Formulation and Characterization of Microemulsion System

conceptuality and image of Microemulsion SystemAbstractFormulation of a new c over-in- piss (o/w) microemulsion be of stovepipe cover/Tween 80/Ethanol/Phosphate weaken storage for enhancing the committal capacity of an anti-inflammatory do medicates piroxicam has been accomplished. The pseudo-ternary signifier diagram has been define at immu duck wetter/cosurfactant ratio (12). The internal structure of so created four-component brass was elucidated by means of an analysis of isotropic celestial sphere magnitudes in the shape diagram. conduction (?), kinematic viscousness (kh) and aerof embrocate tautness (g) studies with the genetic mutation in ?w (weight ingredient of sedimentary strain) show the concomitant of structural changes from piss-in- fossil inunct (w/o) microemulsion to embrocate-in- wet (o/w). on with the solubility and district studies of piroxicam in microemulsion components, the changes in the microstructure of the microemulsion a fter incorporation of medicate construct been evaluated victimisation pH, ?, g, kh and density studies. piroxicam, a poorly water soluble do medicates, displayed high solubility (1.0%) in an optimum microemulsion formulation development Ethanol (55.0%), Tween 80 (26.5%), Castor inunct (7.5%), and Phosphate buffer (11.0%). The results take hold shown that the microemulsion remained static after the incorporation of piroxicam. Fluorescence spectra analysis taking pyrene as fluorescent fixture see was performed and the results showed that pyrene was completely solubilized in the oil strains of the bicontinuous microemulsions. The fluorescence spectrum of model drug piroxicam was use to probe the intrami mobile phonear office of nonionic microemulsion. The results showed that the piroxicam was localized in the interfacial film of microemulsion schemes more deeply in the surround bed with ethanol as the co-surfactant.Keywords Microemulsion piroxicam Isotropic argona Spec troscopy geomorphologic changesIntroductionPiroxicam is a non-steroid anti-inflammatory compound with analgesic and antipyretic effectuate, utilize for the treatment of rheumatoid arthritis, osteoarthritis and traumatic contusions. However, it has been associated with gastrointestinal aspect effects. It is possible to arcminuteimize these problems by developing drug carriers to prevent the charge contact of drug with gastric mucosal or that anyow the topical administration of drug (1, 2).Microemulsions be optically isotropic, transp bent and thermodynamically stable homogeneous solutions of oil and water, stabilized by access of a surfactant and usually a cosurfactant (3, 4). These structures have been con locationrably investigated as drug sales pitch and carrier organisation for a wide range of drugs including analgesics and anti-inflammatory and excessively used to dissolve lipophilic drugs in sedimentary medium or hydrophilic drugs in lipophilic medium (4, 5). Oil in water microemulsions have been described as a reservoir system that derriere inhibit drug release, increasing the topical effect (6). Several mechanisms have been proposed to explain the advantages of microemulsion or the transdermal delivery of drugs (7). First, a large totality of drug shadower be incorporated in the formulation collectible to the high solubilizing capacity, with increased thermodynamic activity towards the skin. Second, the permeation rate of a drug from microemulsion may be increased, since the affinity of the drug to the internal phase in microemulsion tin be easily modified, to favor zoneing, exploitation assorted internal phases and changing the composition of the microemulsion. Third, the surfactant and cosurfactant used in the microemulsion may reduce the dissimilar(a) diffusional barrier by acting as acuteness enhancers (8, 9).For the selection of components of a biocompatible microemulsion system, the use of non-ionic surfactants has been wid ely reliable, since these are compatible and apply its utility over a broad range of pH determine and may affect the skin barrier die (10-12).Microemulsion comprises different structures (water-in-oil (w/o), oil-in-water (o/w) and bicontinuous) and these champion in releasing the drug (13, 14). It is necessary to characterize the microstructure of pure and drug- irritated microemulsion. The changes in the internal structure of a microemulsion can be monitored by analyzing conduction, viscosity, density, line up tension and the fluorescence probe studies, etc. (15-17). The