INTRODUCTION:

Nanoemulsion is a colloidal particulate system which disperses in two immiscible liquid; either oil in water phase (O/W) or water in oil phase (W/O) in the submicron size. In term of their size, there is no definite standard regarding their particle size. Shah et al, 2010 proposed that nanoemulsion is an emulsion system with particle size distribution from 50 nm to 1000 nm.^[1] Whereas Shakeel, et al, 2008 said that nanoemulsion is a transparent emulsion system and consist of the dispersion of oil and water and surfactant as a stabilizer, usually has 50 – 500 nm^[2] or between 20-200 nm particle size.^[3]

Normally, the average of the nanoemulsion size varies from 10 to 1,000 nm.^[4]

Nanoemulsion in drug delivery system, usually acts as drug carriers for improving the oral bioavailability and maintaining the drug in a dissolved state^[5]and also as drug targeting application.^[6]

Diclofenac sodium was used as active ingredient in this study. This drug belongs to NSAIDs and commonly used for the treatment of some diseases including osteoarthritis^[7] and rheumatoid arthritis.^[8] However, taking this drug orally in long period will cause an ulcer.^[9] Currently, many products using diclofenac are widely available in transdermal route in order to give more pleasure usage to the patient. This route offers more advantages like prevent in first pass metabolism and prevent damage in gastrointestinal tract.^[10]

Modification in carrier formulation has become one of the solutions to decrease the drug release rate and increase the penetration to the skin like diclofenac gel or organogel containing sorbitan monoesters.^[11,12] The other method is developing the formulation in nanoemulsion. In previous research, olive oil was used as oil phase and showed very good stability.^[13] Another research used different oil like palm oil kernel esters (PKOES) as the oil phase to prepare the nanoemulsion ^[14], and also lauryl alcohol as oil phase for micro diclofenac formulation.^[15] All of the formulations showed increasing in penetration in the skin and potent to be further developed.

Based on that reason, in this study, the researcher interested to use one of the natural oil, castor oil as oil base for diclofenac sodium nanoemulsion. This oil is one of the commonly used oil all over the world. It was traditionally used for years by people, and it had been proven to successfully enhance the permeation of flurbiprofen.^[16]The aims of this study were to develop nanoemulsion using castor oil as oil phase as well as to evaluate the characteristic and stability of the nanoemulsion.

MATERIALS AND METHODS:

Materials:

Diclofenac sodium was obtained from Aarti Drugs Limited, India. Castor oil, tween 80 (Sigma-Aldrich), 96% ethanol (Systerm), Propylene Glycol (Fluka) and distilled water.

Methods:

Preparation of Diclofenac Sodium Nanoemulsion:

Nanoemulsion was prepared using magnetic stirrer methods. Castor oil in various concentrations (0, 3, 5, 7, 9 and 11%) were used as the oil phase. The aqueous phase and oil phase were prepared separately. In brief, tween 80, distilled water and propylene glycol were mixed in the beaker and heated at 50°C until transparent (Mass I). The ethanol was added to the diclofenac sodium and stirred, followed by adding castor oil drop by drop and stirred until transparent mass was obtained (Mass II). Afterwards, the mass II was gently added over mass I and further stirred using magnetic stirrer at 1000 rpm for 72 hours. The formulation can be seen in Table1.

Tabel 1 The composition of nanoemulsion formulation from diclofenac sodium with castor oil variation.

Composition	Formulation (%)
Composition	F1	F2	F3	F4	F5	F6
Diclofenac Sodium	3.5	3.5	3.5	3.5	3.5	3.5
Castor Oil	0	3	5	7	9	11
Tween 80	32	32	32	32	32	32
Ethanol	20	20	20	20	20	20
Propylene glycol	20	20	20	20	20	20
Distilled water	24.5	21.5	19.5	17.5	15.5	13.5

Physical Evaluation of Nanoemulsion:

PH Determination:

The pH was measured using a pH meter (Mettler-Toledo GmbH, Switzerland). The instrument was checked and calibrated against standard pH 4 ± 0.01 and 7 ± 0.01. The electrode was thoroughly rinsed after every individual sample in order to avoid errors due to electrode oil contamination.

