U.S. researchers separate cancer cells from blood using sound waves

A simple blood test may one day replace invasive biopsies thanks to a new device that uses sound waves to locate and separate cancer cells circulating in patients' blood, U.S. researchers said Monday.

Cancer cells often break free from their original locations and circulate through the bloodstream, but finding them has proven challenging because there might be only one such cell in every one billion blood cells in the sample, the researchers reported in the U.S. journal Proceedings of the National Academy of Sciences.

Most existing cell-sorting technologies require tagging cells with chemicals or exposing them to strong mechanical forces that may damage them, but sound waves offer a gentler alternative, allowing scientists to recover intact cancer cells that are ready for further testing, they said.

The concept behind the new method involves placing two acoustic transducers, which produce sound waves, on either side of a microchannel on a microfluidic chip. When the two waves meet, they combine to form a standing wave, which thus produces pressure nodes, or lines of low pressure, across the channel.

"Because the sound waves are tilted so they run across the microchannel at an angle, each cell encounters several pressure nodes as it flows through the channel," according to a statement released by the researchers from the Massachusetts Institute of Technology, Pennsylvania State University and Carnegie Mellon University. "As cells encounter each node, they are pushed further to the side of the channel; the distance of cell movement depends on their size and other properties, such as compressibility."

According to the researchers, it takes about five hours for the dime-sized device to separate cancer cells from a typical patient sample of about 6 milliliters.

The researchers tested the device with blood samples from three breast cancer patients and found the method is as effective as a commercially available device.

"With further improvements in cell throughput, this work could offer a useful new tool, for both basic research into the complex topic of circulating tumor cells and for clinical assessment of different types of cancer," coauthor Carnegie Mellon University President Subra Suresh said.

The researchers are now working on further improving the device 's flow rate, as well as making it more robust and cost-effective. Endite