International Journal of Cosmetic Science, 2015, 37, 76–81
doi: 10.1111/ics.12172
Preliminary 1 month stability screening of cosmetic multiple emulsions (W/O/W) prepared using cetyl dimethicone copolyol and Polysorbate 80 H. Khan*, N. Akhtar*, T. Mahmood†, A. Jameel* and S. Mohsin* *Faculty of Pharmacy & Alternative Medicine, The Islamia University of Bahawalpur, Bahawalpur 63100, and †Faculty of Pharmacy, University of Central Punjab, Lahore 54000, Pakistan
Received 29 August 2014, Accepted 11 October 2014
Keywords: carbomer, cetyl dimethicone copolyol, droplet size, polysorbate 80, rheology, stability, triethanolamine, W/O/W emulsion
Abstract OBJECTIVES: The objective of this work was to develop W/O/W emulsions with different concentration of paraffin oil, lipophilic (cetyl dimethicone copolyol) and hydrophilic emulsifiers (polysorbate 80) and to check their stability at different storage conditions. METHODS: Approximately, 20 formulations (W/O/W) multiple emulsions were prepared, and their stability was checked at different storage conditions for the period of 30 days. Stability of some multiple emulsions ME12, ME13, ME14, ME19 and ME20 was also checked with carbomer as viscosity-enhancing agent. Microscopic analysis for droplet size determination and rheological characterization of most stable multiple emulsions, that is, ME20 were also performed. RESULTS: It was observed that stability of multiple emulsion increases with the addition of gelling agent. Formulation (ME20) with 13.6% paraffin oil, 2.4% cetyl dimethicone copolyol and 0.8% polysorbate 80 was found more stable at 25°C and 40°C for the period of 30 days. Rheological analysis indicated a decrease in viscosity with the passage of time, while droplet size analysis indicated an increase in droplet size with the passage of time. CONCLUSION: As a conclusion of this work, a stable multiple emulsion with 13.6% paraffin oil, 2.4% cetyl dimethicone copolyol and 0.8% polysorbate 80 can be formulated and can be further studied for any active ingredient for cosmetic purposes. sume Re OBJECTIF: L’objectif des travaux en cours est de developper des emulsions W/O/W avec differentes concentrations d’huile de paraffine, d’emulsifiants lipophile (cetyldimethicone copolyol) et hydro differentes phile (polysorbate 80), et de verifier leur stabilite a conditions de stockage. METHODE: Environ 20 formulations (W/O/W) emulsions multi differentes condiples ont ete faites et leur stabilite a ete verifiee a tions de stockage pour la periode de 30 jours. La stabilite de certaines emulsions multiples stables (ME12, ME13, ME14, ME19 et ME20 a egalement ete verifiee par l’addition d’un carbomer et de la triethanolamine comme agents augmentant la viscosite Correspondence: Hira Khan, Faculty of Pharmacy & Alternative Medicine, The Islamia University of Bahawalpur, Bahawalpur 63100, Pakistan. Tel.: (+92)3340613513; e-mail: [email protected]
76
(gelifiants). L’analyse au microscope pour determiner la taille des gouttelettes et de la caracterisation rheologique de l’ emulsion multiple le plus stable (ME20) a egalement ete effectuee. RESULTAT: Il a ete observe que la stabilite des emulsions multiples augmente avec l’addition d’ un agent gelifiant. La formulation Me 20) avec 13.6% d’huile de paraffine, 2.4% de cetyl dimethicone copolyol et 0.8% de polysorbate 80 a ete trouvee ^etre 25°C. a 40°C pendant la periode de 30 jours. L’anaplus stable a lyse rheologique a indique la diminution de la viscosite avec le passage du temps; l’analyse de la taille des gouttelettes a indique une augmentation de la taille des gouttelettes avec le passage du temps. CONCLUSION: En conclusion de ce travail, une emulsion multiple stable avec 13.6% d’huile de paraffine, de 2.4% cetyldimethicone copolyol et 0.8% de polysorbate 80 peut ^etre formulee et peut ^etre etudiee ulterieurement pour un ingredient actif a des fins cosmetiques.
Introduction Multiple emulsions are complex polydispersed systems, termed ‘emulsions of emulsions’ where the droplets of the dispersed phase encloses even smaller dispersed droplets themselves and the system is stabilized by combination of emulsifiers [1]. One emulsifier with high HLB value is used to stabilize the primary emulsion (W/O) and second emulsifier with low HLB value is used to reduce the interfacial tension between primary emulsion and external aqueous phase [2]. Multiple emulsions are potential matrices for the encapsulation of bioactive compounds for their controlled release [3]. In W/O/W system, an oil phase separates internal and external aqueous phase or oil droplets may be surrounded by an aqueous phase, which in turn encloses one or several aqueous (water) droplets [4]. They act as reservoir system for drug delivery that can be used to prolong the release of active ingredient and that is why they are used in pharmaceutical and cosmetic industries [5]. W/O/W multiple emulsion as compared to simple emulsions have one unique property that there is diffusion of water through the oil phase which is due to the unbalanced osmotic pressure between the internal and external aqueous phases. Polar molecules pass between internal and external aqueous phase through the oil layer by the process of simple diffusion. Water is transported from internal to the external aqueous phase by the osmotic pressure.
