Poly(D,L-lactide) nanoencapsulation to reduce photoinactivation of a sunscreen agent

Synopsis The use of sunscreens is the ‘gold standard’ for protecting the skin from ultraviolet light. Octyl methoxycinnamate (OMC) is one of the most widely used UVB filter but it can act as a sensitizer or photoallergen. When exposed to sunlight, OMC can change from the primary trans‐form to cis‐form and the isomerization, not reversible, conducts to a reduction of the UVB filtering efficiency because the trans‐form has a higher extinction coefficient. Photostability is the most important characteristic of effective sunscreens and it can be influenced by formulation ingredients and by applying technological strategies. In this work, photostability experiments, performed on emulsion–gels containing different percentages of OMC free or loaded in poly(d,l‐lactide) nanoparticles, were carried out. The presence of a polymeric envelop may act to protect the active ingredient. In this study, the influence of poly(d,l‐lactide) matrices on the photochemical stability of the sunscreen agent was investigated. As highlighted in this study, free OMC in different formulations has different photoisomerization degree. Moreover, a dissimilar behaviour was observed by studying different sunscreen concentrations in the same cosmetic formulation. Photostability results show a significant reduction in photoisomerization degree for formulations containing sunscreen loaded in nanoparticles, highlighting that the encapsulation is a suitable strategy to improve OMC photostability. Moreover, sun protection factor (SPF) results show that the UVB filter protective power is also maintained after encapsulation. Résumé L’emploie de filtres solaires est le ‘gold standard’ pour la protection solaire. L’Octyl methoxycinnamate (OMC) est un filtre UVB très utilisé mais il peut agir comme sensibilisant ou fotoallergène. Quand il est exposéà la lumière du soleil il peut changer de la forme primaire transà la forme cis et l’isomerization, pas reversible, mène à la reduction de la capacité filtrant UVB parce que la forme trans a un coefficient d’extinction molaire plus haut. La fotostabilité est une des caractéristiques plus importantes d’un produit solaire et elle peut être influencée des ingrédients des formulations ou bien en appliquant des stratégies technologiques. Dans ce travail les experiences de fotostabilité ont été menées sur des emulsion–gels contenants différents pourcentages d’OMC libre ou encapsulé dans nanoparticules de poly(d,l‐lactide). Les nanoparticules polimeriques ils peuv