Development of an original method to study drug release from polymeric nanocapsules in the skin

Objectives This study aimed to investigate the distribution and release profile in the skin of a lipophilic model molecule, octylmethoxycinnamate (OMC), loaded in poly(epsilon-caprolactone) nanocapsules (NC) by the Franz cell method. Methods Nanocapsules were formulated in a hydroxyethylcellulose gel and compared to the same gel containing 5% of free OMC as control. A new extraction method was used to discriminate the OMC still entrapped in the NC from free OMC released in the skin strata. The OMC extraction from the skin was performed using acetonitrile, which broke the NC, or isopropyl myristate, which kept the NC intact. Key findings When isopropylmyristate was used to determine the OMC released from NC, the results showed that more than 80% of the OMC was released from the NC at the skin surface after 6 h, whereas only 30% was released in the stratum corneum and epidermis. Conclusions It is suggested that the mechanism of release is different at the surface and in viable skin, probably due to the different local environments surrounding the NC. The small amount of OMC that reached the dermis was no longer encapsulated, suggesting that the NC did not reach the dermis. The viable epidermis seemed to be the limiting barrier against NC diffusion into the skin.