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PubMed1994

Persistence of mobile receptors on surface- and suspension-activated platelets.

We examined the distribution of glycoprotein Ib (GPIb) and glycoprotein IIb-IIIa (GPIIb-IIIa) receptors on suspension- and surface-activated platelets before and after exposure to thrombin (1 U/ml, 10 minutes). Frozen thin sections prepared from fixed suspension-activated platelets or grids containing fixed surface-activated platelets were stained with specific antibodies to GPIb (antiglycocalicin) and GPIIb-IIIa (AP2 or 7E3), incubated with the corresponding gold-labeled secondary antibody, and examined in the electron microscope. GPIb and GPIIb-IIIa were evenly distributed on membranes of resting and suspension-activated platelets. GPIb and GPIIb-IIIa were present in the open canalicular system (OCS) of resting and, more prominently, in dilated OCS channels of thrombin suspension-activated platelets. On surface-activated platelets more intense labeling for GPIb was observed along pseudopods of dendritic cells whereas GPIIb-IIIa receptors were slightly increased over the peripheral zone. Morphometric study of labeling on fully spread, surface-activated platelets revealed that the density of GPIb increased significantly after thrombin treatment (60.7 +/- 13.1 vs 40.9 +/- 8.3 gold particles/microns 2, p < 0.05). A flow cytometry assay employing the same antiglycocalicin antibody revealed no down-regulation or clearance of GPIb after exposure of platelets to thrombin. GPIIb-IIIa distribution on spread platelets after exposure to thrombin remained basically unchanged (28.4 +/- 10.5 vs 32.6 +/- 10.9 particles/microns2 in nonactivated platelets). These findings indicate that clearance of GPIIb-IIIa and GPIb on suspension-activated platelets does not take place to the extent suggested in previous studies and does not occur spontaneously or after thrombin activation on surface-activated platelets. Although the presence of mobile receptors on platelets is essential for spreading on immobile surfaces and each other, their clearance to the OCS is not a fundamental mechanism regulating adhesion.

Flow Cytometry↗
PubMed1995

The formation of filopodia-like protrusions during preparation of cell suspensions for scanning electron microscopy.

The standard preparation of cell suspensions (e.g., blood cells, cell suspensions derived from monolayer cultures or from various tissues, etc.) for scanning electron microscopy (SEM) includes fixation of the cells in suspension and subsequent dehydration and critical point drying (CPD) of the cells after their preliminary attachment to the special substrata. In the course of the SEM examination of cell suspensions of various origins, unusual morphological cell surface structures, filopodia-like protrusions (FLP), were consistently detected in 3-20% of the cells in the populations. FLP can be effectively observed only by using a stage tilt angle of no less than 30 degrees. FLP were single or multiple thin threads extending from basal parts of a spherical cell and attaching to the substratum surface used. FLP strikingly resembled substratum-attached filopodia formed by a viable cell at its earliest stages of spreading. The percentages of the cells with FLP were not significantly affected by the character of cell fixation (primary aldehyde fixation alone or primary aldehyde with subsequent OsO4 post-fixation) or the raising of the temperature and pressure inside the CPD bomb. It seems that the protrusions imitating the natural cell surface structures can probably be formed at later stages of the preparation of cell suspensions for SEM, namely during dehydration and (or) CPD when the cells undergo substantial shrinkage. One of the possible mechanisms by which the cell shrinkage could induce FLP formation follows. A prefixed spherical cell which settles down to the substratum sticks to it at some discrete points on the cell surface. As a result of the subsequent cell shrinkage, FLP could be formed and then stretched, connecting the same points on the cell surface with the points of the initial cell-substratum adhesion.

Animals↗
PubMed1998

[Synthesis of three- and tetrapeptides catalyzed by subtilisin suspensions in organic solvents].

