Dynamics of entrapped microbubbles with multiple openings

TL;DR

This paper presents a new semi-analytical model for the dynamics of microbubbles trapped in arbitrarily shaped cavities with multiple openings, challenging the traditional focus on first resonance frequency for optimal actuation.

Contribution

A novel model for entrapped microbubbles in complex geometries is developed, incorporating realistic cavity shapes and multiple openings, with experimental validation and implications for biomedical applications.

Findings

The model accurately predicts bubble dynamics in complex cavities.

Resonance frequency is not always optimal for bubble actuation.

Experimental results validate the computational predictions.

Abstract

Microbubbles excited by acoustic fields inside water oscillate, and generate acoustic radiation forces and drag-induced acoustic streaming. These forces can be harnessed in various biomedical applications such as targeted drug delivery and on-chip biomanipulation. The conventional approach for using microbubbles as actuators is to trap them inside microfabricated cavities. Anisotropic forces are applied by constraining the interfaces where the air interacts with water. The existing analytical models derived for spherical bubbles are incapable of predicting the dynamics of bubbles in such configurations. Here, a new model for bubbles entrapped inside arbitrarily shaped cavities with multiple circular openings is developed. The semi-analytical model captures a more realistic geometry through a solution to an optimization problem. We challenge the assumption that bubbles should be excited at their first resonance frequency to optimize their performance. The natural frequencies and the correlated normal vibration modes are calculated, which are subsequently used to compute the acoustic streaming patterns and the associated thrust by a finite element simulation. An experimental platform was built to measure the deflection of beams loaded by microfabricated bubble actuators, and visualize the generated streaming patterns. The results highlight the contribution of the computational model as a design tool for engineering applications.