Emulsion Drops Research Articles

Eye drop emulsion containing 0.1% cyclosporin (1 mg/mL) for the treatment of severe vernal keratoconjunctivitis: an evidence-based review and place in therapy.

Vernal keratoconjunctivitis (VKC) is a rare, recurrent and multifactorial ocular disease, which typically flares up during spring and affects especially male children and adolescents. This condition does not usually respond to common treatments with antihistamines or mast cells stabilizers, whereas corticosteroids have effective results. Corticosteroids need to be carefully administered, to avoid adverse effects, mainly the secondary development of glaucoma, cataracts, or infections. Immunosuppressive agents, such as cyclosporin (CyA) or tacrolimus are, therefore, frequently employed in VKC patients. Only the 0.1% CyA (1 mg/mL) concentration has an approved and specific clinical indication for the treatment of VKC and this drug was given the denomination of orphan drug by the European Commission (EU/3/06/360) in 2006. So far, few studies have been conducted to evaluate the efficacy and the side effects of topical 0.1% CyA. Different topical CyA concentrations, ranging from 0.05% to 2%, and various types of formulation are available at the moment. In the future, 0.1% CyA will presumably take an important part in the management of VKC. The present review focuses on eye drops containing 0.1% CyA; however, more studies will be needed to define its long-term efficacy in the natural course of this severe ocular disease.

Three dimensional numerical simulation of drops suspended in a channel under uniform electric field

Abstract In this paper, numerical study of emulsion of drops in a channel under uniform electric field is investigated. The electric field is created by imposing an electric potential difference across the channel walls. The leaky dielectric model developed by Taylor is used to compute the electric force. The electric conductivity ratio σ r = σ i σ o and electric permittivity ratio e r = e i e o are used to study oblate and prolate drops The interaction of drop-to-wall and drop-to-drop are investigated by changing the dimensionless numbers. Oblate drops and prolate drops with σ r e r , are always attracted to the walls, but prolate drops with σ r > e r , are attracted by or repelled from the walls depending on the initial distance and electric properties. Drop-to-drop interaction depends on the initial configuration of drops. Drop pairs that are placed at an angle relative to the direction of the electric field, are always attracted towards each other. If they have an initial separation distance in the direction of the electric field, they are attracted to the walls or towards each other depending on their separation distance. Prolate drops with σ r > e r , obtain a different configuration in their final state. They may stick together or have a small separation distance, depending on their electric properties. Increasing the electric capillary number, changes the vertical and horizontal separation distance of drop pairs at steady state configuration. It also decreases the time required to reach steady state configuration. The behavior of emulsion of drops is studied by considering oblate drops, prolate drops with σ r e r and prolate drops with σ r > e r . All drops form fiber chains in the direction of the electric field that will break in stronger Poiseuille flow. Oblate drops either settle on the walls or migrate to the channel center line, but prolate drops form chains of fibers that sometimes extend between the walls. Presence of drops will change the well-known parabolic velocity profile especially for prolate drops that are suspended in the channel. The channel flow rate is also studied for different emulsion of drops and electric field. At a constant electric field and pressure gradient, the channel flow rate for oblate emulsion is higher than prolate ones. As the electric field strength increases, the channel flow rate will also increase for oblate emulsions.