The behavior of subtilisin 72 in some aprotic solvents (acetonitrile, dioxane, and tetrahydrofurane) was studied. The enzyme was shown to be partially soluble in tetrahydrofurane, but it is rendered profoundly inactive in this solution. In acetonitrile and dioxane, subtilisin formed dilute suspensions whose activities were measured after dilution with water. Under these conditions, subtilisin suspended in acetonitrile manifested an activity that was an order of magnitude higher than that of its dioxane suspension, and this activity continued for a long time. Z-Ala-Ala-Leu-pNA was synthesized from Z-Ala-Ala-OCH3 and Leu-pNA under the catalysis by dilute suspension of subtilisin in acetonitrile. p-Nitroanilides of tetrapeptides, Z-Ala-Ala-P1-P'1-pNA, where P1 and P'1 were either Leu or Phe, were similarly synthesized in acetonitrile under catalysis by dilute subtilisin suspension at [S]:[E] = 10(5):1. p-Nitroanilides of tripeptides, Z-Ala-Ala-Leu-pNA, Z-Ala-Ala-Phe-pNA, and Z-Ala-Ala-Phe-NH2, were also synthesized in the presence of a concentrated subtilisin suspension at [S]:[E] = 10(3):1. It was shown that the increase in enzyme concentration resulted in the double coupling of nucleophile, and Z-Ala-Ala-Leu-Leu-pNA, Z-Ala-Ala-Phe-Phe-pNA, and Z-Ala-Ala-Phe-Phe-NH2 were obtained with 13, 33, and 40% yields, respectively. Therefore, such reaction systems can be used for creating long hydrophobic peptides whose synthesis in water-organic mixtures is difficult due to the poor solubility of starting components in aqueous buffer solutions.

Acetonitriles↗
PubMedDate not supplied

Minimally invasive brow suspension for facial paralysis.

OBJECTIVE: To report a new technique for unilateral brow suspension for facial paralysis that is minimally invasive, limits supraciliary scar formation, does not require specialized endoscopic equipment or expertise, and has proved to be equal to direct brow suspension in durability and symmetry. DESIGN: Retrospective survey of a case series of 23 patients between January 1997 and December 2000. SETTING: Metropolitan tertiary care center. PATIENTS: Patients with head and neck tumors and brow ptosis caused by facial nerve paralysis. MAIN OUTCOME MEASURE: The results of the procedure were determined using the following 3-tier rating system: outstanding (excellent elevation and symmetry); acceptable (good elevation and fair symmetry); and unacceptable (loss of elevation). RESULTS: The results were considered outstanding in 12 patients, acceptable in 9 patients, and unacceptable in only 1 patient. One patient developed a hematoma, and 1 patient required a secondary adjustment. CONCLUSIONS: The technique has proved to be superior to standard brow suspension procedures with regard to scar formation and equal with respect to facial symmetry and suspension. These results have caused us to abandon direct brow suspension and to use this minimally invasive method in all cases of brow ptosis due to facial paralysis.

Facial Paralysis↗
PubMedDate not supplied

Multivectored suture suspension: a minimally invasive technique for reanimation of the paralyzed face.

BACKGROUND: Despite advanced techniques for reanimation of the lower face, many patients opt for static suspension procedures, which are less invasive and have a relatively short recovery period. However, even static suspension procedures require general anesthesia, overnight hospital stay, and significant soft tissue manipulation. We present a minimally invasive technique, the multivectored suture suspension, which addresses these drawbacks. OBJECTIVES: To study the technical feasibility and efficacy of the multivectored suture suspension technique in the paralyzed face. DESIGN: The study was carried out prospectively in 12 patients with House-Brackmann grade 6 facial paralysis. Nine patients presented within 6 months of tumor resection and 3 patients presented more than 1 year after surgery. MAIN OUTCOME MEASURES: The parameters evaluated were (1). restoration of nasal breathing; (2). improvement of drooling; (3). restoration of normal speech; (4). cosmetic results; and (5). total surgical time. RESULTS: With an average follow-up of 14 months, patient evaluation of the outcome parameters was as follows: (1). 10 patients (83%) reported significant and 2 (17%) reported moderate restoration of nasal breathing; (2). 10 patients (83%) reported significant improvement and 2 (17%) reported modest drooling improvement; (3). 8 patients (66%) reported significant improvement and 4 (34%) reported modest improvement of speech; (4). 9 patients (75%) reported complete satisfaction and 3 (25%) reported moderate satisfaction with cosmesis. The average surgical time was 46 minutes. Three revisions were required for suture failure. CONCLUSIONS: The multivectored suture suspension technique is a minimally invasive, reversible method of lower facial reanimation that provides improved cosmesis with restoration of nasal breathing. It can be performed under local anesthesia in an outpatient setting, thereby reducing morbidity and cost.