incorporated drug may or may not influence the microstructure. o/w and w/o microemulsions may show different doings for the release of both hydrophilic and lipophilic drugs.In the fork over work, an attempt has been made to construct a microemulsion system, for poorly water soluble non-steroid anti-inflammatory drug piroxicam, comprising castor oil, a non-ionic surfactant Tween 80, a short chain alkanol co surfactant (ethanol) and phosphate buffer (PB) pH 7.4. The pseudo-ternary phase diagram has been constructed for the elect system at a unremitting surfactantcosurfactant ratio (12). The reason for the selection of the particular oil chosen was that the castor oil has a hydroxyl group in addition to unsaturation, making it more polar. Ricinoleic acid is the main component of castor oil and it exerts anti-inflammatory effects (18). Polyoxyethylene fatty acid, stearic acid, oleic acid are used in emulsifiers in oil/water pillowcase creams and lotions.Conductivity, viscosity, surface tension and the fluorescence behavior of the pyrene is employed to investigate the gradual changes occurring in the microstructure of microemulsion. Pyrene is popular fluorescent probe which is used to study the microheterogeneous media. The fluorescence spectrum of Pyrene was used to sense the micropolarity of the o/w microemulsion. In this study, it is analyzed that how stability, optical texture and mi crostructure of microemulsion formulation, is influenced by piroxicam. To improve the solubility of piroxicam, an effort has been made to develop an optimum o/w microemulsion. It is so expected that the use of microemulsion formulation may enhance the solubility of piroxicam and prevent its degradation.Materials and MethodsMaterialsTween 80 (polyoxyethylene sorbitan monooleate), absolute ethanol (99.8 ? %) and castor oil were purchased from Fluka. Pyrene (98 %) was purchased from Sigma-Aldrich. Piroxicam was generously provided by Amson Vaccines Pharma (PVT) Ltd and used without further purification. Phosphate buffer (0.01 M, pH 7.4) was used as the hydrophilic phase. Buffers were prepared employ NaH2PO4/Na2HPO4. 0.1M NaOH and HCl were used to maintain the pH of the solution.MethodsMicroemulsion PreparationThe pseudo-ternary phase diagram was mapped (as shown in Fig. 1) using oil (castor oil), surfactant (Tween 80 HLB = 15), cosurfactant (ethanol) and aqueous phase PB (pH 7.4) a t 250.01 ?C with constant surfactantcosurfactant mass ratio (12). The temperature was unbroken at 250.01 ?C and was maintained by a Lauda M-20 thermostat. Castor oil was first mixed with Tween 80/ethanol concoction PB was then added to have got the desired microemulsion compositions. Transparent, single-phase mixtures were designated as microemulsions. altogether the try outs were stable for over 10 months, remaining clear and transparent.Drug incorporation in Microemulsion 8 microemulsions differing from each other by Fw, were selected from the single-phase region of phase diagram (Fig. 2) with compositions mentioned in table I, to study their potential as drug delivery system. All of them show stability over 10 months and remain clear and transparent. Piroxicam was dissolved into the pre-weight oil component of the system at a density of 1% (w/w) beginning stirring followed by addition of remaining components.Microemulsion CharacterizationOptical TransparencyThe homogeneit y and optical isotropy of pure and drug stung microemulsions were examined by a Polarimeter (ATAGO, AP-100 Automatic Polarimeter) and visual test at room temperature.CentrifugationThermodynamic stability of pure and drug-loaded microemulsions was tested by carrying out centrifugation at 5500 rpm for 20 min using (Hermle Z200) centrifuge. fall out TensionSurface Tension measurements were made at 25 0.010C under atmospheric pressure by Torsion Balance (White Elec. Inst. Co. Ltd.) equipped with a ring having circumference of 4.0 cm. The experimental error was about 0.05 mNm-1.Density and particularized GravityDensities and Specific Gravity of pure and drug loaded microemulsions were metrical by making use of an Anton Paar (Model DMA 5000) density meter at 25 0.01 ?C. The density meter was calibrated before and after each watch of density measurement using the density of air and pure water. deflective IndexThe refractive indices of the formulations were determined using a refractom eter (ATAGO, RX-5000) by placing 1 drop of solution on the slide.pHThe apparent pH of all the selected microemulsions and the drug loaded microemulsion was determined