Dynamics of Vortex Ultrasound Enhanced Acoustic Cavitation

Regents Of The University Of Michigan - Ann Arbor, Ann Arbor MI

Investigators

Abstract

This grant will support research that looks to contribute to new knowledge related to the nonlinear dynamics of acoustic cavitation enhanced by vortex ultrasound. Acoustic cavitation is the process of bubble formation, oscillation, and collapse in a liquid exposed to intense ultrasound. Acoustic cavitation has been widely used in the biomedical field for tissue ablation, thrombolysis, drug delivery, etc., and in industry for metal cleaning in manufacturing processes. Vortex ultrasound is a type of acoustic wave with a helical wavefront rotating as the wave propagates. Previous studies of vortex ultrasound-induced acoustic cavitation in deionized water show that vortex ultrasound can induce acoustic cavitation at a much lower intensity threshold and with stronger cavitation activity than focused ultrasound. However, the fundamental mechanism(s) behind the lower intensity threshold and stronger cavitation activity driven by vortex ultrasound are still unknown. Without this important knowledge, it is challenging to use vortex ultrasound reliably and safely in the suggested biomedical and industrial applications. This research project seeks to understand the fundamental bubble dynamics driven by acoustic cavitation induced by vortex ultrasound and the mechanism behind the reduced cavitation threshold, as well as enhanced cavitation activities. A novel theoretical model of bubble dynamics driven by vortex ultrasound looks to be developed and verified by experimental measurements underwater with and without microbubbles or nanodroplets as ultrasound contrast agents. The results from this research seek to advance knowledge in acoustics, dynamics, fluid mechanics, as well as biomedical engineering, and can potentially lead to novel medical therapy with better efficacy and safety and industrial cleaning with less power consumption. Students at all levels, including graduate and undergraduate students as well as K-12 students, will participate in the interdisciplinary research, which will help train the next generation of leaders in science and engineering. The objective of this research is to create a new theoretical model that will provide a precise characterization of acoustic cavitation dynamics driven by vortex ultrasound and validate the model through experimental studies via high-speed camera tracking, infrared temperature mapping, and underwater acoustic measurements. This research project looks to understand the fundamental mechanism(s) that lead to the reduced cavitation threshold and enhanced cavitation activities driven by vortex ultrasound compared with conventional focused ultrasound. The central hypothesis of this research is that the strong shear effect induced by the large in-plane pressure gradient perpendicular to the propagation direction of vortex ultrasound enhances bubble formation and collapse in acoustic cavitation. This hypothesis will be tested by a newly developed theoretical model as well as experimental characterization in degassed, deionized water. The cavitation bubble dynamics driven by vortex ultrasound will be investigated using lipid-encapsulated microbubbles. The bubble formation and phase transition driven by vortex ultrasound will be studied using phase-transitioning nanodroplets. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.