Alginate microparticles as carriers for the UV filter 2-ethylhexyl 4-methoxycinnamate: Influence on photostability

The organic ultraviolet UVB filter 2-ethylhexyl 4-methoxycinnamate (EHMC) was encapsulated in microparticles (MPs) of sodium alginate and co-loaded with vitamin E (Vit.E) by an extrusion process using an aerodynamically assisted jetting (AAJ) methodology. The aim was to assess the effect of encapsulation concerning UVB filter release from the MPs and its photochemical stability.

The EHMC photostability was analysed by exposing the samples (both MPs in aqueous dispersion and incorporated in a cream preparation) during 1 h to simulated solar light. For the MPs (empty-MP, EHMC-MP and EHMC + Vit.E-MP), the morphology and size were characterized; while in the case of the encapsulated samples, the amount of EHMC-loading was determined. The release of EHMC was evaluated by adding EHMC-MP or EHMC + Vit.E-MP to 65% ethanol in water under mechanical stirring at 32°C.

All MPs showed a homogeneous size distribution with a median of 90.5 ± 2.5 μm for EHMC-MP and 70.4 ± 1.14 μm for EHMC + Vit.E-MP. The encapsulation efficiency was 92.9% and 99.4% for EHMC-MP and EHMC + Vit.E-MP, respectively. The observed release from the MPs was lower than the dissolution of the pure UV filter. EHMC-MP and EHMC + Vit.E-MP were successfully incorporated into a cream formulation, with no evidence of phase separation or colour modification. Upon simulated light exposure, the photoisomerization/phototransformation of EHMC encapsulated in MPs and Vit.E-MP decreased as compared to free EHMC, both in aqueous dispersion and as a cream. The conformational ratio of the isomers (Z-/E-EHMC) was found to be the lowest in the presence of Vit.E.

This work demonstrates that use of these alginate microparticulate carriers could enhance the effectiveness of sunscreen preparations containing this UVB filter.