using a pH cadence (WTW 82362 Weilheim) fitted with a pH electrode (WTW A061414035). The temperature was maintained at 250.01 ?C by a Lauda M-20 thermostat.Conductivity MeasurementsThe effect of the follow of water phase of microemulsion was monitored quantitatively by measuring the electrical conductivity. The electric conductivity (?) was measured by means of a Microprocessor Conductivity Meter (WTW 82362 Weilheim) fitted with an electrode (WTW 06140418) having a cell constant of 1.0 cm-1. The temperature was kept at 250.01 ?C and was maintained by a Lauda M-20 thermostat. Conductivity measurements were carried out by titration of oil and surfactant/cosurfactant mixture with buffer (along the dilution line AB in Fig. 1). Further the conductivity of selected and drug loaded microemulsions was also measured. The erro r jell of conductance measurements was 0.02 ?scm-1.Viscosity MeasurementsViscosities were measured with calibrated Ubbelhode viscosimeter at 250.1 ?C. For each measurement, the viscometer was washed, rinsed and vacuum dried. To follow the cohesive behavior of the microemulsions, work time was measured for all the selected and drug-loaded microemulsions (1 wt% drug). The error limit of viscosities measurements was 3%.Absorption and Steady-State Emission MeasurementsThe absorption and steady-state fluorescence spectra were recorded using a Perkin Elmer Lambda 20 spectrophotometer and a Perkin Elmer LS 55 luminescence spectrometer, respectively, both with an external temperature controlled cell holder at a temperature of 25.00.1C. The fluorescence emission spectrum of pyrene (excitation at 340 nm) was used to obtain the ratio of intensities of the first to the third vibronic peaks (I1/I3). Good resolution of the bands was obtained at the scrape width (ex. 5.0nm, em. 5.0 nm). The sc an range used was from 350-500 nm. The Photo Multiplier pipage voltage was kept at 665V. The concentration of pyrene was 1.0 ?M. The intensities for I1 and I3 are taken at 373 and 384 nm, respectively. The fluorescence emission spectrum of piroxicam at ?exc 370 nm was obtained where the emission and excitation slits were contumacious at. 7.0 nm. The scan range used was from 390-650 nm. The concentration of piroxicam was 10.0 ?M.To quantify the solubilization of piroxicam in micellar media of Tween 80-Ethanol system, differential absorbance measurements were made in such a focussing that drug (piroxicam) solution of a particular concentration (1.0-10-5M) was kept on reference align and the Tween 80-Ethanol-Piroxicam solution on the type side in the spectrophotometer.Partition CoefficientsOil/buffer partition coefficient was determined by adjournment 20 mg piroxicam in 2ml Castor Oil. Buffer was added in 11 ratio (v/v). The mixture was shaken for 10 min and centrifuged for 2 hou rs. The two layers were separated and the subject of piroxicam in aqueous layer (PB) was assayed by UV-Visible spectrophotometer at 371 nm. The final content of drug in the lipophilic phase was calculated by subtracting the content of piroxicam in aqueous phase from initial loaded content of drug in the lipophilic phase. Further, the effect of strawman of Tween 80 and ethanol on the partition of piroxicam in oil/buffer was studied by adding 5% (w/v) of each Tween 80 and ethanol.Results and DiscussionIn the present system, microemulsion was prepared using Castor oil (fatty acid), which induces exceedingly permeable pathways in the stratum corneum (18-20). Tween-80 is a widely accepted non-ionic surfactant, used in many pharmaceutical formulations (21-23). The cosurfactant (ethanol) is used to study the one phase microemulsion region. The presence of alcohol overcomes the deal for any additional input of energy. These properties make the components useful as vehicles for drug d elivery (24-26).In the absence of aqueous phase, a solution-like oily phase consisting only of surfactant, oil, and ethanol exists. Ethanol interacts with the ethoxylated head groups of the Tween 80 by atomic number 1 bonding and affects its critical packing parameter (CPP). When water is progressively added to the centralize it facilitates the organization of the hydrated head groups of the surfactant into a polar impression while the fatty acid tails are immersed in the oil continuous phase. The ethanol suppresses formation of lyotropic liquid crystals. Any free aqueous phase is entrapped in the microstructures. Thus, w/o microstructures are formed. Upon further dilution, the change by reversal nanostructures grow and convert into a bicontinuous phase and finally invert into o/w microstructures without phase separation. shape StudiesFig. 