Aged↗
PubMed2001

Comparison of materials used in frontalis suspension.

OBJECTIVE: To compare various materials used in frontalis suspension surgery for incidence of infection and/or granuloma formation and incidence of recurrent ptosis. DESIGN AND METHODS: A retrospective medical record analysis was performed for 102 frontalis suspension operations performed on 43 patients between January 1, 1991, and December 31, 1996, at Indiana University Medical Center, Indianapolis. Materials used for surgery were compared for incidence of infection and/or granuloma formation and incidence of recurrent ptosis. Materials included autogenous fascia lata, banked fascia lata, monofilament nylon, braided polyester, expanded polytetrafluoroethylene, and polypropylene. RESULTS: Infection and/or granuloma formation occurred in 10.8% of all frontalis suspensions and in less than 10.0% for each material used except expanded polytetrafluoroethylene. Five (45.5%) of the 11 frontalis suspensions using expanded polytetrafluoroethylene required removal of the material because of suspected infection. Ptosis recurred in 32 cases (31.4%). Low incidence of recurrence was found with autogenous fascia lata and expanded polytetrafluoroethylene. CONCLUSIONS: Of the materials compared in this study, autogenous fascia lata may be the material of choice for frontalis suspension surgery in congenital ptosis. Other materials are useful for temporary eyelid elevation. All materials carry the risk of potential infection and/or granuloma formation.

Adolescent↗
PubMed1997

Hindlimb suspension and hind foot reversal in Varecia variegata and other arboreal mammals.

The foot, perhaps more than any other region of the primate body reflects the interaction of positional behaviors with the geometric properties of available supports. The ability to reverse the hind foot during hindlimb suspension while hanging from a horizontal support or descending a large diameter vertical trunk has been noted in many arboreal mammals, including primates. Observations of Varecia variegata in the wild and under seminatural conditions document hindlimb suspension in this lemurid primate. The kinematics and skeletal correlates of this behavior are examined. Analogy is made with the form and function exhibited by nonprimate mammalian taxa employing this behavior. Examples of carnivores and rodents display very similar adaptations of the tarsals while other mammals, such as the xenarthrans, accomplish a similar end by means of different morphologies. However, a suite of features is identified that is shared by mammals capable of hind foot reversal. Hindlimb suspension effectively increases the potential feeding space available to a foraging mammal and represents a significant, and often unrecognized, alternative adaptive strategy to forelimb suspension and prehensile-tail suspension in primates.

Adaptation, Physiological↗
PubMed1995

Suspension osteopenia in mice: whole body electromagnetic field effects.

Whole-body fields were tested for their efficacy in preventing the osteopenia caused by tail suspension in mice. The fields had fundamental frequencies corresponding to the upper range of predicted endogenous impact-generated frequencies (0.25-2.0 kHz) in the long bones. Three distinct whole-body EMFs were applied for 2 weeks on growing mice. Structural, geometric, and material properties of the femora, tibiae, and humeri of suspended mice were altered compared to controls. Comparison of suspended mice and mice subjected to caloric restriction indicates that the changes in caloric intake do not explain either the suspension or the field-induced effects. In agreement with past studies, rather, unloading appears to cause the suspension effects and to be addressed by the EMFs. The EMF effects on bone properties were apparently frequency dependent, with the lower two fundamental frequencies (260 and 910 Hz) altering, albeit slightly, the suspension-induced bone effects. The fields are not apparently optimized for frequency, etc., with respect to therapeutic potential; however, suspension provides a model system for further study of the in vivo effects of EMFs.

Animals↗
PubMed1984

Cyclic nucleotides and haemoglobin concentration in rabbit bone marrow cell suspensions stimulated by purified erythropoietin.

