The pharmaceuticals developed on the basis of nanotechnology are termed as “NANOPHARMACEUTICALS’. Ideals drug delivery system fulfilled the objective of maximizing therapeutic effect while minimizing toxicity. With the progress in time and advances in science and technology, dosage forms have evolved from simple mixtures and pills, to highly sophisticated systems, which are known as novel drug delivery systems. One of the examples of novel drug delivery system is Nano emulsions.

Then an emulsion are defined as thermodynamically stable, isotropically clear dispersion of two immiscible liquids such as oil and water, stabilized by an interfacial film of surfactant molecule

Nano emulsion are made form surfactant approved for humansconsumption and common food substances that are “Generally Recognized as Safe” (GRAS) by the FDA. These emulsions are easily produced in large quantities by mixing a water-immiscible oil phase into an aqueous phase with a high-stress, a mechanical extrusion process that is available worldwide

Nano emulsion posses several advantages such as:

• NEs have a much higher surface area and free energy than macro emulsions that make them an effective transport system.

• NEs do not show the problems of inherent creaming, flocculation, coalescence, and sedimentation, which are commonly associated with macroemulsions.

Classification of Nano emulsion:(7)

On the basis of composition of oil and water portions Nano emulsion are classified into three types:

a) Oil in water (O/W) Nano emulsions in this type the oil droplets are dispersed in continuous aqueous phase

b) Water in oil (W/O) Nano emulsions here the water droplets are dispersed in continuous phase which are oil.

c) Bi-continuous Nano emulsions in this type the microdomains of oil and water are inter-dispersed within the system

Component of Nano emulsion: (8-15)

1. Oil phase
2. Surfactant
3. Co-surfactant
4. Aqueous phase
5. Preservatives & antioxidants

1) Oil phase: after water oil is the most important vehicle because of its properties to solubilize lipophilic drug molecules and improve absorption through lipid layer which are present in body.Oil is very useful for lipophilic active drug delivery because of its unique property of penetrating cell wallb.oilphase influence the swelling of tail group region of the surfactant. As compared to long chainalkane such penetration is to greater extent in case of short chain alkanes

Eg:

Unsaturated fatty acids-  oleic acid, linolenic acid

Saturated fatty acids- lauric acid, capric acid

2) Surfactant:To facilate the dispersion of all components surfactant must be able to reduce the interfacial tension nearest to zero.preparation of W/O Nano emulsion Surfactants with HLB values3-6 are useful where for the preparation of O/W Nano emulsionsurfactants with higher HLB values8-18 are useful. Surfactants which having the HLB value more than 20 are acts as cosurfactant

for reduction of concentrations of the surfactants to an acceptable limit and micro emulsion formation.

Surfactant  can be of following  types :

5. Non ionic Surfactant
5. Ionic Surfactant
5. Cationic Surfactant
5. Zwiiter ion Surfactant

Because of ionic surfactants are get affected. Because of this they are being sensitive in stability issues and are generally nor preferable because of toxicity concern. But in the case of non-ionic surfactants they can produce nontoxic pharmaceutical dosage forms and hence more popular than other type

Eg.

Non-ionic surfactant - Polyoxyl 40, Polysorbate80, d-?-tocopherolpolyethylene glycol1000succinateSolutol-HS-15, Polysorbate20,

Anionic Surfactant –Soaps, Carboxylate Groups

Cationic Surfactant- amines,quaternary ammonium compound.

3)Co-Surfactant- to reduce the interfacial  tension between oil and water to a level to enable to spontaneous formation of Nano emulsion high concentration of single chain Surfactant are required. Due to presence of fluidizing groups like unsaturated bonds cosurfactant raises the fluidity of the interface, then demolishes liquid crystalline or gel structure and alters the HLB value

Eg.

Short chain glycols-propylene glycols

Medium chain alcohols- acids or amines

4) Aqueous phase: Plain water, simulated gastric fluid (pH 1.2), Ringer's solution, simulated intestinal fluid (pH 6.8) andphosphate buffered saline can be used as aqueous phase for the evaluation of spontaneous nanoemulsi?cation of Nano emulsion. From the above properties of aqueous phase pH of the aqueous phase can have a dramatic influence on the phase behavior of Nano emulsions when a drug with pH-dependent solubility is loaded in the system . To understand the composition of Nano emulsion consider the next example Samira khanietal designed and evaluated a of oral Nano emulsion drug delivery system by using drug mebudipine. Nano emulsion was prepared by using component such as ethyl oleate, polyethylene glycol 400, Tween 80, Span 80, ethanol and deionized water. In this case ethyl oleate used as oil phase, Tween 80 and Span 80 assurfactant, ethanol as cosurfactant and deionized water as aqueous phase.

