Fig. 3.

Ultrasound-triggerable liposomes triggered by sonochemistry. (A) Schematic of ultrasound-sensitive liposomes. The liposomes are composed of lipids susceptible to ROS. Upon insonation, sonosensitizer-mediated ROS generation induces lipid peroxidation, thereby enhancing the permeability of the liposomes and releasing the encapsulated cargo. (B) Quantification of ROS generation using an ROS-specific fluorescent indicator, carboxy-H2DCFDA. A higher fluorescence indicates higher ROS generation. (C) Dye release kinetics, with and without insonation, from sonosensitizer-containing liposomes loaded with the fluorescent dye sulforhodamine B. red: with ultrasound; blue: without ultrasound. Each arrow represents insonation at 3W/cm², 1 MHz, for 10 min. (D) Fluorescent image of a rat with subcutaneous injection of sonosensitizer-containing, dye-loaded, ultrasound-triggerable liposomes. The fluorescence intensity increased by 68.0 ± 17.1% (mean, SD) after insonation. This enhancement demonstrates that cargo release from this system can be triggered by ultrasound in vivo. Left: before ultrasound (US), right: after ultrasound. Figures were adapted from [134], copyrighted by Nature Publishing Group; and [135], copyrighted by National Academy of Sciences, USA.