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PubMed2006

Development of an ab initio emulsion atom transfer radical polymerization: from microemulsion to emulsion.

Atom transfer radical polymerization (ATRP) has been successfully extended to an ab initio emulsion system using a "two-step" procedure, in which the final emulsion polymerization system was formed by adding monomer to an ongoing microemulsion ATRP. The newly developed AGET (activators generated by electron transfer) initiation technique was employed in the first stage of this ab initio ATRP. It allows using oxidatively stable Cu(II) species that is reduced in situ by ascorbic acid. The surfactant concentration in the final emulsion system was efficiently decreased to approximately 2 wt % (approximately 10 wt % vs monomer) by decreasing the catalyst concentration and changing the ratio of the monomer added at the microemulsion stage to the monomer added during the second stage. This two-step procedure avoids the necessity of transporting catalysts through the aqueous media during polymerization, resulting in a controlled emulsion polymerization, as evidenced by a linear first-order kinetic plot and formation of a polymer with a relatively narrow molecular weight distribution (Mw/Mn = 1.2-1.4). The polymerization typically reached 70-90% monomer conversion in 5-6 h. The resulting polymer had high chain-end functionality and was successfully chain extended to form in situ block copolymers by adding the second monomer to an ongoing emulsion polymerization. The stable latex from the ab initio emulsion ATRP had a particle size approximately 120 +/- 10 nm.

Emulsions↗
PubMed1999

Perflubron emulsion delays blood transfusions in orthopedic surgery. European Perflubron Emulsion Study Group.

BACKGROUND: Fluorocarbon emulsions have been proposed as temporary artificial oxygen carriers. The aim of the present study is to compare the effectiveness of perflubron emulsion with the effectiveness of autologous blood or colloid infusion for reversal of physiologic transfusion triggers. METHODS: A multinational, multicenter, randomized, controlled, single-blind, parallel group study was performed in 147 orthopedic patients. Patients underwent acute normovolemic hemodilution with colloid to a target hemoglobin of 9 g/dl with an inspiratory oxygen fraction (FIO2) of 0.40. Patients were then randomized into one of four treatment groups after having reached any of the protocol-defined transfusion triggers including tachycardia (heart rate > 125% of posthemodilution rate or > 110 bpm), hypotension (mean arterial pressure < 75% of posthemodilution level or < or = 60 mmHg), elevated cardiac output (> 150% of posthemodilution level) or decreased mixed venous oxygen partial pressure (PVO2; < 38 mmHg). Treatments in the four groups were 450 ml autologous blood harvested during acute normovolemic hemodilution given at FO2 = 0.40; 450 ml colloid at FIO2 = 1.0; 0.9 g/kg perflubron emulsion with colloid (total = 450 ml) at FIO2 = 1.0; and 1.8 g/kg perflubron emulsion with colloid (total = 450 ml) at FIO2 = 1.0. The primary endpoint was duration of transfusion-trigger reversal. A secondary end-point was percentage of transfusion-trigger reversal. RESULTS: Perflubron emulsion was well tolerated with no serious adverse event attributed to drug treatment. Duration of reversal was longest in the 1.8 g/kg perflubron group (median, 80 min; 95% confidence interval, 60-100 min; P = 0.014 vs. autologous blood, P < 0.001 vs. colloid) followed by the 0.9 g/kg perflubron group (median, 59 min; 95% confidence interval, 40-90 min), the autologous blood group (median, 55 min; 95% confidence interval, 30-70 min) and the colloid group (median, 30 min; 95% confidence interval, 27-60 min). Percentage of reversal was also highest in the 1.8 g/kg perflubron group (97%; P < 0.001 vs. autologous blood; P = 0.014 vs. colloid), followed by 0.9 g/kg perflubron (82%), colloid (76%), and autologous blood (60%). CONCLUSIONS: Perflubron emulsion (1.8 g/kg) combined with 100% oxygen ventilation is more effective than autologous blood or colloid infusion in reversing physiologic transfusion triggers.

