Acoustic cavitation is the process of producing, oscillating and breaking down bubbles in a liquid to generate shear forces that affect surrounding objects. A versatile tool in biomedicine, acoustic cavitation can help mediate therapies for blood clots and tumors, and aid in the processing of biological samples. However, cavitation directed off target can cause unwanted biological effects, making controlled ultrasound delivery difficult or impossible if the target geometry is complex.

Using a carefully designed, 3D-printed hologram lens, Kim et al. demonstrated a technique for tailoring the acoustic excitation field generated from a standard ultrasound transducer, which otherwise would have been limited in its focal area.

“There are many applications in biomedicine where it would be beneficial to expose the sample to acoustic cavitation in a custom pattern, and previously, this was not possible without a mechanically translatable transducer and complex positioning system,” said author Jinwook Kim.

Their method helps achieve the desired customization, allowing for site-specific patterns of cavitation. Testing on an artificial tissue-like material, the group was able to create a noticeable, selective cavitation pattern in the shape of a seven.

To achieve this, the researchers designed an acoustic hologram for their targeted 2D geometry. They simulated the phase profile of the acoustic hologram, which they encoded as a thickness map in a 3D-printed lens. When excited, the pressure field transmitted from the lens is in the shape desired for cavitation – in this case, the shape of a seven.

In its current setup, the technique is useful for studies aimed at understanding the effects of ultrasound on cells or tissues in laboratory environments. Eventually, extending this into 3D could be a major innovation for cavitation therapies.

Source: “Acoustic holograms for directing arbitrary cavitation patterns,” by Jinwook Kim, Sandeep Kasoji, Phillip G. Durham, and Paul A. Dayton, Applied Physics Letters (2021). The article can be accessed at https://doi.org/10.1063/5.0035298.