Efficient Encapsulation of a Water-Soluble Molecule into Lipid Vesicles Using W/O/W Multiple Emulsions via Solvent Evaporation

We developed a novel method for preparing lipid vesicles with high entrapment efficiency and controlled size using water‐in‐oil‐in‐water (W/O/W) multiple emulsions as vesicle templates. Preparation consists of three steps. First, a water‐in‐oil (W/O) emulsion containing to‐be‐entrapped hydrophilic molecules in the water phase and vesicle‐forming lipids in the oil phase was formulated by sonication. Second, this W/O emulsion was introduced into a microchannel emulsification device to prepare a W/O/W multiple emulsion. In this step, sodium caseinate was used as the external emulsifier. Finally, organic solvent in the oil phase was removed by simple evaporation under ambient conditions to afford lipid vesicles. The diameter of the prepared vesicles reflected the water droplet size of the primary W/O emulsions, indicating that vesicle size could be controlled by the primary W/O emulsification process. Furthermore, high entrapment yields for hydrophilic molecules (exceeding 80 % for calcein) were obtained. The resulting vesicles had a multilamellar vesicular structure, as confirmed by transmission electron microscopy.     

Preparation of W1/O/W2 emulsions and droplet size distribution measurements by pulsed‐field gradient nuclear magnetic resonance (PFG‐NMR) technique

Multiple emulsions of W₁/O/W₂ type are of major interest in life sciences, offering possibilities for the encapsulation of water‐soluble active agents. In food science, they are also applied for fat reduction. The droplet size distributions of the inner and outer emulsions are of main importance as they influence the rheological and sensorial properties, the release kinetics, as well as the structural and microbial stability. However, the determination of the inner and outer droplet size distributions is a major challenge, as conventional measurement techniques cannot be applied. Pulsed‐field gradient nuclear magnetic resonance (PFG‐NMR) is well known as a non‐destructive tool for droplet size determination, especially in simple emulsions. In this work, double emulsions of the W₁/O/W₂ type were prepared with polyglycerol‐polyricinoleate (PGPR) and polyoxyethylen‐20‐sorbitan monolaurate (Tween 20) as emulsifiers by means of rotor‐stator emulsification machines. PFG‐NMR was applied for measurements of the inner phase (W₁) droplet size distribution as well as for the characterization of the O phase. The W₁ values were compared with results from laser light diffraction of simple emulsions (W₁/O type) and were found to be consistent within the experimental errors, if restricted diffusion in the outer water phase (W₂) and additional effects are considered.     

Preparation and characterization of highly stable monodisperse argan oil‐in‐water emulsions using microchannel emulsification

Argan oil is well known for its nutraceutical properties. Its specific fatty acid composition and antioxidant content contribute to the stability of the oil and to its dietetic and culinary values. There is an increasing interest to use argan oil in cosmetics, pharmaceutics, and food products. However, the formulation of highly stable emulsions with prolonged shelf life is needed. In this study, argan oil‐in‐water (O/W) emulsions were prepared using microchannel (MC) emulsification process, stabilized by different non‐ionic emulsifiers. The effects of processing temperature on droplet size and size distribution were studied. Physical stability of argan O/W emulsions was also investigated by accelerated stability testing and during storage at room temperature (25 ± 2°C). Highly monodisperse argan O/W emulsions were produced at temperatures up to 70°C. The obtained emulsions were physically stable for several months at room temperature. Furthermore, emulsifier type, concentration, and temperature were the major determinants influencing the droplet size and size distribution. The results indicated that a suitable emulsifier should be selected by experimentation, since the interfacial tension and hydrophilic–lipophilic balance values were not suitable to predict the emulsifying efficiency. Practical applications: MC emulsification produces efficiently monodisperse droplets at wide range of temperatures. The findings of this work may be of great interest for both scientific and industrial purposes since highly stable and monodisperse argan oil‐in‐water emulsions were produced which can be incorporated into food, cosmetic, or pharmaceutical formulations.     

