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BACKGROUND: Colloids are widely used in the replacement of fluid volume, however doubts remain as to their benefits. Different colloids vary in their molecular weight and therefore in the length of time they remain in the circulatory system. Because of this and their other characteristics, they may differ in their safety and efficacy. OBJECTIVES: To compare the effects of different colloid solutions in patients thought to need volume replacement. SEARCH STRATEGY: The Cochrane Injuries Group specialised register, The Cochrane Controlled trials register (all years), MEDLINE (1994-98), EMBASE (1974-98) were searched. Bibliographies of trials retrieved were searched and drug companies manufacturing colloids were contacted for information. SELECTION CRITERIA: Randomised and quasi randomised trials comparing colloid solutions in critically ill and surgical patients thought to need volume replacement. The main outcomes measured were death, amount of whole blood transfused and incidence of adverse reactions. DATA COLLECTION AND ANALYSIS: Two authors independently extracted the data and assessed the quality of the trials. MAIN RESULTS: 46 trials met the inclusion criteria, with a total of 2884 participants. Many of the trials were small. In the majority of trials quality was poor or uncertain. Deaths were obtained from 27 trials. Twenty three trials recorded the amount of blood transfused, however quantitative analysis was not possible due to skewness and variable reporting. Thirteen trials recorded adverse reactions, but none occurred. For albumin or PPF versus hydroxyethyl starch (HES) 20 trials reported mortality. The pooled relative risk (RR) was 1.17 (95% CI 0.91, 1.50). For albumin or PPF versus gelatin 3 trials reported mortality. The RR was 0.99 (0.69, 1.42). For gelatin vs HES 3 trials reported mortality, RR was 0.97 (0.65, 1.44). RR was not estimable in the albumin vs dextran, gelatin vs dextran, and HES vs dextran groups. REVIEWER'S CONCLUSIONS: From this review, there is no evidence that one colloid solution is more effective or safe than any other, although the confidence intervals are wide and do not exclude clinically significant differences between colloids. Larger trials of fluid therapy are needed if clinically significant differences in mortality are to be detected or excluded.
Two different priming solutions for the heart-lung machine were compared in 14 patients during aortic valve replacement. Colloid osmotic pressure (COP), and albumin in plasma, blood erythrocyte volume fraction (B-EVF) and arterial oxygen tension (PaO2) (FIO2 = 1.0) were followed before, during and after perfusion. The two priming solutions were 2,000 ml Ringerdex (7 patients) or 1,800 ml Ringerdex + 200 ml 20% albumin (7 patients). COP and B-EVF were normal before bypass. After 10 min on bypass, when about 1,000 ml of crystalloid cardioplegic solution had been given, COP was reduced by about 50% and B-EVF fell to 23%, indicating a small loss of water from the circulation when compared with in vitro dilution curves. COP was slightly lower in the non-colloid group (p less than 0.02). Both COP and B-EVF remained unchanged during perfusion, despite transfusion from the heart-lung machine of a mixture of blood and crystalloid solution with a calculated very low COP (6 mmHg) and B-EVF (15%). After perfusion the restitution of COP and B-EVF was rapid and parallel. Both returned to normal levels after 2 hours. There was a good correlation between COP and albumin measured in the same plasma samples (r = 0.83, p less than 0.001). At one hour after bypass PaO2 (FIO2 = 1.0) tended to decrease in the non-colloid group, compared with preperfusion level. 40 g of albumin was a too small amount of colloid to diminish substantially the reduction of COP during perfusion. The unchanged levels of COP and B-EVF during perfusion, despite further dilution as well as the parallel normalization after perfusion, can only be explained by loss of water from the circulation.
We report the results of a study, using digital video microscopy, of the melting transition in a quasi-two-dimensional suspension of uncharged silica spheres. This system was chosen to further test the dependence of the two-dimensional melting transition on the functional form of the colloid-colloid interaction. Our experimental data show that the solid phase undergoes a first order transition directly to the liquid phase. The system studied yields no evidence of the existence of a hexatic phase interpolating between the solid and liquid phases in the melting process.
Numerical simulations of colloid transport in discretely fractured porous media were performed to investigate the importance of matrix diffusion of colloids as well as the filtration and remobilization of colloidal particles in both the fractures and porous matrix. To achieve this objective a finite element numerical code entitled COLDIFF was developed. The processes that COLDIFF takes into account include advective-dispersive transport of colloids, filtration and remobilization of colloidal particles in both fractures and porous matrix, and diffusive interactions of colloids between the fractures and porous matrix. Three sets of simulations were conducted to examine the importance of parameters and processes controlling colloid migration. First, a sensitivity analysis was performed using a porous block containing a single fracture to determine the relative importance of various phenomenological coefficients on colloid transport. The primary result of the analysis showed that the porosity of the matrix and the process of colloid filtration in fractures play important roles in controlling colloid migration. Second, simulations were performed to replicate and examine the results of a laboratory column study using a fractured shale saprolite. Results of this analysis showed that the filtration of colloidal particles in the porous matrix can greatly affect the tailing of colloid concentrations after the colloid source was removed. Finally, field-scale simulations were performed to examine the effect of matrix porosity, fracture filtration and fracture remobilization on long-term colloid concentration and migration distance. The field scale simulations indicated that matrix diffusion and fracture filtration can significantly reduce colloid migration distance. Results of all three analyses indicated that in environments where porosity is relatively high and colloidal particles are small enough to diffuse out of fractures, the characteristics of the porous matrix that affect colloid transport become more important than those of the fracture network. Because the properties of the fracture network tend to have greater uncertainty due to difficulties in their measurement relative to those of the porous matrix, prediction uncertainties associated with colloid transport in discretely fractured porous media may be reduced.