© 2014 Society of Cosmetic Scientists and the Societe Francßaise de Cosmetologie
H. Khan et al.
Stability screening of cosmetic multiple emulsions
There is swelling, bursting or shrinkage of the internal aqueous droplets because of diffusion of water affecting the stability as well as release profile of active ingredients loaded in inner aqueous phase of W/O/W emulsion [6]. Multiple emulsions are unlikely to be acceptable at commercial level until the problem of their instability is solved [7]. Number of factors affect the W/O/W emulsion stability. The most common one are type and concentration of emulsifier, type of oil, phase volume ratio and nature of electrolyte [8]. In practice, significant problems with multiple emulsions might arise because of their thermodynamic instability and strong tendency for coalescence, flocculation and creaming at accelerated temperature conditions [5]. In last two decades, a number of attempts have been made for improving stability by several methods which include polymerization gelling, additives in different phases, surfactant concentration modulation, interfacial complexation, pro-multiple emulsion approach and steric stabilization [9]. The composition and method of preparation are of significant importance for emulsion stability as by reducing the droplet size of the inner emulsion instability problems can be overcome [10]. Current work designed to develop a stable multiple emulsion by using minimum concentration of paraffin oil, cetyl dimethicone copolyol and polysorbate 80. Different compositions were tested and formula with acceptable stability of multiple emulsion further investigated for the stability studies at varying storage conditions. Furthermore, effect of adding a suitable thickening agent on stability of multiple emulsion was also tested by adding carbomer as thickening agents.
Materials and methods Material Following chemicals were used for developing the multiple emulsions; Abil EM90 (Franken-Chemie GmbH & Co. Wendelstein, Germany), Paraffin oil (Merck, Darmstadt, Germany), polysorbate 80 (Merck, Darmstadt, Germany), MgSO4, Carbomer (BDH Chemicals Ltd, Pool, U.K.), triethanolamine (TEA) and Purified water (Prepared at Department of pharmacy, The Islamia University of Bahawalpur, Pakistan). Procedure Several pre-formulation studies lead us in the development of W/ O/W multiple emulsion [11]. A two-step procedure was adopted for the development of multiple emulsions. The first step consisted of the preparation of the primary emulsion (W/O); the second step required dispersing a given amount of the primary emulsion (W/O) in the external aqueous phase containing the secondary emulsifier. In preparing the primary emulsion, oil phase consisted of cetyl dimethicone copolyol and paraffin oil while aqueous phase contained water with hydrated magnesium sulphate. Both oily and aqueous phases were heated up to 75°C. Aqueous phase was then added drop wise to the oily phase at 2000 rpm for 5 min. Then, mixing was continued at 1000 rpm for 10 min. Further, homogenization was completed at 500 rpm for 5 min until emulsion cooled at room temperature. Primary emulsion was then added to external
Table I The results of stability study of formulations kept at 25°C in incubator for 30 days
Oil phase F
Internal aqueous phase
External aqueous phase
Water
After 30 days
18% 18% 18% 18% 18.5% 18% 19% 18% 18% 19% 19.2% 19.2 19.5 19.2 19.2 19.2 19.2 19.5 19.4 19.2
Phase separation Phase separation Phase separation Phase separation Phase separation Little Phase separation Little Phase separation Little Phase separation Viscosity decrease Viscosity decrease Viscosity decrease Viscosity decrease Viscosity decrease Viscosity decrease Phase separation Phase separation Phase separation Little phase separation Little phase separation Stable
100 g W/O/W emulsion
Effect at 25°C
S/No
F code
Cetyl dimethicone copolyol
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
ME1 ME2 ME3 ME4 ME5 ME6 ME7 ME8 ME9 ME10 ME11 ME12 ME13 ME14 ME15 ME16 ME17 ME18 ME19 ME20
5% 5% 5% 4.5% 4.5% 4.7% 5% 4.5% 4.5% 3.5% 3.5% 3.5% 3.5% 3% 3% 3.6% 3% 3% 3% 2.40
Paraffin oil
MgSO4
Water
Polysorbate 80
30% 26% 25% 23% 23% 22% 22% 21% 21% 19% 19% 18% 18% 18% 17% 17% 14% 14% 14% 13.6%
0.7% 0.7% 0.7% 0.7% 0.7% 0.7% 0.7% 0.7% 0.7% 0.7% 0.7% 0.7% 0.7% 0.7% 0.7% 0.7 0.7% 0.7% 0.7% 0.56%
64.3% 68.3% 69.3% 71.8% 71.8% 72.6% 72.3% 73.8% 73.8% 76.8% 76.8% 77.8% 77.8% 78.3% 79.3% 78.7 82.3% 82.3% 74.5% 63.44%
2% 2% 2% 2% 1.5% 2% 1% 2% 1% 1% 0.8% 0.8% 0.5 0.8 0.8 0.8 0.8 0.5 0.6 0.8
Where, F = Formulation, ME = multiple emulsion.
© 2014 Society of Cosmetic Scientists and the Societe Francßaise de Cosmetologie International Journal of Cosmetic Science, 37, 76–81
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H. Khan et al.