Aged↗
PubMed1995

Growth of food-borne pathogenic bacteria in oil-in-water emulsions: II--Effect of emulsion structure on growth parameters and form of growth.

The growth rates and yields of Listeria monocytogenes and Yersinia enterocolitica were determined in liquid culture media, and in model oil-in-water emulsions that contained 30, 70 or 83% (v/v) hexadecane. In emulsions with a mean droplet size of 2 microns containing 83% (v/v) hexadecane, the growth of both organisms resulted in decreased yields. Additionally, in these emulsions adjusted to pH 5.0 or 4.4 the growth rate of L. monocytogenes was significantly less than in other model systems which had an aqueous phase of equivalent chemical composition. Microscopic examination of the 83% (v/v) emulsion showed that its microstructure immobilized the bacteria, which were constrained to grow as colonies. Bacteria behaved similarly in model emulsions of either hexadecane or sunflower oil. Manipulation of the droplet size distribution of the emulsions changed the form and rate of growth of bacteria within them.

Alkanes↗
PubMedDate not supplied

Effect of primary emulsions on microsphere size and protein-loading in the double emulsion process.

Incorporation of a protein drug in microspheres made of a hydrophobic polymer is commonly achieved via double liquid-liquid emulsification (w/o/w) or by dispersing a powdered protein in a polymer solution followed by liquid-liquid emulsification (s/o/w). This study focused on the effect of the first operating step in both processes on the size and protein-loading of the microspheres. Bovine serum albumin (BSA) was used as the model protein and poly(methyl methacrylate) (PMMA) was used as the model polymer. The w/o emulsion was characterized based on the degree of emulsion fineness which was controlled using rotor/stator homogenization. The s/o emulsion was characterized based on protein powder size and shape. Protein powders of different sizes and shapes were produced using different powder preparation methods. In both emulsification processes, the second operating step which produced the microspheres was conducted in either a continuously stirred tank reactor (CSTR) or a static mixer. The size of the microspheres thus prepared was found to increase with increasing size of the protein powder in the s/o/w system but increase with decreasing size of the liquid emulsion droplets in the w/o/w system. Empirical correlations can accurately predict the size of the microspheres if the size of w/o emulsion droplets and protein powder is 10 x less than the microsphere size. Protein loading in the microspheres decreased with respect to increases in w/o emulsion droplet size or in protein powder size. We propose that these phenomena are attributed to two mechanisms, fragmentation along the weak routes in the w/o/w system and particle redistribution as the result of terminal velocity in the s/o/w system. The role of protein powder shape was not significant until the protein powder size exceeded 5 microns. Irregular-shaped protein powders resulted in lower encapsulation efficiency than spherical-shaped protein powders.

Animals↗
PubMed2006

Pickering emulsions stabilized solely by layered double hydroxides particles: the effect of salt on emulsion formation and stability.

The formation and stability of liquid paraffin-in-water emulsions stabilized solely by positively charged plate-like layered double hydroxides (LDHs) particles were described here. The effects of adding salt into LDHs dispersions on particle zeta potential, particle contact angle, particle adsorption at the oil-water interface and the structure strength of dispersions were studied. It was found that the zeta potential of particles gradually decreased with the increase of salt concentration, but the variation of contact angle with salt concentration was very small. The adsorption of particles at the oil-water interface occurred due to the reduction of particle zeta potential. The structural strength of LDHs dispersions was strengthened with the increase of salt and particle concentrations. The effects of particle concentration, salt concentration and oil phase volume fraction on the formation, stability and type of emulsions were investigated and discussed in relation to the adsorption of particles at the oil-water interface and the structural strength of LDHs dispersions. Finally, the possible stabilization mechanisms of emulsions were put forward: the decrease of particle zeta potential leads to particle adsorption at the oil-water interface and the formation of a network of particles at the interface, both of which are crucial for emulsion formation and stability; the structural strength of LDHs dispersions is responsible for emulsion stability, but is not necessary for emulsion formation.

