Scientists in the US have proposed a design for small channels that could sort cells according to their stiffness, with the potential to rapidly detect disease.

Cell stiffness is emerging as an important property. In medicine, for example, researchers have shown that cancerous cells are less rigid than their healthy counterparts. Measuring a cell's mechanical properties, however, requires expensive, time-intensive techniques such as atomic force microscopy, which physically probe individual cells. A cheap and efficient means of evaluating stiffness could therefore be an invaluable diagnostic tool.

Particles show strain (brown) as they pass through diagonal ridges allowing them to be separated based on their stiffness

'Cancer cells are softer,' says Alexander Alexeev, who works in the field of fluid mechanics at the Georgia Institute of Technology, Atlanta. 'But there could be just a few cells present in a sample, so you need a high-throughput device to be able to select those cells.' To this end, Alexeev and colleague John Arata have used computer modelling to simulate cell-like particles flowing through a microfluidic channel. They found that when their models included diagonal ridges across the channel, the calculations suggest the cells will migrate to opposite sides according to their stiffness, thus segregating them. 'Our results need to be experimentally verified,' points out Alexeev, 'but this should be a very low-cost, express method for analysis.'

For Andreas Fery, an expert in colloid and interface science at the University of Bayreuth, Germany, the study is also an important demonstration that mechanical properties can be exploited, and not simply measured. 'In nature, mechanical stability is used to create smart systems,' he says. 'This work is a step in that direction: using mechanical stability to make decisions. We need these visionary, concept papers to open minds,' Fery adds. 'This is something we will see much more in the future.'

Alexeev now intends to refine his model to enable the physical realisation of his idea. 'There are many design parameters which can be changed to improve the device,' he explains. 'We need to understand these before we build a working system.'

Philip Robinson

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