5) preservatives & antioxidants: Preservatives employed in Nano emulsions should meet criteria likelow toxicity, stability to heat and storage, physical and chemical compatibility, reasonable cost, ease of availability, acceptable odor, tasteandcolor and should have a broad antimicrobial spectrum. Microorgan-isms thrive in both oil and water, and consequently selected preserva-tive should attain effective concentration in both the phases. Use ofpreservatives in parenteral Nano emulsions is more or less avoided dueto their toxic potential. Acid and acid derivatives viz. benzoic acid, sorbicacid, propionic acid, dehydro acetic acid can be used as antifungal agentsin formulation. Alcohols like cholorobutanol and phenoxy-2-ethanol areroutinely used in ophthalmics. Phenolics and quarternary ammoniumcompounds serve as broad spectrum preservatives . Emulsified oiland lipids are subject to autoxidation upon exposure to air; manydrugs used in Nano emulsion are also highly susceptible to oxidativedegradation. Upon oxidation, unsaturated oils give rise to rancidityIf oxidation is to be avoided it is advisable to employ syntheticlipids which lack the sensitive acyl group. This however is not alwaysfeasible, so an extra component namely an antioxidant is added. Antioxidants offer oxidative stability to formulation by acting either as: Reducing agents - e.g. ascorbic acid, sodium bisulfite, metabisulfite, thioureaand sodium formaldehyde or Blocking agents e.g. ascorbic acid esters,butylhydroxytoluene and tocopherols or Synergists e.g. ascorbic acid,citranoic acid, phosphoric acid, citric acid and tartaric acid.Nano emulsions are usually transparent which implies that entire spectrum of radiation including visible and UV rays can easily penetrate oillayers and catalyzephotodegradation of drug molecule. Inclusion ofchelating agents, pH stabilizers, UV protectants etc. is therefore sometimes required to counter environmental degradat

Method of preparation:(16-19)

1) High Energy Approach Based on selected composition, i.e. surfactant compound, functional compound, and on the quantity of energy supplied the Nano emulsions are formed by high-energy methods. High energy methods depend on mechanical devices to create powerful disruptive forces for size reduction. Disruptive forces are achievedvia ultrasonicators, microfluidizer and high pressure homogenizers which are industrially scalable. Their versatility lies in the fact that almost any oil can be subjected to nanoemulsification. Major disadvantages include instrumental cost and generation of high operational temperatures which sometimes rules out thermolabile drugs.

HighPressure Homogenizer ion(35, 36)

This method produces a Nano emulsions of low particle size which is of 10-100nm. The oil and water mixture is force through a small inlet orifice at very high pressure such as 500 to 5000psi to achieve a dispersion of it, which subjects the product to hydraulic shear and intense turbulence which resulting in extremely fine particles ofemulsions. The particles which are formed by then nj a liquid, lipophilic core which is separated from the surrounding aqueous phase by a monomolecular layer of phosphuolipids.

Microfluidizer: A microfluidizer (MicrofluidicsTM Inc., U.S.A.) concomitantly useshydraulic shear, impact, attrition, impingement, intense turbulenceand cavitation, to effect size reduction.  It forces feed material through an interaction chamber consisting of microchannels under influence of a highpressure displacement pump (500–50,000 psi), resulting in very finedroplets.Usually a coarse emulsion is passed repeatedly (sometimes up to100 cycles) through a microfluidizer until desired size and dispersityis obtained. Impaction energy generated by collision of droplets dissipepates in form of heat and requires cooling. Weber number is a dimensionless number in fluid mechanics which analyses pattern of fluid flow and correlates homogenization efficiency with viscosity ratio ofdispersed and continuous phase and can be a good starting point togauge overall efficiency of high pressure homogenization . Biggestadvantage of this highly scalable process is zero contamination of feedmaterial as reduction is effected by source material itself.

Piston gap Homogenizer: Piston gap homogenizers work on principle of colloid mills. A coarseemulsion is made to pass through a narrow gap (of dimension b 10 ?m)between a fixed stator and a rapidly moving rotor. Size reduction iscaused by high shear, stress and grinding forces generated betweenrotor and stator . The upper ceiling of droplet size can be ascertainedby fixing dissipation gap to required size, which implies that a yield willnot be obtained unless and until emulsion is ground down to a size

which is equal or lower to that of the gap between rotor and stator.