Stability screening of cosmetic multiple emulsions Table II The results of stability study of formulations kept at 40°C in incubator for 30 days
Oil phase F
Internal aqueous phase
External aqueous phase
Water
After 30 days
18% 18% 18% 18% 18.5% 18% 19% 18% 18% 19% 19.2% 19.2 19.5 19.2 19.2 19.2 19.2 19.5 19.4 19.2
Phase separation Phase separation Phase separation Phase separation Phase separation Phase separation Phase separation Phase separation Phase separation Phase separation Phase separation Little decrease in viscosity Phase separation Little decrease in viscosity Phase separation Phase separation Phase separation Phase separation Phase separation Stable
100 g w/o/w emulsion
At 40°C
S/No
F code
Cetyl dimethicone copolyol
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
ME1 ME2 ME3 ME4 ME5 ME6 ME7 ME8 ME9 ME10 ME11 ME12 ME13 ME14 ME15 ME16 ME17 ME18 ME19 ME20
5% 5% 5% 4.5% 4.5% 4.7% 5% 4.5% 4.5% 3.5% 3.5% 3.5% 3.5% 3% 3% 3.6% 3% 3% 3% 2.40
Paraffin oil
MgSO4
Water
Polysorbate 80
30% 26% 25% 23% 23% 22% 22% 21% 21% 19% 19% 18% 18% 18% 17% 17% 14% 14% 14% 13.6%
0.7% 0.7% 0.7% 0.7% 0.7% 0.7% 0.7% 0.7% 0.7% 0.7% 0.7% 0.7% 0.7% 0.7% 0.7% 0.7 0.7% 0.7% 0.7% 0.56%
64.3% 68.3% 69.3% 71.8% 71.8% 72.6% 72.3% 73.8% 73.8% 76.8% 76.8% 77.8% 77.8% 78.3% 79.3% 78.7 82.3% 82.3% 74.5% 63.44%
2% 2% 2% 2% 1.5% 2% 1% 2% 1% 1% 0.8% 0.8% 0.5 0.8 0.8 0.8 0.8 0.5 0.6 0.8
Where, F = Formulation, M = Multiple Emulsion.
aqueous phase containing water plus polysorbate 80 at room temperature and stirring speed was initially 700 rpm for 10 min and further, 500 rpm for 1 h.
Table III Results of stability study of multiple emulsion after the addition of viscosity imparting agent
Formulation code
Viscosity imparting agent
pH adjuster
Effect at 25°C
Effect at 40°C
ME12 ME13 ME14
0.5% Triethanolamine 0.5% Triethanolamine 0.5% Triethanolamine
0.7% TEA 0.7% TEA 0.7% TEA
ME19
0.5% Triethanolamine
0.7% TEA
Stable Stable Slight decrease in viscosity Stable
Results and discussion
ME20
0.5% Triethanolamine
0.7% TEA
Stable
Stable Stable Slight Phase separation Slight Phase separation Stable
Development of multiple emulsions requires no. of variables to be considered which include primary W/O emulsifier, nature of the oil phase, secondary emulsifier, that is, high HLB number polymer or surfactant, secondary volume fraction, nature of electrolyte, thickeners or additives, and processing of primary emulsion at high shear mixing while of secondary emulsion at low shear mixing [12]. In this study, total twenty formulations (W/O/W) were formulated using different formulas and their stability was checked at different storage conditions for the period of 30 days. Chemical composition of multiple emulsions results of stability studies is given in Tables I and II. Compositions in Table I indicate that as concentration of paraffin oil and cetyl dimethicone copolyol decreases in primary W/O emulsion, stability of multiple emulsion improves consistently. By using 18% paraffin oil, 3.5% cetyl dimethicone copolyol, 0.8% polysorbate 80, multiple emulsion (ME12) with acceptable stability
are obtained when studied at 25°C for the period of one month. When same multiple emulsion was observed at 40°C, a slight decrease in viscosity was observed after 30 days (Table II). Multiple emulsion (ME14) with a composition; 18% paraffin oil, 3% cetyl dimethicone copolyol and 0.8% polysorbate 80 also shown acceptable stability at 25°C. ME20 formulation with 13.6% paraffin oil, 2.40% cetyl dimethicone copolyol and 0.8% polysorbate 80 was found most stable at 25°C and 40°C in a 30 days followup period. Carbomer was added to formulations ME12, ME13, ME14, ME19 and ME20 in 0.5% concentration to increase the viscosity of multiple emulsions while 0.7% triethanolamine (TEA) was added to adjust pH of emulsions (Table III). It was observed that by increasing viscosity,
Microscopic analysis Microscopic analysis of fresh samples as well as samples kept at different storage conditions was performed with optical microscope (Nikon E200, Tokyo, Japan) with a camera (DCM-35 USB 2.0 and MINISEE IMAGE software, Scopetek Electric, Hangzhou, China). Samples were observed at 1009 magnification after making very thin smear on glass slide.
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© 2014 Society of Cosmetic Scientists and the Societe Francßaise de Cosmetologie International Journal of Cosmetic Science, 37, 76–81
H. Khan et al.
Stability screening of cosmetic multiple emulsions
stability of multiple emulsion gets improved at 25°C but at 40°C, slight phase separation was observed after 30 days. Microscopic analysis is a useful and direct method to assure formation of multiple emulsions, globule size analysis and to predict stability of multiple globules over time (Fig. 1). When analysing the droplet size, it was found that the droplet size increases when kept at different storage conditions (8°C, 25°C, 40°C and 40°C + 75RH). The reason may be the penetration of water from the outer aqueous phase into the inner aqueous phase due to osmotic pressure differences. The resulting water flow causes an increase in the internal water droplets size. Consequently, the oil globules swell until a critical size is reached. Beyond this critical size, the multiple globules may split by breakdown of the oily membrane. It was assumed that the swelling of the multiple globules may be due to an increase in the system elasticity, owing to the decrease in the volume of the external aqueous phase. A comparison between freshly prepared ME20 and MeE20 kept at different temperatures for 30 days is shown in the Fig. 2.