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Colloid-polymer (CP) mixtures extend between two limiting cases, the colloid limit with the polymer coil size small compared to the colloid radius Rcol and the protein limit with the colloidal particles much smaller in size than the radius of gyration of the polymer chains Rg. In the present work, model systems are developed for the protein limit. The colloid-solvent pairs are optimized in terms of their isorefractivity in order to facilitate the characterization of large polystyrene chains in suspensions of small colloids. The degree of isorefractivity of colloidal particles was successfully evaluated in terms of a reduced scattering intensity. Two polystyrene samples with radii of gyration of Rg = 96 nm and Rg = 78 nm, respectively, are used. The radii of the colloidal particles are close to Rcol = 12 nm, leading to size ratios of Rg/Rcol = 8 and Rg/Rcol = 6.5. Four colloid solvent systems were found to be suitable for polymer characterization by light scattering, one based on silica particles and three systems with acrylate particles. The present investigation is focused on the three acrylate systems: poly(methyl methacrylate) in ethyl benzoate (ETB) at 7 degrees C, poly(ethyl methacrylate) in toluene at 7 degrees C and poly(ethyl methacrylate) in ETB at 40 degrees C. Characterization of PS chains is for the first time performed in colloid concentrations up to 2.5% by weight. In all cases, the size and shape of the polymer chains remain unchanged. A slight mismatch of the colloid scattering or a limited colloid solubility prevented investigation of PS chains at higher colloid concentration.
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As a generator-produced beta-emitting radionuclide, the importance of 188Re for radionuclide therapy is increasing rapidly. We prepared 188Re-tin colloid and compared its properties with 188Re-sulfur colloid. Labeling efficiencies reached >98% for tin colloid at 2 h and 89-94% for sulfur colloid at 3 h. All the preparations were stable for 72 h in water, serum, and synovial fluid. If labeled at higher temperature, the particle size of tin colloid increased. The residual radioactivity of 188Re-sulfur colloid in disposable polypropylene syringes after injecting mice was high (62.0+/-7.0%) due to its hydrophobic nature, while that of 188Re-tin colloid was low (2.9+/-1.6%). Although both 188Re-tin colloid and 188Re-sulfur colloid might be useful for radionuclide therapy, we conclude that 188Re tin colloid is more advantageous over 188Re sulfur colloid, due to higher labeling efficiency, control of the particle size, and lower residual activity in the injection syringes.
In this review article, the authors present up-to-date developments on experimental, modeling and field studies on the role of subsurface colloidal fines on contaminant transport in saturated porous media. It is a complex phenomenon in porous media involving several basic processes such as colloidal fines release, dispersion stabilization, migration and fines entrapment/plugging at the pore constrictions and adsorption at solid/liquid interface. The effects of these basic processes on the contaminant transport have been compiled. Here the authors first present the compilation on in situ colloidal fines sources, release, stabilization of colloidal dispersion and migration which are a function of physical and chemical conditions of subsurface environment and finally their role in inorganic and organic contaminants transport in porous media. The important aspects of this article are as follows: (i) it gives not only complete compilation on colloidal fines-facilitated contaminant transport but also reviews the new role of colloidal fines in contaminant retardation due to plugging of pore constrictions. This plugging phenomenon also depends on various factors such as concentration of colloidal fines, superficial velocity and bead-to-particle size ratio. This plugging-based contaminant transport can be used to develop containment technique in soil and groundwater remediation. (ii) It also presents the importance of critical salt concentration (CSC), critical ionic strength for mixed salt, critical shear stressor critical particle concentration (CPC) on in situ colloidal fines release and migration and consequently their role on contaminant transport in porous media. (iii) It also reviews another class of colloidal fines called biocolloids and their transport in porous media. Finally, the authors highlight the future research based on their critical review on colloid-associated contaminant transport in saturated porous media.
