Monoolein-based nanodispersions for cutaneous co-delivery of methylene blue and metformin: Thermal and structural characterization and effects on the cutaneous barrier, skin penetration and cytotoxicity

•Monoolein (MO)-based nanodispersions exhibited nanometric size (<200 nm) and thermal and physical stability.•The effect of MO-based nanodipersions on topical/transdermal delivery of methylene blue (MB) and metformin (MET) was composition-dependent.•The most promising MO nanodispersion-mediated combination therapy using MET and MB presented high cytotoxicity potential to tumor cells, which can be further enhanced by MB photoactivation.