Ultrasonically Induced Release from Nanosized Polymer Vesicles

Vesicles made from synthetic diblock copolymers, polymersomes, have great potential for targeted imaging and drug delivery. Ultrasound is gaining attention as a therapeutic tool in addition to its use in diagnostics. We report on the response of nanoscale vesicles made from PEO‐b‐PBD copolymers to ultrasound at 20 kHz. Leakage of a fluorescent dye from vesicle core was measured to study the permeation. Ultrasound causes significant leakage from the core above threshold intensity, suggesting that leakage is governed by acoustic cavitation. Size measurements and direct visualization of vesicles show that ultrasound does not completely rupture them into fragments but causes transient poration. The extent of leakage inversely depends on membrane thickness and directly depends on sonication time and intensity. Nanosized polymer vesicles were made from the block co‐polymer OB‐29, polyethylene oxide polybutadiene, and exposed to ultrasound of 5.5 W. A and B are cryo‐TEM images of vesicles before (A) and after (B) sonication, indicating that vesicles remained largely intact and that release resulted from transient poration. Panel C illustrates the percent release as a function of time and sonication field strength for OB‐29 vesicles.