Page 21 - Spring 2019
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Snap, Crackle, and Pop:
Ther-acoustic Cavitation
Michael D. Gray Emerging techmquesfor making. mapping, and using acoustically driven
Addms: bubbles within the body enable a broad range of innovative therapeutic
Biomedical Ultrasonics, “PP1““"""“
Biotheiapy and Biopharmaceuticals
Laboratory (BUBBL) "’“=‘°d|-“=39”
msfimte of momedjcal Enginefling The screams from a football stadium full of people barely produce enough sound
Univamty of oxford energy to boil an egg (Dowling and Ffowcs Williams, 1983). This benign view of
oxford OX3 7DQ acoustics changes dramatically in the realm of focused ultrasound where biological
United Kingdom tissue can be brought to a boil in mere milliseconds (ter l-laar and Coussios, 2007).
_ Although the millimeter-length scales over which these elfects can act may seem
_ Ema“: “surgical,” therapeutic ultrasound (0.5-3.0 MHz) is actually somewhat of a blunt
‘m°hael'gmy@eng'°x'a°'uk instrument compared with drug molecules (<().0O02 mm) and the cells (<0.1 m)
that they are intended to treat.
Eleanor E stride ls therapeutic acoustics necessarily that limiting? Not quite. Another key phenom-
Addmssl enon, acoustic cavitation, has the potential to enable subwavelength therapy. Dj-
Biomedkal Uhrasonics‘ finsd 3tShtl1:fil1neafi’ or nonhne;rIosc1llation of a gas oglvapofr cavitzl (gr bubble )f
Lnsfimte of BiDI;::jr::l°;‘yn;:::Il::é not only by the ultrasound wavelength but also by the typically micron-sized di-
University of oxford ameter of therapeutic bubbles (Coussios and Roy, 2008). Under acoustic excitation,
Oxford OX3 7DQ such bubbles act as “energy transformers,” facilitating conversion of the incident
_ _ field’s longitudinal wave energy into locally enhanced heat and fluid motion. The
United Kingdom broad range of thermal, mechanical, and biochemical eflects (“theracoustics”) re-
Email: sulting from ultrasound-driven bubbles can enable successful drug delivery to the interior of cells, across the skin, or to otherwise inaccessible tumors; noninvasive
surgery to destroy, remove, or debulk tissue without incision; and pharmacological
or biophysical modulation of the brain and nervous system to treat diseases such as
Constantin-C. Coussios Parkinsons or Alzheimer’s.
Address: Where do these bubbles come from in the human body? Given that nucleating
Biomedical Ultrasonics, (forming) a bubble within a pure liquid requires prohibitively high and potentially
Biotherapy and Biopharmaceuticals unsafe acoustic pressures (10-100 atmospheres in the low-megahertz frequency
Laboratory (BUBBL) range), cavitation has traditionally been facilitated by injection of micron-sized
Institute of Biomedical Engineering bubbles into the bloodstream. However, the currently evolving generation of thera-
University of Oxford peutic applications requires the development of biocompatible subrnicron cavita-
Oxford OX3 7DQ tion nucleation agents that are of comparable size to both the biological barriers
United Kingdom they need to cross and the size of the drugs alongside which they frequently travel
Email: Furthermore, the harnessing and safe application of the bioeflects brought about by
mnsmmn_c0ussi°S@eng_0X_ac_uk ultrasonically driven bubbles requires the development of new techniques capable
of localizing and tracking cavitation in real time at depth within the human body.
And thus begins our journey on making, mapping, and using bubbles for “thera-
coustic" cavitation.
©2019 Acoustical Society ufamerim. All rights reserved. volume 15, issue 1 1 SPring 2019 | Acnulclcl Thday | 1 a

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