Study of the breakup under shear of a new thermally reversible water-in-oil-in-water (W/O/W) multiple emulsion.
PURPOSE: Thickening of the external aqueous phase of W/O/W multiple emulsions is essential to increase the release under shear. However, it leads to globules bursting during fabrication. To reduce this problem, we have tested a novel thermally reversible hydrogel, EMP hydrogel. This way, the corresponding multiple emulsion (EMPME) would gel only at skin temperature, which may increase the active ingredient delivery when topically applied. METHODS: Samples were sheared at different shear rates and temperatures (20, 30, and 35 degrees C) with a controlled rheometer. A granulometric analysis was then performed with a laser diffraction granulometer, to assess the break up as a function of the shear rate at the three temperatures. Conductometric measurements (CDM 230 conductometer) provided the corresponding release curves. RESULTS: As we expected, EMPME exhibited a thermally reversible behavior. Compared to a reference emulsion thickened by carbopol, this new thermo-sensitive multiple emulsion displayed higher break up and fraction released at 35 degrees C. CONCLUSION: The first thermally reversible multiple emulsion has been developed in the present work. This one presents interesting advantages: (1) an easy fabrication process with a higher entrapment yield and (2) a higher fraction released at 35 degrees C compared with the reference emulsion.