Hierarchically structured emulsions for brain therapy

In this paper, we developed a doxorubicin-loaded double emulsion, with a specific pH-triggered drug release mechanism, and with functionalized drops’ surfaces as an effective drug (doxorubicin-DOX) delivery implant for brain tumor therapy. The functionalization of double emulsions with antibodies at oil-water interfaces was performed for targeting brain tumor cells - glioblastoma multiforme (GBM). The functionalization involved physical adsorption of antibodies: anti-CD15 (GBM-targeting surface proteins) on oil drops of double water-in-oil-in-water emulsions. The interactions between molecules of antibodies and compounds of the oil drops were measured using isothermal titration calorimetry (ITC). Double emulsions with different structures and pH-sensitive polymer (sodium carboxymethylcellulose) in the external phase were prepared by a one-step method, in a Couette-Taylor flow contactor. The release rates of DOX from emulsions were analysed in phosphate buffers with a pH of 6.3 (acidic microenvironment of solid tumors) and a pH of 7.4 (normal cells). The release study demonstrated an expected morphology/structure, composition and pH-responsive controlled release behaviour. The ITC analysis showed that antibodies interacted with emulsion compounds, which was vital for functionalization of drops of emulsion for targeting cancer cells. This was demonstrated by changes in the heat rates reflecting molecular interactions and proved that proteins adhered to oil-drop interfaces.

Shear-induced collective diffusivity down a concentration gradient in a viscous emulsion of drops

The shear-induced collective diffusivity down a concentration gradient in a viscous emulsion is computed using direct numerical simulation. A layer of randomly packed drops subjected to a shear flow, shows the layer width to increase with the $1/3$ power of time, consistent with a semi-dilute theory that assumes a diffusivity linear with concentration. This characteristic scaling and the underlying theory are used to compute the collective diffusivity coefficient. This is the first ever computation of this quantity for a system of deformable particles using fully resolved numerical simulation. The results match very well with previous experimental observations. The coefficient of collective diffusivity varies non-monotonically with the capillary number, due to the competing effects of increasing deformation and drop orientation. A phenomenological correlation for the collective diffusivity coefficient as a function of capillary number is presented. We also apply an alternative approach to compute collective diffusivity, developed originally for a statistically homogeneous rigid sphere suspension – computing the dynamic structure factor from the simulated droplet positions and examining its time variation at small wavenumber. We show that the results from this alternative approach qualitatively agree with our computation of collective diffusivity including the prediction of the non-monotonic variation of diffusivity with the capillary number.

DEVELOPMENT OF A PROCESS CONTROL SYSTEM FOR DYNAMIC SEDIMENT OF OIL EMULSION


 
 
 Using heat balance and geometric features of horizontal cylindrical sedimentation, a new method and algorithm for controlling the dynamic sediment of emulsified water drops of oil emulsion have been developed. The mechanism of oil emulsion dynamic sediment on the proposed method is that the redistribution of the flow contributes to the cyclic change in the flow rate of the oil emulsion in the settling apparatus and the oscillatory motion (compression and expansion) of the intermediate emulsion layers, leading to the destruction of armoring casings, coalescence of emulsified water drops and transfer mechanical impurities into water cushion of the settling apparatus, as a result of which the quality of commercial oil increases (the content of water and mineral salts decrease in the prepared oil) and the risk of flooding the settling apparatus decreases. In the settling apparatus, where the volume of the oil emulsion is greater than the average value, the intermediate emulsion layer expands, the kinetic energy increases, and it increases the efficiency of collisions between the drops, leading to the destruction of the armoring casings and coalescence of the drops. When the volume is less than the average value, the intermediate emulsion layer is compressed, the distance between the drops decreases, leading to a coalescence of the drops and an increase in the efficiency of oil preparation.
 
 

Millimeter-Size Pickering Emulsions Stabilized with Janus Microparticles.

The ability to make stable water-in-oil and oil-in-water millimeter-size Pickering emulsions is demonstrated using Janus particles-particles with distinct surface chemistries. The use of a highly cross-linked hydrophobic polymer network and the excellent water-wetting nature of a hydrogel as the hydrophobic and hydrophilic sides, respectively, permit distinct wettability on the Janus particle. Glass capillary microfluidics allows the synthesis of Janus particles with controlled sizes between 128 and 440 μm and control over the hydrophilic-to-hydrophobic domain volume ratio of the particle from 0.36 to 12.77 for a given size. It is shown that the Janus particle size controls the size of the emulsion drops, thus providing the ability to tune the structure and stability of the resulting emulsions. Stability investigations using centrifugation reveal that particles with the smallest size and a balanced hydrophilic-to-hydrophobic volume ratio (Janus ratio) form emulsions with the greatest stability against coalescence. Particles eventually jam at the interface to form nonspherical droplets. This effect is more pronounced as the hydrogel volume is increased. The large Janus particles permit facile visualization of particle-stabilized emulsions, which result in a better understanding of particle stabilization mechanisms of formed emulsions.

