Skin penetration enhancing properties of the plant N-alkylamide spilanthol - De Spiegeleer, B; Boonen, J; Malysheva, S V; Mavungu, J DD; De Saeger, S; Roche, N; Blondeel, P; Taevernier, L; Veryser, L (J Ethnopharmacol, 2013)