Viscosity:

The viscosity of the nanoemulsion was measured using Viscometer Brookfield (DV-III Ultra Programmable Rheometer). Five millilitres of sample was used for detected the viscosity with the equipment.

Determination of Particle Size Distribution:

The particle size distributions were performed to observe the distribution of particle in the nanoemulsion. This test was performed using a Particle Size Analyzer (Zetasizers Nano ZS, Malvern Instrument). This instrument is appropriate to measure the globule size from 3 nm to 3 µm. One hundred microlitres of nanoemulsion were diluted with water (1:400) before using the instrument.

Determination of Zeta Potential:

The purpose of this test was to measure electricity of particle in the nanoemulsion. One hundred microlitres of nanoemulsion were diluted with distilled water in ratio 1:600 and put into the cuvette and measured the zeta potential using Particle Size Analyzer (Zetasizers Nano ZS, Malvern Instrument).

Stability Test:

The stability of the nanoemulsion was assessed by monitoring the changes in the particle sizes distribution of the nanoemulsion during 3 months. The nanoemulsions were stored at room storage condition and the Particle Size distribution was measured by using Zetasizers Nano ZS (Malvern Instrument).

RESULT:

Viscosity and pH value determination

Viscosity and pH value of formulations were presented in Table 2. It revealed that pH value of formulations in various concentrations of castor oil was slightly stable in the range 6.48 ± 0.03 to 7.66 ± 0.02. It can be observed that pH of the nanoemulsions was still in the safety range for the topical dosage form and lie in the normal pH range of the skin.^[17]

Table 2. The Viscosity and pH value of formulations

Formula	Viscosity (cps)	pH
F1	58.17 ± 1.42	6.48 ± 0.03
F2	66.80 ± 1.13	7.59 ± 0.01
F3	71.40 ± 0.20	7.58 ± 0.01
F4	74.47 ± 0.32	7.59 ± 0.01
F5	77.30 ± 020	7.66 ± 0.02
F6	81.70 ± 1.12	7.63 ± 0.01

For viscosity values, the result showed that the viscosity of the nanoemulsion increased in concentration-dependent manner. Its mean that the concentration of oil affected the viscosity of the nanoemulsion dosage forms. The measurement of viscosity showed that diclofenac sodium nanoemulsion contained very well dispersed particle, therefore it had good flow rate and could be used as topical dosage form and stacked longer on the skin. In general, the flow characteristics will be affected by some factors, such as the continuation of the dispersed phase, the ratio of the volume from both phase and the distribution of the particle size.^[18]

Zeta Potential:

The zeta potential values for all of the nanoemulsion were in the range –36.7±2.3 to – 11.3± 3.1 mV (Table 3). Nanoemulsions will be stable if their zeta potential value lower than – 30 mV and more than +30 mV.^[19] The results indicated that formula 2 until formula 5 tend to be more stable compared with formula 1 and 6. Zeta potential is one of the parameters that shows the electricity between the particles. The higher value of zeta potential will prevent the flocculation of the nanoemulsion.

Table 3. Zeta potential measurement of diclofenac sodium nanoemulsion

Formula	Zeta Potential (mV)
F1	-17.2 ± 2.1
F2	-34.6± 1.6
F3	-33.2 ± 1.5
F4	-35.4 ± 2.7
F5	-36.7 ±2.3
F6	-11.3 ±3.1

Particle size distribution:

The result of the particle size distribution for nanoemulsion is presented in Table 4. As shown in Table 4, particle size distribution for all of the formulations were in the range 135.0 until 181.1 nm, in which formula 5 showed the smallest globule size (135.0 nm). However, its particle size distribution was still high because it had high polydispersity index value compared others formula. It indicated that nanoemulsion with 5% castor oil (F3) is the best formula compared to the others because it showed the smallest polydispersity index value as well as homogenous in particle distribution. The comparison on the particle size distribution of each formula could be seen in Figure 2.

