Cross-scale mechanistic insights into ultrasound pulse-length dependent BBB opening

Ultrasound-mediated blood-brain barrier (BBB) opening enables non-invasive and targeted brain drug delivery. However, the underlying mechanisms are poorly understood. We resolve how ultrasound pulse regulates microbubble dynamics, endothelial bioeffects and BBB opening characteristics in real-time and at a cross-scale manner. High speed imaging revealed coalescence and heterogenous bubble distribution at long pulses, where stable cavitation with intriguing cyclic jetting leads to localized endothelial detachment and irreversible sonoporation. In vivo mouse two-photon imaging revealed higher but heterogeneous dextran extravasation, and endothelial cell loss visualized for the first time. In contrast, short pulses induced milder, more uniform bubble dynamics, resulting in reversible sonoporation and calcium signaling, and produced uniform delivery and rapid BBB recovery in vivo. The differential bubble dynamics and cellular bioeffects correlate well with the observations from mice models. The insights gained could guide the future developments of safer and more efficient BBB opening with ultrasound technology.