Figure 2 Comparison between mean droplet size of fresh ME20 and ME20 kept at different temperatures for 30 days (n = 10).
(a)
(b)
(c)
(d)
(e)
Figure 1 Photomicrographs of multiple emulsions (ME20 samples) kept at different storage conditions. a and b = Fresh sample; c and d = 25°C; e = 40°C.
© 2014 Society of Cosmetic Scientists and the Societe Francßaise de Cosmetologie International Journal of Cosmetic Science, 37, 76–81
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H. Khan et al.
Stability screening of cosmetic multiple emulsions
The viscosities of multiple emulsion samples were measured at 100–200 rpm speed (with 50 increments) and spindle (CP41). All the readings were taken at 25°C on rheometer (Brookfield Digital Rheometer, Model DV-III, U.K., Brookfield engenering laboratories, Middleborough, United States). Measurements were taken in triplicate. For evaluation, the results of viscosity measurements were fitted to the Power’s Law, known as: s ¼ kDn Results for the rheology of the fresh sample and for the samples kept at different conditions of storage (followed for 30 days) are shown in (Table IV). As the shear rate and shear stress increased, viscosity decreased. ANOVA one-way test described a significant reduction in the viscosity of emulsion sample kept at 40°C with 75% relative humidity. Multiple emulsions have shown shear thinning pseudo plastic behaviours on varying shear rates. Viscosities of multiple emulsion samples kept at 8°C and 25°C increased whereas viscosity of samples kept at 40°C and 40°C + 75%RH decreased after 30 days. It was observed that with the passage of time, viscosities of multiple emulsions decreased continuously during storage. There may be two reasons behind this phenomenon; (i) diffusion of water molecules from the internal to the external aqueous phase or (ii) bursting of multiple globules due to osmotic pressure [13]. This decrease seems due to the migration of internal water globules through the oil (paraffin oil) layer. Further, accelerated centrifugation tests at different time intervals have not revealed any phase separation in any sample of ME20. However, it was obvious that fresh samples and samples stored at different conditions have shown some unusual non-newtonian ‘dilatant’ behaviour (Fig. 3) which is rarely seen in cosmetic emulsions. Conclusion W/O/W emulsions based on lipophilic polymeric emulsifiers offer potential advantages as a vehicle for dermatological and cosmetic preparations. From pre-formulation studies, it was concluded that ME20 with composition 13.6% paraffin oil, 2.40% cetyl dimethicone copolyol and 0.8% polysorbate 80 was most stable at different storage conditions including accelerated conditions for the period of 30 days. With the addition of viscosity imparting agent, stability of multiple emulsion improved over time. So, it is possible to further
Table IV Results of Rheological analysis of Me fresh sample and samples stored at different conditions for 30 days
After 30 days
Consistency index (cP) Flow index Confidence of fit Apparent viscosity (cP)*
Fresh
8°C
25°C
40°C
40°C + 75RH
309.6 0.63 98.9 59.71
458.5 0.57 99.6 66.71
531.8 0.65 99.8 92.63
599.7 0.60 99.7 83.53
181.9 0.70 99.7 43.53
*Apparent viscosity is the mean of all viscosities.
120 100
Viscosity (cP)
Rheological characterization
80
Fresh 8°C
60
25°C
40
40°C
20 0
45°C+75%RH
60 80 100 120 140 160 180 200 220 240
Shear rate (1/Sec) Figure 3 Viscosities of ME20 samples kept in different conditions.
study the composition ME20 while loading it with active compounds for cosmetic benefits. Acknowledgements Author would like to thank Prof. Dr. Mahmood Ahmad, Dean Faculty of pharmacy and alternative medicine, The Islamia university of Bahawalpur Pakistan for providing cosmetic laboratory services.
References 1. Sahu, D., Sanjay, K. and Piyush, A. Recent advancement, technology & applications of multiple emulsions. Innovare J. Health Sci. 1, 19–23 (2013). 2. Jiao, J. and Burgess, D.J. Rheology and stability of water-in-oil-in-water multiple emulsions containing Span 83 and Polysorbate 80. AAPS Pharmsci. 5, 62–73 (2003). 3. Thau, P. Recent developments related to the formulation of Water-in-Oil-in-Water (W/O/ W) emulsions with improved emulsion stability. Cosmetiscope 20, 1–17 (2014). 4. Khan, A.Y., Talegaonkar, S., Iqbal, Z., Ahmed, F.J. and Khar, R.K. Multiple
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emulsions: an overview. Curr. Drug Deliv. 3, 429–443 (2006). 5. Vasiljevic, D.D., Parojcic, J.V., Primorac, M.M. and Vuleta, G.M. Rheological and droplet size analysis of W/O/W emulsions containing low concentrations of polymeric emulsifiers. J. Serb. Chem. Soc. 74, 801–816 (2009). 6. Akhtar, N., Ahmad, M., Khan, H.M.S., Akram, J., Gulfishan, A., Mahmood, A. and Uzair, M. Formulation and characterization of a multiple emulsion containing 1% Lascorbic acid. Bull. Chem. Soc. Ethiopia 24, 1–10 (2010).
