ABSTRACT
A large number of investigations have been made with oil-in-water-in-oil (О/ W/O) and water-in-oil-in-water (W/O/W) systems from different standpoints of emulsion science and technology. Multiple-emulsion technology provides a mechanism for the encapsulation and in vivo delivery of drugs and other materials which would otherwise be degraded, released rapidly, or be toxic to the host. During recent years, a number of approaches have been used in the attempt to develop drug delivery systems using the liquid membrane technology: the study of antigen adjuvants and other drug systems [1,2], and other biochemical and biomedical applications [3-6], such as immobilization of enzymes [7], treatment of chronic uremia [8], and as an oxygen delivery system [9,10]. A wide variety of oils and surfactants can be used in making W/O/W multiple emulsions, but only a few of them can be used in the food and biomedical fields. The choice of materials in a multiple-emulsion system is dependent on the application of the product. For intravenous administration in humans, the range of oils and emulsi fiers is severely limited. Purified paraffin oils (mineral oils) are used for intramus cular use, as are vegetable oils. Vegetable oils are used almost exclusively for intravenous purposes as nutritional aids. Oils derived from vegetable sources are biodegradable, whereas purified mineral oils are not [11]. Surfactants are used in the membrane or middle phase and outer phase to form and stabilize the multipleemulsion droplets. The choice of the optimum surfactants in the primary and secondary emulsions is often based on the hydrophile-lipophile balance (HLB).
