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PubMed1996

Field-Induced Layering of Colloidal Crystals

An electrohydrodynamic methodology has been developed that makes possible the precise assembly of two- and three-dimensional colloidal crystals on electrode surfaces. Electrophoretically deposited colloidal particles were observed to move toward one another over very large distances (greater than five particle diameters) to form two-dimensional colloidal crystals for both micrometer- and nanometer-size particles. This coalescence of particles with the same charge is opposite to what is expected from electrostatic considerations and appears to result from electrohydrodynamic fluid flow arising from an ionic current flowing through the solution. The ability to modulate this "lateral attraction" between particles, by adjusting field strength or frequency, facilitates the reversible formation of two-dimensional fluid and crystalline colloidal states on the electrode surface. Further manipulation allows controlled structures to be assembled.

Journal Article↗
PubMed1999

Surfactant-mediated two-dimensional crystallization of colloidal crystals

Colloidal particles can form unexpected two-dimensional ordered colloidal crystals when they interact with surfactants of the opposite charge. Coulomb interactions lead to self-limited adsorption of the particles on the surface of vesicles formed by the surfactants. The adsorbed particles form ordered but fluid rafts on the vesicle surfaces, and these ultimately form robust two-dimensional crystals. This use of attractive Coulomb interaction between colloidal particles and surfactant structures offers a potential new route to self-assembly of ordered colloidal structures.

Journal Article↗
PubMed2000

Three-dimensional direct imaging of structural relaxation near the colloidal glass transition

Confocal microscopy was used to directly observe three-dimensional dynamics of particles in colloidal supercooled fluids and colloidal glasses. The fastest particles moved cooperatively; connected clusters of these mobile particles could be identified; and the cluster size distribution, structure, and dynamics were investigated. The characteristic cluster size grew markedly in the supercooled fluid as the glass transition was approached, in agreement with computer simulations; at the glass transition, however, there was a sudden drop in their size. The clusters of fast-moving particles were largest near the alpha-relaxation time scale for supercooled colloidal fluids, but were also present, albeit with a markedly different nature, at shorter beta-relaxation time scales, in both supercooled fluid and glass colloidal phases.

Journal Article↗
PubMed1991

Effect of colloidal bismuth subcitrate on age related gastric lesions in the rat.

The purpose of this study was to determine the changes in rat gastric functional morphology that take place with age and to study the action of colloidal bismuth subcitrate on the age related degeneration of the stomach. At 95 weeks of age erosions were apparent over 80% of the gastric mucosa and this was associated with a significant decline in the numbers and mucus content of the mucosal epithelial cells. The rate of stem cell proliferation in the neck region was also significantly lower than that found in 9 week old animals. The administration of 50 mg/kg colloidal bismuth subcitrate for 14 days to 9 week old animals resulted in slight hypertrophy of the mucosal epithelial cells. When 95 week animals were placed on the same regimen there was a decline in the number of deep erosions in the mucosa and an increase in the number and mucin content of the mucosal epithelial cells. A significant increase in the proliferation of the stem cell population was also observed after colloidal bismuth subcitrate administration. It is suggested that colloidal bismuth subcitrate may ameliorate the increased susceptibility to harmful agents that occurs with age.

Age Factors↗
PubMed2003

Segment-sphere size ratio influence on the stability of a polymer-colloid mixture.

The influence of the sphere to segment size ratio on the effective depletion layer thickness around a sphere and the resulting phase behaviour of a colloid-polymer mixture is considered. An analytical expression for the excluded volume between an ideal freely jointed chain and a sphere [L. Lue, J. Colloid Interface Sci. 202, 558 (1998)] allows the effect of polymer characteristics (chain length, segment/sphere size ratio) on the depletion interaction in polymer-colloid mixtures to be calculated. For both small and intermediate polymer-to-colloid size ratios the respectively gas-solid and gas-liquid coexistence curves shift to larger polymer coil volume fractions as the relative segment size increases. It is further demonstrated that the conditions for optimal (protein) crystallization are affected when the segment to sphere size is altered.

Journal Article↗
PubMed2002

Structure of colloidal complexes obtained from neutral/poly-electrolyte copolymers and oppositely charged surfactants.