7. Florence, A.T. and Whitehill, D. Stabilization of water/oil/water multiple emulsions by polymerization of the aqueous phases. J. Pharm. Pharmacol. 34, 687–691 (1982). 8. Ozer, O., Muguet, V., Roy, E., Grossiord, J.L. and Seiller, M. Stability study of W/O/W viscosified multiple emulsions. Drug Dev. Ind. Pharm. 26, 1185–1189 (2000). 9. Kumar, R., Kumar, M.S. and Mahadevan, N. Multiple emulsions: a review. Int. J. Recent Adv. Pharm. Res. 2, 9–19 (2012). 10. Erdal, M.S. and Araman, A. Development and evaluation of multiple emulsions systems
© 2014 Society of Cosmetic Scientists and the Societe Francßaise de Cosmetologie International Journal of Cosmetic Science, 37, 76–81
Stability screening of cosmetic multiple emulsions
containing cholesterol and squalene. Turk. J. Pharm. Sci. 3, 105–121 (2006). 11. Mahmood, T., Akhtar, N., Khan, B.A. and Rasul, A. Formulation and characterization of a green tea extract containing emulsion prepared with Cetyl dimethicone copolyol as
a lipophilic surfactant. Afr. J. Pharm. Pharmacol. 6, 1395–1399 (2012). 12. Schmidts, T., Dobler, D., Nissing, C. and Runkel, F. Influence of hydrophilic surfactants on the properties of multiple W/O/W emulsions. J. Colloid Interface Sci. 338, 184–192 (2009).
© 2014 Society of Cosmetic Scientists and the Societe Francßaise de Cosmetologie International Journal of Cosmetic Science, 37, 76–81
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13. Mahmood, T., Akhtar, N., Khan, B.A., Rasul, A. and Khan, H.M.S. Fabrication, physicochemical characterization and preliminary efficacy evaluation of a W/O/W multiple emulsion loaded with 5% green tea extract. Braz. J. Pharm. Sci. 49, 341–349 (2013).
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doi: 10.1111/ics.12172
Preliminary 1 month stability screening of cosmetic multiple emulsions (W/O/W) prepared using cetyl dimethicone copolyol and Polysorbate 80 H. Khan*, N. Akhtar*, T. Mahmood†, A. Jameel* and S. Mohsin* *Faculty of Pharmacy & Alternative Medicine, The Islamia University of Bahawalpur, Bahawalpur 63100, and †Faculty of Pharmacy, University of Central Punjab, Lahore 54000, Pakistan
Received 29 August 2014, Accepted 11 October 2014
Keywords: carbomer, cetyl dimethicone copolyol, droplet size, polysorbate 80, rheology, stability, triethanolamine, W/O/W emulsion
Abstract OBJECTIVES: The objective of this work was to develop W/O/W emulsions with different concentration of paraffin oil, lipophilic (cetyl dimethicone copolyol) and hydrophilic emulsifiers (polysorbate 80) and to check their stability at different storage conditions. METHODS: Approximately, 20 formulations (W/O/W) multiple emulsions were prepared, and their stability was checked at different storage conditions for the period of 30 days. Stability of some multiple emulsions ME12, ME13, ME14, ME19 and ME20 was also checked with carbomer as viscosity-enhancing agent. Microscopic analysis for droplet size determination and rheological characterization of most stable multiple emulsions, that is, ME20 were also performed. RESULTS: It was observed that stability of multiple emulsion increases with the addition of gelling agent. Formulation (ME20) with 13.6% paraffin oil, 2.4% cetyl dimethicone copolyol and 0.8% polysorbate 80 was found more stable at 25°C and 40°C for the period of 30 days. Rheological analysis indicated a decrease in viscosity with the passage of time, while droplet size analysis indicated an increase in droplet size with the passage of time. CONCLUSION: As a conclusion of this work, a stable multiple emulsion with 13.6% paraffin oil, 2.4% cetyl dimethicone copolyol and 0.8% polysorbate 80 can be formulated and can be further studied for any active ingredient for cosmetic purposes. sume Re OBJECTIF: L’objectif des travaux en cours est de developper des emulsions W/O/W avec differentes concentrations d’huile de paraffine, d’emulsifiants lipophile (cetyldimethicone copolyol) et hydro differentes phile (polysorbate 80), et de verifier leur stabilite a conditions de stockage. METHODE: Environ 20 formulations (W/O/W) emulsions multi differentes condiples ont ete faites et leur stabilite a ete verifiee a tions de stockage pour la periode de 30 jours. La stabilite de certaines emulsions multiples stables (ME12, ME13, ME14, ME19 et ME20 a egalement ete verifiee par l’addition d’un carbomer et de la triethanolamine comme agents augmentant la viscosite Correspondence: Hira Khan, Faculty of Pharmacy & Alternative Medicine, The Islamia University of Bahawalpur, Bahawalpur 63100, Pakistan. Tel.: (+92)3340613513; e-mail: [email protected]
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(gelifiants). L’analyse au microscope pour determiner la taille des gouttelettes et de la caracterisation rheologique de l’ emulsion multiple le plus stable (ME20) a egalement ete effectuee. RESULTAT: Il a ete observe que la stabilite des emulsions multiples augmente avec l’addition d’ un agent gelifiant. La formulation Me 20) avec 13.6% d’huile de paraffine, 2.4% de cetyl dimethicone copolyol et 0.8% de polysorbate 80 a ete trouvee ^etre 25°C. a 40°C pendant la periode de 30 jours. L’anaplus stable a lyse rheologique a indique la diminution de la viscosite avec le passage du temps; l’analyse de la taille des gouttelettes a indique une augmentation de la taille des gouttelettes avec le passage du temps. CONCLUSION: En conclusion de ce travail, une emulsion multiple stable avec 13.6% d’huile de paraffine, de 2.4% cetyldimethicone copolyol et 0.8% de polysorbate 80 peut ^etre formulee et peut ^etre etudiee ulterieurement pour un ingredient actif a des fins cosmetiques.
