Chapter 6 - Water-in-Oil-in-Water Nanoencapsulation Systems

Abstract

Emulsion systems have attracted increasing attention during the last few years as alternative carriers for the delivery of bioactive entities such as peptides, proteins, antioxidants, and inert bacteriophage particles, among other types of (macro)molecules, in order to overcome (in)stability issues. Recently, a newly developed technique for stabilization of proteins and enzymes based on nanoencapsulation procedures has started to gain momentum, based on entrapment of macromolecules in a nanoporous matrix by the gelation of a solution. Due to being entrapped in a very confined environment, the molecular motions of water molecules are altered, slowing down, and thus the increased viscosity associated to entropic confinement (physical entrapment), slows down (degradation) reaction rates, and biological materials can be stabilized for storage. Water-in-oil-in-water (W/O/W) multiple emulsions are examples of complex emulsions, in which dispersions of small water droplets within the core of larger oily droplets are themselves dispersed in a continuous (external) aqueous phase. Emulsions are utilized in many methods of processing, and are extensively used by the food, cosmetic, pharmaceutical, and coating industries. Due to their compartmentalized internal structure, multiple emulsions present advantages over simple oil-in-water (O/W) or water-in-oil (W/O) emulsions for encapsulation, including the ability to carry both polar and nonpolar molecules, and better control over the release of therapeutic molecules. The basic thermodynamic principles governing the stability of multiple emulsions are therefore tackled in a systematic fashion. Emphasis is placed on the formation and composition of W/O/W multiple emulsions, instability/stabilization issues, major characteristics of W/O/W multiple emulsions such as droplet size distribution and entrapment efficiency (EE), release kinetics of water-soluble molecules, and potential applications of W/O/W multiple emulsions. Additionally, modification of the microenvironment of biomolecules via physical containment within the aqueous core of W/O/W multiple emulsions is discussed as a strategy aiming at full structural and functional stabilization of said biomolecules. Potential applications of these systems are also approached.