsy was performed with a gamma probe, followed by standard axillary node dissection. The radiation exposure received by the surgical team during the operation was monitored. Histopathological comparison between SNs and axillary nodes was performed. Patient characteristics that might affect the radiocolloid uptake by SNs were assessed. SNs were identified in all patients regardless of the dose or administration protocol used. Two patients showed false negative pathological SN results, and the negative predictive value was 96% and the positive predictive value was 100%. In addition, radiation exposure to the surgical team and the amount of radioactive surgical waste were low, especially at lower doses. Two groups of patient characteristics were related to SN uptake. One was the body mass index (BMI) and the other was the age or menopausal status. Patients with a larger BMI tended to take up a smaller amount of 99mTc colloid. Older or post-menopausal patients showed lower SN uptake. 99mTc-rhenium sulphide colloid is an efficient radiopharmaceutical for SN detection. Both 1 day and 2 day protocols have equally good efficacy, and the recommended dose is 7.4 MBq for the 1 day protocol and 37 MBq for the 2 day protocol. Patients with larger BMI and older or post-menopausal patients tend to take up less 99mTc colloid.

Adult↗
PubMed2003

188Re-tin-colloid as a new therapeutic agent for rheumatoid arthritis.

Radiation synovectomy is a useful treatment modality in patients with refractory synovitis. We have developed a 188Re-tin-colloid as a new radiopharmaceutical agent and investigated its efficacy and safety in patients with rheumatoid arthritis. Radiation synovectomy was performed using 188Re-tin-colloid in 22 knees from 21 rheumatoid arthritis patients refractory to intra-articular corticosteroid injection. The efficacy and safety of administration of 370-1110 MBq of 188Re-tin-colloid were evaluated after 1, 3, 6, 9 and 12 months. Pain intensity on a visual analogue scale decreased significantly 12 months after therapy (mean+/-SD: 68.0+/-26.1 mm vs. 25.1+/-23.4 mm; P=0.0001 by the paired t-test). Pain decreased in 19 cases (86.3%), joint tenderness improved in 14 cases (63.6%) and joint swelling was reduced in all cases (100%). 188Re-tin-colloid was safe. The residual activity of 188Re in the blood was 0.077%+/-0.25% of the injected dose. The radioactivity of 188Re in the urine was 0.14%+/-0.13% of the injected dose. Transient reactive synovitis was observed in 18 cases (81.8%). No clinical side-effects or abnormalities in leucocyte count, platelet count, liver function tests or urine analysis were observed in any patient. In conclusion, in this first study of radiation synovectomy using 188Re-tin-colloid for patients with rheumatoid arthritis, the treatment resulted in the improvement of arthritis and was well tolerated.

Arthritis, Rheumatoid↗
PubMed2007

Evaluation of hepatic function with (99m)Tc-galactosylated serum albumin scintigraphy in patients with malaria: comparison with (99m)Tc-colloid scintigraphy and liver ultrasonography.

OBJECTIVE: Malarial parasites injected by the mosquito rapidly target hepatocytes, and hepatomegaly is commonly observed during the progress of the disease in malaria patients. To evaluate the degree of hepatic damage and functional status of hepatocytes in malaria patients, we performed liver scintigraphy using (99m)Tc-galactosylated serum albumin (GSA) prospectively and the findings were compared with those of (99m)Tc-colloid scintigraphy, ultrasonography and clinical results in the same subject. METHODS: Eight malaria patients (all male, mean age 22 years) confirmed to be infected with Plasmodium vivax underwent (99m)Tc-GSA liver scintigraphy, followed by liver ultrasonography and (99m)Tc-colloid scintigraphy using phytate within 3 days. For hepatocyte scintigraphy, anterior images of cardiac blood-pool and liver were continuously acquired for 30 min after injection of 185 MBq (99m)Tc-GSA (3 mg). In addition to visual interpretation of the images, quantitative measurement of hepatic function was performed with several functional parameters, such as hepatic uptake index (LHL15), blood clearance index (HH15) and modified receptor index (LHL/HH) calculated from the radioactivity of the liver and heart. (99m)Tc-colloid images were assessed and graded visually. Severity of hepatic dysfunction or reticuloendothelial system activation was classified as normal, mild, moderate and severe on GSA or colloid images. RESULTS: Hepatomegaly was observed in five and splenomegaly in seven of the eight patients. Serum levels of transaminase and alkaline phosphatase were mildly elevated in two. Visual assessment of GSA scintigraphy revealed normal findings in all subjects, except for mild increases in size. The mean values of LHL15, HH15 and LHL/HH were 0.928+/-0.014, 0.537+/-0.031 and 1.732+/-0.106, respectively. They were graded as normal in five, and near-normal to mild dysfunction in three subjects. In contrast, (99m)Tc-colloid scintigraphy revealed abnormal findings in all of the subjects, and graded as moderate in three or severe reticuloendothelial system activation in five subjects. Liver ultrasonographic findings were normal for all subjects except mild hepatomegaly. CONCLUSIONS: Malaria-induced injury of the hepatocyte is likely to be minimal whereas hepatomegaly is commonly seen during disease process. This suggests that hepatic damage in malarial infection is mainly due to involvement of the reticuloendothelial system. (99m)Tc-GSA scintigraphy can be used in differentiating hepatocellular damage from reticuloendothelial system involvement in patients with infectious disease showing hepatomegaly.

