Paul Graham Wildgust

The development of colour-encapsulated microspheres for novel colour cosmetics

In the present study, the preparation, characterization and colour retention properties of organic colour-loaded microspheres are described. The study aimed to produce shatter-resistant, low-bleeding polymeric microspheres with particle diameters of 20 µm containing 10–20% (w/w) of the Food, Drug, and Cosmetic grade colourants FD&C Blue No. 1 Al Lake, FD&C Yellow No. 5 Al Lake and D&C Red No. 36 by utilizing an aqueous-dispersed polymer water-in-oil (W/O) solvent evaporation process featuring styrene/acrylates-based copolymers. The influences of matrix polymeric components on the shape, integrity and dye retention of the microspheres were studied. Encapsulation matrices based on alkali soluble polymers yielded misshapen spheroids that were prone both to swelling and decreased dye retention in aqueous environments, as well as loss of shape at 70°C in cosmetic oils under shear. A resin supported emulsion (RSE)-based matrix, in comparison, yielded highly spherical microspheres resistant to shape deformation and swelling. Additions of up to 15% (w/w) of an alkali soluble polymer to the RSE system improved colour dispersion without detrimentally affecting the structural integrity of the microspheres while also slightly decreasing dye concentrations released into aqueous solutions. The in vitro dye release of the colour-loaded microspheres in a cosmetic-type water-in-silicone (W/Si) emulsion was evaluated and compared to the in vitro dye release studies in aqueous solutions. No direct correlations between the emulsion system and single-component aqueous solutions could be made. Dye-release levels evaluated from contacting the microspheres with a complex aqueous medium (CAM5), which incorporated ingredient classes typically encountered in the aqueous phase of an emulsion, were found to correlate to levels determined in the generic W/Si emulsion with a 93% linear regression between the data sets. This study demonstrates that the CAM5 protocol (or, alternatively, a CAM2.5 protocol) satisfactorily predicted that the commercial materials derived, in part, from this study (Ciba: ENCAPSULENCE™ Blue 1, ENCAPSULENCE™ Yellow 5 and ENCAPSULENCE™ Red 36) are well suited to retain their colour and shape in liquid cosmetic foundations.