Factors affecting droplet size of sodium caseinate‐stabilized O/W emulsions containing β‐carotene

This work was initiated to prepare an oil‐in‐water (O/W) emulsion containing β‐carotene by microfluidization. The β‐carotene was dissolved in triolein and microfluidized with an aqueous phase containing sodium caseinate (SC) as the emulsifier. Microfluization at 140 MPa resulted in O/W emulsions with a mean droplet diameter of ca. 120 nm, which was further confirmed by transmission electron microscopy analysis. The influences of SC concentration and microfluidization parameters on the droplet size of the emulsions were studied. The results showed that the mean droplet diameter decreased significantly (p <0.05) from 310 to 93 nm with the increase in SC concentration from 0.1 to 2 wt‐%. However, a further increase in SC concentration did not much change the droplet diameter, although the polydispersity of the emulsions was slightly improved. The droplet diameter of the emulsions was found to decrease from 200 to 120 nm with increasing microfluidization pressure, with narrower droplet size distribution. The storage study showed that the emulsions were physically stable for about 2 weeks at 4 °C in the dark. The results provide a better understanding of the performance of SC in stabilizing the O/W emulsions.     

Preparation of water-in-oil and ethanol-in-oil emulsions by membrane emulsification

In this work, water-in-oil emulsions (W/O) and ethanol-in-oil emulsions (E/O) emulsions were prepared successfully by membrane emulsification. The emulsifiers selected were PGPR and MO-750 for the W/O and E/O emulsions, respectively. For W/O emulsions prepared with an oil pre-filled membrane, the dispersed flux was lower and the droplet size sharper than that obtained with a water pre-filled membrane. On the contrary, for E/O emulsions prepared with the membrane pre-filled with oil, the dispersed phase (ethanol) rapidly pushed out the oil from the membrane pores. Therefore, the pre-treatment of the membrane had almost no effect on the dispersed phase flux and on the droplet size. The droplet size distribution of the E/O emulsion was close to that obtained with a classical homogenizer. The dispersed phase fluxes were high and no fouling was observed for our experimental conditions (1.6 l emulsion, 10 wt% ethanol). These results confirm that membrane emulsification could be an interesting alternative for the preparation of E/O emulsions for the purpose of biodiesel fuels, considering the scale-up ability of membranes and their potentiality for industrial processes.     

Ansatz zur Beschreibung der zerkleinerungsrelevanten Strömungsverhältnisse beim Emulgieren von W/O‐Emulsionen mit Lochblenden

This paper presents an indirect way to classify the flow during emulsification with orifices and deals with the influence of the flow type on droplet size distribution of the resulting w/o emulsions. Based on the different areas in the slope of the discharge coefficient it was possible to identify different flow conditions. W/O emulsions of two material systems were prepared in the different flow conditions and the droplet size distributions of these emulsions were measured. It was observed that the resulting droplet size distributions of the emulsions strongly depend on the present flow pattern.     

Effect of emulsifiers on the preparation of food‐grade oil‐in‐water emulsions using a straight‐through extrusion filter

This paper describes the preparation characteristics of food‐grade soybean oil‐in‐water (O/W) emulsions using a novel straight‐through extrusion filter, named a silicon straight‐through microchannel (MC). Polyglycerol fatty acid ester (PGFE), polyoxyethelene sorbitan monolaurate (Tween 20), and sucrose fatty acid ester were tested as emulsifiers. Optical observations of the emulsification process exhibited that monodisperse oil droplets were stably formed from an oblong straight‐through MC for PGFE and Tween 20. The effect of the emulsifier on the straight‐through MC emulsification behavior is discussed. The selected PGFE‐ and Tween 20‐containing systems enabled us to prepare monodisperse O/W emulsions with droplet diameters of 38—39 μm and coefficients of variation below 3% using an oblong straight‐through MC with a 16 μm‐equivalent channel diameter.     