1 shows the pseudo-ternary phase diagram and area of existence of microemulsion for Tween-80/ethanol/castor oil/phosphate buffer. Microemulsi on in the present study formed spontaneously at ambient temperature when their components were brought in contact.Phase behavior investigations of this system demonstrated the suitable approach of determining the water phase, oil phase, surfactant concentration, and cosurfactant concentration with which the transparent, 1-phase low-viscous microemulsion system was formed. The phase behavior, as shown by figure 1, manifests a two-phase region, a three-phase region and a large single-phase region which gradually and continuously transformed from buffer rich side of binary solution (buffer/surfactant micellar phase) of pseudo-ternary phase diagram towards the oil rich region. This stresses a continuous diversity from a water rich compositions to oil swollen-headed micelles.The phase study revealed that the maximum proportion of oil was incorporated in microemulsion systems when the surfactant-to-cosurfactant ratio was 12. From a formulation viewpoint, the increased oil content in m icroemulsions may provide a greater opportunity for the solubilization of piroxicam. octad microemulsions (1-8) were selected from the single-phase isotropic region (Fig. 2), with compositions mentioned in table I. Selected Microemulsion (ME) was further analyzed by conductivity, viscosity, density, surface tension, refractive index and pH. The comforts of measured parameters have been presented in table II.Conductivity MeasurementsConductometry is a useful tool to assess microemulsion structure. Conductivity studies have explained the existence of a characteristic zone with an isotropic microemulsion humans in a continuum. Determination of electric conductivity (s) as a function of weight fraction of aqueous component Fw (% wt) for the oil, surfactant/cosurfactant mixture along the dilution line AB (shown in Fig. 2) has been carried out. The results of variation of s vs Fw (% wt) are shown in Fig. 3 (a). The behavior exhibits profile characteristic of percolative conductivity (2 7-29). The conductivity is initially low in an oil-surfactant mixture but increases with increase in aqueous phase.As the volume fraction of water increases, the electrical conductivity of the system slightly increases as salubrious, until the critical Fw is reached. At this stage, a sudden increase in conductivity is observed. This phenomenon is known as percolation, and the critical Fw at which it occurs is known as percolation threshold Fp (27).The time order of conductivity beneath Fp apprizes that the reverse droplets are discrete (forming w/o microemulsion) and have picayune interaction. Above Fp the value of s increases linearly and steeply till it touches the value of Kb. The interaction amidst the aqueous domains becomes progressively more important and forms a network of conductive channel (bicontinuous microemulsion) (30).Rapid increase in conductivity beyond the percolation threshold (Fp ? 6%) up to approximate value of 20% of Fw indicates the existence of networ k of conductive channels, which corresponds to the formation of water cylinders or channels in an oil phase due to the attractive interactions between the spherical micro-droplets of water phase in the w/o microemulsion.increase water content above Fb (Fw 20%), the s shows a dodge in the measured values which may be due to substantive attractive forces as system becomes more viscous (16, 30).Fig. 3 (b) take ups the variation of log s vs weight fraction of water (Fw). The change in the slope of log s can be attributed to the structural transition to bicontinuous from w/o (23), nearly at Fw = 6%. The transition takes name once the aqueous phase becomes continuous phase i.e. at Fb. This is in line with the observation made in phase study. purpose 3(a) illustrates occurrence of three different structures (namely w/o, bicontinuous, o/w). The conductivity of the microemulsions containing more than 20 wt% water decreased significantly, probably due to the higher viscosity.The percola tion threshold can be determined from the plot (ds/dFw), as a function of the water weight fraction, Fw (% wt) (30). A maximum in the first derivative instrument of conductance Fw at 12wt % water is observed (Fig. 4) confirming the presence of percolation behavior (bicontinuous microstructure) in this region (31). The electric