Kinetics of swelling-breakdown of a W/O/W multiple emulsion: possible mechanisms for the lipophilic surfactant effect.

The properties and behavior of a W/O/W multiple emulsion formulation were analyzed during a swelling-breakdown process. Various experimental analyses, such as granulometry, rheology and conductimetry were performed, as well as a micropipette aspiration method. The predominant role of the lipophilic surfactant during the swelling phase confirmed. Two different mechanism can be proposed. Both imply the migration of the lipophilic surfactant from one interface to another and probably take place successively. The lipophilic surfactant could diffuse from the first to the second interface, thus rigidifying the membrane, or from the oily phase to the first interface, resulting in delayed coalescence of the aqueous droplets during swelling.

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Synopsis Stable multiple emulsions, which contain skin moisturizing factors, including glycolic acid in the internal aqueous phase, have been formulated. Drug incorporation and storage at 4 degrees C and 50 degrees C for 30 days do not modify macroscopic and microscopic aspects. The nature of the release mechanism for the active ingredients has been studied in different dilution conditions. Rheological and conductimetric analyses, successively realized in isoosmotic and hypoosmotic conditions, show that the active release appears after dilution by a swelling-breakdown phenomenon. The release velocity of the water soluble active ingredients can be modulated by a modification of some formulation parameters: it can be decreased by an increase of the lipophilic surfactant concentration, it can also be increased by a hydrophilic surfactant concentration, by osmotic pressure and by a decrease of the internal globule size.