Journal Article↗
PubMed1990

Effect of phospholipid emulsifiers on physicochemical properties of intravenous fat emulsions and/or drug carrier emulsions.

The physicochemical properties of soy bean oil emulsions stabilized with purified egg lecithins (phosphatides) of various concentrations have been examined. The zeta potential of the emulsion droplets and the mean particle size of oil droplets in 10% (w/w) o/w-type emulsion decreased with increasing emulsifier concentration and then levelled off at more than 1.2% (w/w). In rheological measurements, at the initial stage, the viscosity of 10% (w/w) o/w-type emulsion gradually increased with increasing purified egg lecithin concentration, at the next stage, a plateau was reached at about 1.0-1.4% (w/w), and at the final stage, the viscosity curve showed a dramatic increase. These results indicate that emulsions stabilized by purified egg lecithin at more than 1.2% (w/w) are likely to be sufficiently stable.

Drug Carriers↗
PubMed1996

Physical states of surface and core lipids in lipid emulsions and apolipoprotein binding to the emulsion surface.

Plasma triglyceride-rich lipoproteins vary in lipid composition during their metabolism. We investigated the effects of the lipid composition of emulsion particles, specifically those of cholesterol enrichment and core replacement (replacing core triglyceride with cholesteryl oleate), on the physical states of surface and core lipids. Steady-state and time-resolved fluorescence anisotropies were measured in lipid emulsions using 1,6-diphenylhexatriene to probe the core and 1,6-diphenylhexatriene analogues for the outer and inner hydrophobic portions of surface phospholipids. In the absence of cholesterol, core replacement had little effect on the surface rigidity, despite the large difference in core mobility. However, core replacement caused a marked increase in surface rigidity in the presence of cholesterol. Quenching experiments using the fluorescent cholesterol analogue, dehydroergosterol, indicated that core replacement allowed surface dehydroergosterol to redistribute from the inner to the outer regions in the emulsion surface. These results indicated that core replacement modulates the surface properties of the emulsion particles through the redistribution of cholesterol in the surface layers. Furthermore, core replacement significantly decreased the binding of apolipoprotein E to the emulsion surface, whereas the binding of apolipoprotein CII responded to the cholesterol enrichment. This binding behavior of exchangeable apolipoproteins may closely correlate with the location of surface cholesterol and the mobility of core lipids.

Apolipoproteins↗
PubMed1987

A metabolic comparison of a pure long-chain triglyceride lipid emulsion (LCT) and various medium-chain triglyceride (MCT)-LCT combination emulsions in dogs.

Two 20% lipid emulsions containing mixtures of long-(LCT) and medium-chain triglycerides (MCT) were compared with a 20% LCT lipid emulsion. Beagles were infused with emulsions containing either 100% LCT, 75% LCT-25% MCT, or 50% LCT-50% MCT. The emulsions were part of a total parenteral nutrition (TPN) regimen that included 10% dextrose and 5.5% amino acids. Basic nutritional parameters as well as elimination kinetics were monitored. Plasma linoleic acid, ketone, lactate, pyruvate, insulin, glucose, and carnitine were analyzed. The 75% LCT-25% MCT emulsion offers little advantage over 100% LCT as a metabolic substrate. The 50% LCT-50% MCT combination proved to be a potentially better caloric source due to rapid elimination kinetics, increased ketone production, lack of deposition, and no interference with linoleic acid metabolism.

Animals↗
PubMed2006

Formation and stability of paraffin oil-in-water nano-emulsions prepared by the emulsion inversion point method.

Paraffin oil-in-water nano-emulsions stabilized by Tween 80/Span 80 were prepared using the emulsion inversion point method at different emulsification temperatures. Nano-emulsions with droplet size below 200 nm were formed above a critical surfactant-to-oil ratio of 0.20 at 50 degrees C. The main destabilization mechanism of the systems was found to be Ostwald ripening. An interesting phenomenon was that the Ostwald ripening rate declined as the surfactant concentration rose. Furthermore, flocculation was also found to contribute to the instability of the nano-emulsions, especially for those with low surfactant concentrations. Study on the electrophoretic properties of emulsion droplets revealed a negative value of the zeta potential, which was strongly dependent on the pH of the systems.

