Ultrasound-mediated drug delivery using liposomes modified with a thermosensitive polymer

•Liposomes were modified with thermosensitive polymer poly(NIPMAM-co-NIPAM).•Thermosensitive polymer (TSP)-modified liposomes became sensitive to ultrasound.•Drug released from TSP-modified liposomes could be internalized into cells by ultrasound.•The cancer cell viability was 60% by using ultrasound and TSP-modified liposomes. Ultrasound-mediated drug delivery was established using liposomes that were modified with the thermosensitive polymer (TSP) poly(NIPMAM-co-NIPAM), which sensitized the liposomes to high temperatures. TSP-modified liposomes (TSP liposomes) released encapsulated calcein under 1MHz ultrasound irradiation at 0.5W/cm2 for 120s as well as the case under incubation at 42°C for 15min. In addition, uptake of the drug released from TSP liposomes by cancer cells was enhanced by ultrasound irradiation. In a cell injury assay using doxorubicin (DOX)-loaded TSP liposomes and ultrasound irradiation, cell viability of HepG2 cells at 6h after ultrasound irradiation (1MHz, 0.5W/cm2 for 30s) with DOX-loaded TSP liposomes (TSP/lipid ratio=1) was 60%, which was significantly lower than that of the control conditions such as DOX-loaded TSP liposomes alone and DOX-loaded intact liposomes under ultrasound irradiation.