Explosion Breakdown of Drops of Emulsions of Water with Petroleum Products as a Result of Their Intensive Heating

The conditions and characteristics of intensive evaporation of very inhomogeneous drops of emulsions of water with petroleum products (gasoline, kerosene, residual oil, heavy crude, transformer oil, turbine oil) were experimentally investigated at relative volume concentrations of these products in emulsions varying in the wide range from 10 to 70% corresponding to a large number of high-temperature (1100 K) processes occurring with gas and vapor drops, such as the heat and flame purifications of water and the production of a synthetic gas from fuel emulsions and suspensions based on water. The conditions of explosion breakdown of emulsion drops in the process of their heating have been determined. Three regimes of breakdown of emulsion drops, differing in the number of small droplets formed and in their surface area, were separated. Proposals were made on the mechanisms of the physical processes leading to the transformation of the surface of emulsion drops and their explosion breakdown.

Explosive disintegration of two-component drops under intense conductive, convective, and radiant heating

The disintegration of drops of liquids, suspensions, solutions, emulsions, and fuels is one of the most effective ways to enhance heating and evaporation. However, in some cases, the preliminary disintegration of drops for creating a fine dispersed aerosol, i.e. at the entrance to the appropriate heat exchange unit (or combustion chamber), is an ineffective way because of the effects of coagulation, as well as the entrainment and deceleration of the dropwise flow by high-temperature flue gases. As a result, researches are mostly focused on intensification of drops disintegration directly in the heat exchange chamber. Heterogeneous drops are mainly of interest for the fuel technologies and thermal purification of water from irregular impurities. This paper presents the results of experimental studies of heating, evaporation, surface transformation and micro-explosion of two-component drops under different conditions of energy supply. The studies are carried out for drops consisting of liquid combustible (oil product) and non-combustible (water) components. Two-liquid drops are heated on a substrate (conductive heating), in a stream of heated air (convective heating), and in a muffle furnace (radiant heating). The study demonstrates various modes of heating and disintegration (puffing and micro-explosion) of drops, as well as the consequences in terms of the number and size of the formed droplets in the aerosol cloud. The results show that the micro-explosion of drops during the conductive heating requires much lower temperatures compared to radiant and convective heating. The longest warming-up times of drops prior to disintegration are recorded at the radiant heating due to smaller heat fluxes as compared to other heating schemes. At the same time, the relative disintegration coefficient of drops is maximum at the radiant heating. As a result, the maximum evaporation surface area of liquid after the disintegration of the initial two-component drop has been found. We have analyzed the vaporization process of liquid combustible (petroleum) and non-combustible (water) components, as well as products of their oxidation.

Microfluidic fabrication of vesicles with hybrid lipid/nanoparticle bilayer membranes.

Hybrid lipid/nanoparticle membranes are suitable model systems both to study the complex interactions between nanoparticles and biological membranes, and to demonstrate technological concepts in cellular sensing and drug delivery. Unfortunately, embedding nanoparticles into the bilayer membrane of lipid vesicles is challenging due to the poor control over the vesicle fabrication process of conventional methodologies and the fragility of the modified lipid bilayer assembly. Here, the utility of water-in-oil-in-water double emulsion drops with ultrathin oil shells as templates to form vesicles with hybrid lipid/nanoparticle membranes is reported. Moreover, upon bilayer formation, which occurs through dewetting of the oil solvent from the double emulsion drops, a phase separation is observed in the vesicle membrane, with solid-like nanoparticle-rich microdomains segregated into a continuous fluid-like nanoparticle-poor phase. This phase coexistence evidences the complex nature of the interactions between nanoparticles and lipid membranes. In this context, this microfluidic-assisted fabrication strategy may play a crucial role in thoroughly understanding such interactions given the uniform membrane properties of the resulting productions. Furthermore, the high encapsulation efficiency of both the vesicle membrane and core endows these vesicles with great potential for sensing applications and drug delivery.

