Logo: University of Southern California

Viterbi Team Creates 'Acoustic Tweezers' for Micromanipulation

The device can hold and move a single cell using a focused sound beam
By: Eric Mankin
February 06, 2013 —

How does a medical researcher manipulate a fragile cell 10 microns (that is four ten-thousandths of an inch) in diameter without injuring it? Researchers at the USC Viterbi School of Engineering have devised a new method: acoustic tweezers.

    Transverse cell trapping
In a paper published in Biotechnology and Bioengineering, an international team led by Professor K. Kirk Shung of Viterbi's Department of Biomedical Engineering demonstrated that their newly built device can hold and move a single human leukemia cell using a focused sound beam.

Holding and moving single leukemia and white blood cells would be a useful research tool in investigating how and with what strength these types of cells adhere to blood vessel cells (vascular endothelial cells), a medically important phenomenon.

In the past, researchers have used other approaches, including light beam tweezer and micropipette aspiration, to measure intercellular forces. But these can be expensive, intrusive and damaging to the experimental material, or both.

A mechanism using sound instead was not realized until recently. Working at the USC Ultrasonic Transducer Resource Center, Viterbi School postdoctoral researcher Jungwoo Lee first used an ultrasonic

Tweezers grab, move and then hold a single leukemis cell.
transducer at a frequency of 34 MHz to trap lipid spheres of 100 micron diameter. He then proceeded to carry out experiments at 200 MHz in which a sound beam was demonstrated to be capable of moving the smaller leukemia cells.

The device is noninvasive, and does not involve high energy consumption. It consists of a thin layer of zinc oxide lodged between two gold electrodes on the back surface of a sapphire buffer rod. Energizing the zinc oxide produced sound that transmitted through the rod and was then focused by a spherical cavity on the tip that served as an acoustic lens.

The research group plans to continue the path and actually make measurements of cell adhesion forces. In addition to Shung and Lee, the scientists include Ph.D. candidate Changyang Lee, and research associates Hyung Ham Kim of USC, Anette Jacob and Robert Lemor of the Fraunhofer IBMT for Biomedical Engineering in St. Ingbert, Germany, and Shia-Yen Teh and Abraham Lee of the University of California, Irvine Department of Biomedical Engineering. The National Institutes of Health funded the research.