Adult↗
PubMed2001

Adsorption properties of a colloid-polymer mixture confined in a slit pore.

The soft fundamental-measure theory, which was based on the additive colloid-polymer mixture [M. Schmidt, Phys. Rev. E 62, 3799 (2000)] has been employed to investigate the adsorption of a colloid-polymer mixture within a hard slit pore. The calculated results show that the adsorption for the confined colloid-polymer mixture is very different from those of the colloid-colloid and polymer-polymer mixtures. The equilibrium particle density distribution strongly depends on the softness of a star polymer. The local relative concentration oscillates with a spatial period close to the diameter of a large particle in the same way as the equilibrium particle density distribution. The size selectivity in adsorption depends both on the softness of a star polymer and on the particle size ratio in a binary mixture. In particular, the strong adsorption occurs at the ultra-soft polymer and high bulk packing fraction.

Journal Article↗
PubMed2002

Symmetry breaking and interaction of colloidal particles in nematic liquid crystals.

We propose a general approach to the description of the long-ranged elastic interaction in the nematic colloids, based on the symmetry breaking of the director field. The type of the far-field interaction between particles immersed in a nematic host is determined by the way the symmetry is broken in the near-field region around the colloidal particle. This is caused both by the particle's shape and the anchoring at the surface. If the director field near the particle has a set of three symmetry planes, the far-field interaction falls off as d(-5) with d being the distance between particles. If one symmetry plane is absent, a dipolar moment perpendicular to it is allowed and yields dipole-dipole interactions, which decays as d(-3). If both the horizontal and vertical mirror symmetries are broken (it is equivalent to the case when the nonzero torque moment is applied to the particle by the nematic liquid crystal), the particles are shown to attract each other following the Coulomb law. We propose a simple method for the experimental observation of this Coulomb attraction. The behavior of colloid particles in curved director fields is analyzed. Quadrupolar particles with planar anchoring are shown to be attracted toward the regions with high splay deformations, while quadrupoles with homeotropic anchoring are depleted from such regions. When there are many colloidal particles in the nematic solvent, the distortions of the director from all of them are overlapped and lead to the exponential screening in the elastic pair interaction potential. This is a many-body interaction effect. This screening is essential in the real dense colloid systems, such as ferronematics--suspensions of magnetic cylindrical grains in the nematic liquid crystal. External magnetic field induces an elastic Yukawa attraction between them. We apply this attraction to the explanation of the cellular texture in magnetically doped liquid crystals.

Journal Article↗
PubMed2002

Surface tension and nucleation rate of phases of a charged colloidal suspension.

The square gradient approximation is used to calculate the surface tension between two phases of differing density in a charged colloidal suspension, and the results are compared with experimental and theoretical evidence from various colloidal systems. The nucleation rate of a colloidal liquid cluster from a metastable colloidal gas is estimated using a version of classical nucleation theory. We explain in terms of nucleation phenomena the recently described "Swiss cheese effect," which involves the formation of crystals from an initial disordered state, followed by the formation of disordered regions within the crystals and at the interfaces between them. We argue that this sequence of events shows evidence both of homogeneous and of heterogeneous nucleation. The experimental prominence of homogeneous nucleation suggests that metastability is very important in colloidal systems, and therefore that the consideration of nucleation rates is essential to the study of phase behavior in such systems. We also predict that the occurrence or nonoccurrence of phase separation into a dense and a rarefied phase is governed by the ratio of the macroion charge to the macroion radius.

Journal Article↗
PubMed2004

Directional locking effects and dynamics for particles driven through a colloidal lattice.

We examine the dynamics of a single colloidal particle driven through a colloidal lattice which can distort in response to the driven particle. We find a remarkably rich variety of dynamical locking phenomena as we vary the angle of the applied drive with respect to the orientation of the colloidal lattice. When the driven colloid locks to certain lattice symmetry directions, its motion is not necessarily aligned with the drive. Applying a transverse force to the driven particle can result in either increased or decreased drag in the driving direction, depending on the angle of the drive. The dynamical locking produces anomalies in both the longitudinal and the transverse velocity vs driving force curves, including steps and regimes of negative differential resistance. As the interaction of the driven particle with the surrounding lattice increases, significant distortion or dislocations in the surrounding media occur, and as a result the directional locking is enhanced. We compare these results to those obtained for driving particles over fixed substrates, and show that a far richer variety of behaviors occurs when the underlying lattice is allowed to distort. We discuss how this system can be used for particle species segregation when the onset of different locking angles occurs at different drives for varied particle charges. We also show that the most pronounced locking phases should be observable at temperatures up to the melting transition of the colloidal lattice.

Journal Article↗
PubMed2004

Key-lock mechanism in nematic colloidal dispersions.

We consider the interaction between two-dimensional nematic colloids and planar or sculpted walls. The elastic interaction between colloidal disks and flat walls, with homeotropic boundary conditions, is always repulsive. These repulsions may be turned into strong attractions at structured or sculpted walls, with cavities that match closely the shape and size of the colloids. This key-lock mechanism is analyzed in detail for colloidal disks and spherocylindrical cavities of various length to depth ratios, by minimizing the Landau-de Gennes free energy functional of the nematic orientational order parameter. We find that the attractions occur only for walls with cavities within a small range of the colloidal size and a narrow range of orientations with respect to the cavity's symmetry axis.

Journal Article↗