Fig. 3

In vitro skin permeation and retention study of free drug, flexible nano-liposomes and liposomal gel: a The permeation profile of TRA in different formulations; b skin retention of TRA at 24 h; c the permeation profile of BT in different formulations; d the skin retention of BT at 24 h. (mean ± SD, n = 3; ^*p < 0.05, ^**p < 0.01, compared with TRA-BT-FNL group)