Thixotropic Behavior of Oil‐in‐Water Emulsions Stabilized with Ethoxylated Amines at Low Shear Rates

Oil‐in‐water (O/W) emulsification is a lubricating pipeline method based on the reduction of the energy frictional loss produced during viscous flow. The flow behavior of heavy O/W emulsions formulated with nonionic surfactants is described. The effects of pH and salinity of the aqueous phase on droplet diameter, stability, and apparent viscosity of O/W emulsions were evaluated. The low‐shear Couette flow of O/W emulsions displayed intense shear‐thinning and thixotropic behavior. Thixotropy was associated to the droplet deformation energy caused by shear rate changes. The droplet deformation and alignment led to the apparent viscosity reduction compared to the fluid at rest. Thixotropic behavior is supposed to balance between the breakdown and recovery of droplet ordered structures. Emulsion formulation parameters were influenced by the aqueous phase pH, enabling to manage the emulsion properties. The droplet mean diameter of < 18 µm resulted in very stable emulsions.     

Effects of droplet size on the oxidative stability of oil-in-water emulsions

The effects of droplet size and emulsifiers on oxidative stability of polyunsaturated TAG in oil-in-water (o/w) emulsions with droplet sizes of 0.806±0.0690, 3.28±0.0660, or 10.7±0.106 μm (mean ± SD) were investigated. Hydroperoxide contents in the emulsion with a mean droplet size of 0.831 μm were significantly lower than those in the emulsion with a mean droplet size of 12.8 μm for up to 120 h of oxidation time. Residual oxygen contents in the headspace air of the vials containing an o/w emulsion with a mean droplet size of 0.831 μm were lower compared with those of the emulsion with a mean droplet size of 12.8 μm. Hexanal developed from soybean oil TAG o/w emulsions with smaller droplet size showed significantly lower residual oxygen contents than those of the larger droplet size emulsions. Consequently, oxidative stability of TAG in o/w emulsions could be controlled by the size of oil droplet even though the origins of TAG were different. Spin-spin relaxation time of protons of acyl residues on TAG in o/w emulsions measured by ¹H NMR suggested that motional frequency of some acyl residues was shorter in o/w emulsions with a smaller droplet size. The effect of the wedge associated with hydrophobic acyl residues of emulsifiers was proposed as a possible mechanism to explain differences in oxidative stability between o/w emulsions with different droplet sizes.     

Influence of Coagulant Salt Addition on the Treatment of Oil‐in‐Water Emulsions by Centrifugation,Ultrafiltration, and Vacuum Evaporation

Abstract

Droplet size is a key factor in the treatment of oil‐in‐water (O/W) emulsions, because of its influence on emulsion properties. The addition of a coagulant salt generally causes emulsion destabilization, increasing the droplet size, and enhancing coalescence between oil droplets, which helps its further treatment. The influence of CaCl₂ addition on droplet size distribution of a commercial O/W emulsion used in machining processes was studied in order to facilitate oil removal and to improve its further treatment by centrifugation, ultrafiltration (UF) and vacuum evaporation. The critical coagulation concentration (CCC) was observed at a CaCl₂ concentration of 0.05 M. The quality of the final aqueous effluent, expressed as its chemical oxygen demand (COD) value, was compared for all treatments. The highest COD values were obtained for centrifugation, while the COD of the UF permeate was approximately constant for all UF trials. The best effluent quality was obtained by vacuum evaporation. A combination of these techniques should be appropriate for most industrial treatments of O/W emulsions, depending on the subsequent use of the resulting aqueous effluent.     