Journal Article↗
PubMed2004

Synthesis of polystyrene/poly[2-(dimethylamino)ethyl methacrylate-stat-ethylene glycol dimethacrylate] core-shell latex particles by seeded emulsion polymerization and their application as stimulus-responsive particulate emulsifiers for oil-in-water emulsions.

Surfactant-stabilized polystyrene (PS) latex particles with a mean hydrodynamic diameter of 155 nm were prepared by aqueous emulsion polymerization using 2,2'-azobis(2-amidinopropane) hydrochloride as a cationic radical initiator. Seeded aqueous emulsion copolymerizations of 2-(dimethylamino)ethyl methacrylate (DMA) and ethylene glycol dimethacrylate (EGDMA) were conducted in the presence of these PS particles to produce two batches of colloidally stable core-shell latex particles, in which the shell comprised a cross-linked P(DMA-stat-EGDMA) overlayer. Both the PS and PS/P(DMA-stat-EGDMA) latexes were characterized in terms of their particle size, morphology, and composition using dynamic light scattering, electron microscopy, and FT-IR spectroscopy, respectively. Using the PS/P(DMA-stat-EGDMA) latex particles as a pH-responsive particulate ('Pickering'-type) emulsifier, polydisperse n-dodecane-in-water emulsions were prepared at pH 8 that could be partially broken (demulsified) on lowering the solution pH to 3. These emulsions were characterized in terms of their emulsion type, mean droplet diameter, and morphology using electrical conductivity and Mastersizer measurements, optical microscopy, and scanning electron microscopy (using critical point drying for sample preparation).

Journal Article↗
PubMed1998

Constant infusion rates of lipid emulsions to stabilize plasma triglyceride concentrations: medium-chain triglyceride/long-chain triglyceride emulsions (MCT/LCT) versus LCT.

As medium-chain triglyceride emulsions (MCT) are more rapidly hydrolyzed than long-chain triglyceride emulsions (LCT), MCT/LCT tends to be infused faster than LCT. The purpose of the present study was to determine the most appropriate infusion rate for MCT/LCT to stabilize plasma concentrations of triglyceride (TG), being equivalent to the optimal infusion rate of the emulsion. A TG clamp was set up by raising the mean +/- SD concentrations of TG in plasma, being 1.08 +/- 0.18 delta mmol l(-1) for LCT, and 1.65 +/- 0.31 delta mmol l(-1) for MCT/LCT after a 50-min priming infusion of each emulsion. Thereafter, the infusion rate of lipid was controlled every 10 min to maintain a steady concentration of TG for a period of 150 min. A constant infusion of glucose at 0.32 g/kg body weight (BW) per h was administered for the test period. The weight-based rate of the infusion to maintain a steady state of plasma TG concentrations did not differ between MCT/LCT and LCT, being 0.125 +/- 0.013 vs 0.117 +/- 0.021 g/kg BW per h, while the molar-based infusion rate was 0.203 +/- 0.021 mmol/kg BW per h for MCT/LCT and 0.132 +/- 0.023 mmol/kg BW per h for LCT (P < 0.05). These results suggest that although 54% more molar MCT/LCT-TG can be hydrolyzed during a constant infusion, MCT/LCT should not be infused at a rate faster than 0.1 g/kg BW per h under a steady state.

Fat Emulsions, Intravenous↗
PubMed1992

Novel affinity separations based on perfluorocarbon emulsions. Use of a perfluorocarbon affinity emulsion for the purification of human serum albumin from blood plasma in a fluidised bed.

