Self-nanoemulsifying Drug Delivery Systems: Formulation Insights, Applications and Advances

Abhijit A Date; Neha Desai; Rahul Dixit; Mangal Nagarsenker

Disclosures

Nanomedicine. 2010;5(10) 

In This Article

Nanoemulsions

Nanoemulsions are heterogeneous dispersions of two immiscible liquids (oil-in-water [O/W] or water-in-oil [W/O]) having a mean droplet size in the nanometric scale (typically 20–200 nm), regardless of method of preparation.[4–7] These heterogeneous dispersions were initially referred to as submicron emulsions, miniemulsions, ultrafine emulsions and unstable microemulsions.[4–7] However, terms such as submicron emulsions/miniemulsions do not clearly represent the size of the droplets and might be confused with the microemulsions that are thermodynamically stable systems. The term 'nanoemulsion' clearly indicates the nanoscale size range of the emulsion droplets and is distinctly different from the term 'microemulsions'. Owing to their characteristic size, some nanoemulsions are optically transparent and possess very high stability against sedimentation and creaming. These nanoemulsions possess low viscosity, very high interfacial area and can have long-term colloidal stability.[4–7] Unfortunately, on several occasions such nanoemulsions have been confused with microemulsions and are used as misnomers. It is important to know that microemulsions are thermodynamically stable systems, whereas nanoemulsions (even optically transparent high-kinetic-energy nanoemulsions) are nonequilibrium systems. Furthermore, unlike pharmaceutical microemulsions, which require a high surfactant concentration (usually ~20% and higher) to enable optimal drug delivery, nanoemulsions can be fabricated with a relatively small surfactant concentration of 3–10%. These interesting features of nanoemulsions have propelled scientists to explore applications of nanoemulsions in various fields, including pharmaceutical sciences.

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