We report on the phase behavior and scattering properties of colloidal complexes made from block copolymers and surfactants. The copolymer is poly(sodium acrylate)-b-poly(acrylamide), hereafter abbreviated as PANa-PAM, with molecular weight 5000 g/mol for the first block and 30000 g/mol for the second. In aqueous solutions and neutral pH, poly(sodium acrylate) is a weak polyelectrolyte, whereas poly(acrylamide) is neutral and in good-solvent conditions. The surfactant is dodecyltrimethylammonium bromide (DTAB) and is of opposite charge with respect to the polyelectrolyte block. Combining dynamical light scattering and small-angle neutron scattering, we show that in aqueous solutions PANa-PAM diblocks and DTAB associate into colloidal complexes. For surfactant-to-polymer charge ratios Z lower than a threshold (Z(C) approximately 0.3), the complexes are single surfactant micelles decorated by few copolymers. Above the threshold, the colloidal complexes reveal an original core-shell microstructure. We have found that the core of typical radius 100-200 A is constituted from densely packed surfactant micelles connected by the polyelectrolyte blocks. The outer part of the colloidal complex is a corona and is made from the neutral poly(acrylamide) chains. Typical hydrodynamic sizes for the whole aggregate are around 1000 A. The aggregation numbers expressed in terms of numbers of micelles and copolymers per complex are determined and found to be comprised between 100-400, depending on the charge ratio Z and on the total concentration. We have also shown that the sizes of the complexes depend on the exact procedure of the sample preparation. We propose that the driving mechanism for the complex formation is similar to that involved in the phase separation of homopolyelectrolyte/surfactant systems. With copolymers, the presence of the neutral blocks prevents the macroscopic phase separation from occurring.

Journal Article↗
PubMed1994

Colloid cysts in children.

Three patients with colloid cysts were identified among approximately 1,400 patients with brain tumors seen at the Hospital for Sick Children in Toronto between 1952 and 1992. These and 34 previously published cases of colloid cysts in children were reviewed. Colloid cysts are rare causes of headaches and papilloedema in children. They usually present with chronic headaches and increased intracranial pressure. Although acute deterioration can occur at any time, it is uncommon. A CT scan or MRI with intravenous contrast is necessary to identify them, particularly those which are isodense. The growth, and subsequent postoperative recurrence of a colloid cyst in 1 youth argues for treatment by complete surgical excision in children.

Adolescent↗
PubMed2006

Unexpected death after headache due to a colloid cyst of the third ventricle.

BACKGROUND: Colloid cysts of the third ventricle are rare benign intracranial non-neoplastic cysts. Headache is the most common symptom. We present a case of sudden death due to colloid cyst in a 17 year old female who had symptoms of intermittent headaches. CASE PRESENTATION: A 17 year old female presented with intermittent mild headaches for a period of two years. She complained of severe headache in the night and was found unresponsive the next morning. Resuscitation team was called on site but the patient was already dead. At post mortem examination a dilated ventricular system was found with a colloid cyst of the third ventricle. CONCLUSION: This report highlights the difficulty in the diagnosis and importance of recognizing colloid cyst of the third ventricle which should be in the differential diagnosis of headaches in children and young adults and of hydrocephalus at autopsy.

Journal Article↗
PubMed1985

Paradoxical effects of thyrotropin on diffusion of thyroglobulin in the colloid of rat thyroid follicles after long term thyroxine treatment.

Autoradiographs of human goiters demonstrate that the speed of diffusion of newly iodinated thyroglobulin (Tgb) molecules through the colloid space may vary widely from one follicle to another. Since the mechanisms which govern the mixing of the colloid are unknown, we investigated the effect of TSH on these processes in rat thyroid glands. Autoradiographs were prepared from thyroids of rats killed 1 h after 125I or 4 h after [3H]leucine injection. In animals treated with T4 for 2 days, 70% of all follicles showed ring labeling of the colloid periphery with both isotopes, indicating slow mixing of newly synthesized and newly iodinated Tgb molecules with preexisting ones. TSH markedly enhanced the mixing process, thereby diminishing the incidence of ring reactions to roughly 10% of all follicles. These results were expected. Unexpected however, was, the nearly total absence of rings in thyroids treated with T4 for 25 days. Semiquantitative autoradiography revealed a higher absolute number of both newly iodinated and newly synthesized Tgb molecules in the core of follicles in chronically suppressed compared to acutely suppressed thyroids. Moreover, after chronic T4 pretreatment, the effect of TSH on diffusion was the opposite of that observed in acutely T4-treated glands, since 0.5 IU TSH injected twice daily between days 21 and 25 caused the reappearance of 125I and [3H]leucine labeled rings in 44% and 33%, respectively, of all follicles. We conclude that acute TSH suppression slows intraluminal diffusion of thyroglobulin molecules and acute TSH injection accelerates the mixing process, whereas, in contrast, chronic TSH suppression improves and acute TSH action on chronically suppressed follicles impairs diffusion. Therefore, the impact of TSH-mediated processes on the hydrodynamic properties of colloid, and thereby on the intraluminal iodination and coupling process, is more complex than hitherto thought.

