In vitro targeted microbubble adhesion exhibits a maximum at intermediate acoustic pressures

Introduction Ultrasound molecular imaging (USMI) relies on the adhesion of targeted microbubbles (MBs) to endothelial biomarkers. Acoustic radiation force ( F rad ) enhances this process by translating circulating MBs toward the vessel wall. Size- isolated MB populations can be designed so that their resonance frequency matches the transmitted ultrasound frequency, thereby increasing F rad -induced displacement under physiological flow. However, increasing peak negative pressure (PNP) may also destabilize MBs and reduce their ability to establish firm adhesion.We therefore investigated how PNP and pulse duration influence the balance among MB oscillation, translation, stability and targeted adhesion. Methods A modified Rayleigh–Plesset equation with the Marmottant shell model was coupled to the Cattaneo–Supponen scaling relationships to predict radial oscillation, displacement and dissolution of monodisperse 5-µm diameter lipid- coated MBs exposed to 4 MHz pulses. Model predictions were evaluated using in vitro flow channel experiments with αvβ3-targeted MBs at PNPs of 10, 50 and 133 kPa and pulse lengths of 27 and 54 cycles. Results The model predicted increasing radial expansion and displacement with increasing PNP, but the sequential model predicted that repeated exposure at 133 kPa could reduce MB size and thereby decrease cumulative transport. Experimentally, PNP significantly affected targeted adhesion, with the highest mean adhesion observed at 50 kPa for both pulse lengths. Discussion These results demonstrate that maximizing F rad -induced displacement does not necessarily maximize targeted adhesion. Instead, USMI protocols should balance MB transport, stability and wall interactions, with an intermediate PNP providing the most favorable F rad -induced targeting conditions.