| Nanoemulsions can be defined as oil-in-water (o/w) emulsions with mean droplet diameters ranging from 50 to 1000 nm. Usually, the average droplet size is between 100 and 500 nm. The terms sub-micron emulsion (SME) and mini-emulsion are used as synonyms. Emulsions which match this definition have been used in parenteral nutrition for a long time. Usually, SMEs contain 10 to 20 per cent oil stabilized with 0.5 to 2 per cent egg or soybean lecithin. A typical formulation is given in Table 1. Table 1. Examples of a nanoemulsion. | | | | | Evening Primrose Oil | Lipid | 25,0 | | Tocopherol | Antioxidant | 5,0 | | Lecithin | Emulsifying Agent | 4,0 | | Water | Diluent | ad 100,0 | Preparing Nanoemulsions Using the High-Pressure Homogenization Method The preparation of nanoemulsions requires high-pressure homogenization. The particles which are formed exhibit a liquid, lipophilic core separated from the surrounding aqueous phase by a monomolecular layer of phospholipids. The structure of such lecithin stabilized oil droplets can be compared to chylomicrons. Nanoemulsions therefore differ clearly from the liposomes, where a phospholipid bilayer separates an aqueous core from a hydrophilic external phase (see figures 1 and 2). If nanoemulsions are prepared with an excess of phospholipids, liposomes may occur concurrently. 
| | Figure 1. Nanoemulsion: Lipid monolayer enclosing a liquid lipid core. | 
| | Figure 2. Liposome: Lipid bilayer enclosing an aqueous core. | What are the Benefits of Using Nanoemulsions in Skincare Products? Due to their lipohilic interior, nanoemulsions are more suitable for the transport of lipophilic compounds than liposomes. Similar to liposomes, they support the skin penetration of active ingredients and thus increase their concentration in the skin. Furthermore, nanoemulsions gain increasing interest due to their own bioactive effects. Nanoemulsions are able to favor the transport of suitable lipids into the skin. This may reduce the transepidermal water loss (TEWL), indicating that the barrier function of the skin is strengthened. Nanoemulsions Do Not Cream - How This Can Benefit New Products In addition, a special product feature is to be mentioned: nanoemulsions do not cream. This allows us to formulate liquid products which are sprayable and do not show a phase separation during storage. As an alternative to phospholipid-containing nanoemulsions, emulsifier-free o/w submicron emulsions may also be prepared. |
