Preparation of fine W/O/W emulsion through membrane filtration of coarse W/O/W emulsion and disappearance of the inclusion of outer phase solution

Droplet breakup mechanisms in premix membrane emulsification and related microfluidic channels

Premix membrane emulsification (PME) is a pressure driven process of droplet breakup, caused by their motion through membrane pores. The process is widely used for high-throughput production of sized-controlled emulsion droplets and microparticles using low energy inputs. The resultant droplet size depends on numerous process, membrane, and formulation factors such as flow velocity in pores, number of extrusions, initial droplet size, internal membrane geometry, wettability of pore walls, and physical properties of emulsion. This paper provides a comprehensive review of different mechanisms of droplet deformation and breakup in membranes with versatile pore morphologies including sintered glass and ceramic filters, SPG and polymeric membranes with sponge-like structures, micro-engineered metallic membranes with ordered straight-through pore arrays, and dynamic membranes composed of unconsolidated particles. Fundamental aspects of droplet motion and breakup in idealized pore networks have also been covered including droplet disruption in T-junctions, channel constrictions, and obstructed channels. The breakup mechanisms due to shear interactions with pore walls and localized shear (direct breaking) or due to interfacial tension effects and Rayleigh-Plateau instability (indirect breaking) are systematically discussed based on recent experimental and numerical studies. Non-dimensional droplet size correlations based on capillary, Weber, and Ohnesorge numbers are also presented.

Microencapsulation of Flaxseed Oil—State of Art

Microencapsulation is a well-known technology for the lipid delivery system. It prevents the oxidation of fatty acids and maintains the quality of lipid after extraction from oil seed and processing. In flaxseed oil, the amount of ω-3 and ω-6 polyunsaturated fatty acids are 39.90–60.42% and 12.25–17.44%, respectively. A comprehensive review article on the microencapsulation of flaxseed oil has not been published yet. Realizing the great advantages of flaxseed oil, information about different technologies related to the microencapsulation of flaxseed oil and their characteristics are discussed in a comprehensive way, in this review article. To prepare the microcapsule of flaxseed oil, an emulsion of oil-water is performed along with a wall material (matrix), followed by drying with a spray-dryer or freeze-dryer. Different matrices, such as plant and animal-based proteins, maltodextrin, gum Arabic, and modified starch are used for the encapsulation of flaxseed oil. In some cases, emulsifiers, such as Tween 80 and soya lecithin are used to prepare flaxseed oil microcapsules. Physico-chemical and bio-chemical characteristics of flaxseed oil microcapsules depend on process parameters, ratio of oil and matrix, and characteristics of the matrix. As an example, the size of the microcapsule, prepared with spray-drying and freeze-drying ranges between 10–400 and 20–5000 μm, respectively. It may be considered that the comprehensive information on the encapsulation of flaxseed oil will boost the development of functional foods and biopharmaceuticals.

Enhancing trans-Resveratrol loading capacity by forcing W1/O/W2 emulsions up to its colloidal stability limit

Trans-Resveratrol (3, 5, 4'-trihydroxystilbene) is a naturally occurring polyphenol easily oxidizable and extremely photosensitive with a short biological half-life that must be encapsulated to maintain its beneficial properties on the human body. The aim of this work is to increase the amount of resveratrol encapsulated using concentrated double water-in-oil-in-water (W₁/O/W₂) emulsions, making these systems more interesting as ingredient for functional food products and/or pharmaceutical formulations. The concentration of the inner emulsion (W₁/O) for several external (W₁O/W₂) ratios was optimized in terms of encapsulation efficiency (EE), colloidal stability and rheological behaviour. W₁/O emulsions formulated with ratios of 30/70 and 40/60 were used to obtain double emulsions (with ratios of 20/80 up to 80/20 of W₁O/W₂). Trans-Resveratrol EE increased up to 90 % when the most concentrated double emulsions were prepared for both W₁/O ratios tested. The maximum resveratrol concentrations on double emulsions were 10.8 mg/L and 14.4 mg/L when 30/70 and 40/60 of W₁/O ratios were used, respectively. However, longer time stability was found for double high internal phase emulsions (W₁O/W₂) with a ratio of 30/70 of W₁/O. The double emulsion formulated with a 80/20 W₁O/W₂ volumetric ratio together with 30/70 of W₁/O seems suitable to be used as ingredient for pharmaceutical and food devices/products due to its high colloidal stability, clearly pseudoplastic and elastic behaviour, high EE and large trans-Resveratrol carrier capacity.

