Figure 1.

Schematic diagram of the sildenafil microemulsion-loaded hydrogels for transdermal drug delivery directly to the penis and smooth muscle cell relaxation mechanism (EDHF is endothelium derived hyperpolarizing factor; PGI₂ is prostacyclin; NO is nitric oxide; eNOS is endothelial nitric oxide synthase; VEGF is vascular endothelial growth factor; ATP is adenosine triphosphate; GTP is guanine triphosphate; cAMP is cyclic adenosine monophosphate; cGMP is cyclic guanosine monophosphate; PKA is protein kinase A; PKG is protein kinase G).