Impact of Surface Chemistry and Particle Size on Inertial Cavitation Driven Transport of Silica Nanoparticles and Microparticles

Abstract This study investigated the high‐intensity focused ultrasound (HIFU)‐mediated propulsion of mesoporous silica nanoparticles (MSNs) and microspheres (MSMs). Nanoparticles are heavily sought as vehicles for drug delivery, but their transport through tissue is often restricted. Here, MSNs and MSMs are hydrophobically modified and coated with phospholipids to facilitate inertial cavitation to promote propulsion under HIFU. Modified nanoparticles show significantly enhanced cavitation and propulsion, achieving a maximum displacement of 250 µm (≈2500 body length) and speed of ≈1600 µm s −1 (16 000 body length s −1 ), compared to unmodified nanoparticles (2 µm, 20 body length, 60 µm s −1 , 600 body length). In contrast, microparticles demonstrate comparable cavitation responses. Modified microparticles reached a maximum speed of 4000 µm s −1 (800 body length s −1 ) and displacement of 230 µm (46 body length), and unmodified microparticles achieved 2000 µm s −1 (400 body length s −1 ) and 75 µm (15 body length). In all HIFU‐responsive samples, displacement and speed decreased with successive pulses, implying that particles fatigue with continued pulsing. Analyses of particle trajectories and rotational diffusion times suggest that cavitation occurs uniformly on particle surfaces rather than at specific sites. These principles are important for the design of future drug‐delivery vehicles capable of ultrasound‐triggered motion.