Multiple Microemulsion

Thymopentin Stearic acid w/o/w multiple microemulsion, o/w multiple microemulsion [39]... 

A different approach of protein encapsulation is reported by Morel, Gasco, and Cavalli [38], These authors describe a method of applying a warm multiple microemulsion in which the peptide is dissolved in an aqueous solution and added to a mixture of melted stearic acid, egg lecithin, and butyric acid at 70°C. This primary microemulsion is then added at 70°C to an aqueous solution of egg lecithin, butyric acid, and taurodeoxycholate sodium salt. Addition of warm multiple microemulsions to water at 2°C leads to precipitation of the lipid phase, forming solid lipospheres. 

Microporous zincophosphate crystals of zeolitic structure have been synthesized by Dutta and colleagues [335, 222] via multiple microemulsions. In the first investigation [335], these authors used two reverse microemulsions, based on the system AOT/n-hexane, containing (a) aqueous solution of Zn(N03)2.6H20 and (b) aqueous solution with H3PO4 and tetramethylammonium hydroxide (the latter was required for incorporation of the phosphate in the reverse micelle). For the Zn-micelle, the [AOT]/[H20] ratio was 13, while for the phosphate-micelle, the value went up to 21. Uptake of the constituents in the micelles was examined by chemical analysis. The two microemulsions were finally mixed at room temperature. Particles grew from 14 nm to - 150 nm in three days, and then became stable at --140 nm. 

Lipid microspheres 0.2-100 ixm Lipids or phospholipids with high melting points Melt method, multiple microemulsions, and preincorporation into lipophilic carriers... 

Castro D, Moreno MA, Lastres JL. 2001. First-derivative spectrophotometric and LC determination of nifedipine in Brij 96 based oil/water/oil multiple microemulsions on stability studies. J Pharm Biomed An 26 563-572. 

Microencapsulation can be used to provide a temporary barrier between a chemical species and its surrounding environment see also Section 14.3). This permits controlled (slow) release of the active agents following application. Depending on the product and the situation, an active ingredient such as a pesticide may need to be released slowly at low concentration, or slowly at high concentrations. Such controlled release can both reduce the number of crop applications that are required and also help prevent over use and subsequent run-off. The barrier can be provided by a polymer film, in the case of suspensions [867], or a liquid membrane, in the case of single or multiple emulsions [865], Microemulsions have also been used [234,865],... 

A microemulsion, Fig. 1, has a similar organization to that characteristic of a micelle but employs, rather than one, multiple surfactant components, allowing for introduction of other additives into the hydrophobic core [11], As with micelles, microemulsions are optically transparent and can be easily studied by standard spectroscopic methods. One important use of such microemulsions is in the photoinduced initiation of polymerization of monomers with low water solubility many such reactions involve a mechanism occurring through photoinduced interfacial electron transfer. 

In some cases, substrates and enzymes are not soluble in the same solvent. To achieve efficient substrate conversion, a large interface between the immiscible fluids has to be established, by the formation of microemulsions or multiple-phase flow that can be conveniently obtained in microfluidic devices. Until now only a couple of examples are published in which a two-phase flow is used for biocatalysis. Goto and coworkers [431] were first to study an enzymatic reaction in a two-phase flow in a microfluidic device, in which the oxidation ofp-chlorophenol by the enzyme laccase (lignin peroxidase) was analyzed (Scheme 4.106). The surface-active enzyme was solubilized in a succinic acid aqueous buffer and the substrate (p-chlorophenol) was dissolved in isooctane. The transformation ofp-chlorophenol occurred mainly at... 

Lipid-based formulations of poorly water soluble drugs offer large versatility for oral administration as they can be formulated as solutions, gels, suspensions, emulsions, self-emulsifying systems, multiple emulsions, microemulsions, liposomes, and solid dispersions. " Administration of a drug in a lipidic vehicle/formu-lation can enhance the absorption and oral bioavailability via a combination of various mechanisms " " that are briefly summarized as follows ... 

In addition to traditional dermal and transdermal delivery formulations, such as creams, ointments, gels, and patches, several other systems have been evaluated. In the pharmaceutical semisolid and liquid formulation area,these include sprays, foams, multiple emulsions, microemulsions, liposomal formulations, transfersomes, niosomes, ethosomes, cyclodextrins, glycospheres, dermal membrane structures, and microsponges. Many of these novel systems use vesicles to modulate drug delivery. Novel transdermal... 

Polyoxyethylene alkyl ethers are nonionic surfactants widely used in topical pharmaceutical formulations and cosmetics, primarily as emulsifying agents for water-in-oil and oil-in-water emulsions and the stabilization of microemulsions and multiple emulsions. 

Sesame oil may be used as a solvent in the preparation of subcutaneous injections, oral capsules, rectal suppositories, and ophthalmic preparations it may also be used in the formulation of suspensions and emulsions. Multiple-emulsion formulations, in which sesame oil was one of the oil phases incorporated, have been investigated as a prolonged-release system for rifampicin microemulsions containing sesame oil have been prepared for the transdermal delivery of ketoprofen. Sesame oil has also been used in the preparation of liniments, pastes, ointments, and soaps. A sesame paste... 

Emulsions - liquid dispersions usually of an oil phase and an aqueous phase - are a traditional pharmaceutical dosage form. Oil-inwater systems have enjoyed a renaissance as vehicles for the delivery of lipid-soluble dmgs (e.g. propofol). Their use as a dosage form necessitates an understanding of the factors governing the formulation and stability of oil-in-water (o/w) and water-in-oil (w/o) emulsions, multiple emulsions (w/o/w or o/w/o) and microemulsions, which occupy a position between swollen micelles and emulsions with very small globule sizes. Photomicrographs of o/w, w/o systems and multiple emulsions are shown in Fig. 7.10. It is also possible to formulate nonaqueous or anhydrous emulsions, that is oil-in-oil systems and even multiple oil-in-oil-in-oil systems. 

The chapter has dealt with the stability and stabilisation of colloidal systems and covered topics such as their formation and aggregation. If the particle size of a colloidal particle determines its properties (such as viscosity or fate in the body), then maintenance of that particle size throughout the lifetime of the product is important. The emphasis in the section on stability is understandable. Various forms of emulsions, microemulsions and multiple emulsions have also been discussed, while other chapters deal with other important colloidal systems, such as protein and polymer micro- and nanospheres and phospholipid and surfactant vesicles. 

The current state OF THE ART of various aspects of macro- and microemulsions is reflected in this volume. The symposium upon which this volume is based was organized in six sessions emphasizing major areas of research. Major topics discussed include a review of macro- and microemulsions, enhanced oil recovery, reactions in microemulsions, multiple emulsions, viscoelastic properties of surfactant solutions, liquid crystalline phases in emulsions and thin films, photochemical reactions, and kinetics of microemulsions. 

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