In order to determine the normal biodistribution and reproducibility of Tc-99m sulfur colloid and Tc-99m microalbumin colloid, each of ten normal subjects was studied twice with each of the two agents. In overexposed delayed analog images of the anterior chest, some thyroid radioactivity was demonstrated in all of 20 microalbumin colloid studies and in none of 20 sulfur colloid studies; lung radioactivity was seen in 19 of 20 (95%) sulfur colloid studies and in none of the microalbumin colloid studies (both p less than 0.001). Delayed digital images showed that the sulfur colloid gave a higher lung-to-heart ratio, a higher lung-to-liver ratio, and a lower bone marrow-to-liver ratio compared with microalbumin colloid (all p less than 0.05). In general, reproducibility was poor for both agents. We conclude that while there are some differences between these two radiocolloids, the differences do not indicate a superiority of the newer Tc-99m microalbumin colloid over the established Tc-99m sulfur colloid for liver-spleen imaging.
Nonspherical colloids and their ordered arrays may be more attractive in applications such as photonic crystals than their spherical counterparts because of their lower symmetries, although such structures are difficult to achieve. In this letter, we describe the fabrication and characterization of colloidal crystals constructed from nonspherical polyhedrons. We fabricated such nonspherical colloidal crystals by pressing spherical polymer colloidal crystal chips at a temperature slightly lower than the glass-transition temperature (T(g)) of these polymer colloids. During this process, the polymer microspheres were distinctively transformed into polyhedrons according to their crystal structures, whereas the long-range order of the 3D lattice was essentially preserved. Because a working temperature lower than T(g) effectively prevented the colloidal crystals from fusing into films, the spherical colloidal crystals were transformed greatly under pressure, which lead to obvious change in the optical properties of colloidal crystals. Besides their special symmetry and optical properties, these nonspherical colloidal crystals can be used as templates for 2D or 3D structures of special symmetry, such as 2D nano-networks. We anticipate that this fabrication technique for nonspherical colloidal crystals can also be extended to nonspherical porous materials.
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This paper reports a novel reaction of metallotetraphenylporphyrins on hydroxyl-modified silver colloid and Ag2O colloid. Surface-enhanced Raman spectra of Ag(II) and Cu(II) complexes of tetraphenylporphyrin (TPP) adsorbed on the hydroxyl-modified Ag colloid and Ag2O colloid have been studied. The time-dependent SERS spectra of MTPP (M = Ag, Cu) on hydroxyl-modified Ag colloid were recorded and dramatic change on SERS spectra was observed. The final spectra were found to be strikingly different from the corresponding normal Raman spectra (NRS), with the appearance of new Raman bands at 1614. 1417, 947, 674 and 292 cm(-1). The UV-visible absorption spectrum of MTPP on hydroxyl-modified Ag colloid exhibits a broad shoulder near 460 nm. Similar spectral phenomena were also observed for AgTPP and CuTPP adsorbed on Ag2O colloid. The observed spectral alterations were ascribed to new species formation due to the irreducible oxidation of MTPP on the colloids.
Plasma colloid osmotic pressure acts to retain fluid in the intravascular space. Intravenous crystalloids have been identified as one of the major factors contributing to the consistent peripartum decline in colloid osmotic pressure. This study was undertaken to compare the effect of two crystalloid infusions (1000 and 2000 mL Plasma-Lyte A) and a colloid infusion (1000 mL 5% albumin) on the peripartum colloid osmotic pressure. Before elective cesarean section, 45 parturients received one of the three infusions. The lowest mean maternal colloid osmotic pressure (16.6 +/- 1.1 mmHg, P less than .05 compared with baseline) occurred in the 2000-mL crystalloid infusion group eight to 16 hours postpartum. Although the colloid osmotic pressure fell in all groups postpartum, this reduction was significantly (P less than .05) less during the first 24 hours in the colloid infusion group. Minimizing this disruption of the colloid osmotic pressure to pulmonary capillary wedge pressure gradient may be clinically important in selected patients.
We study theoretically the equilibrium phase behavior of a mixture of polydisperse hard-sphere colloids and monodisperse polymers, modeled using the Asakura-Oosawa model [S. Asakura and F. Oosawa, J. Chem. Phys. 22, 1255 (1954)] within the free volume approximation of H. N. W. Lekkerkerker, W. C. K. Poon, P. N. Pusey, A. Stroobants, and P. B. Warren [Europhys. Lett. 20, 559 (1992)]. We compute full phase diagrams in the plane of colloid and polymer volume fractions, using the moment free energy method. The intricate features of phase separation in pure polydisperse colloids combine with the appearance of polymer-induced gas-liquid coexistence to give a rich variety of phase diagram topologies as the polymer-colloid size ratio xi and the colloid polydispersity delta are varied. Quantitatively, we find that polydispersity disfavors fluid-solid against gas-liquid separation, causing a substantial lowering of the threshold value xi(c) above which stable two-phase gas-liquid coexistence appears. Phase splits involving two or more solids can occur already at low colloid concentration, where they may be kinetically accessible. We also analyze the strength of colloidal size fractionation. When a solid phase separates from a fluid, its polydispersity is reduced most strongly if the phase separation takes place at low colloid concentration and high polymer concentration, in agreement with experimental observations. For fractionation in gas-liquid coexistence we likewise find good agreement with experiment, as well as with perturbative theories for near-monodisperse systems.