This study was conducted to determine the possible correlations between cyclic nucleotides cyclic adenosine monophosphate (cAMP) and cyclic guanine monophosphate (cGMP), and haemoglobin (Hb) concentration in nucleated cell suspensions of rabbit bone marrow incubated with erythropoietin (Ep). The levels of cAMP and cGMP were measured following the addition of different Ep concentrations to the suspensions. The Hb concentration was also measured in suspensions treated with Ep, dibutyryl cAMP (db-cAMP) or dibutyryl cGMP (db-cGMP), respectively. The following results were obtained: (1) upon the addition of 1 IU ml-1 Ep, an increase of cAMP levels was related to an increase in Hb concentration; while a decrease of Hb concentration was related to an increase of cGMP levels obtained when 0.1 IU ml-1 Ep was present in the incubation mixture. (2) A mimetic effect on Hb concentration was obtained upon the addition of db-cAMP or db-cGMP to the suspensions. (3) A quantitative correlation was found between the cAMP/cGMP ratio and Hb levels in cellular suspensions. This rapport was reviewed with respect to the controls as a decrease in Hb concentration when the ratio is less than one and an increase in Hb concentration when the ratio is greater than one.

Animals↗
PubMed2004

HEK 293 cell suspension culture using fibronectin-adsorbed polymer nanospheres in serum-free medium.

Previously, we reported on suspension culture of anchorage-dependent animal cells using plain polymer nanospheres in serum-containing medium. For commercial cell culture, it is more advantageous to use serum-free medium than serum-containing medium. To culture anchorage-dependent animal cells using polymer nanospheres in serum-free medium, the nanospheres need to be coated with cell adhesion proteins. In this study, we utilized fibronectin-adsorbed polymer nanospheres for suspension culture of anchorage-dependent animal cells in serum-free medium. Fibronectin was adsorbed onto poly(lactic-co-glycolic acid) nanospheres (433 nm in average diameter) by immersing the nanospheres in fetal bovine serum. The nanospheres were used to culture human embryonic kidney (HEK) 293 cells in serum-free medium in stirred suspension bioreactors. Nanospheres attached between HEK 293 cells and promoted cell aggregate formation compared with culture without nanospheres. Most cells in the aggregates were viable over a 10-day culture period. Importantly, the use of poly(lactic-co-glycolic acid) nanospheres promoted the cell growth significantly, compared with culture without nanospheres (3.8- vs 1.8-fold growth). The nanosphere culture method developed in this study removes the time-consuming and costly process of adaptation of anchorage-dependent animal cells to suspension culture in serum-free medium. This culture method may be useful for the large-scale suspension culture of various types of anchorage-dependent animal cells in serum-free medium.

Animals↗
PubMed1994

Influence of antiorthostatic suspension on resistance to murine Listeria monocytogenes infection.

The present study was designed to evaluate the influence of antiorthostatic suspension, a ground-based modeling system employed to simulate certain aspects of weightlessness that occur during space flight, on the capacity of mice to resist infection with the facultative intracellular bacterial pathogen Listeria monocytogenes. Female BDF1 mice were suspended by the tail in the orthostatic or antiorthostatic position and were infected with a sublethal dose of virulent L. monocytogenes at various times during the suspension. It was found that suspension did not influence the kinetics of bacterial growth in vivo if the infection was started concurrently with the suspension. However, mice that were antiorthostatically suspended 2, 4, or 7 days before the onset of infection exhibited an enhanced capacity to eliminate the challenge infection. Suspending mice on day 2 of the infection did not alter the kinetics of bacterial growth. Finally, the enhancement of resistance to the primary Listeria infection was accompanied by failure of the mice to generate long-term protective immunological memory to the challenge organism. Collectively, these results indicate that the stress of antiorthostatic suspension can influence the capacity of mice to resist bacterial infection.

Animals↗
PubMed2004

Toxicity testing of heavy-metal-polluted soils with algae Selenastrum capricornutum: a soil suspension assay.