Animals↗
PubMed2003

Colloidal gold submonolayer-coated thin-film glass plates for waveguide-coupled surface plasmon resonance sensors.

A novel optical sensor based on spectroscopic measurement of the plasmon absorption of a colloidal gold submonolayer immobilized upon a planar waveguide has been developed for label-free detection of biomolecular interactions at the sensor's surface. We fabricated the sensor by locally modifying a 50-microm-thick glass plate with hemoglobin (Hb) and then self-assembling gold colloids from the aqueous solution onto the Hb-modified area of the glass plate. Polychromatic light from a xenon-arc lamp was launched into the thin-film glass plate by use of a broadband fiber-coupling method. With the use of a CCD detector to monitor the light beam emitted from an end face of the glass plate, the plasmon absorption spectrum of the colloidal gold submonolayer was determined to depend on the polarization states of the guided light and to change with the refractive index of the medium in contact with the colloids. In addition to simplicity of fabrication and the ease of use, the sensor yields a larger absorbance sensitivity than the normal transmission measurement.

Journal Article↗
PubMed2004

Surface-enhanced Raman scattering from oleate-stabilized silver colloids at a liquid/liquid interface.

Oleate-stabilized silver colloids of 5-nm-diameter were adsorbed to a toluene/water interface, and surface enhanced Raman scattering (SERS) spectra from these colloids were measured under the total internal reflection (TIR) condition. From the observed spectra, we examined the states of oleate ions and toluene molecules on silver colloids at the liquid/liquid interfacial region. The TIR-SERS spectra of oleate ions showed stronger peaks of the carboxylate group and the ethylene group than those of alkyl chains. From these results, it was found that the oleate ions were adsorbed on the silver surface in two different ways at the liquid/liquid interface; the carboxylate group adsorbed in the organic phase side, while the ethylene group adsorbed in the aqueous phase side. The shifts of the toluene in the interfacial SERS spectra were identical to those of bulk toluene, though the relative intensities among the peaks were not same. This result suggested that the toluene was adsorbed with a weak interaction, but was significantly enhanced by the local electromagnetic field at the colloid surface.

Journal Article↗
PubMed1990

Colloid cysts of the third ventricle: correlation of MR and CT findings with histology and chemical analysis.

Eight patients with colloid cysts of the third ventricle were examined with CT and MR. In six, surgical resection was performed and the material was subjected to histologic evaluation; the concentrations of trace elements were determined by particle-induced X-ray emission. Stereotaxic aspiration was performed in two. The investigation showed that colloid cysts are often iso- or hypodense relative to brain on CT (5/8), but sometimes have a center of increased density. Increased density did not correlate with increased concentration of calcium or other metals but did correlate with high cholesterol content. Colloid cysts appear more heterogeneous on MR (6/8) than on CT (3/8), despite a homogeneous appearance at histology. High signal on short TR/TE sequences is correlated with a high cholesterol content. A marked shortening of the T2 relaxation time is often noticed in the central part of the cyst. Analysis of trace elements showed that this phenomenon is not related to the presence of metals with paramagnetic effects. Our analysis of the contents of colloid cysts does not support the theory that differing metallic concentrations are responsible for differences in MR signal intensity or CT density. We did find that increased CT density and high MR signal correlated with high cholesterol content.

Adult↗
PubMed1987

Changing concepts in the treatment of colloid cysts. An 11-year experience in the CT era.

