Ultrasound-Responsive Nanomedicine

This chapter describes the recent developments and breakthroughs in ultrasound-responsive nanomedicine. Clinical therapeutic ultrasound applications primarily utilize high-intensity focused ultrasound to generate large pressure changes locally in tissue. More recently, therapeutic ultrasound has been developed for thermal ablation applications. Recent research efforts have focused on developing a new therapeutic ultrasound approach utilizing low acoustic pressures for targeted drug and gene delivery applications. As the field of nanomedicine has emerged, it has intersected with therapeutic ultrasound in areas. When driven at relatively low-pressure amplitudes, oscillating microbubbles radiate pressure waves, which are used in diagnostic ultrasound to enhance contrast in the images. An application that has garnered considerable attention is the use of focused ultrasound and ultrasound contrast agents to permeabilize the blood-brain barrier. However, clinical ultrasound imaging systems generally operate at frequencies above 1 MHz and the onset of cavitation at these frequencies requires higher ultrasound intensities in the absence of cavitation nuclei.