Bioeffects elicited by acoustic cavitation

Abstract

Ultrasound has been developed as both a diagnostic tool and a potent promoter of beneficial bioeffects for the treatment of cardiovascular disease and cancer. Ultrasound exposure can induce the release, delivery and enhanced efficacy of lytics, antibiotics, anti-inflammatory drugs or bioactive gases from echogenic liposomes. Other carriers for cancer therapeutics and small interfering ribonucleic acid (siRNA) and genes have also been developed. By encapsulating drugs and bubbles into micron-sized and nano-sized lipid-shelled particles, the therapeutic can be shielded from degradation within the vasculature until delivery is triggered by ultrasound exposure. The endothelial barrier between the bloodstream and vascular tissue presents a significant challenge to drug delivery. Most research on drug delivery from the blood vessel lumen into the tissue bed has been focused on blood-brain barrier disruption. Microbubbles oscillate when exposed to ultrasound and create stresses directly on nearby tissue or induce fluid effects that effect drug penetration into vascular tissue, lyse thrombi or direct drugs to optimal locations for delivery. Insonification accelerates clot breakdown in combination with a lytic and an ultrasound contrast agent, which nucleates sustained bubble activity. Mechanisms for ultrasound enhancement of clot dissolution, bactericide, and drug delivery, with a special emphasis on acoustic cavitation, radiation force and biological responses, will be reviewed.