conductivity of pure selected and drug loaded microemulsion (1.0%) is given in table II. A comparison of two systems shows that drug incorporation does not affect the microstructure of the microemulsion.Viscosity MeasurementsTo avoid the ambiguity of non-Newtonian flow behavior of microemulsion the flow time has been used as an index of viscosity (32). Flow time of oil, surfactant/cosurfactant mixture along the dilution line AB (shown in Fig. 2), was measured as a function of weight fraction of water Fw (wt %) and is shown in Fig. 5.Similar trend has been observed for the viscosity of oil, surfactant/cosurfactant mixture as a function of Fw (Fig. 6). The rapi d change in the viscosity is probably due to the change in the microstructure of the microemulsion. The change in the internal structure could be due to either the change in the shape of droplets or may be due to the transition from w/o to bicontinuous microemulsion. It is well known that increase of volume fraction of sprinkle phase in microemulsion increases viscosity of the system (33). For the system studied viscosity increases with increase in Fw (wt% of aqueous phase).Difference in the viscosities is more abstruse for lower water content values in comparison to the subdue system. The microemulsion system is turning to be more viscous with addition of water and thus may help in the slow diffusing of drug at infinite dilution. The microemulsion system thus, shows a structural change from oil continuous system to water continuous, which has higher viscosities than the former (34). The plots of hk (kinematic viscosity), d2?/d2Fw and 1/? d?/dFw versus Fw reflect that the transit ion occurs at 11% weight fraction of aqueous phase (Fig. 6). The transition point of surface tension, conductivity and viscosity plots coincides well at 11% weight fraction of aqueous phase and confirms the presence of percolative behavior.Surface TensionThe surface tension increases linearly over the homogeneous range of water content (Fig. 7), but two breaks (at 7.0 and 20 wt% water) bespeak that structure changes occur at these compositions. The surface tension measurements showed increment, when measured as a function of weight fraction of aqueous component, except for the 12% weight fraction where the value suddenly decreased and on that pointafter a regular increase was observed. This low surface tension value showed the presence of bicontinuous microemulsion between oil and water rich system, which is because of presence of self-assembled organize microstructure in it (14, 35). The results coincide well with the electric conductivity and viscosity measurements. It can be a ssumed that the added alcohol (ethanol) is incorporated in the interfacial structure in such a way that more water is on the outside of the oil drops, causing the increase in surface tension. Incorporation of drug showed a negligible change in the surface tension measurements, thence indicting the possibility of piroxicam jots into the palisade layer on the inner side of microemulsion.Fluorescence MeasurementsIn the case of oil-in-water microemulsions, the steady-state fluorescence technique was successfully applied (36). Fluorescence measurements of the hydrophobic probe mainly depend on the polarity of the medium and hence in bicontinuous microemulsions it is a good indication of the polarity of the micro milieu in the microemulsion structure (37). The fluorescence spectra for pyrene molecule in water, singular oil phase, in alcohols, in ethanol/oil and in all the selected microemulsions are shown in Figure 8.There are four principal vibronic bands in the fluorescence spectrum (Fig. 8a), labeled I to IV. The peak strength ratio I1/I3 in the steady-state fluorescence spectra is a measurement of the relative polarity of pyrenes environment (17). Since pyrene reactant is substantially more soluble in oil phases, I1/I3 is expected to be lower in these phases (38). In the present work, for oil phase, the I1/I3 value is 0.68. In relatively polar methanol and ethanol media, I1/I3 values were base to be 1.20 and 1.09 respectively. Water is a extremely polar solvent the solubility of pyrene in this solvent is less than 2 ?M. Hence the possibility of formation of excimer hint to I3 signal is extremely low in water. experimentally I1/I3 value is 1.70 was obtained for this medium. maculation of I1/I3 versus weight fraction of aqueous component composition in microemulsion is shown in Figure 9. The value of I1/I3 varies between 0.85 and 0.91, which is comparable to a