Abstract
Contactless manipulation of microparticles using acoustic waves holds promise for applications ranging from cell sorting to three-dimensional (3D) printing and tissue engineering. However, the unique potential of acoustic trapping to be applied in biomedical settings remains largely untapped. In particular, the main advantage of acoustic trapping over optical trapping, namely the ability of sound to propagate through thick and opaque media, has not yet been exploited in full. Here we demonstrate experimentally the use of the recently developed technique of single-beam acoustical tweezers to trap microbubbles, an important class of biomedically relevant microparticles. We show that the region of vanishing pressure of a propagating vortex beam can confine a microbubble by forcing low-amplitude, nonspherical, shape oscillations, enabling its full 3D positioning. Our interpretation is validated by the absolute calibration of the acoustic trapping force and the direct spatial mapping of isolated bubble echos, for which both find excellent agreement with our theoretical model. Furthermore, we prove the stability of the trap through centimeter-thick layers of bio-mimicking, elastic materials. Finally, we demonstrate the simultaneous trapping of nanoparticle-loaded microbubbles and activation with an independent acoustic field to trigger the release of the nanoparticles. Overall, using exclusively acoustic powering to position and actuate microbubbles paves the way toward controlled delivery of drug payloads in confined, hard-to-reach locations, with potential in vivo applications.
Highlights
Contactless manipulation of microparticles using acoustic waves holds promise for applications ranging from cell sorting to threedimensional (3D) printing and tissue engineering
In this paper we explore the capabilities of a single-beam acoustical trap to manipulate individual microbubbles, which are an important class of biomedically relevant microparticles [19,20,21,22,23], in crowded and complex environments including through biological tissue phantoms
We show that trapped bubbles can be precisely maneuvered through centimeter-thick, tissue-mimicking, opaque-tolight elastic layers immersed in liquids and use this further to assess the influence of the bubble habitat on its dynamics
Summary
Contactless manipulation of microparticles using acoustic waves holds promise for applications ranging from cell sorting to threedimensional (3D) printing and tissue engineering. We demonstrate experimentally the use of the recently developed technique of single-beam acoustical tweezers to trap microbubbles, an important class of biomedically relevant microparticles. The ability to individually manipulate a large range of object materials with the precision and selectivity of single-beam acoustical traps would enable designing complex procedures; each particle used as an elementary building block for localized chemistry, drug delivery, or assembly in tissue or organoid engineering [9, 18] and the large penetration of ultrasound in tissue make these procedures viable perhaps even in vivo. In this paper we explore the capabilities of a single-beam acoustical trap to manipulate individual microbubbles, which are an important class of biomedically relevant microparticles [19,20,21,22,23], in crowded and complex environments including through biological tissue phantoms. Acousticbased techniques have emerged as powerful tools covering several length scales for applications ranging from cell sorting [6] and biomolecular force spectroscopy [7] to cell patterning and tissue engineering [8, 9], with appealing characteristics of ultrasound such as abundant forces at low incident powers and deep penetration into complex and absorbing media like tissue [10, 11]
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