Introduction Multiple emulsions are complex polydispersed systems, termed ‘emulsions of emulsions’ where the droplets of the dispersed phase encloses even smaller dispersed droplets themselves and the system is stabilized by combination of emulsifiers [1]. One emulsifier with high HLB value is used to stabilize the primary emulsion (W/O) and second emulsifier with low HLB value is used to reduce the interfacial tension between primary emulsion and external aqueous phase [2]. Multiple emulsions are potential matrices for the encapsulation of bioactive compounds for their controlled release [3]. In W/O/W system, an oil phase separates internal and external aqueous phase or oil droplets may be surrounded by an aqueous phase, which in turn encloses one or several aqueous (water) droplets [4]. They act as reservoir system for drug delivery that can be used to prolong the release of active ingredient and that is why they are used in pharmaceutical and cosmetic industries [5]. W/O/W multiple emulsion as compared to simple emulsions have one unique property that there is diffusion of water through the oil phase which is due to the unbalanced osmotic pressure between the internal and external aqueous phases. Polar molecules pass between internal and external aqueous phase through the oil layer by the process of simple diffusion. Water is transported from internal to the external aqueous phase by the osmotic pressure.
© 2014 Society of Cosmetic Scientists and the Societe Francßaise de Cosmetologie
H. Khan et al.
Stability screening of cosmetic multiple emulsions
There is swelling, bursting or shrinkage of the internal aqueous droplets because of diffusion of water affecting the stability as well as release profile of active ingredients loaded in inner aqueous phase of W/O/W emulsion [6]. Multiple emulsions are unlikely to be acceptable at commercial level until the problem of their instability is solved [7]. Number of factors affect the W/O/W emulsion stability. The most common one are type and concentration of emulsifier, type of oil, phase volume ratio and nature of electrolyte [8]. In practice, significant problems with multiple emulsions might arise because of their thermodynamic instability and strong tendency for coalescence, flocculation and creaming at accelerated temperature conditions [5]. In last two decades, a number of attempts have been made for improving stability by several methods which include polymerization gelling, additives in different phases, surfactant concentration modulation, interfacial complexation, pro-multiple emulsion approach and steric stabilization [9]. The composition and method of preparation are of significant importance for emulsion stability as by reducing the droplet size of the inner emulsion instability problems can be overcome [10]. Current work designed to develop a stable multiple emulsion by using minimum concentration of paraffin oil, cetyl dimethicone copolyol and polysorbate 80. Different compositions were tested and formula with acceptable stability of multiple emulsion further investigated for the stability studies at varying storage conditions. Furthermore, effect of adding a suitable thickening agent on stability of multiple emulsion was also tested by adding carbomer as thickening agents.
Materials and methods Material Following chemicals were used for developing the multiple emulsions; Abil EM90 (Franken-Chemie GmbH & Co. Wendelstein, Germany), Paraffin oil (Merck, Darmstadt, Germany), polysorbate 80 (Merck, Darmstadt, Germany), MgSO4, Carbomer (BDH Chemicals Ltd, Pool, U.K.), triethanolamine (TEA) and Purified water (Prepared at Department of pharmacy, The Islamia University of Bahawalpur, Pakistan). Procedure Several pre-formulation studies lead us in the development of W/ O/W multiple emulsion [11]. A two-step procedure was adopted for the development of multiple emulsions. The first step consisted of the preparation of the primary emulsion (W/O); the second step required dispersing a given amount of the primary emulsion (W/O) in the external aqueous phase containing the secondary emulsifier. In preparing the primary emulsion, oil phase consisted of cetyl dimethicone copolyol and paraffin oil while aqueous phase contained water with hydrated magnesium sulphate. Both oily and aqueous phases were heated up to 75°C. Aqueous phase was then added drop wise to the oily phase at 2000 rpm for 5 min. Then, mixing was continued at 1000 rpm for 10 min. Further, homogenization was completed at 500 rpm for 5 min until emulsion cooled at room temperature. Primary emulsion was then added to external
Table I The results of stability study of formulations kept at 25°C in incubator for 30 days
Oil phase F
Internal aqueous phase
External aqueous phase
Water
After 30 days
18% 18% 18% 18% 18.5% 18% 19% 18% 18% 19% 19.2% 19.2 19.5 19.2 19.2 19.2 19.2 19.5 19.4 19.2
Phase separation Phase separation Phase separation Phase separation Phase separation Little Phase separation Little Phase separation Little Phase separation Viscosity decrease Viscosity decrease Viscosity decrease Viscosity decrease Viscosity decrease Viscosity decrease Phase separation Phase separation Phase separation Little phase separation Little phase separation Stable
100 g W/O/W emulsion
Effect at 25°C
S/No
F code
Cetyl dimethicone copolyol
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
ME1 ME2 ME3 ME4 ME5 ME6 ME7 ME8 ME9 ME10 ME11 ME12 ME13 ME14 ME15 ME16 ME17 ME18 ME19 ME20
5% 5% 5% 4.5% 4.5% 4.7% 5% 4.5% 4.5% 3.5% 3.5% 3.5% 3.5% 3% 3% 3.6% 3% 3% 3% 2.40
Paraffin oil
MgSO4
Water
Polysorbate 80
30% 26% 25% 23% 23% 22% 22% 21% 21% 19% 19% 18% 18% 18% 17% 17% 14% 14% 14% 13.6%
0.7% 0.7% 0.7% 0.7% 0.7% 0.7% 0.7% 0.7% 0.7% 0.7% 0.7% 0.7% 0.7% 0.7% 0.7% 0.7 0.7% 0.7% 0.7% 0.56%
64.3% 68.3% 69.3% 71.8% 71.8% 72.6% 72.3% 73.8% 73.8% 76.8% 76.8% 77.8% 77.8% 78.3% 79.3% 78.7 82.3% 82.3% 74.5% 63.44%
2% 2% 2% 2% 1.5% 2% 1% 2% 1% 1% 0.8% 0.8% 0.5 0.8 0.8 0.8 0.8 0.5 0.6 0.8
Where, F = Formulation, ME = multiple emulsion.