Since computerized tomography (CT) scanning became available at the University Health Center of Pittsburgh in July, 1975, 17 patients have undergone removal of colloid cysts of the third ventricle by transfrontal, transcallosal, or stereotaxic surgery. All patients presented with symptoms and signs of increased intracranial pressure; CT scanning proved to be the best neurodiagnostic test to define the colloid cysts. Since the development of CT-guided stereotaxic surgery, the authors have preferentially performed stereotaxic aspiration in seven patients; three of these subsequently required craniotomies to remove residual cysts producing persistent symptoms. The viscosity of the intracystic colloid material and/or displacement of the cyst away from the aspiration needle were reasons for unsuccessful aspiration; the CT appearance did not correlate with the ability to aspirate the lesion by the sterotaxic technique. Postoperative patency of the ventricular system was documented by intraoperative CT ventriculography performed during stereotaxic surgery. Removal of the cyst wall was not necessary. Because of the low associated morbidity rate, percutaneous stereotaxic aspiration is recommended as the initial treatment of choice for colloid cysts of the third ventricle. If stereotaxic aspiration fails and symptoms persist, craniotomy should be performed.

Adult↗
PubMed1991

Stereotactic management of colloid cysts: factors predicting success.

Stereotactic aspiration is a valuable surgical alternative for colloid cysts when used alone or in conjunction with microsurgical resection. Since 1981, the authors have performed computerized tomography (CT)-guided stereotactic aspiration as the initial procedure in 22 patients with colloid cysts; stereotactic aspiration alone was successful in 11 patients (50%). Of the 11 patients in whom aspiration failed, stereotactic endoscopic resection was attempted in three and was successful in one. Seven patients required a craniotomy and microsurgical removal of the cyst performed via a transcortical approach. The preoperative CT appearance in eight cases of a hypodense or isodense cyst correlated favorably with successful aspiration of the cyst in six patients. A hyperdense appearance on the preoperative CT scan in 14 cases was associated with subtotal aspiration in 13 patients; five required craniotomy for removal. Preoperative magnetic resonance (MR) imaging in eight patients provided excellent anatomical definition of the cyst and its relationship to other structures of the third ventricle, but it was not possible to correlate successful aspiration with cyst appearance on MR images with short or long relaxation time sequences. The authors' 9-year experience suggests that preoperative CT studies accurately determine size, predict viscosity, and help to define a group of colloid cyst patients for whom stereotactic cyst aspiration will likely be successful. Unsuccessful stereotactic aspiration was related to two features: the high viscosity of the intracystic colloid material (nine patients), or deviation of the cyst away from the aspiration needle due to small cyst volume (two patients). Because of its simplicity and low risk, stereotactic surgery can be offered to selected patients as the initial procedure of choice. Craniotomy can be reserved for those whose imaging studies predict failure or for those whose cyst cannot be aspirated.

Adult↗
PubMed1994

Surgical resection of third ventricle colloid cysts. Preliminary results comparing transcallosal microsurgery with endoscopy.

It is still not determined which is the best surgical option for third ventricle colloid cysts. Since 1990, the authors have used a steerable fiberscope to remove colloid cysts in seven patients and have performed microsurgery via a transcallosal approach in eight patients. The two techniques were compared for operating time, length of hospital stay, incidence of complications, recurrence, and hydrocephalus, and days spent recuperating before return to work to determine if endoscopic removal of colloid cysts is a safe and effective alternative to microsurgery. Statistical analysis was adjusted for age, sex, and presenting symptoms. Microsurgical cases averaged 206 minutes of operating time whereas endoscopic cases averaged 127 minutes (p = 0.01). For combined days spent in the intensive care unit and on the ward, the patients averaged 9.5 days after microsurgery and 4 days after endoscopy (p = 0.05). Postoperative complications occurred in five of eight patients after microsurgery and in one of seven patients after endoscopy (p = 0.09); complications were transient and primarily related to short-term memory loss. In all patients, preoperative symptoms resolved and the cysts have not recurred. Postoperatively, one patient required a ventriculoperitoneal shunt after microsurgery but all patients were shunt-independent after endoscopy. Patients returned to work an average of 59 days after discharge following microsurgery compared with an average of 26 days after endoscopy (p = 0.05). Compared with transcallosal microsurgery for the removal of colloid cysts, these preliminary results show that a steerable endoscope reduced operating time and that patients spent fewer days in the hospital and returned to work sooner after endoscopy.

