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Highlights in Chemical Technology

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Microfluidics doesn't shock cells

07 April 2009

Scientists have used microfluidic technology to improve the survival rates of frozen cells.

Cryopreservation is a process in which cells are cooled down to subzero temperatures, which stops their biological activity. Unfortunately, this freezing process can damage the cells. Scientists add chemicals called cryoprotectants (CPAs) to lower the cells' freezing temperatures and reduce the formation of ice crystals, which can crush the cells. When they want to use the cells, they warm them up to body temperature and remove the CPAs. But even these chemicals designed to protect the cells can cause damage.

Now, Utkan Demirci, at Harvard Medical School, Cambridge, US, and colleagues have increased the chance of cell survival by 25 per cent over standard cryopreservation methods.

Microfluidic device

The microfluidic device has a long microfluidic channel with three inputs and one outlet

Demirci explains that osmotic shock is one of the major causes of cell damage during cryopreservation. It is caused by water moving into and out of the cell. When CPA is added to the cell mixture, the CPA concentration outside of the cell is high, which draws water out of and CPA into the cell. The reverse occurs during CPA unloading and the water flow into the cell can cause the cell to swell and burst.

Demirci used a microfluidic channel with three input channels - one in the middle for the cells and one at each side for the CPAs. Cells travelling along the channel experienced a gradual increase in CPA concentration. After thawing, Demirci removed the CPAs using a buffer solution injected into the side channels. By controlling the flow rates, and so the concentration of CPAs, he was able to greatly reduce the incidence of osmotic shock.

"The microfluidic device automates the entire process, while at the same time ensuring uniform processing conditions throughout the entire sample"
- Palaniappan Sethu, University of Louisville, US

'Our microfluidic chip was designed to achieve high throughput processing of cells to allow higher flow rates,' says Demirci. 'It is easily applicable to the cryopreservation field and can be built as a prototype automated device for general lab use in the future.'

Palaniappan Sethu, an expert in microfluidic systems at the University of Louisville, US, is impressed by the technology. 'The microfluidic device automates the entire process, while at the same time ensuring uniform processing conditions throughout the entire sample. This minimises inter- and intra-sample variability that is common with conventional macroscale techniques,' he comments.

Sylvia Pegg

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Link to journal article

Microfluidics for cryopreservation
Young S. Song, SangJun Moon, Leon Hulli, Syed K. Hasan, Emre Kayaalp and Utkan Demirci, Lab Chip, 2009, 9, 1874
DOI: 10.1039/b823062e

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