A feasibility study of in vivo applications of single beam acoustic tweezers

Abstract

Tools that are capable of manipulating micro-sized objects have been widely used in such fields as physics, chemistry, biology, and medicine. Several devices, including optical tweezers, atomic force microscope, micro-pipette aspirator, and standing surface wave type acoustic tweezers have been studied to satisfy this need. However, none of them has been demonstrated to be suitable for in vivo and clinical studies. Single beam acoustic tweezers (SBAT) is a technology that uses highly focused acoustic beam to trap particles toward the beam focus. Its feasibility was first theoretically and experimentally demonstrated by Lee and Shung several years ago. Since then, much effort has been devoted to improving this technology. At present, the tool is capable of trapping a microparticle as small as 1 lm, as well as a single red blood cell. Although in comparing to other microparticles manipulating technologies, SBAT has advantages of providing stronger trapping force and deeper penetration depth in tissues, and producing less tissue damage, its potential for in vivo applications has yet been explored. It is worth noting that ultrasound has been used as a diagnostic tool for over 50 years and no known major adverse effects have been observed at the diagnostic energy level. This paper reports the results of an initial attempt to assess the feasibility of single beam acoustic tweezers to trap microparticles in vivo inside of a blood vessel. The acoustic intensity of SBAT under the trapping conditions that were utilized was measured. The mechanical index and thermal index at the focus of acoustic beam were found to be 0.48 and 0.044, respectively, which meet the standard of commercial diagnostic ultrasound system. V C 2014 AIP Publishing LLC.[http://dx.doi.org/10.1063/1.4900716] Similar to physics involved in optical trapping, 1 a steep intensity gradient of the acoustic microbeam coupled with a minimal difference in acoustic impendence between microparticles and the surrounding medium results in a net acoustic radiation force (gradient force) on the particle in moving it towards the beam axis. It was first theoretically and experimentally demonstrated by Lee and Shung. 2 Several in vitro applications of single beam acoustic tweezers (SBAT) have been explored. It has been demonstrated to be capable of manipulating a single cell and estimating the deformability of red blood cells and assaying the invasion potential of breast cancer cells. 3,4 However, its enormous potentials for in vivo applications have not been explored.Obviously, technologies like micro-pipette aspiration and atomic force microscopy, which have very short working distance or requires direct contact with the objects to be controlled, are not suitable for the in vivo study. Technologies for noncontact manipulation of microparticles also are available, i.e., laser beam 1 and electron beam, 5 but they suffer from poor penetration in skin and other human tissues. Additionally, heat generated by the highly focused laser and electron beams may cause tissue dama...

A One-Sided View of Acoustic Traps

“…Obtaining a three-dimensional restoring force by tightly focusing an acoustic beam has proven to be challenging: Wu reported on a dual beam trap [23], whereas lateral manipulation with an ultrasonic beam was successfully implemented while the axial expelling force was canceled by a membrane [24,25]. Both concepts are similar to those reported in Ashkin's seminal work on particle acceleration [1].…”

Quantification of Inter-Erythrocyte Forces with Ultra-High Frequency (410 MHz) Single Beam Acoustic Tweezer

“…8 Also, the SBAT was shown to be capable of manipulating cell-sized microparticles inside of an excised blood vessel. 21 Although previous versions of SBAT’s capability of measuring cell deformability was previously demonstrated 9 , it was neither possible to obtain absolute values of elastic constants of cells including RBC nor possible to measure the interactive forces between cells due to the frequency of the SBAT. This is because the beam width of an ultrasonic transducer is inversely proportional to the center frequency.…”

Three-dimensional ultrasonic trapping of micro-particles in water with a simple and compact two-element transducer

“…Another approach for 2D trapping suggested by Lee 18,19 and Lam 20 is to operate outside of the Rayleigh regime. A focused beam generated by a single element can trap a particle in 2D in the Mie regime (i.e., particle diameter of the order of wavelength).…”