A perfluorocarbon affinity emulsion has been generated by homogenisation of a saturated perfluorocarbon oil with a polymeric fluorosurfactant based on poly(vinyl alcohol) (relative molecular mass 9000-10,000) previously derivatised with the triazine dye CI Reactive Blue 4. This affinity emulsion has subsequently been cross-linked in situ and used in a fluidised bed for the purification of human serum albumin (HSA) from blood plasma. HSA was quantitatively recovered in a semi-continuous fashion from plasma at an average purity of 90 +/- 3.3%. The albumin binding capacity of the emulsion has been shown to be 0.59 mg/ml by frontal analysis corresponding to a mol/mol ligand usage of 13.5%. In all regards, when used in a fluidised bed, the emulsions have been shown to behave as a normal chromatographic material. They are stable under operational conditions with no coalescence being observed for periods greater than 1 year. These novel liquid affinity supports present an exciting opportunity to develop a range of unit operations for the continuous purification of proteins.

Chromatography, Affinity↗
PubMed1993

Characterization of oil-in-water emulsions prepared from solid-state emulsions: effect of matrix and oil phase.

Emulsions (o/w) were prepared from solid-state emulsions comprised of various matrix materials and oils and the resultant particle size properties determined. Results suggest that for those matrices that can form solid-state emulsions, the droplet size decreased as a function of time, as previously observed. The final droplet size was dependent on the oil utilized but was independent of the matrix material. The use of mineral oil resulted in the smallest droplet diameter (approximately 1.5 microns) while isopropyl myristate resulted in the largest droplet diameter (approximately 3 microns). With the exception of mineral oil, the oil/water interfacial tension was found to be directly proportional to the droplet diameter. The rate of emulsification appeared to be biphasic. The initial emulsification phase appeared to be independent of the matrix material while the terminal phase was a function of the matrix material. Most importantly, it was found that solid state emulsions could be prepared from a diverse, yet specific, list of matrices.

Chemical Phenomena↗
PubMed1989

Competitive effects of long-chain-triglyceride emulsion on the metabolism of medium-chain-triglyceride emulsions.

This study was conducted to assess the potential metabolic competitive interactions of intravenous medium-chain-triglyceride (MCT) and long-chain-triglyceride (LCT) lipid emulsions. To assess this competition increasing concentrations of LCT emulsion were added to an intravenous dose of MCT emulsion of 3.0 g/kg body wt up to a maximum dose of 3.0 g LCTs/kg body wt. Blood samples were assessed for competitive interactions by analyzing the following metabolites: glucose, insulin, lactate, pyruvate, ketones (acetoacetate, beta-hydroxybutyrate), elimination of triglycerides, and free fatty acids. Evaluation of the data showed a strong competitive interaction between the MCT and LCT emulsions. This competition was evident as soon as LCTs were added to the MCT infusions and appeared to favor LCTs for removal and metabolism over MCTs. This appears to indicate that there is a peripheral, strong affinity site for LCT removal and metabolism and a shared peripheral site and specific visceral site for MCT removal and metabolism.

Animals↗
PubMed2003

Use of olive oil based emulsions as an alternative to soybean oil based emulsions in total parenteral nutrition and their effects on liver regeneration following hepatic resection in rats.

BACKGROUND/AIM: The main objective of this study was to compare the effects of olive oil to those of soybean oil on liver tissue regeneration following hepatic resection in rats. METHODS: Seventy albino Wistar rats were randomly assigned to seven groups which contained 10 rats each. Group 1 was the sham-treated group; groups 2 and 3 received total parenteral nutrition (TPN) containing soybean oil lipid emulsions (20% Lipofundin MCT/LCT) for 48 or 72 h; groups 4 and 5 received TPN containing olive oil (80%)/soybean oil (20%) lipid emulsions (ClinOleic 20%) for 48 or 72 h; group 6 was the control group for 48 h, and group 7 was the control group for 72 h. TPN was given via internal jugular vein, and 70% hepatic resection was performed in the study groups. In addition, hepatic resections with no TPN were performed in the control groups, except the sham group. Relative liver weight, mitotic index, proliferating cell nuclear antigen labeling index, and carnitine levels in liver tissue samples were used to assess hepatic regeneration. Thiobarbituric acid reactive substances were measured as an index of lipid peroxidation and oxidative tissue damage. Alanine aminotransferase, aspartate aminotransferase, and alkaline phosphatase were parameters for the liver function. RESULTS: The relative liver weight increased significantly with minimal hepatosteatosis in the olive oil treated groups. Lipid peroxidation significantly decreased with near-normal serum levels of the liver function parameters in the olive oil/soybean oil treated groups, and mitotic index and proliferating cell nuclear antigen labeling index reached their maximum level in rats receiving TPN containing any kind of lipid emulsions for 48 h following resection. CONCLUSIONS: The use of olive oil/soybean oil lipid emulsions in TPN has important beneficial effects on the liver regeneration, and the antioxidant properties of olive oil originating from its natural components indirectly contribute to the liver regeneration in rats.