Hydrodynamic cavitation as an efficient method for the formation of sub-100 nm O/W emulsions with high stability

Hydrodynamic cavitation, a newly developed process intensification technique, has demonstrated immense po-tential for intensifying diverse physical and chemical processes. In this study, hydrodynamic cavitation was ex-plored as an efficient method for the formation of sub-100 nm oil-in-water (O/W) emulsions with high stability. O/W emulsion with an average droplet size of 27 nm was successful y prepared. The average droplet size of O/W emulsions decreased with the increase of the inlet pressure, number of cavitation passes and surfac-tant concentration. The formed emulsion exhibited admirable physical stability during 8 months. Moreover, the hydrodynamic cavitation method can be generalized to fabricate large varieties of O/W emulsions, which showed great potential for large-scale formation of O/W emulsions with lower energy consumption.     

31P nuclear magnetic resonance studies on alkyl phosphate emulsifiers in cosmetic oil-in-water emulsions

Cosmetic oil-in-water emulsions with a stearyl phosphate emulsifier are examined by means of static and dynamic ³¹P nuclear magnetic resonance (NMR) techniques to characterize the molecular properties of the emulsifier in situ. The interfacially bound emulsifier can be deteced by high-resolution NMR spectroscopy, whereas the excess emulsifier exists as a solid lipid phase not detectable by this technique. The emulsions and the emulsifier raw material, consisting of monostearyl phosphate as well as distearly phosphate, are examined by solid state cross polarization magic angle spinning NMR spectroscopy to prove the existence of solid emulsifier phases in the emulsions. By applying dynamic ³¹P NMR methods to the interfacially bound emulsifier, information about the molecular dynamics at the interface is obtained. The results of the T ₁ and T ₂ relaxation time measurements indicate a restricted motion of the molecules that is dependent on the oil droplet size in the emulsions. This is verified by ³¹P NMR pulsed gradient spin echo self-diffusion measurements on emulsions with different droplet sizes. Only about 5 wt% of the total emulsifier used is bound at the interface; the excess forms solid lipid phases. The coverage of the interface seems to be independent of the emulsifier concentration. Only the monoester of the emulsifier raw material shows interfacial activity. Its mobility indicates the two-dimensional environment of the molecules on the surface of the oil droplets.     

A low‐energy emulsification batch mixer for concentrated oil‐in‐water emulsions

This work shows the formation of a high internal phase ratio oil‐in‐water (O/W) emulsion using a new type of a two‐rod batch mixer. The mixture components have sharply different viscosities [1/3400 for water‐in‐oil (W/O)], similar densities (1/0.974 for W/O), and an O/W ratio of 91% (wt/wt). The simple design of this mixer leads to a low‐energy process (10⁶ < energy density [J m^?3] < 10⁷), characterized by low rotational speed and laminar flow. The droplet size distribution during the emulsification was investigated according to different physical and formulation parameters such as stirring time (few minutes < t < 1 h), rotational speed (60 < Ω < 120 rpm), surfactant type (Triton X‐405 and X‐100), concentration (from 1 to 15.9 wt % in water), and salt addition (30 g/L). We show that all studied parameters allow a precise control of the droplet size distribution and the rheology. The resulting emulsions are unimodal and the mean droplet diameter is between 30 μm and 8 μm. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

A novel and facile liquid whistle hydrodynamic cavitation reactor to produce submicron multiple emulsions

Ferrous fumarate, [C₄H₂FeO₄] is widely utilized in the effective treatments and prevention of iron deficiency anemia. But, its administration has been oftentimes linked with quite a few side effects than ferric products. To overcome the side effects, multiple water‐in‐oil‐in‐water (W/O/W) emulsion formulations had been proposed as a new drug delivery system for the controlled release of entrapped active iron compound. In this study, high‐pressure liquid whistle hydrodynamic cavitation reactor has been developed to produce highly stable W/O/W multiple emulsions containing Ferrous Fumarate in submicron scale (～600 nm) with the droplet‐size distribution polydispersity index in the narrow regime (0.35–0.40). The microscopic observations confirmed that that the physical stability of the W/O/W emulsions was increased significantly with operating pressure and number of emulsification passes. Looking at the potential for scale‐up, this could be a promising technique to produce multiple emulsions incorporated with active constituents. © 2012 American Institute of Chemical Engineers AIChE J, 59: 155–167, 2013     

