Strategies for increasing acoustic susceptibility of liposomes for controlled drug delivery

Polyethylene glycol (PEG) grafted and echogenic liposomes have been investigated to achieve controlled drug delivery with ultrasound as an external trigger. This study was devised to systematically explore the individual and combined effects of PEG grafting, echogenicity, and lipid phase on acoustic susceptibility. Liposome formulations were exposed to 20 kHz ultrasound and the release of calcein was monitored to quantify acoustic susceptibility. Consistent with previous results, PEG grafting and echogenicity were observed to increase acoustic susceptibility; additionally, the enhancement from echogenicity was greater than PEG grafting for both liposome phases. The release profile of calcein from non-echogenic liposomes appeared to be described by a model with two superimposed first order processes whereas that of the echogenic liposomes was better described with a single first order process. These results indicate that acoustic susceptibility is strongly dependent on liposome chemistry and better underst...