Nanomaterial Preparation by Extrusion through Nanoporous Membranes

Template synthesis represents an important class of nanofabrication methods. Herein, recent advances in nanomaterial preparation by extrusion through nanoporous membranes that preserve the template membrane without sacrificing it, which is termed as "non-sacrificing template synthesis," are reviewed. First, the types of nanoporous membranes used in nanoporous membrane extrusion applications are introduced. Next, four common nanoporous membrane extrusion strategies: vesicle extrusion, membrane emulsification, precipitation extrusion, and biological membrane extrusion, are examined. These methods have been utilized to prepare a wide range of nanomaterials, including liposomes, emulsions, nanoparticles, nanofibers, and nanotubes. The principle and historical context of each specific technology are discussed, presenting prominent examples and evaluating their positive and negative features. Finally, the current challenges and future opportunities of nanoporous membrane extrusion methods are discussed.

Preparation and evaluation of water-in-soybean oil-in-water emulsions by repeated premix membrane emulsification method using cellulose acetate membrane

The purpose of this study was to investigate the preparation of formulated water- in-soybean oil-in-water emulsions by repeated premix membrane emulsification method using a cellulose acetate membrane. The effect of selective membrane emulsification process parameters (concentration of the emulsifiers, number of passes of the emulsions through the membrane and storage temperature) on the properties and stability of the developed emulsions were also investigated. 1, 3, 6, 8-pyrenetetrasulfonic acid tetrasodium salt (PTSA) was used as a hydrophilic model ingredient for the encapsulation of bioactive substances. W/O emulsions with 7 wt% (weight percentage) PGPR displays homogeneous and very fine dispersions, with the median diameter at 0.640 μm. Meanwhile, emulsions prepared by membrane emulsification (fine W/O/W) showed the highest stability at Tween 80 concentrations of 0.5 wt.% (weight percentage). It concluded that at 7 wt.% (weight percentage) PGPR concentration and 0.5 wt.% (weight percentage) Tween 80 concentrations, the most uniform particles with minimum mean size of oil drops (9.926 μm) were obtained after four passes through the membrane. Thus, cellulose acetate membrane can be used for preparing a stable W/O/W emulsions by repeated premix ME due to low cost and relatively easy to handle.

Advances in membrane emulsification. Part A: recent developments in processing aspects and microstructural design approaches

Modern emulsion processing technology is strongly influenced by the market demands for products that are microstructure-driven and possess precisely controlled properties. Novel cost-effective processing techniques, such as membrane emulsification, have been explored and customised in the search for better control over the microstructure, and subsequently the quality of the final product. Part A of this review reports on the state of the art in membrane emulsification techniques, focusing on novel membrane materials and proof of concept experimental set-ups. Engineering advantages and limitations of a range of membrane techniques are critically discussed and linked to a variety of simple and complex structures (e.g. foams, particulates, liposomes etc.) produced specifically using those techniques.

Oxidative stability and in vitro digestibility of fish oil-in-water emulsions containing multilayered membranes

The oxidative stability and lipid digestibility of fish oil-in-water emulsions (d(43); 5.26-5.71 microm) laminated by primary, secondary, and/or tertiary layers of interfacial membranes have been investigated. The primary emulsion (5 and 0.5% wt % of fish oil and Citrem in acetate buffer) was produced through a membrane homogenizer. The second and tertiary emulsions were prepared by electrostatic deposition of chitosan and sodium alginate on the surfaces of the oil droplets, respectively. The lamination of biopolymers was measured by zeta potential. The lipid oxidative stability was assessed with peroxide value, thiobabituric acid reactive substances, and headspace aldehydes of the emulsions stored at 20 degrees C for 40 days. The positively charged secondary emulsions (+56.27 +/- 2.5 mV) were more stable to lipid oxidation compared to negatively charged primary (-45.13 +/- 1.7 mV) and tertiary emulsions (-24.8 +/- 1.2 mV). An in vitro digestion model was used to study the impact of different layers on the digestibility of oil droplets. Lipid digestion was decreased with multilayer coating, and chitosan coating further reduced the digestion. These findings have implications for the design of structured emulsions to achieve better oxidative stability with more controlled digestibility of lipids.