Adolescent↗
PubMed1999

Natural history of asymptomatic colloid cysts of the third ventricle.

OBJECT: To determine the natural history of colloid cysts of the third ventricle in patients in whom the cysts were incidentally discovered, the authors retrospectively reviewed cases observed during the modern neuroimaging era (1974-1998). METHODS: During this 25-year interval, 162 patients with colloid cysts were examined and cared for at our center. Sixty-eight patients (42%) were thought to be asymptomatic with regard to their colloid cyst and observation with serial neuroimaging was recommended. The mean patient age was 57 years at the time of diagnosis (range 7-88 years) and the mean cyst size was 8 mm (range 4-18 mm). Computerized tomography scanning revealed a hyperdense cyst in 49 (84%) of 58 patients. Three patients were excluded from the study because they died of unrelated causes within 6 months of scanning and seven patients were lost to follow-up review. Clinical follow-up evaluation was available at a mean of 79 months (range 7-268 months) in the remaining 58 patients. The numbers of patients who participated in follow-up review at 2, 5, and 10 years after diagnosis were 40, 28, and 14, respectively. The incidences of symptomatic progression related to the cyst were 0%, 0%, and 8% at 2, 5, and 10 years, respectively. No patient died suddenly during the follow-up interval. Two (6%) of 34 patients in whom follow-up imaging was performed either exhibited cyst growth (one patient) or experienced hydrocephalus (one patient) at a mean of 41 months after diagnosis (range 4-160 months). CONCLUSIONS: Patients in whom asymptomatic colloid cysts are diagnosed can be cared for safely with observation and serial neuroimaging. If a patient becomes symptomatic, the cyst enlarges, or hydrocephalus develops, prompt neurosurgical intervention is necessary to prevent the occurrence of neurological decline from these benign tumors.

Adolescent↗
PubMed2002

[Juvenile colloid milium].

INTRODUCTION: Colloid Milium is a rare disease. It is characterized by the development, on sun-exposed areas, of clusters of yellow and translucid, hard papules, that seeps a gelatinous substance when opened. This dermatitis predominantly affects elderly patients and, exceptionally, children. We report a case of juvenile colloid milium. OBSERVATION: A 14 year-old boy consulted for papular, translucid or amber-brown lesions, occasionally hemorrhagic on the cheeks, nose upper lip and the upper edge of the helix of both ears. He was born to consanguineous parents. Living in a rural area, he was exposed to sun during agricultural activities. The lesions had progressed since he was 6 years old and were exacerbated in the summertime. There was no similar case in the family. Histological exploration of a papular lesion showed areas of atrophic epidermis and the presence of a few vacuolized keratinocytes. The epidermis was lifted by nodular lumps of amorphous eosinophilic material deposited in the superficial dermis. Staining with Congo red was negative. DISCUSSION: Juvenile colloid milium is a benign but unesthetic dermatitis. The inducing role of sun exposure is obvious, as in colloid milium of adults, but other pathogenic hypotheses also exist.

Adolescent↗
PubMed1992

Double blind trial of colloidal bismuth subcitrate versus placebo in Helicobacter pylori positive patients with non-ulcer dyspepsia.

We have carried out a double blind placebo controlled trial to assess the effects of treatment with colloidal bismuth subcitrate in Helicobacter pylori associated non-ulcer dyspepsia. Eighty patients with dyspepsia, normal upper gastrointestinal appearances at endoscopy and H pylori associated active chronic gastritis on histology of gastric antral biopsies were included in the trial. The patients were randomised to receive colloidal bismuth subcitrate 240mg twice daily for four weeks or matching placebo and were reassessed four weeks after completing treatment. Twenty-six patients (67%) receiving colloidal bismuth subcitrate had normal histology or improved inflammation compared with five (13%) receiving placebo (p less than 0.001), and symptoms were absent or improved in 32 (82%) and two (5%) respectively (p less than 0.001). Serum IgG level was a marker of infection, and fell with successful treatment. Colloidal bismuth subcitrate is effective treatment for H pylori associated non-ulcer dyspepsia with improved gastric antral histological appearances and has a beneficial effect on symptoms.

Adult↗