Single-step assembly of asymmetric vesicles.

Asymmetric vesicles are membranes in which amphiphiles are asymmetrically distributed between each membrane leaflet. This asymmetry dictates chemical and physical properties of these vesicles, enabling their use as more realistic models of biological cell membranes, which also are asymmetric, and improves their potential for drug delivery and cosmetic applications. However, their fabrication is difficult as the self-assembly of amphiphiles always leads to symmetric vesicles. Here, we report the use of water-in-oil-in-oil-in-water triple emulsion drops to direct the assembly of the two leaflets to form asymmetric vesicles. Different compositions of amphiphiles are dissolved in each of the two oil shells of the triple emulsion; the amphiphiles diffuse to the interfaces and adsorb differentially at each of the two oil/water interfaces of the triple emulsion. These middle oil phases dewet from the innermost water cores of the triple emulsion drops, leading to the formation of membranes with degrees of asymmetry up to 70%. The triple emulsion drops are fabricated using capillary microfluidics, enabling production of highly monodisperse drops at rates as high as 300 Hz. Vesicles produced by this method can very efficiently encapsulate many different ingredients; this further enhances the utility of asymmetric vesicles as artificial cells, bioreactors and delivery vehicles.

Effect of fatty acid-based anionic surfactants on the emulsion properties of self-emulsifying poly(ethylene-co-acrylic acid) waxes

Self-emulsifying polyethylene waxes (SE-PEA) were prepared by saponification of KOH with poly(ethylene-co-acrylic acid) (PEA) wax in the presence of surfactants. The viscosity, softening point and penetration of SE-PEA were compared according to the structure of surfactants. After simple preparation of the emulsions, the storage stability, particle size and accelerated stability were evaluated. Using the mixture of nonionic and unsaturated fatty acid emulsifiers, excellent emulsion stabilities and drop emulsion size of <3μm were achieved. The emulsion of SE-PEA prepared using a fatty acid surfactant having unsaturated groups showed stable emulsion characteristics because of the double bond on hydrophobic chain.

Intermolecular and surface forces at solid/oil/water/gas interfaces in petroleum production

Many challenging issues are encountered along the petroleum production such as the wettability alteration of reservoir solids due to deposition of petroleum materials, stabilization/destabilization of water-in-oil and oil-in-water emulsions and treatment of tailings water. All these problems are essentially driven by the fundamental intermolecular and surface forces among the different components (i.e., water, oil, solid and gas) in the surrounding complex fluid media, and comprehensive understanding of the interactions among these components will pave the way to the development of advanced materials and technologies for improved petroleum production processes.In this work, we have reviewed the quantitative force measurement methods in different petroleum systems by using nanomechanical techniques including surface forces apparatus (SFA) and atomic force microscope (AFM). Interaction forces between petroleum components (e.g., asphaltenes) and mineral solids in both organic solvents and aqueous solutions are reviewed and correlated to the wettability change of the reservoir solids. The recent key progress in quantifying the surface forces of water-in-oil and oil-in-water emulsion drops using AFM drop probe techniques are discussed. The interaction forces of polymer flocculants and colloidal particles are correlated to the performance of tailings water treatment. The current knowledge gap and future perspectives are also presented.

