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.