Ultra sonication : To prepare a Nano emulsion this method is best way by this method only small batches of Nano emulsions can be prepared . Snehpriyaetal provided an eficient screening approach for the excipients selection fortheoptimumNano emulsionformulation development. Quetiapine fumarate was used as a model drug. For the preparation of Nano emulsionultrasonication method is used by using probe sonicator. By appropriately varying the level of oil, surfactants, and secondary surfactants it is possible to achieve desirable properties.

Microfluidization: It is a patented mixing technology. In this method microfluidizer device is uses. A high pressure positive displacement  pump(500-2000) Psi used by this device that forces the product through the interaction chamber.This chamber consists of small channels called microchannels.On to an impingement area the product flows and resulting in very fine particles of submicron range. In this case in an inline homogenizer, two solutions (aqueous phase and oily phase) are combined together and processed to yield a coarse emulsion. This coarse emulsion passes into a microfluidizer where it is further processed to obtain a stable Nano emulsion . It is found to be more effcient than ultrasound however due to production costs, equipment contamination, aseptic processing, this technique is less practicable

Low energy approach: Nano emulsions prepared by low-energy emulsification methods(20)

were developed after studying cumulative behavior of oil, surfactants, co-surfactants, drug, aqueous component, hydrophilic lipophilic balance of utilized oil surfactant blend, and operativetemperature.

Low-energy methods include spontaneous emulsification, phaseinversion and the less utilized catastrophic phase inversion Method.

A key character of these methods is utilization of energy stored inthe system to produce ultra-fine droplets. Low energy methods aresometimes limited by oil type and emulsifiers that can be used.

Spontaneous Emulsification: Spontaneous emulsification is akin to nanoprecipitation method utilized in manufacturing polymeric nanoparticles. However, instead ofpolymer, oil is used. The procedure involves preparation of two phases,

one a hydrophilic surfactant containing aqueous phase and other an organic or oil phase such as mygliol containing a drug, an oil soluble surfactant such as Span and a partially water miscible organic solventsuch as acetone or ethyl acetate. Organic phase is added drop wise toaqueous stirred phase (although the reverse i.e. adding water to oil isequally feasible in case of W/O emulsions) to form small nanoscaleemuslions

Daniel Fasoloet al, validated an isocratic LC method for the quantification of either quercetin or methylquercetin (MQ) incorporated in topical Nano emulsions. By using the spontaneous emulsification method the Nano emulsions were prepared. This method consists of injecting an organic phase containing components of the oil core into the water phase under magnetic stirring for 15 min. Then the organic solvent was removed by evaporation under reducedpressure at 40-45 °C

Phase inversion methods(21,22):

Phase inversion temperature (PIT) methods form Nano emulsions by

exploiting changes in aqueous/oil solubility of surfactants in response totemperature fluctuation (Fig. 6). It involves ordered conversion of a W/O to O/W emulsion or vice versa via an intermediary bicontinuousphase. Usually an oil, water, and surfactant blend is heated past apredetermined temperature, termed as PIT (specific for the utilized formulation blend), and then cooled rapidly. Temperature change from

low to high leads to opening and reversal of interfacial structure causingphase inversion. When this is followed by rapid quenching, interfacialstructure closes again trapping oil or water. This is a bottom up processand nascent droplets remain stable over a considerable period of timedue to rich surfactant coverage. Since input of heat is necessary, PITmethods may rule out of thermosensitive drugs. Also goodutilizationmutual solubility of water, oil, surfactant and drug is a prerequisite to facilitate smooth phase transition. Any destabilization is governed by Ostwald ripening only.

Characterization of Nano emulsion:(23-30)

1. Droplets size:in this case either by using light scattering technique or by using electron microscopy, the droplet size distribution of Nano emulsion vesicles can be determined. However to predicting the stability of Nano emulsion this method is considered as best method
2. Viscosity Measurements: in the case of Nano emulsion preparation viscosity is decrease if the water content is increase. While in case if the amount of surfactant or co-surfactant is decreased in the formulation the interfacial tension between the water and oil is increase. Due to this the viscosity of Nano emulsion formulation is increase. For the measurement of viscosity following instruments are use