Interfacial Crystallization of Diacylglycerols Rich in Medium‐ and Long‐Chain Fatty Acids in Water‐in‐Oil Emulsions

The effects of diacylglycerols rich in medium‐ and long‐chain fatty acids (MLCD) on the crystallization of hydrogenated palm oil (HPO) and formation of 10% water‐in‐oil (W/O) emulsion are studied, and compared with the common surfactants monostearoylglycerol (MSG) and polyglycerol polyricinoleate (PGPR). Polarized light microscopy reveals that emulsions made with MLCD form crystals around dispersed water droplets and promotes HPO crystallization at the oil‐water interface. Similar behavior is also observed in MSG‐stabilized emulsions, but is absent from emulsions made with PGPR. The large deformation yield value of the test W/O emulsion is increased four‐fold versus those stabilized via PGPR due to interfacial crystallization of HPO. However, there are no large differences in droplet size, solid fat content (SFC), thermal behavior or polymorphism to account for these substantial changes, implying that the spatial distribution of the HPO crystals within the crystal network is the driving factor responsible for the observed textural differences. MLCD‐covered water droplets act as active fillers and interact with surrounding fat crystals to enhance the rigidity of emulsion. This study provides new insights regarding the use of MLCD in W/O emulsions as template for interfacial crystallization and the possibility of tailoring their large deformation behavior. Practical Applications: MLCD is applied in preparing W/O emulsion. It is found that MLCD forms unique interfacial Pickering crystals around water droplets, which promote the surface‐inactive HPO nucleation at the oil‐water interface. Thus MLCD‐covered water droplets act as active fillers and interact with surrounding fat crystals, which can greatly enhance the rigidity of emulsion. This observation would provide a theoretical reference and practical basis for the application of the MLCD with appreciable nutritional properties in lipid‐rich products such as whipped cream, shortenings margarine, butter and ice cream, so as to substitute hydrogenated oil. MLCD‐stabilized emulsions can also be explored for the development of novel confectionery products, lipsticks, or controlled release matrices.     

Formation of O/W emulsions by static mixers for pharmaceutical applications

Oil-in-water (O/W) emulsions produced by static mixers in the laminar flow regime are characterized for their oil drop size spectra. The emulsions are used in the first process step for the production of microspheres for pharmaceutical applications by the emulsion extraction method. However, emulsion generation by static mixers in the laminar flow regime is rarely discussed in the scientific literature. Here we deduce a non-dimensional correlation for predicting the Sauter mean oil drop size as a function of the static mixer operation parameters and the liquid properties. First, the material properties of the organic and water phases are characterized. Second, the oil drop size spectra of the emulsions are measured by laser diffraction. Dimensional analysis is used to describe the relationship between the process parameters of the static mixer and the Sauter mean oil droplet size. Emulsion production experiments using SMX static mixers with two different diameters are carried out with the mixing of the two liquids taking place in the laminar flow regime. We provide results covering a wide range of all process parameters, which were identified influencing the droplet size of the emulsion. The correlation achieved is related to the non-dimensional drop-size based Ohnesorge number of the emulsification process and allows for the prediction of the mean oil droplet size with good accuracy, which is an essential information about the emulsion properties relevant for the pharmaceutical application.     

