New device separates cancer cells from blood

Scientists, including one of Indian-origin, have developed a low-cost device that uses sound to separate circulating cancer cells from blood samples for diagnostic, prognostic and treatment purposes.
"Typically, the circulating tumour cells (CTCs) are about one in every one billion blood cells in the sample," said Tony Jun Huang, professor of engineering science and mechanics at Penn State University.
Unlike conventional separation methods that centrifuge for 10 minutes at 3000 revolutions per minute, surface acoustic waves can separate cells in a much gentler way with a simple, low-cost device.
Acoustic-based separations are potentially important because they are non-invasive and do not alter or damage cells. However, in order to be effective for clinical use, they also need to be rapidly and easily applicable.

"With an integrated experimental/modelling approach, the new generation of the device has improved cell sorting throughput more than 20 times higher than previously achieved and made it possible for us to work with patient samples," said Ming Dao, from Massachusetts Institute of Technology.
Researchers, including Subra Suresh, president, Carnegie Mellon University, worked both experimentally and with models to optimise the separation of CTCs from blood.

They used an acoustic-based microfluidic device so that the stream of blood could continuously pass through the device for separation.
Using the differential size and weight of the different cells they chose appropriate acoustic pressures that would push the CTCs out of the fluid stream and into a separate channel for collection.

Tilted-angle standing surface acoustic waves can separate cells using very small amounts of energy.
All these features make the acoustic separation method, termed acoustic tweezers, extremely biocompatible and maximise the potential of CTCs to maintain their functions and native states.
If two sound sources are placed opposite each other and each emits the same wavelength of sound, there will be a location where the opposing sounds cancel each other.
Because sound waves have pressure, they can push very small objects, so a cell or nanoparticle will move with the sound wave until it reaches the location where there is no longer lateral movement, in this case, into the fluid stream that moves the separated cells along.

The researchers used two types of human cancer cells to optimise the acoustic separation - HELA cells and MCF7 cells. These cells are similar in size.
They then ran an experiment separating these cells and had a separation rate of more than 83 per cent. They then did the separation on other cancer cells, ones for which the device had not been optimised, and again had a separation rate of more than 83 per cent.
The research was published in the journal PNAS.