Engineering novel topical foams using hydrofluroalkane emulsions stabilised with pluronic surfactants

Aesthetics are very important for topical products and as a consequence elegant vehicles such as sprays and foams are often preferred by patients. Pressurised systems are ideal to dose foams, however, as so little is known about the influence of formulation characteristics on foam properties, the rational design of these systems difficult. This study aimed to assess the capability of pluronic surfactants to stabilise topical pressurised hydrofluoroalkane (HFA) emulsions and attempted to define the formulation characteristics that had an impact upon foam properties. In situ phase diagrams and conductivity measurements were used to characterise the HFA emulsions. Cryo-scanning electron microscopy images, collapse time (Ct) and wetting time (Wt) were used to assess the foams post dosing, i.e. after removal of the HFA. The results indicated that foam stability was a direct function of HFA emulsion type; HFA-in-water (HIW) emulsions generated stable foams, they had 30–100 μm bubble diameter with c.a. 40 bubbles in a 0.45 mm × 0.40 mm area; water-in-HFA (WIH) emulsions created quick-breaking foams they contained 20–200 μm sized bubbles and had 20 bubbles in an area of 0.45 mm × 0.40 mm. Therefore, the rational design of pressurised topical foams can be achieved if the formulation is analysed in situ.