• Brookfold viscometer
• Other viscometer

3. Surface charge:for the determination of surface chargeequipment used  is ZetasizerNano Z.To identify  the surface charge zeta potential is used.The particles and droplets posse a repulsive force between then information about this is gives by zeta potential. If Zeta potential valve of a formulation is about 30mV the formulation is considered as a stable formulation.
4. Electrical conductivity measurement: The Instrument used to measure the electric conductivity of Nano emulsion sample is conductivity meter. Conductivity meter has cell constant of 0.11cm-1 at a frequency of 94Hz. At temperature Of 25±1 °C the measurements were performed in triplicate manner
5. Percentage Transmitancestudies: by using a spectrophotometry the percentage transmittance of the prepared Nano emulsion formulation is determined. If the formulation has the highest percentage transmittance or close to 100% this indicated that formulation is transparent and clear. For this the 1ml Nano emulsion formulation is diluted 100 times using particular solvent and this then analyzed at ?max using solvent as blank.
6. Refractive index: the refractive index of a medium is the ratio of the speed of a wave such as light or sound in a reference medium to the phase speed of the wave in the medium. For the determination of refractive index the It Abbes type refractrometer is used at 25±0.5 °C.

       
           
       
If Zeta potential valve of a formulation is about 30mV the formulation is considered as a stable formulation

       
           
       
Permeation pathways in the skin (the stratum corneum, SC, is illustrated). (A) The transcellular route associated with the proteins inside corneocytes. (B) The intercellular route and the appendageal route through (C) hair follicles with associated sebaceous glands (D) via sweat ducts.

Biocidal Property of NE(31)

Surfactant NEs have been proven to have a broad-spectrum biocidal activity against a variety of microorganisms, including gram-positive and gram-negative bacteria, spores, and enveloped viruses]. Soybean oil nanodroplets, when stabilized by a detergent and solvent, selectively fuse with the bacterial membrane or viral envelope, destabilizing lipids and initiating the disruption of the pathogen. Myc et al. demonstrated an effective anti-fungal activity through a novel NE consisting of oil, three non-ionic detergents, solvents, and water.

Previously, such a combination of properties against microbes could only be achieved with antibiotics and disinfectant. This capability shows great selectivity as a standalone mode of action and as an added feature to formulations, without the need of preservatives to maintain stability. Moreover, this particular property implies the direct application of the NE on the skin surface, even without the need of disinfecting the area of application. Despite this antimicrobial activity, NEs do not exert any toxicity to skin layers or to normal cells.

reported, these antimicrobial NEs were composed of detergents, oils, and 20% water, forming a w/o system. Eucalyptus oil, which has a broad-spectrum antibacterial activity, was used as an oil phase in a NE applied to a Listeria monocytogenes strain. Here, the NE showed a sporicidal activity, mediated by both Triton X-100 and tri-n-butyl phosphate components. This unique sporicidal action of the emulsion is interesting because Bacillus spores are generally resistant to most disinfectants, including many commonly used detergents . NE also possesses a broad-spectrum activity against a variety of bacterial strains, such as Salmonella, E. coli, S. aureus . It has been reported that a novel NE composed of tributyl phosphate, soybean oil, and Triton X-100, has the potential to be used as a topical antimicrobial agent against several pathogens]. Although all the previous studies done on antimicrobial NEs were intended for topical use, this property could be exploited for transdermal applications.

Application of Nano emulsion in different drug delivery systems:(32,33)

Nano emulsion is proving itself to be an effective drug delivery system overcoming the barriers confronted by the conventional methods.

Various difficulties in oral, topical and other routes of drug delivery can be removed precisely by the nanoemulsification techniques.

Performance of the drugs has increased in Nano emulsions with the increasing retention time.

Antimicrobial drugs, as Nano emulsions, can easily penetrate through the microbial cell membrane and ensure rapid destruction of the organisms.

Oral delivery :

Nano emulsion can bring a great revolution in oral drug delivery system. It has overcome several limitations of the traditional systems. Drug solubility, rate of absorption, and targeted drug delivery were always the matters of concern during designing oral dosage forms. Nanoemulsified drug delivery system has come out with a one step solution for all of these problems. In case of drug solubility, both hydrophilic and lipophilic drugs can be solubilized in either O/W or W/O Nano emulsion which in turn ensures a better dissolution because of extremely small size of the particles having both hydrophilic and lipophilic units. Furthermore, these small particles can easily penetrate through the epithelial layer to ensure good rate of absorption of the drug. Small particle size facilitates the scientists to fix and control optimum dosing which prevents dose related toxicities. Therefore, Nano emulsion has created a new opportunity for the scientists to design poorly soluble and less bioavailable drugs in a more accurate way which could not be formulated through the conventional methods. Nano emulsions have both hydrophilic and lipophilic units, thus different targeting moieties and drugs from various classes can be incorporated . These nanoemulsified drugs may even enter the cytoplasm and give more specific pharmacodynamic action inside the cell (cancer treatment). Thus it can be an ideal delivery system for drugs such as steroids, proteins, hormones, diuretic and antibiotics. Oils are effectively absorbed in the GIT through various lipid absorption mechanisms. Therefore, one of the best ways to increase the absorption of the protein drugs is to load them inside the oils so that the absorption of drugs can increase significantly along with the oil droplets