Preparation of uniform-sized multiple emulsions and micro/nano particulates for drug delivery by membrane emulsification

Much attention has in recent years been paid to fine applications of drug delivery systems, such as multiple emulsions, micro/nano solid lipid and polymer particles (spheres or capsules). Precise control of particle size and size distribution is especially important in such fine applications. Membrane emulsification can be used to prepare uniform-sized multiple emulsions and micro/nano particulates for drug delivery. It is a promising technique because of the better control of size and size distribution, the mildness of the process, the low energy consumption, easy operation and simple equipment, and amendable for large scale production. This review describes the state of the art of membrane emulsification in the preparation of monodisperse multiple emulsions and micro/nano particulates for drug delivery in recent years. The principles, influence of process parameters, advantages and disadvantages, and applications in preparing different types of drug delivery systems are reviewed. It can be concluded that the membrane emulsification technique in preparing emulsion/particulate products for drug delivery will further expand in the near future in conjunction with more basic investigations on this technique.

Microfluidic consecutive flow-focusing droplet generators

This article describes emulsification in a microfluidic double droplet generator (DDR) comprising two consecutive flow-focusing devices with locally modified surface chemistry. We generated W/O/W, O/O/W and O/W/O double emulsions with precisely controlled sizes and morphology of droplets. Secondly, by combining two mechanisms of droplet formation (the flow-focusing mechanism and the break up of liquid threads at T-junction) we produced multiple populations of droplets with varying size and/or composition. These droplets were used as the structural units for the formation of complex dynamic lattices.

Effects of inner-phase components of water-in-oil-in-water emulsion on low-pH tolerance of Lactobacillus acidophilus incorporated into inner-water phase

The incorporation of Lactobacillus acidophilus, which has a low acid tolerance, into the inner-water phase of water-in-oil-in-water (W/O/W) emulsion improved the bacterial survival rate in a model gastric juice. The components that enhanced the acid tolerance of the bacterium in W/O/W emulsion were investigated. Although the acid tolerance enhancement induced by the tested components was low at pH 2, some components significantly improved the tolerance at pH 4. In particular, the acid tolerance enhancement induced by yeast extract and sodium caseinate was marked.

Effect of emulsifier type on droplet disruption in repeated shirasu porous glass membrane homogenization

The influence of various emulsifier types (anionic, nonionic, and zwitterionic) on the mean particle size, transmembrane flux, and membrane fouling in repeated membrane homogenization using a Shirasu porous glass (SPG) membrane has been investigated. Oil-in-water (O/W) emulsions (40 wt % corn oil stabilized by 0.06-2 wt % sodium dodecyl sulfate (SDS) or 0.1-2 wt % Tween 20 at pH 3 or 0.5-2 wt % beta-lactoglobulin (beta-Lg) at pH 7) were prepared by passing coarsely emulsified feed mixtures five times through the membrane with a mean pore size of 8.0 microm under the transmembrane pressure of 100 kPa. The flux increased as the number of passes increased, tending to a maximum limiting value. The maximum flux for the Tween 20-stabilized emulsions (5-47 m3.m(-2).h(-1)) was smaller than that for the SDS-stabilized emulsions (29-60 m3.m(-2).h(-1)) because less energy was needed for the disruption of a SDS-stabilized droplet due to the lower interfacial tension. The mean particle size after five passes was 4.1-6.8 and 6.4-8.7 mum for 0.1-2 wt % SDS and Tween 20, respectively. The flux in the presence of beta-Lg was much smaller than that in the presence of SDS and Tween 20, which was a consequence of more pronounced membrane fouling, due to the protein adsorption to the membrane surface. After five passes through the membrane, the fouling resistance in the presence of 2 wt % beta-Lg (1.1 x 10(10) 1/m) was 2 orders of magnitude higher than that for 0.5 wt % Tween 20 and an order of magnitude higher than the membrane resistance. If a clean membrane was used in the fifth pass, a 2-fold reduction of the fouling resistance was observed.

Recent developments in manufacturing emulsions and particulate products using membranes

Membrane emulsification (ME) is a relatively new technique for the highly controlled production of particulates. This review focuses on the recent developments in this area, ranging from the production of simple oil-in-water (O/W) or water-in-oil (W/O) emulsions to multiple emulsions of different types, solid-in-oil-in-water (S/O/W) dispersions, coherent solids (silica particles, solid lipid microspheres, solder metal powder) and structured solids (solid lipid microcarriers, gel microbeads, polymeric microspheres, core-shell microcapsules and hollow polymeric microparticles). Other emerging technologies that extend the capabilities into different membrane materials and operation methods (such as rotating membranes, repeated membrane extrusion of coarsely pre-emulsified feeds) are introduced. The results of experimental work carried out by cited researchers in the field together with those of the current authors are presented in a tabular form in a rigorous and systematic manner. These demonstrate a wide range of products that can be manufactured using different membrane approaches. Opportunities for creation of new and novel entities are highlighted for low throughput applications (medical diagnostics, healthcare) and for large-scale productions (consumer and personal products).