Multiple Emulsions: An Overview

Abstract

Multiple emulsions are complex polydispersed systems where both oil in water and water in oil emulsion exists simultaneously which are stabilized by lipophillic and hydrophilic surfactants respectively. The ratio of these surfactants is important in achieving stable multiple emulsions. Among water-in-oil-in-water (w/o/w) and oil-in-water-in-oil (o/w/o) type multiple emulsions, the former has wider areas of application and hence are studied in great detail. Formulation, preparation techniques and in vitro characterization methods for multiple emulsions are reviewed. Various factors affecting the stability of multiple emulsions and the stabilization approaches with specific reference to w/o/w type multiple emulsions are discussed in detail. Favorable drug release mechanisms and/or rate along with in vivo fate of multiple emulsions make them a versatile carrier. It finds wide range of applications in controlled or sustained drug delivery, targeted delivery, taste masking, bioavailability enhancement, enzyme immobilization, etc. Multiple emulsions have also been employed as intermediate step in the microencapsulation process and are the systems of increasing interest for the oral delivery of hydrophilic drugs, which are unstable in gastrointestinal tract like proteins and peptides. With the advancement in techniques for preparation, stabilization and rheological characterization of multiple emulsions, it will be able to provide a novel carrier system for drugs, cosmetics and pharmaceutical agents. In this review, emphasis is laid down on formulation, stabilization techniques and potential applications of multiple emulsion system.

Emulsion Micro Emulsion and Nano Emulsion: A Review

“…Commonly used components of Micro-emulsion [5][6][7][8][9][10][11][12][13][14][15] Components Some newly evolved cosurfactants are as follows :…”

“…But non-ionic surfactants can produce nontoxic pharmaceutical dosage forms and hence more popular. 8 Surfactants with HLB values [3][4][5][6] are useful in preparation of W/O micro emulsion and surfactants with higher HLB values [8][9][10][11][12][13][14][15][16][17][18] are useful in preparation of O/W micro emulsion. Surfactants with more than 20 HLB values are acts as co-surfactant to reduce concentrations of surfactants to a acceptable limit and micro emulsion formation.…”

“…1 Choice of surfactant on the basis of hydrophilic-lipophilic balance (HLB) value or critical packing parameter (CPP) helps to develop desired emulsion. Surfactants with low HLB [3][4][5][6][7][8] values as shown in Figure 1 are useful to form W/O emulsion and that of with high HLB values [8][9][10][11][12][13][14][15][16][17][18] are used to form O/W emulsion. [2][3][4] critical packing parameter (CPP) is ratio of hydrophilic and hydrophobic parts of surfactant molecule.…”

“…CPP also gives idea of nature of aggregates. 5 recently two new concepts are emerged in emulsion that is as follows: Micro-emulsion is clear, thermodynamically stable, isotropic liquid mixture. It is prepared by using oil, water, surfactant and a co-surfactant.…”

“…6,7 IUPAC defines micro-emulsion as dispersion made of water, oil, and surfactant(s) that is an isotropic and thermodynamically stable system with dispersed domain diameter varying approximately from 1 to 100 nm, usually 10 to 50 nm. [5][6] Nano-emulsions are very similar to micro-emulsions that are dispersions of nano scale particles but obtained by mechanical force unlike to micro-emulsions which forms spontaneously. 7,8…”