A small-scale Selenastrum capricornutum (Rhapidocelis subcapitata) growth inhibition assay was applied to the toxicity testing of suspensions of heavy-metal-polluted soils. The OECD 201 standard test procedure was followed, and algal biomass was measured by the fluorescence of extracted chlorophyll. The soils, which contained up to (per kilogram) 1390 mg of Zn, 20 mg of Cd, and 1050 mg of Pb were sampled around lead and zinc smelters in northern France. The water extractability of the metals in suspensions (1 part soil/99 parts water w/v) was not proportional to the pollution level, as extractability was lower for soil samples that were more polluted. Thus, the same amount of metals could be leached out of soils of different levels of pollution, showing that total concentrations of heavy metals in soil (currently used for risk assessment purposes) are poor predictors of the real environmental risk via the soil-water path. Despite high concentrations of water-extracted zinc (0.6-1.4 mg/L of Zn in the test), exceeding by approximately 10-fold the EC(50) value for S. capricornutum (0.1 mg Zn/L), 72-h algal growth in the soil extracts was comparable or better than growth in the standard control OECD mineral medium. The soil suspension stimulated the growth of algae up to eightfold greater than growth using the OECD control medium. Growth stimulation of algae was observed even when soil suspensions contained up to 12.5 mg Zn/L and could not be explained by supplementary nitrogen, phosphorous, and carbonate leached from the soil. However, if the growth of algae in suspensions of clean and polluted soils was compared, a dose-dependent inhibitory effect of metals on algal growth was demonstrated. Thus, as soil contains nutrients/supplements that mask the adverse effect of heavy metals, a clean soil that has properties similar to the polluted soils should be used instead of mineral salt solution as a control for analysis of the ecotoxicity of soils.

Cadmium↗
PubMed1996

Magnetohydrodynamic Aggregation of Cholesterol and Polystyrene Latex Suspensions

The aggregation state of flowing (0.49 m s-1 linear velocity) colloidal dispersions of polystyrene latex microspheres (certified particle diameter of 156 &plusmn; 6 nm; measured diameter, 156 &plusmn; 3 nm at pH 5.3 in 50 mM NaCl) in NaCl solution and cholesterol (measured diameter, 533 &plusmn; 9 nm at pH 5.3), stabilized in NaCl solution by sodium taurodeoxycholate, was studied using photon correlation spectroscopy. For cholesterol suspensions having electrolyte concentrations close to the critical coagulation concentration (50 mM NaCl), pronounced aggregation was observed after 15 to 30 min of recirculation in the presence of an orthogonally applied magnetic field (2.0, 1.0 and 0.15 T). In all experiments with cholesterol, aggregation was followed by a period of deaggregation, after which aggregation again occurred. Comparable effects were not observed when cholesterol suspensions were recirculated in the absence of the magnetic field or when the suspensions were exposed to an equivalent magnetic field in the absence of flow. For cholesterol suspensions, the increase in particle size was most pronounced at 0.15 and 1.0 T rather than at 2.0 T. Aggregation effects were also observed when suspensions of polystyrene latex in 200 mM NaCl were made to flow through a 1.0-T field. In both systems, the magnetic aggregation does not appear to involve direct interaction between the field and the solid phase, but is interpreted in terms of orthokinetic effects involving magnetohydrodynamic changes in the flow profile resulting from the presence of the transverse field.

Journal Article↗
PubMed1997

Rheological and Solid-Liquid Separation Properties of Bimodal Suspensions of Colloidal Gibbsite and Boehmite

Bimodal suspensions of nanometer-sized boehmite particles and micron-sized gibbsite particles in 0.10 M NaNO3 are used as models to gain insight into the physical properties of agglomerating colloidal suspensions containing bimodal distributions of primary particles. Results on the gibbsite-boehmite mixtures show that the presences of small particles in a suspension can have a dramatic impact on the rheological, sedimentation, and filtration characteristics of suspensions of larger particles. Transmission electron micrographs show that boehmite forms a coating on the larger gibbsite particles. The coating provides steric repulsion and reduces the attractive interactions between the larger particles, leading to viscosity decreases and greater densification of sediments and filter cakes. A model has been developed to rationalize observed property changes based on the range of agglomerate structures that can form in mixtures of large and small particles. Results are discussed in the content of the processing of nuclear waste sludges, but are applicable to a wide range of bimodal suspensions.

