SILICONE VEHICLES FOR ALOE VERA 261 700 600 500 400 300 200 lOO o 5 lO 15 20 25 30 35 11sec Figure 8. Fluidity curves of the two preparations as a function of temperature: Abil EM 90 at 20øC (•), Abil EM 90 at 30øC ('), Abil EM 90 at 40øC (I), Abil WE 09 at 20øC (¸), Abil WE 09 at 30øC (/•), and Abil WE 09 at 40øC ([•). able is the stirring process to obtain a suitable preparation. We recommend vigorous stirring at least at 2000 rpm (Eurostar Ika Labortechnik). The release study was performed next to observe the influence of the type of surfactant and the preparation technique on the faster or slower release of Aloe vera. The results of the four preparations (Figure 9) show that Abil WE 09 preparations release more Aloe vera. In contrast, Abil EM 90 has a more prolonged release, as is to be expected, since this surfactant is more powerful and therefore retains the Aloe vera longer. The method of incorporating Aloe vera in the preparation has also been observed to influence its subsequent release, which can be explained by the mechanism of action of these silicone surfactants. Due to the flexibility of the siloxane bonds and the size of these molecules, they do not form monomolecular layers on the droplets as occurs with classic surfactants. Instead, they trap the component for which they have the least affinity (the aqueous phase) within a three-dimensional structure (16). For this to take place, the Table III Addition of Aloe vera to the Two Latexes With the Best Properties Formulation 7 Formulation 8 DC 245 23% 23% n-decane 0.3 % 0.3 % Aloe vera 2% 2% H20 69.7% 69.7% Abil EM 90 5% -- Abil WE 09 5%

262 JOURNAL OF COSMETIC SCIENCE 100 90 80 70 6o 50 40 3o 2o 10 0 0 4 8 12 16 20 24 Time (h) Figure 9. Percentage of Aloe vera released as a function of time: Formulation with Abil EM 90 at 5% added at the start (•) and at the end (I). Formulation with Abil WE 09 5% added at the start ('), and at the end (0). aqueous-phase components must be added very slowly at the start of the formation of the latex so that this three-dimensional structure can form. Otherwise, small agglomerates of the surfactant silicones may form, covering the oily components like micelies and hampering the positioning of the rest of the aqueous phase. All of the above control the release of the cosmetic active ingredient, retaining it longer when it is incorporated at the start and releasing it more easily when it is added at the end. CONCLUSION We conclude that the formula that performs the best is as follows: Aloe vera: 2% DC 245: 23% Abil EM 90: 5% n-decane: 0.3% Distilled water: 69.7% ACKNOWLEDGMENTS We thank Christine Marie Laurin for translating the original manuscript into English. REFERENCES (1) J. McGinity, Aqueous Polymeric Coatings for Pharmaceutical Dosage Forma (Marcel Dekker, New York, 1989), p. 63.