Sound waves pick tumor cells out of blood sample

The new device uses only a gentle mechanical force created by sound waves, allowing scientists to recover whole, unaltered CTCs (circulating tumor cells) that are ready for further testing. (Credit: Tess Watson/Flickr)

A new microfluidic chip uses sound waves to separate blood-borne circulating tumor cells (CTCs) from white blood cells. The device is up to 20 times faster than prior attempts, say researchers.

The findings enable the use of the device for basic research and suggest that clinicians could one day use remove intact CTCs from a standard blood sample.

Additionally, the researchers tested their device, for which a patent application has been filed, using patient samples for the first time. These tests show that their method for separating CTCs from cancer cells is as effective as the current FDA-approved technique.

“Using computer modeling, we were able to significantly improve the chip’s throughput. With further refinements, this device could enhance our ability to diagnose and treat cancer,” says coauthor Subra Suresh, president of Carnegie Mellon University with faculty appointments in the College of Engineering, School of Computer Science, and Heinz College.

“The current gold-standard for finding CTCs requires scientists to tag the cells using antibodies. Our technique has the added advantage of being label-free, without the need for any tagging that could chemically alter the cells. Our new approach would allow scientists and clinicians to gain more information on cell pathology and cancer metastasis than is currently possible.”

tumor cell device
This schematic illustration shows the high-throughput device that separates cancer cells from white blood cells. (Credit: Carnegie Mellon)

‘Liquid biopsy’

When a physician wants to determine whether or not a tumor is cancerous, or learn more about a patient’s cancer—for instance, whether or not a tumor has metastasized, or if a tumor is genetically predisposed to respond to a certain therapy—a sampling of cells is removed from the tumor through a biopsy. Depending on the location of the tumor, a biopsy can be painful and invasive.

CTCs offer the promise of a much less invasive option, often referred to as a “liquid biopsy.” CTCs are cells that have been shed from a primary tumor and circulate through the body via the blood stream. They are of great interest to cancer researchers and clinicians because they offer a way to gather cancer cells through a routine blood draw rather than a biopsy. CTCs can provide more information about metastasis, response to treatment and the genetic nature of a patient’s cancer than cells taken directly from a tumor.

In many cases, CTCs are too rare to be detectable because there might be only one CTC among hundreds of thousands of white blood cells. Currently, most researchers find and isolate the traveling tumor cells either by using fluorescence and magnetic techniques or by mechanical means.

Gentler on cells

Some of these methods require the cancer cells to be tagged using antibodies, which can alter the cell’s genetic and physical make-up. Other research groups have developed ways to remove CTCs using strong mechanical forces, which also can damage the cells.

While all of these techniques allow researchers to count the number of CTCs in a blood sample for possible cancer diagnosis, researchers often can’t use the altered cells to reliably perform any additional functional tests.

The new device could help to solve this problem. It doesn’t require the use of any damaging tags. It uses only a gentle mechanical force created by sound waves, allowing scientists to recover whole, unaltered CTCs that are ready for further testing. The authors also have demonstrated that, at the cell level, the device preserves the integrity of the separated CTCs, somewhat similar to the gentle way in which ultrasound has long been used in medical imaging and diagnostics.

5 hours for 5 milliliters

To test a blood sample using the device, the researchers remove the red blood cells from the sample, and introduce the remaining blood product into a channel in the dime-sized chip. As the sample travels along the channel, it passes through sound waves that have been angled across the channel. By angling the sound waves, the researchers have created a gauntlet of pressure nodes that push the cells away from the center of the channel.

Since cancer cells have different size and compressibility than normal white blood cells, they are propelled at different trajectories by the sound waves. The researchers were able to establish what path each cell type would take, and created two channels along those paths to collect the separated cells.

In previous versions of the device, the throughput rate was too slow for clinical use—it would have taken between 30 and 60 hours to separate the cells in one vial of blood (approximately 5 milliliters). The researchers used computer modeling and parametric numerical simulations to find ways to alter the device to make it more efficient. From models, they were able to come up with an optimized design for the geometry of the channels on the chip, and tilt angles of and width of the acoustic transducers.

They took the information generated by the simulations and created new sample prototypes. The most efficient prototype processed a sample 20 times faster than their original prototype, taking only approximately five hours to process a 5-milliliter sample.


The researchers used this faster version of the chip to test blood samples from three women with diagnosed breast cancer. In terms of counting CTCs, their results were found to be consistent with previous tests performed using the traditional FDA-approved CellSearch cell-tagging method.

Furthermore, in one of the samples, they found only one CTC. On further consultation with that patient’s doctor, they found that the patient was responding well to treatment, further demonstrating the device’s promise for detecting cancer and metastasis, and monitoring the effectiveness of treatment.

The increased speed of the device makes it ready to use for laboratory research, but researchers warn that it’s still too slow for broad clinical use. They plan to continue to refine the device to make it more suitable for separating CTCs from a vial of blood in less than 30 minutes, which will make it more amenable to commercialization. They also hope to develop a version of the device that can be used with whole blood samples, eliminating the need to remove the red blood cells.

Coauthors, whose research was supported by the National Institutes of Health, the Penn State Center for Nano Scale Science, and the National Science Foundation, are from Penn State and MIT. The findings appear in the Proceedings of the National Academy of Sciences.

Source: Carnegie Mellon University