Table 4. Particle size distribution of diclofenac sodium nanoemulsion

Formula	Z-AV (nm)	Polydispersity index
F1	181.1	0.375
F2	138.0	0.238
F3	136.3	0.204
F4	147.4	0.246
F5	135.0	0.296
F6	144.0	0.266

Stability Test:

The stability test was performed to confirm the stability of the nanoemulsion formula during storage. The stability result can be seen in Figure 1. The emulsions still showed very good stability once keeping in the room temperature for 3 months. The particle sizes slightly increased but were still not too big.

Figure 1. The particle size distribution of diclofenac sodium nanoemulsion in different castor oil concentration after 3 months.

Figure 2. The particle size distribution of diclofenac sodium nanoemulsion in different castor oil concentration.

DISCUSSION:

Recently, nanoemulsion formulation has become an interesting topic due to its advantages and stability. Development of nanoemulsion as drug carrier has been intensively studied in various types of route system such as in parenteral, ocular, oral as well as transdermal drug delivery system.^[20-27]Nanoemulsion was commonly used as a carrier of immiscible drugs, either lipophilic and hydrophilic drug in order to increase the rate of absorption for the poorly water-soluble drug^[28], eliminates the variability in absorption and increase the bioavailability.^[29] Some stability studies of nanoemulsion showed that the drug in nanoemulsion form had very good stability. ^[30-31]

In this study, tween 80 was used as the emulsifier to formulate the nanoemulsion. Based on the physical evaluation, the resulted nanoemulsion showed very good stability. It indicated that in nanoemulsion system, emulsifier not only acts as a mechanical barrier but also through the formation of surface charges zeta potential, which can produce repulsive electrical forces among approaching oil droplets and this hinders coalescence. There was a study that showed the stability of the zeta potential value.^[32] The more negative zeta potential, greater the net charge of droplets, the more stable the emulsion is. Zeta potential value lower than -30 mv generally indicates a high degree of physical stability. It should be noted that a comparison of the zeta potential with the particle size results showed in common, that a decrease in a particle size of the nanoemulsion was accompanied by a decrease in negative surface charge values.^[33] Occasionally, the use of a single surfactant is not able to reduce interfacial tension of the nanoemulsion, therefore, it is needed to add more co-surfactant eg. propylene glycol to enhance the stability of the nanoemulsion.^[34]

Evaluation of the physical parameter of the nanoemulsion is important to determine the stability of the dosage form during the storage period. Particle size is a pivotal factor in nanoemulsion stability. A steady formula will give constant in size and stable for long period. Polydispersity index of particle size is also important to assure the stability of the nanoemulsion. High polydispersity index values of the nanoemulsions indicate non-uniformity in size of those formulations and in this regard the formulation tends to be unstable during storage. From the polydispersity index value, it can be obtained some information about the ratio of standard deviation to the mean droplet size.^[4] The small particle size from nanoemulsion that has the small polydispersity index value also assist to increase the stability against the sedimentation or creaming because the Brownian motion and the diffusion rate are higher than the sedimentation or creaming rate induced by the gravity force. ^[35]

CONCLUSION:

Diclofenac sodium nanoemulsion is successfully prepared using castor oil as the oil phase. It is suggested that castor oil can be used as a good oil phase in nanoemulsion formulation.

CONFLICT OF INTEREST:

Authors declare no conflict of interest.

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Received on 26.03.2018 Modified on 05.04.2018

Research J. Pharm. and Tech 2018; 11(9): 3861-3865.

DOI: 10.5958/0974-360X.2018.00707.2