Control of Drug Release in Ultrasound-Responsive Liposome-Encapsulated Gel Patches

Transdermal drug delivery systems deliver drugs via transdermal absorption, and microcapsule-embedded gel patches for these systems have been studied previously. The microcapsules contained the drug to prevent leakage through the gel pores and to provide sustained release. The drug could also be released by breaking the microcapsules with ultrasound irradiation. However, the amount of drug released without irradiation was large, and the release was difficult to control. In this study, we prepare an ultrasound-responsive liposome-encapsulated gel patch. In comparison, microcapsules have a monolayer structure and liposomes have a lipid bilayer structure which has been seen to be more robust. Also, microcapsules in the previous study were micro-sized, whereas liposomes in the present study are nano-sized which are more stable and able to provide sustained release. To observe the effectiveness of sustained drug release and the on-off control of drug release by ultrasound irradiation, liposomes containing a fluorescent compound as a drug model are embedded in agarose gel. The fluorescent intensity of the buffer solution outside the liposome-encapsulated gel patch after 24 h are observed with a spectrophotometer. The amount of drug leakage is lower than that of the microcapsule-embedded gel patch. Furthermore, the amount of drug released without irradiation is smaller than in the previous study. The fluorescent intensity after ultrasound irradiation is higher than that before irradiation indicating that the drug release is accelerated by ultrasound and that the amount of drug released can be controlled.