Gene and oligonucleotide delivery via micro- and nanobubbles by ultrasound exposure

In recent years, the use of stimuli-responsive carriers and physical energies, such as ultrasound, magnetic force, electric force, and light, in combination therapy has attracted attention as useful gene and oligonucleotide delivery systems. These systems allow target-specific delivery to be achieved relatively easily at the application site of physical energy. Ultrasound-mediated delivery has attracted particular interest because of its noninvasive nature. Microbubbles are ultrasound contrast agents that can act as echo enhancers. Under appropriate conditions, microbubbles or nanosized bubbles can also enhance the efficiency of drug, gene, and oligonucleotide delivery by ultrasound exposure. Therefore, the combination of ultrasound technology and bubbles is expected to be a fusion diagnostic and therapeutic system known as the theranostic system. In this review, we summarize the use of micro- and nanobubbles in ultrasound-mediated gene and oligonucleotide delivery systems, and discuss their potential as therapeutic tools.