Nanoemulsionas a novel carrier for drug delivery system: an overview
Nanoemulsions (NE) are submicron sized emulsions that are under research as drug carriers to improve the delivery of therapeutic agents. These are thermodynamically stable transparent or translucent nano-sized dispersions having the droplet size 10-100 nm. These are stabilized by an interfacial film of surfactant and cosurfactant molecule. Several techniques are to be used for preparation of nanoemulsions including microfluidization, high pressure homogenization, low energy emulsification and solvent evaporation methods and the parameters that are to be used for its characterization includes droplet size analysis, viscosity determination, drug content, refractive index, pH, zeta potential, Electron microscopy (TEM & SEM), thermal stability, release and in-vitro & in-vivo studies. This review focusesin brief on current status of nanoemulsions in the delivery of drugs and cosmetics, formulation aspects, advantage and disadvantage of nanoemulsion.
KEYWORDS: Nanoemulsion, Physicochemical properties, Drug delivery system, Surfactant, Co-surfactant, Applications
Nanoemulsion (NE)is one of the most proficient dispersed nanosystems of droplet size ranging to submicron size. Nanoemulsions are thermodynamically stable transparent or translucent nano-sized dispersions of oil-in-water (o/w) or water-in-oil (w/o) stabilized by an interfacial film of surfactant and cosurfactant molecule having the droplet size 10-100 nm . One of the unique characteristics of the NE technology is the relatively high percentage of total particle volume occupied by the internal hydrophobic oil core of the droplets. Nanoemulsions are also referred to as mini-emulsions and ultrafine emulsions. Phase behaviour 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. This provides high solubilization of lipophilic compound as compared toother lipoidal vehicle such as liposomes. The capacity of nanoemulsions to dissolve large quantities of hydrophobics, along with their mutual compatibility and ability to protect the drugs from hydrolysis and enzymatic degradation make them ideal vehicles for the purpose of parenteral transport[4, 5]. Further, the frequency and dosage of injections can be reduced throughout the drug therapy period as these emulsions guarantee the release of drugs in a sustained and controlled manner over long periods of time. Additionally, the lack of flocculation, sedimentation and creaming, combined with a large surface area and free energy, offer certain advantages over emulsions of larger particle size. Their very large interfacial area positively influences the drug transport and their delivery, along with targeting them to specific sites . Reducing droplet sizes to the nanoscale leads to some very interesting physical properties, such as optical transparency and unusual elastic behavior. In the world of nanomaterials, nanoemulsions hold great promise as useful dispersions of deformable nanoscale droplets that can have flow properties ranging from liquid to highly solid and optical properties ranging from opaque to nearly transparent. Moreover, it is very likely that nanoemulsions will play an increasingly important role commercially, since they can typically be formulated by using significantly less surfactant than is required for nanostructured lyotropicmicroemulsion phases [8, 9]. Nanoemulsions are part of a broad class of multiphase colloidal dispersions. Although some lyotropic liquid crystalline phases,...