Journal Article↗
PubMed1997

The Electric Conductivity of Dilute Suspensions of Charged Porous Spheres

The effective electric conductivity of a dilute suspension of polyelectrolyte molecules or charged flocs in an electrolyte solution is analytically studied. The model used for the particles is a porous sphere in which the density of hydrodynamic frictional segments, and therefore also that of the fixed charges, is constant. The equations which govern the electrochemical potential distributions of ionic species and the fluid flow field inside and outside a porous particle migrating in an unbounded solution are linearized assuming that the system is only slightly distorted from equilibrium. Using a perturbation method, these linearized equations are solved for a porous sphere in a uniform applied electric field with the density of the fixed charges as the small perturbation parameter. An analytical expression for the effective conductivity of a dilute suspension of identical charged porous spheres is obtained from the average electric current density calculated using the solution of electrochemical potential distributions of the ions. The result demonstrates that the presence of the fixed charges in the porous particles can lead to an augmented or a diminished electric conductivity of the suspension relative to that of a corresponding suspension of uncharged porous particles, depending on the characteristics of the electrolyte solution and the suspending particles. When the anionic and cationic diffusion coefficients of a symmetric electrolyte are the same, the correction for the effect of the fixed charges of the particles on the electric conductivity of the suspension is proportional to the square of the fixed charge density. Copyright 1997Academic Press

Journal Article↗
PubMed1998

Effect of Size Polydispersity on the Dielectric Relaxation of Colloidal Suspensions: A Numerical Study in the Frequency and Time Domains.

In this article, a systematic numerical study is described of the effect of the polydispersity of suspensions of spherical particles on their dielectric behavior, in both the frequency and time domains, starting from the model proposed by DeLacey and White (J. Chem. Soc., Faraday Trans. 2 77, 2007 (1981)) for monodisperse suspensions. The distribution function of relaxation times, characterizing the dielectric response of the systems, is also calculated. It is found that in both the frequency and time domains the predicted behavior does not differ in any essential way from the one obtained for a monodisperse suspension with particle radius close to the volume-averaged mean radius of the polydisperse system. Hence, no arguments related to polydispersity seem to be useful for explaining the discrepancies frequently found between measured and calculated dielectric increments in suspensions, namely, those concerning the magnitude of the dielectric constant of the suspension (its low-frequency value), the value of the characteristic or relaxation frequency, or the overall shape of the relaxation pattern. Copyright 1998 Academic Press.

Journal Article↗
PubMed1998

Characterization of Turbid Colloidal Suspensions Using Light Scattering Techniques Combined with Cross-Correlation Methods.

The ability to characterize colloidal suspensions by means of dynamic light scattering is in general limited to systems with negligible contributions from multiple scattering. For larger particle sizes with high scattering contrast this immediately limits the technique to very low concentrations. A promising solution of this problem is to suppress multiple scattering in dynamic light scattering experiments using cross-correlation schemes. Based on these considerations we have constructed a so-called 3D cross-correlation experiment with which we are able to characterize extremely turbid suspensions. We have measured monomodal and bimodal suspensions of latex particles of relatively high volume fraction. The results show clearly that we are able to measure the dynamic structure factor in concentrated polydisperse suspensions with dynamic light scattering. Combining static and dynamic light scattering measurements for characterizing turbid suspensions the single scattering particle form factor and also the static structure factor can be evaluated. We demonstrate that the implementation of a 3D cross-correlation scheme is a powerful method in suppressing multiple scattering contributions in light scattering experiments and opens a wide field of characterization of colloidal dispersions with high turbidity without having to resort to high dilution. Copyright 1998 Academic Press.

Journal Article↗
PubMed2001

Rheology of Dilute Suspensions of Hard Platelike Colloids.

The concentration dependence of the viscosity is studied for suspensions of approximately hard, i.e., short-range repulsive, platelets. We combine rheological measurements on suspensions of sterically stabilized platelike colloids with dissipative particledynamics simulation for disks. This yields, for the first time, results for the intrinsic viscosity of (nearly) hard plate suspensions, as well as the second- and third-order &phi; (platelet volume fraction) coefficients in the viscosity. The intrinsic viscosity is used to calculate the number-average aspect ratio of the platelets, which is found to be 6.5 and 12 respectively for the two suspensions studied. The measured Huggins coefficients are intermediary between the theoretical value for hard spheres and hard rods. The combined results from viscosity measurements and simulations provide insight into the effect of Péclet number, particle model, and polydispersity on the viscosity of approximately hard platelet suspensions. Copyright 2001 Academic Press.

Journal Article↗