© 2014 Society of Cosmetic Scientists and the Societe Francßaise de Cosmetologie International Journal of Cosmetic Science, 37, 76–81
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Stability screening of cosmetic multiple emulsions Table II The results of stability study of formulations kept at 40°C in incubator for 30 days
Oil phase F
Internal aqueous phase
External aqueous phase
Water
After 30 days
18% 18% 18% 18% 18.5% 18% 19% 18% 18% 19% 19.2% 19.2 19.5 19.2 19.2 19.2 19.2 19.5 19.4 19.2
Phase separation Phase separation Phase separation Phase separation Phase separation Phase separation Phase separation Phase separation Phase separation Phase separation Phase separation Little decrease in viscosity Phase separation Little decrease in viscosity Phase separation Phase separation Phase separation Phase separation Phase separation Stable
100 g w/o/w emulsion
At 40°C
S/No
F code
Cetyl dimethicone copolyol
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
ME1 ME2 ME3 ME4 ME5 ME6 ME7 ME8 ME9 ME10 ME11 ME12 ME13 ME14 ME15 ME16 ME17 ME18 ME19 ME20
5% 5% 5% 4.5% 4.5% 4.7% 5% 4.5% 4.5% 3.5% 3.5% 3.5% 3.5% 3% 3% 3.6% 3% 3% 3% 2.40
Paraffin oil
MgSO4
Water
Polysorbate 80
30% 26% 25% 23% 23% 22% 22% 21% 21% 19% 19% 18% 18% 18% 17% 17% 14% 14% 14% 13.6%
0.7% 0.7% 0.7% 0.7% 0.7% 0.7% 0.7% 0.7% 0.7% 0.7% 0.7% 0.7% 0.7% 0.7% 0.7% 0.7 0.7% 0.7% 0.7% 0.56%
64.3% 68.3% 69.3% 71.8% 71.8% 72.6% 72.3% 73.8% 73.8% 76.8% 76.8% 77.8% 77.8% 78.3% 79.3% 78.7 82.3% 82.3% 74.5% 63.44%
2% 2% 2% 2% 1.5% 2% 1% 2% 1% 1% 0.8% 0.8% 0.5 0.8 0.8 0.8 0.8 0.5 0.6 0.8
Where, F = Formulation, M = Multiple Emulsion.
aqueous phase containing water plus polysorbate 80 at room temperature and stirring speed was initially 700 rpm for 10 min and further, 500 rpm for 1 h.
Table III Results of stability study of multiple emulsion after the addition of viscosity imparting agent
Formulation code
Viscosity imparting agent
pH adjuster
Effect at 25°C
Effect at 40°C
ME12 ME13 ME14
0.5% Triethanolamine 0.5% Triethanolamine 0.5% Triethanolamine
0.7% TEA 0.7% TEA 0.7% TEA
ME19
0.5% Triethanolamine
0.7% TEA
Stable Stable Slight decrease in viscosity Stable
Results and discussion
ME20
0.5% Triethanolamine
0.7% TEA
Stable
Stable Stable Slight Phase separation Slight Phase separation Stable
Development of multiple emulsions requires no. of variables to be considered which include primary W/O emulsifier, nature of the oil phase, secondary emulsifier, that is, high HLB number polymer or surfactant, secondary volume fraction, nature of electrolyte, thickeners or additives, and processing of primary emulsion at high shear mixing while of secondary emulsion at low shear mixing [12]. In this study, total twenty formulations (W/O/W) were formulated using different formulas and their stability was checked at different storage conditions for the period of 30 days. Chemical composition of multiple emulsions results of stability studies is given in Tables I and II. Compositions in Table I indicate that as concentration of paraffin oil and cetyl dimethicone copolyol decreases in primary W/O emulsion, stability of multiple emulsion improves consistently. By using 18% paraffin oil, 3.5% cetyl dimethicone copolyol, 0.8% polysorbate 80, multiple emulsion (ME12) with acceptable stability
are obtained when studied at 25°C for the period of one month. When same multiple emulsion was observed at 40°C, a slight decrease in viscosity was observed after 30 days (Table II). Multiple emulsion (ME14) with a composition; 18% paraffin oil, 3% cetyl dimethicone copolyol and 0.8% polysorbate 80 also shown acceptable stability at 25°C. ME20 formulation with 13.6% paraffin oil, 2.40% cetyl dimethicone copolyol and 0.8% polysorbate 80 was found most stable at 25°C and 40°C in a 30 days followup period. Carbomer was added to formulations ME12, ME13, ME14, ME19 and ME20 in 0.5% concentration to increase the viscosity of multiple emulsions while 0.7% triethanolamine (TEA) was added to adjust pH of emulsions (Table III). It was observed that by increasing viscosity,
Microscopic analysis Microscopic analysis of fresh samples as well as samples kept at different storage conditions was performed with optical microscope (Nikon E200, Tokyo, Japan) with a camera (DCM-35 USB 2.0 and MINISEE IMAGE software, Scopetek Electric, Hangzhou, China). Samples were observed at 1009 magnification after making very thin smear on glass slide.