Explosive Decay of Emulsion Drops Based on Water and Oil Products under Conditions of High-Temperature Purification of Liquids

In the present paper, we established the conditions and the main characteristics of the stable boiling and subsequent explosive disintegration of emulsion droplets based on water and oil products under high-temperature (from 350 to 1100 K) heating using high-speed video recording (up to 105 frames per second). The studies were carried out under various conditions of energy supply to the droplet: on a massive substrate, in contact with a heated rod (local heating), and in a heated air flow. The times of heating up the emulsion droplets before the explosive decay are determined. The scale of the effect of the ambient temperature (up to 1100 K), the heat flux density (up to 104 kW/m2), and the oil product concentration (up to 70%) in the emulsion on these characteristics is established. Using high-speed video tracking, the main characteristics of the emulsion droplet decay are determined: the duration, surface transformation stages, and the number of liquid fragments formed (up to 300) and their total area (7–8 times higher than the initial one). The conditions for the emulsion drop decay both before and after its ignition were studied.

2-Dimensional colloidal micropatterning of cholesteric liquid crystal microcapsules for temperature-responsive color displays

This work offers a promising approach for development of a temperature-responsive colorimetric display platform. For this purpose, uniform thermochromic microcapsules consisting of a cholesteric liquid crystal (CLC) core and a thin polyurethane shell layer were fabricated by conducting in-situ condensation polymerization at the interface of monodisperse CLC-in-water emulsion drops. Colloidal packing-driven microcapsule registry led to exact 2-dimensional positioning of CLC microcapsules into a holes-patterned flexible film stencil. Furthermore, we showed that the designated registry of different color types of CLC microcapsules on the stencil enabled development of a microwriting display technology capable of reversible text representation according to temperature change.

All‐Aqueous Emulsions: Generation of High‐Order All‐Aqueous Emulsion Drops by Osmosis‐Driven Phase Separation (Small 39/2018)

All‐Aqueous Emulsions: Generation of High‐Order All‐Aqueous Emulsion Drops by Osmosis‐Driven Phase Separation (Small 39/2018)

Generation of High-Order All-Aqueous Emulsion Drops by Osmosis-Driven Phase Separation.

Droplets containing ternary mixtures can spontaneously phase-separate into high-order structures upon a change in composition, which provides an alternative strategy to form multiphase droplets. However, existing strategies always involve nonaqueous solvents that limit the potential applications of the resulting multiple droplets, such as encapsulation of biomolecules. Here, a robust approach to achieve high-order emulsion drops with an all-aqueous nature from two aqueous phases by osmosis-induced phase separation on a microfluidic platform is presented. This technique is enabled by the existence of an interface of the two aqueous phases and phase separation caused by an osmolality difference between the two phases. The complexity of emulsion drops induced by phase separation could be controlled by varying the initial concentration of solutes and is systematically illustrated in a state diagram. In particular, this technique is utilized to successfully achieve high-order all-aqueous droplets in a different aqueous two-phase system. The proposed method is simple since it only requires two initial aqueous solutions for generating multilayered, organic-solvent-free all-aqueous emulsion drops, and thus these multiphase emulsion drops can be further tailored to serve as highly biocompatible material templates.

Dynamic Microcapsules with Rapid and Reversible Permeability Switching

AbstractDynamic microcapsules are reported that exhibit shell membranes with fast and reversible changes in permeability in response to external stimuli. A hydrophobic anhydride monomer is employed in the thiol–ene polymerization as a disguised precursor for the acid‐containing shells; this enables the direct encapsulation of aqueous cargo in the liquid core using microfluidic fabrication of water‐in‐oil‐in‐water double emulsion drops. The poly(anhydride) shells hydrolyze in their aqueous environment without further chemical treatment, yielding cross‐linked poly(acid) microcapsules that exhibit trigger‐responsive and reversible property changes. The microcapsule shell can actively be switched numerous times between impermeable and permeable due to the exceptional mechanical properties of the thiol–ene network that prevent rupture or failure of the membrane, allowing it to withstand the mechanical stresses imposed on the capsule during the dynamic property changes. The permeability and molecular weight cutoff of the microcapsules can dynamically be controlled with triggers such as pH and ionic environment. The reversibly triggered changes in permeability of the shell exhibit a response time of seconds, enabling actively adjustable release profiles, as well as on‐demand capture, trapping, and release of cargo molecules with molecular selectivity and fast on‐off rates.

