A NOVEL IN VITRO METHOD FOR EVALUATING FORMULATION INTERACTIONS WITH THE CUTANEOUS HYDROLIPIDIC FILM

In the development of formulations for cutaneous application, understanding their affinity for the skin is crucial. This affinity is influenced by factors such as the drug partition coefficient, the type of excipients used, and skin composition. The hydrolipidic film, composed of Skin Surface Lipids (SSLs) and sweat, serves as the primary interface between the epidermis and the external environment. SSLs, a mixture of sebaceous and epidermal lipids, are largely determined by sebum composition, which is influenced by oxidative processes induced by microbial activity, UV radiation, and exposure to chemicals and cosmetics. Variations in SSL composition have diagnostic significance in dermatological conditions characterized by altered sebum production, such as pityriasis versicolor, acne, atopic or seborrheic dermatitis, and photoaging. Changes in SSL composition can disrupt the hydrolipidic film, compromising skin barrier integrity. In the formulation development phase, investigating interactions between formulations and the hydrolipidic film is essential to optimize skin contact and enhance drug delivery, particularly for personalized medicine approaches in dermatology. This research aimed to develop an artificial hydrolipidic film replicating human skin conditions to assess the interaction of the formulations with the skin. The first step involved selecting key components for artificial sebum and sweat preparation. The resulting hydrolipidic film was characterized and used as a substrate to evaluate the behavior of commonly used non-ionic surfactants in pharmaceutical formulations. These surfactants were solubilized in aqueous and/or lipophilic solvents at concentrations above their critical micellar concentration. The interaction between formulations and the artificial hydrolipidic film was assessed using contact angle measurements, providing quantitative data on wettability. Results obtained with the artificial model were compared with those from natural skin to validate the method. The ultimate goal of this study was to establish a reproducible and reliable method to reduce experimental testing and predict formulation behavior based on composition, thereby optimizing excipient selection for improved skin compatibility and drug delivery.