Nanoemulsion: an Innovative Drug Delivery

Nanoemulsions/Sub-micron emulsions (SMEs)/Mini-emulsions are thermodynamically stable transparent or translucent dispersions of oil and water stabilized by an interfacial film of surfactant and co surfactant molecules having a globule size of less than 100 nm. Recently nanoemulsions are frequently used for delivery of vaccine, DNA encoded drug, antibiotics, cosmetic and topical preparations and are administrated via various routes like oral, pulmonary, intranasal, and ocular, and transdermal etc.

Nanoemulsion, which is categorized as multiphase colloidal dispersion, is generally characterized by its stability and clarity. The dispersed phase typically comprises small particles or droplets, with a size range of 5 nm-200 nm, and has very low oil/water interfacial tension. Because the droplet size is less than 25% of the wavelength of visible light, Nanoemulsions are transparent. Nanoemulsion is formed readily and sometimes spontaneously, generally without high-energy input. In many cases a co-surfactant or co-solvent is used in addition to the surfactant, the oil phase and the water phase

Nanoemulsions are defined as isotropic, thermodynamically stable, transparent or translucent dispersions of oil and water which is stabilized by an interfacial film of surfactant molecules with droplet size of 20-500nm.

The Nanoemulsions are also referred as miniemulsions, ultrafine emulsions and submicron emulsions. Phase behavior studies have shown that the size of the droplets is governed by the surfactant phase structure (bicontinuous microemulsion or lamellar) at the inversion point induced by either temperature or composition. Studies on Nanoemulsions formation by the phase inversion temperature method have shown a relationship between minimum droplet size and complete solubilization of the oil in a microemulsion biocontinuous phase independently of whether the initial phase equiliribum is single or multiphase.

Nanoemulsions are isotropic, thermodynamically stable transparent (or translucent) systems of oil, water, surfactant and co-surfactant with a droplet size usually in the range of 20– 200 nm. Their long-term stability, ease of preparation (spontaneous emulsification), and high solubilization of drug molecules make it promising tool for drug delivery. Recently, much attention has been focused on the colloidal drug delivery systems such as microemulsions, solid lipid nanoparticles and liposome for topical delivery of drugs because of low side effects, high bioavailability, good patient compliance, etc.

Nanoemulsions (also called mini emulsions, ultrafine emulsions or submicron emulsions) that are used for parenteral nutrition are polydispersed, isotropic, kinetically stable, but thermodynamically unstable systems of oil-in-water (O/W) type, which should be sterile and apyrogenic.

Three types of Nanoemulsions are most likely to be formed depending on the composition:

• Oil in water Nanoemulsion where in oil droplets are dispersed in the continuous aqueous phase;
• Water in oil Nanoemulsion where in water droplets are dispersed in the continuous oil phase;
• Bi-continuous Nanoemulsion, wherein micro domains of oil and water, are interdispersed within the system.

In all three types of Nanoemulsions, the interface is stabilized by an appropriate combination of surfactants and/or co-surfactants.

The key difference between emulsions and Nanoemulsions are that the former, whilst they may exhibit excellent kinetic stability, are fundamentally thermodynamically unstable and will eventually phase separate.

Factors to Be Considered During Preparation of Nanoemulsion:

• Surfactants must be precisely chosen so that an ultra-low interfacial tension (
• Concentration of surfactant must be sufficiently high so that it can provide sufficient surfactant molecules which required stabilizing the micro droplet to be created by ultra-low interfacial tension.
• The interface must be fluid enough to promote the formation of nanoemulsion.