change from oil to water (0.68 and 1.70, respectively).The I1/I3 fluorescence ratios of pyrene st rongly suggest that this probe absorbs in microenvironments of polarity untold lower (oil phase) than that of water or alcohol (39). The polarities of these microphases are similar to those of cosurfactant/oil mixtures (0.94). The interest generalizations may be made regarding the fluorescence probe behavior in bicontinuous microemulsions. The I1/I3 values obtained by fluorescence measurements for all the stable bicontinuous microemulsions are closer to 0.88. These results suggest that pyrene is efficiently segregated from the water phase (40). The I1/I3 values in bicontinuous microemulsions systems are closer to the respective pure oil phase. This is due to complete solubility of pyrene in oil phases of the bicontinuous microemulsions. We conclude that all the microemulsions have separate oil microphases, in which pyrene resides.Fluorescence Behavior of PiroxicamThe fluorescence spectra for piroxicam molecule in water, individual oil phases, in surfactant/cosurfactant mixture (1 2) and in the optimum microemulsion system are shown in Figure 10.For oil phase the emission maxima (lem) is 465nm. In S/CoS (12) system lem is 451nm. Water is a highly polar solvent the solubility of piroxicam in this solvent is low than 10 ?M. The lem of piroxicam in water is 442nm. The emission maximum in bicontinuous microemulsion system is (462nm) closer to the respective pure oil phase. The results showed that the piroxicam was localized in the interfacial film of microemulsion systems more deeply in the palisade layer.Partition CoefficientPartition coefficients influence drug transport characteristics which move drug absorption, retention, distribution and elimination. Since drugs are distributed by the blood, they must penetrate and underwrite many cells to reach the site of action. Hence, partition coefficients will determine what tissues a given compound can reach.Oil/buffer Partition CoefficientsThe partition coefficient (log p) of piroxicam in oil/buffer is 5.030.20. T he presence of ethanol (5% in buffer) does not affect the partition coefficient (data shown in table III) whereas Tween 80 (5% in buffer) reduces the log p. The presence of surfactant reduces the concentration of drug in oil. Thus, solubility and partition studies indicate that piroxicam may be present at interface. The drug is entering into the palisade layer on the inner side of droplet which may help to increase the solubility of piroxicam. The partition coefficients were calculated using equation 1 (41)where A(org) is the absorbance of the organic layer, A(aq) is the absorbance of the aqueous layer, Vf(org) is the final volume of the sample from the organic layer, V(org) is the volume of the aliquot from the organic layer, Vf(aq) is the final volume of the sample from the aqueous layer, V(aq) is the volume of the aliquot of the aqueous layer.Micelle/buffer Partition CoefficientFigure 11 shows the differential absorption spectra of drug (piroxicam) in presence of various concentr ations of Tween 80 having constant S/CoS ratio (12).The buffer-micelle partition coefficient Kc (dm3 mol-1), a useful parameter to quantify the solubilization of piroxicam in micellar media of Tween 80-Ethanol system, can be calculated by using equation 2 (42). present Ca is the drug concentration (1.0-10-5M), Csmo represents Cs-CMC0 (CMC0 is the CMC of Tween 80 in water i.e. 11.0mM), ?A? is the differential absorbance at the infinity of Cs. Kc can be obtained by intercept and slope values of the straight line plot of 1/?A against 1/ (Ca+ Csmo), as shown in Figure 12. The value of Kc is given in table IV.The dimensionless partition coefficient p is related to Kc as p = Kc.nw, where nw is the number of moles of water per dm3 (55.5 mol dm-3), and is inform in table IV. The standard free energy change of the reposition of additive, from bulk water to micelle can be calculated using the following relation (equation 3)Here T is absolute temperature and R is the gas constant. The value of ?Gp for the piroxicam, using p is reported in table IV.High disconfirming value of indicates the ease of sagacity of drug intimate the micelles. This is clearly exhibited by the higher values of p and more negative for piroxicam, as shown in table IV. Tween 80 is nonionic surfactant and there is no electrostatic interaction, the hydrogen bonding between the polyoxyethylene groups of Tween 80 and piroxicam makes the complex (Tween 80-piroxicam) more hydrophobic, which