The term nano was often used in microscopic technology and relates to any material or devise having a size of only a few nanometer. The nanoemulsions represent the extremely small limit of emulsions of submicron droplets known as “mini emulsions.” The use of nano technology in medicine and in pharmaceuticals has increased in the last few years. The pharmaceutical development based on nanotechnology is termed nanopharmaceuticals.
Various products developed or in the process of development based on nano technology are Nanoemulsion (sub-micron sized emulsion), Nanosuspension (sub-micron sized suspensions), Nanospheres (drug nanoparticles in polymer matrix), Nanotubes (sequence of nanoscale C60 atoms arranged in a long thin cylindrical structure), Nanoshells (concentric sphere nanoparticles consisting of a dielectric core and a metal shell), Nanocapsules (encapsulated drug nanoparticles), Lipid nanoparticles (lipid monolayer enclosing a solid lipid core), Dendrimers (nanoscale three- dimensional macromolecules of polymer).
The nano emulsions are defined as the nano scale droplets of one immiscible liquid dispersed with another liquid. The average size of nano emulsion droplet diameter is between 50 to 1000 nm. The usual procedure is to keep the average droplet size between 100 to 500 nm. The synonyms for nano emulsion are termed as sub-micron emulsion (SME) and mini-emulsion. The size of the droplet distribution of an emulsion will govern the emulsion properties like the long-term stability, texture and optical appearance.
The method of preparation can be classified in to two types namely the dispersion or high-energy methods, in which mechanical energy is required to form an emulsion. In condensation or low-energy method, which utilise the transitions taking place during the emulsification process. The nano emulsion can also be effectively produced by high-pressure homogenization and microfluidization methods, both of which can be used both in laboratory and in industrial production. In high pressure homogenization the dispersion of two liquids is achieved by forcing the mixture to pass through a small inlet at high pressure and can be used to prepare nano emulsion with a size range up to 1nm. The other methods like ultrasonification and in-situ emulsification can only be utilised in laboratory. The microfluidization utilise a high-pressure positive displacement pump that forces the mixture to pass through an interaction chamber consisting of micro channels on to an impingement area to produce a particle of submicron size.
To make a stable emulsion with reproducible result, a large number of factors must be controlled such as selecting an appropriate composition, controlling the order of addition of the components, and applying the shear in a manner that effectively ruptures the droplets. The other additional requirements for nanoemulsions include choice of components, especially surfactant, which do not result in the formation of lyotropic liquid crystalline ‘microemulsion’ phases. Systems containing short chain alkanes, alcohols, water, and surfactants are known to form these phases.
There is another class of nano emulsion in which the continuous phase has a significant excess of surfactant. This excess enables the new surface area of the nanoscale droplets to get rapidly coated during emulsification, thereby inhibiting shear-induced coalescence. This excess is generally in the form of surfactant micelles in the continuous phase. The next class involve the application of extreme shear to rupture microscale droplets into nanodroplets. Typically, the stress level must reach the Laplace pressure of droplets having the desired size, usually in the range of 10–100 atm. The microfluidization is a patented mixing technology, which makes use of a device called microfluidizer. This device uses a high-pressure positive displacement pump (500-2000 psi) that forces the product through the interaction chamber, which consists of small channels called microchannels. The product flows through the microchannels on to an impingement area resulting in very fine particles of submicron range.
The different characterization parameters to stabilize the emulsion include transmission electron microscopy, droplet size analysis, viscosity determination, refractive index, skin irritation test, invitro skin permeation studies, in vivo efficacy studies, thermodynamic stability studies and surface characteristics.
The surface charge of the emulsion has a marked influence on the stability of the emulsion. The emulsions are prepared using surfactants approved for the human use and also from other food substances, generally recognized safe by the FDA. The emulsions are produced easily in large quantities by mixing a water-immiscible oil phase into an aqueous phase with a high- stress, mechanical extrusion process.
The major advantage of nano emulsion is its surface area which facilitates easy transport system. The nanoemulsions do not show creaming, flocculation, coalescence and can be prepared in the form of foams, creams, liquids and sprays. The nano emulsion does not damage healthy human and animal cells hence can be used for human and veterinary for therapeutic purpose.
The nanoemulsions have wide applications as potential vehicle for the controlled delivery of cosmetics due to their own bioactive effects and to reduce trans-epidermal water loss and there by strengthens the barrier functions of skin. The nanoemulsion used as antimicrobials in the droplet size ranging from 200-600nm are having broad spectrum of activity against bacteria and fungi. The nanoemulsion is used in bio-terrorism for the protection against Anthrax and Ebola. The nanoemulsions are used to deliver recombinant proteins or inactivated organisms to mucosal surface to produce an immune response against influenza and HIV. The experimental results with recombinant gp120 with a single mucosal exposure to the virus mixed with the emulsion have a significant response against HIV.
The nanoemulsion as disinfectant and cleansing activity for use in commercial markets such as healthcare, travel, hospitality, food processing and military application to act against many pathogenic microbes. The disinfectant formulations make use of nanospheres of oil droplets suspended in water to create nanoemulsion and the surface charge present in nanospheres can penetrate inside the microbs. The nanoemulsions are used in cell cultures for invitro assays for biological compounds. The optimizations of cell growth in culture medium are supplemented with defined molecule or with blood serum, which was otherwise difficult to supplement an oil soluble substance. The deliveries of nano emulsion stabilized by phospholipids and sterilized by 0.1-im filters are easily taken up by the cell producing a high bioavailability.
The usage of nanoemulsion will allow to conduct toxic studies of oil soluble drugs in cell culture and will improve the growth and vitality of cultured cells. The patents filed based on nanoemulsion include method of preventing and testing microbial infections (US paten number 6506803), non-toxic antimicrobial compositions and methods (US patent 6559189), nanoemulsion based on phosphoric acid fatty acid esters and its use in the cosmetics , dermatological, pharmaceuticals, ophthalmological(US patent 6274150), nanoemulsion based on oxyethylenated or non-oxyethylenated sorbitan fatty esters and it is used in cosmetics, dermatological and /or ophthalmogical fields (US patent 6335022), nano emulsion based on glycerol fatty esters and it is use in cosmetics, dermatological and/or ophthalmological ( US patent 6541018), transparent nanoemulsion less than 100 nm based on fluid non-ionic amphiphilic lipids and use in cosmetics (US patent 5753241).
The development of Amiloride loaded mucoadhesive nanoemulsion based formulation has shown to be non toxic on nasal mucosa and is effective in the treatment of epilepsy. The ramipril nanoemulsion were successfully prepared using sefsol 218 as oil phase and found to have good therapeutic response with better stability.
The Author is Asst Professor, National College of Pharmacy,
Manassery, Calicut