Fig. 3.

Diagrams of the process and mechanism for pH gradient active loading of drugs into a binary ethosomes and b traditional liposomes. Empty lipid vesicles were obtained by passive loading method in citrate buffer (pH = 3.0). After adjusting the external pH of lipid vesicles with 0.5 M NaOH solution to form ΔpH (inside acidic) and shift the alkaloids from protonated form to unionized form, the neutral drugs can across the lipid bilayer by incubation and can be trapped into the vesicles and protonated again