De-emulsification of 2-ethyl-1-hexanol/water emulsion using oil-wet narrow channel combined with low-speed rotation

Low-speed rotation of disc in an internal circulation of a novel de-emulsification with rotation-dise horizental contactor (RHC-D) realized de-emulsification for O/W emulsions due to repeated coalescence in oil-wet narrow channels at a low rotation speed. For three emulsions included ethanol/water/2-ethyl-1-hexanol, ethanol/water/2-ethyl-1-hexanol/SDS (Sodium Dodecyl Sulfonate) and 2-ethyl-1-hexanol/water/SDS emulsion, deemulsification ratios of oil phase could reach 1, 1 and 0.67 respectively at 170 r·min^-1, and de-emulsification ratios increased obviously after agitating 10 min. De-emulsification experiment in the seam indicated that oil droplet sizes in O/W emulsion became larger after de-emulsification. The main de-emulsification mechanism in RHCD was the coalescence of oil droplets in oil-wet narrow channels. With increase of the rotation speed, oil droplets dispersed better in the aqueous phase. However, de-emulsification effect enhanced due to the increase of the coalescence rate at a bit higher rotation speed. In addition, internal circulation made those O/W emulsions to be broken repeatedly, consequently de-emulsification ratio increased. Repeated de-emulsification through internal circulation might make continuous extraction of ethanol come true at a low rotation speed.     

Predicting the Viscosity of Non‐Newtonian Water‐in‐Oil Emulsions Based on the Lederer Model

The accurate prediction of the viscosity of emulsions is highly important for oil well exploitation. Commonly used models for predicting the viscosity of water‐in‐oil (W/O) emulsions composed by two or three factors cannot always fit well the viscosity of W/O emulsions, especially in the case of non‐Newtonian W/O emulsions. An innovative and comprehensive method for predicting the viscosity of such emulsions was developed based on the Lederer, Arrhenius, and Einstein models, using experimental data. Compared with the commonly applied W/O emulsion viscosity models, the proposed method considers more factors, including temperature, volume fraction of water, shear rate, and viscosity of the continuous (oil) and dispersed phase (water). Numerous published data points were collected from the literature to verify the accuracy and reliability of the method. The calculation results prove the high accuracy of the model.     

Pipeline Flow Behavior of Water‐in‐Oil Emulsions with and without a Polymeric Additive in the Aqueous Phase

New experimental results are presented on the pipeline flow behavior of water‐in‐oil (W/O) emulsions with and without a polymeric additive in the aqueous phase. The emulsions were prepared from three different oils of different viscosities (2.5 mPa s for EDM‐244, 6 mPa s for EDM‐Monarch, and 5.4 mPa s for Shell Pella, at 25 °C). The W/O emulsions prepared from EDM‐244 and EDM‐Monarch oils (without any polymeric additive in the dispersed aqueous phase) exhibited drag reduction behavior in turbulent flow. The turbulent friction factor data of the emulsions fell well below the Blasius equation. The W/O emulsions prepared from EDM‐244 oil exhibited stronger drag reduction as compared with the EDM‐Monarch oil. The W/O emulsions prepared from Shell Pella oil exhibited negligible drag reduction in turbulent flow and their friction factor data followed the Blasius equation. The Shell Pella emulsions were more stable than the EDM‐244 and EDM‐Monarch emulsions. When left unstirred, the EDM‐244 and EDM‐Monarch emulsions quickly coalesced into separate oil and water phases whereas the Shell Pella emulsions took a significantly longer time to phase separate. The Shell Pella oil emulsions were also milkier than the EDM emulsions. The addition of a polymer to the dispersed aqueous phase of the W/O emulsions had a significant effect on the turbulent drag reduction behavior.     

稠油包水乳状液的表观黏度

以渤海SZ36-1稠油、矿化水为工质配制了2组不同液滴直径的W/O型乳状液,研究了温度、含水率、剪切率和液滴直径对乳状液黏度的影响。结果表明,温度对乳状液表观黏度的影响非常明显,而对相对黏度的影响却较小;同时含水率、剪切率和液滴直径也是影响乳状液黏度的重要因素,低含水率下,剪切率、液滴直径对黏度的影响不明显,而当含水率较高时,剪切率、液滴直径的影响非常突出,乳状液呈现出强烈的剪切稀释特性。利用国内外现有的一些黏度模型对实验获得的黏度数据进行了预测分析,发现Brinkman(1952)模型具有较好的预测精度。