A recent research has been carried out in order to improve in vitro dissolution and in vivo absorption of itraconazole (ITZ), a poorly water-soluble drug, by means of novel pectin-based nanoparticles prepared from Nano emulsion templates. Nano emulsion templates were prepared by a high-pressure homogenization method using pectin (high-methoxyl pectin HMP) as an emulsifier and chloroform as an oil phase. The in vivo absorption study in fasted rats demonstrated that pectin-based nanoparticles prepared from Nano emulsion templates could improve absorption of ITZ, which is about 1.3-fold higher than the ITZ commercial product. These findings suggested that HMP-based nanoparticles can be a promising formulation due to their high AUC₀–_{24 h} and C_max

Topical delivery :(34)

Topical drug delivery has some advantages over the oral route which include no drug loss by first pass metabolism, no damage of the drug in GI environment, no gastric irritation, no unpleasant taste or difficulty to administer and no need of disintegration and dissolution step. The main difficulty regarding topical drug delivery is the skin barrier which prevents the drug entering the systemic circulation. Nano emulsion-based topical drug delivery can significantly overcome this barrier. Usually, drugs penetrate through the skin in three routes which are hair follicle, sweat duct and directly through the stratum corneum. The small sized nanoparticles in Nano emulsions can pass through the pores easily Moreover, the hydrophobic and hydrophilic units facilitate to penetrate through the hydrophobic stratum corneum as well as the hydrophilic sweat ducts. Ropinirole, a drug with low oral bioavailability and frequent dosing, shows better penetration and greater extended release when prepared as Nano emulsion gel. The relative bioavailability of ropinirole was found to be enhanced more than two folds than the conventional marketed gel (38). Nano emulsion can be used effectively against dermatitis and psoriasis (39). Positively charged Nano emulsions were found to be better penetrable and performable than the negatively charged Nano emulsions because positively charged nanoparticles interact more with the negatively charged skin to penetrate through

       
           
       
Comparison of Nano emulsion with the conventional transdermal formulations in case of crossing skin barrier.

Parenteral delivery:

Drugs with low solubility are always considered unsuitable for parenteral administration, however, with the help of nanoemulsification techniques, they can now be formulated as parenteral dosage form. The use of biodegradable surfactants ensures good pharmacological action with no interference to the regular biological activities of the body. A recent research shows that Carbamazepine, a widely used anticonvulsant drug which is poorly soluble, can be prepared as Nano emulsion by spontaneous emulsification method containing 2 mg/mL where about 95% drug is released within 11 h (44). Another study shows that IV preparation of thalidomide (0.01%–0.05% w/w) by spontaneous emulsification releases 95% drug within 4 h (45).

       
           
       
COMMERCIAL NANO EMULSIONS

Many Nano emulsion preparations are commercialized to products available in market for use.

Commercial Nano emulsion Formulations Table:

       
           
       
Determination of Nano emulsion Morphology by (TEM):

The Nano emulsion recipe was additionally described by transmission electron magnifying instrument working at 30 KV. Where a drop of the weakened equation could store on the roundabout film of copper work colored with gold and cast aside to dry. The droplets size and shape were determined by watching the slide under the amplifying instrument.

Thermodynamic stability examines:

Amid the thermodynamic dependability of medication stacked Nano emulsions, the accompanying pressure tests can be connected:

1-Heating cooling cycle:

Nano emulsion definitions were exposed to six cycles between cooler temperature (4° C) and 45° C. Stable plans were then exposed to centrifugation test.

2-Centrifugation:

Nano emulsions were centrifuged at 3500 rpm,then those that did not demonstrate any stage partition was taken for the stop defrost pressure test.

3-Freeze-defrost cycle:

The plan was exposed to three stops defrost cycles between 21° C and +25°C which held under standard research center conditions. These tests were performed for a time of 3 months. Three bunches of plans were kept at a quickened temperature of 30° C, 40° C, 50° C and 60° Cat surrounding stickiness. The examples were pulled back at normal interims of 0, 1, 2 and 3 months and were investigated for medication content by soundness showing HPLC technique

Patents On Nano emulsions :

Though many of the patents of Nano emulsions have not been commercialized but that patency has been granted on those formulations. Some of the patents are presented in table.

Table- Patents on Nano emulsion Preparations.(35)