Animals↗
PubMedDate not supplied

Preparation of multi-phase microspheres of poly(D,L-lactic acid) and poly(D,L-lactic-co-glycolic acid) containing a W/O emulsion by a multiple emulsion solvent evaporation technique.

Multi-phase microspheres of poly(D,L-lactic acid) (PLA) or poly(D,L-lactic-co-glycolic acid) (PLGA) containing a water-in-oil (W/O) emulsion were prepared by a multiple emulsion solvent evaporation technique. Acetonitrile was used as the solvent for the polymers and light mineral oil as the dispersion medium for the encapsulation procedure. Process and formulation parameters to optimize the microencapsulation of a W/O emulsion containing water-soluble drugs were investigated. Drug loading efficiencies of 80-100 per cent were obtained under specific preparative conditions. The drug loading efficiency in the microspheres was dependent upon the ratio of the W/O emulsion to polymer and the concentration of surfactant in the mineral oil. Compared to conventional microspheres, in which fine drug particles are homogeneously dispersed in the polymer beads, the multi-phase microspheres permit the higher encapsulation efficiency of water-soluble drugs and eliminate partitioning into the polymer-acetonitrile phase which results in low encapsulation efficiency with conventional solvent evaporation techniques.

Acetonitriles↗
PubMed1978

Studies on the adjuvant effect of water-in-oil-in-water (w/o/w) emulsion of sesame oil. 2. Mode of action of the w/o/w emulsion.

The water-in-oil-in-water (w/o/w) emulsion showed potent adjuvant effect on the antibody formation to thymus-dependent antigens, but not to thymus-independent antigens. In hapten-carrier system the priming with carrier in the w/o/w emulsion enhanced more effectively the carrier specific helper function than did the priming with carrier in free solution. The cells responsible for the helper function were radioresistant. In the adoptive cell transfer system, the w/o/w emulsion was shown to enhance helper cell function. It is discussed that our w/o/w emulsion exerts the adjuvant effect by enhancing helper T cell activity.

Adjuvants, Immunologic↗
PubMed2003

Synthesis of porous emulsion-templated polymers using high internal phase CO2-in-water emulsions.

Highly porous emulsion-templated materials were synthesized by polymerization of concentrated CO(2)-in-water (C/W) emulsions. The method does not use any organic solvents, in either the synthesis or purification steps, and no solvent residues are left in the materials. It was found that the emulsion stability is strongly affected both by the nature of the surfactant and by the viscosity of the aqueous continuous phase. By optimizing these parameters, it was possible to generate a highly porous, low-density polyacrylamide material with a pore volume of 5.22 cm(3)/g, an average pore diameter of 9.72 microm, and a bulk density of 0.14 g/cm(3). We have broadened the scope of this approach significantly by identifying inexpensive hydrocarbon surfactants to stabilize the C/W emulsions (e.g., Tween 40) and by developing redox initiation routes that allow the synthesis to be carried out at modest temperatures and pressures (20 degrees C, 65 bar). We have also extended the method to the polymerization of monomers such as hydroxyethyl acrylate, which suggests that it is possible to prepare a range of solvent-free biomaterials by this route.

Journal Article↗