A team of engineers from MIT, Penn State University, and Carnegie Mellon University is developing a novel way to isolate cancer cells that circulate in the bloodstream: using sound waves to separate them from blood cells. Cancer cells often break free from their original locations and circulate through the bloodstream, allowing them to form new tumors elsewhere in the body. Detecting these cells could give doctors a new way to predict whether patients’ tumors will metastasize, or monitor how they are responding to treatment, but finding these extremely rare cells has proven challenging because there might be only one to 10 such cells in a 1-milliliter sample of a patient’s blood.
…KurzweilAI has reported on several cancer-cell-sorting techniques. Most existing cell-sorting technologies require tagging cells with chemicals or exposing them to strong mechanical forces that may damage them, according to the MIT/Penn State/Carnegie team. To sort cells using sound waves, which offer a gentler alternative, the researchers built microfluidic devices with two acoustic transducers, which produce sound waves, on either side of a microchannel. When the two waves meet, they combine to form a standing wave (a wave that remains in constant position). This wave produces pressure nodes, or lines of low pressure. 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. 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. In the previous study, the researchers were able to separate cancer cells from red and white blood cells, but the sample flow rate through the device was only 1 to 2 microliters per minute. At that rate, it would take more than 50 hours to process a typical patient sample of about 6 milliliters. The new version of the device has a working flow rate about 20 times faster, allowing it to process a patient sample in about five hours.