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© 2014 Society of Cosmetic Scientists and the Societe Francßaise de Cosmetologie International Journal of Cosmetic Science, 37, 76–81
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Stability screening of cosmetic multiple emulsions
stability of multiple emulsion gets improved at 25°C but at 40°C, slight phase separation was observed after 30 days. Microscopic analysis is a useful and direct method to assure formation of multiple emulsions, globule size analysis and to predict stability of multiple globules over time (Fig. 1). When analysing the droplet size, it was found that the droplet size increases when kept at different storage conditions (8°C, 25°C, 40°C and 40°C + 75RH). The reason may be the penetration of water from the outer aqueous phase into the inner aqueous phase due to osmotic pressure differences. The resulting water flow causes an increase in the internal water droplets size. Consequently, the oil globules swell until a critical size is reached. Beyond this critical size, the multiple globules may split by breakdown of the oily membrane. It was assumed that the swelling of the multiple globules may be due to an increase in the system elasticity, owing to the decrease in the volume of the external aqueous phase. A comparison between freshly prepared ME20 and MeE20 kept at different temperatures for 30 days is shown in the Fig. 2.
Figure 2 Comparison between mean droplet size of fresh ME20 and ME20 kept at different temperatures for 30 days (n = 10).
(a)
(b)
(c)
(d)
(e)
Figure 1 Photomicrographs of multiple emulsions (ME20 samples) kept at different storage conditions. a and b = Fresh sample; c and d = 25°C; e = 40°C.
© 2014 Society of Cosmetic Scientists and the Societe Francßaise de Cosmetologie International Journal of Cosmetic Science, 37, 76–81
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The viscosities of multiple emulsion samples were measured at 100–200 rpm speed (with 50 increments) and spindle (CP41). All the readings were taken at 25°C on rheometer (Brookfield Digital Rheometer, Model DV-III, U.K., Brookfield engenering laboratories, Middleborough, United States). Measurements were taken in triplicate. For evaluation, the results of viscosity measurements were fitted to the Power’s Law, known as: s ¼ kDn Results for the rheology of the fresh sample and for the samples kept at different conditions of storage (followed for 30 days) are shown in (Table IV). As the shear rate and shear stress increased, viscosity decreased. ANOVA one-way test described a significant reduction in the viscosity of emulsion sample kept at 40°C with 75% relative humidity. Multiple emulsions have shown shear thinning pseudo plastic behaviours on varying shear rates. Viscosities of multiple emulsion samples kept at 8°C and 25°C increased whereas viscosity of samples kept at 40°C and 40°C + 75%RH decreased after 30 days. It was observed that with the passage of time, viscosities of multiple emulsions decreased continuously during storage. There may be two reasons behind this phenomenon; (i) diffusion of water molecules from the internal to the external aqueous phase or (ii) bursting of multiple globules due to osmotic pressure [13]. This decrease seems due to the migration of internal water globules through the oil (paraffin oil) layer. Further, accelerated centrifugation tests at different time intervals have not revealed any phase separation in any sample of ME20. However, it was obvious that fresh samples and samples stored at different conditions have shown some unusual non-newtonian ‘dilatant’ behaviour (Fig. 3) which is rarely seen in cosmetic emulsions. Conclusion W/O/W emulsions based on lipophilic polymeric emulsifiers offer potential advantages as a vehicle for dermatological and cosmetic preparations. From pre-formulation studies, it was concluded that ME20 with composition 13.6% paraffin oil, 2.40% cetyl dimethicone copolyol and 0.8% polysorbate 80 was most stable at different storage conditions including accelerated conditions for the period of 30 days. With the addition of viscosity imparting agent, stability of multiple emulsion improved over time. So, it is possible to further
Table IV Results of Rheological analysis of Me fresh sample and samples stored at different conditions for 30 days
After 30 days
Consistency index (cP) Flow index Confidence of fit Apparent viscosity (cP)*
Fresh
8°C
25°C
40°C
40°C + 75RH
309.6 0.63 98.9 59.71
458.5 0.57 99.6 66.71
531.8 0.65 99.8 92.63
599.7 0.60 99.7 83.53
181.9 0.70 99.7 43.53
*Apparent viscosity is the mean of all viscosities.
120 100
Viscosity (cP)
Rheological characterization
80
Fresh 8°C
60
25°C
40
40°C
20 0
45°C+75%RH
60 80 100 120 140 160 180 200 220 240
Shear rate (1/Sec) Figure 3 Viscosities of ME20 samples kept in different conditions.
study the composition ME20 while loading it with active compounds for cosmetic benefits. Acknowledgements Author would like to thank Prof. Dr. Mahmood Ahmad, Dean Faculty of pharmacy and alternative medicine, The Islamia university of Bahawalpur Pakistan for providing cosmetic laboratory services.
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