Ultrasound-induced nanofragmentation of bubbles

ORAL

Abstract

Micron-sized bubbles are of considerable interest for use in biomedical imaging and drug delivery. Lipid-coated bubbles have been reported to rapidly shrink in the presence of short (3 $\mu$s) ultrasound pulses, purportedly by shedding of the coat during compression. Loss of coat would increase the internal pressure, enhancing diffusive gas loss long after the pulse. Note that during such a short pulse, diffusive gas loss is insignificant. If lipid-shedding is the mechanism for bubble shrinkage, a coated bubble in ultrasound may shrink no faster than a quiescent uncoated bubble; the shrinkage rate is entirely dominated by diffusive loss between pulses. Remarkably, we find that most insonated lipid-coated bubbles do shrink faster than quiescent uncoated bubbles. If bubbles cannot shrink by diffusive gas loss, they must fragment, though no fragmentation was observed. The results are consistent with ``nanofragmentation,'' where sub-micron fragments (which entrap gas) are lost from the bubble. Entrapment of gas in fragments may have important consequences for their efficacy in ultrasound-mediated drug delivery, and could affect their ability to transfer drugs to cells.

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Authors

  • Debra Cox

    University of New Mexico

  • Young-Yeal Song

    Brigham Young University, Colorado School of Mines, Colorado State University, Yale University, Department of Physics and Astronomy, Brigham Young University, Department of Mechanical Engineering, University of Utah, JILA, NIST and University of Colorado, University of Arizona, MIT, National Institute for Materials Science, Japan, Department of Mechanical Engineering, Brigham Young University, University of New Mexico, Iowa State University, Los Alamos National Lab XCP-2, Utah State University, Weber State University, New Mexico State University, College of Optical Science, University of Arizona, University of Nebraska, Lincoln, J.A. Woollam Co., U.S. Naval Research Laboratory, Arizona State University, BYU Nuclear Physics Group, Brigham Young University Physics and Astronomy, Los Alamos National Laboratory, University of Tsukuba, Japan, Colorado State University, NSF ERC for EUV science and technology, Center for Functional Nanomaterials, Brookhaven National Laboratory, University of Wisconsin, Madison, Utah Valley University, Argonne National Lab