Hydrogel Microcapsules with Dynamic pH-Responsive Properties from Methacrylic Anhydride

Dynamic microcapsules are a highly sought-after class of encapsulant for advanced delivery applications with dynamically tunable release profiles, as actively manipulatable microreactors, or as selective microtraps for molecular separation and purification. Such dynamic microcapsules can only be realized with a nondestructive trigger-response mechanism that changes the permeability of the shell membrane reversibly, as found in hydrogels. However, the direct synthesis of a trigger-responsive hydrogel membrane around a water drop without the use of sacrificial templates remains elusive due to the incompatibility of the synthesis chemistry with aqueous emulsion processing. Here, we report on a facile approach to fabricate reversibly responsive hydrogel microcapsules utilizing reactive anhydride chemistry. Cross-linked and hydrophobic poly(methacrylic anhydride) microcapsules are obtained from microfluidic double emulsion drop templating that enables direct encapsulation of hydrophilic, water-suspended cargo ...

On the shear stability of water-in-water Pickering emulsions stabilized with silica nanoparticles

HypothesisWater-in-water (w/w) emulsions are known for their low interfacial tensions (IFT) which makes their stability to shear questionable. This is because of low particle attachment energies, which can be just a few kT. Therefore, emulsions stabilized with larger particles should display greater stability to shear because of larger attachment energies (10–100 or more kT). This is typically not an issue with traditional oil-in-water Pickering emulsions because particle attachment energies are much larger due to higher interfacial tensions, even when very small particles are used. ExperimentsSilica nanoparticles were silanized with 2-(methoxy(polyethyleneoxy)6-9propyl)trimethoxysilane (PEG-silane) to aid in emulsion stabilization. The phase behavior of an aqueous, two-phase system consisting of 20,000 g mol−1 polyethylene glycol (PEG) and magnesium sulfate (MgSO4) was characterized. Optical microscopy was used to characterize the static properties of the particle stabilized emulsions and shear rheology was used to study the stability of emulsions stabilized with 6 nm and 50 nm PEG-silane functionalized particles. ResultsWe demonstrated that silica nanoparticles silanized with PEG-silane can stabilize MgSO4 drops to produce MgSO4-in-PEG emulsions. We found emulsions stabilized with 6 wt% particles, regardless of particle size (6 nm or 50 nm), had similar viscosities, emulsion drop size, and were statically stable for one week. Emulsion drops stabilized with 6 wt% 50 nm particles doubled in size after 80 min of shear at 10 s−1 whereas those stabilized with 6 wt% 6 nm particles required only 25 min to double in size. We attribute these differences in doubling time to the larger particle attachment energies associated with the 50 nm particles.

Microfluidic device for real-time formulation of reagents and their subsequent encapsulation into double emulsions

Emulsion drops are often employed as picoliter-sized containers to perform screening assays. These assays usually entail the formation of drops encompassing discrete objects such as cells or microparticles and reagents to study interactions between the different encapsulants. Drops are also used to screen influences of reagent concentrations on the final product. However, these latter assays are less frequently performed because it is difficult to change the reagent concentration over a wide range and with high precision within a single experiment. In this paper, we present a microfluidic double emulsion drop maker containing pneumatic valves that enable real-time formulation of different reagents using pulse width modulation and consequent encapsulation of the mixed solutions. This device can produce drops from reagent volumes as low as 10 µL with minimal sample loss, thereby enabling experiments that would be prohibitively expensive using drop generators that do not contain valves. We employ this device to monitor the kinetics of the cell-free synthesis of green fluorescent proteins inside double emulsions. To demonstrate the potential of this device for real-time formulation, we perform DNA titration experiments to test the influence of DNA concentration on the amount of green fluorescence protein produced in double emulsions by a coupled cell-free transcription / translation system.