corresponds to high ?Gp value.ConclusionThe pseudo-ternary phase diagram and area of existence of microemulsion for Tween 80/ethanol/castor oil/buffer was delineated. The conductivity and viscosity studies along the dilution line (in phase diagram) depict the structural transition from w/o to o/w via bicontinuous phase at 11% ?w (wt% fraction of aqueous phase). Among the eight selected microemulsions, ME was found to be optimum for the incorporation of piroxicam. After the incorporation of the drug, microemulsion remained stable and optically clears with no phase separation. The surface tension and fluorescence studies indicated that the drug may reside at the interface of oil and aqueous phase. The drug is entering into the palisade layer on the inner side of the droplet, resulting in controlled release of drug. Thus, we can conclude that this microemulsion system helps in increasing the solubility of a highly hydrophobic drug, with the help of hydrophobic component of microemulsion and lipophilic part of surfactant. In addition, the formulation can be explored with high concentration of drug. Pharmaceutically usable microemulsion system was prepared from water and castor oil with a constant amount of Tween-80 and ethanol at a mass ratio of 12. Its type and structure was examined by measuring surface tension, viscosity, electric conductivity, and the fluorescence techniques were assessed. Results of conductivity, viscosity, density and surface tension measurements confirm the prediction of a percolation transition to a bicontinuous structure. In future, the ability to determine type and structure of such microemulsion system could enable partitioning and release rates of drugs from microemulsion to be predicted.AcknowledgementThe fiscal support of Quaid-i-Azam University and Higher Education Commission of Pakistan is duly acknowledged.ReferencesLopes LB, Scarpa MV, Pereira NL, De Oliveira LC, Oliveira AG. Interaction of atomic number 11 diclofenac with freeze-dried soya phosphatidylcholine and unilamellar liposomes. Revista Brasileira de Ciencias Farmaceuticas/Brazilian Journal of Pharmaceutical Sciences. 200642(4)497-504.Park ES, Cui Y, Yun BJ, Ko IJ, Chi SC. Transdermal delivery of piroxicam using microemulsions. Arch Pharmacal Res. 200528(2)243-8. yuan Y, Li Sm, Mo Fk, Zhong Df. Investigation of microemulsion system for transdermal delivery of meloxicam. Int J Pharm. 2006321(1-2)117-23.Sarciaux JM, Acar L, Sado PA. Using microemulsion formulations for oral drug d elivery of therapeutic peptides. Int J Pharm. 1995120(2)127-36.Ristsehel WA. Experimental and Clinical Pharmacol. 1991.Mehta SK, Kaur G, Bhasin KK. Analysis of Tween based microemulsion in the presence of TB drug rifampicin. Colloids and Surfaces B Biointerfaces. 200760(1)95-104.Sebastien H, Devin VM, Mark GA, Mark RP. Microfabricated microneedles A novel approach to transdermal drug delivery. J Pharm Sci. 199887(8)922-5.Sintov AC, Botner S. Transdermal drug delivery using microemulsion and aqueous systems Influence of skin storage conditions on the in vitro permeability of diclofenac from aqueous vehicle systems. Int J Pharm. 2006311(1-2)55-62.Spernath A, Aserin A. Microemulsions as carriers for drugs and nutraceuticals. Adv Colloid Interface Sci. 2006128-13047-64.Lawrence MJ, Rees GD. Microemulsion-based media as novel drug delivery systems. Adv Drug Delivery Rev. 200045(1)89-121.Lpez A, Llinares F, Cortell C, Herrez M. Comparative enhancer effects of Span20 with Tween20 and Azone on the in vitro percutaneous penetration of compounds with different lipophilicities. Int J Pharm. 2000202(1-2)133-40.Fang JY, Yu SY, Wu PC, Huang YB, Tsai YH. In vitro skin permeation of estradiol from various proniosome formulations. Int J Pharm. 2001215(1-2)91-9.Krauel K, Davies NM, Hook S, Rades T. Using different structure types of microemulsions for the preparation of poly(alkylcyanoacrylate) nanoparticles by interfacial polymerization. J Controlled Release. 2005106(1-2)76-87.Mehta SK, Kaur G, Bhasin KK. Incorporation of antitubercular drug isoniazid in pharmaceutically accepted microemulsion Effect on microstructure and physical parameters. Pharm Res. 200825(1)227-36.He D, Yang C, Ma M, Zhuang L, subgenus Chen X, Chen S. Studies of the chemical properties of tri-n-octylamine-secondary octanol-kerosene-HCl-H2O microemulsions and its extraction characteristics for cadmium(II). Colloids Surf A. 2004232(1)39-47.Podlogar F, Gasperlin M, Tomsic M, Jamnik A, Rogac MB. Structural m otion-picture show of water-Tween 40