A thermoreversible polymer gel that sorts fluorescently labelled cells in a microfluidic device could aid stem cell research. 

Cell sorting is important for a number of applications, such as infectious diseases research, and although methods for separating cells such as fluorescence activated cell sorting (FACS) are well established they are not always suitable to use when the sample needs to be sterilised or when handing infectious materials. Microfluidic devices have the potential to provide a better way of sorting cells which need to be contained in such an environment is but their use has been limited due to low throughput. 

Now Takashi Funatsu at University of Tokyo and colleagues have tackled this problem by combining a 3D channel network with eight parallel sorters on a single chip. Heat from an IR laser manipulates a polymer so that it changes from a gel to a solid, which allows cells travelling through each sorter to be directed either into a waste or collection channel. 

Funatsu demonstrated the platform capability using a sample solution containing Escherichia coli cells expressing green or red fluorescent protein. Normally the solutions would run to waste but when a fluorescence signal is detected from a labelled cell the infrared laser heats a specific area of the channel so the polymer forms a solid, blocking the waste channel and forcing the flow into specific channels to separate the differently labelled cells. 

'One way to improve the throughput in microfluidic devices is to have a number of sorting channels running in parallel on a single chip but individual control of these channels can be problematic,' comments David Holmes an expert in cell sorting at University College London, UK, 'the technique proposed here allows individual channels to be separately addressed using an external laser without the need for complex fabrication of micromechanical valves.' Funatsu adds, 'our sorter is suitable for sorting rare cells without damage.' He expects it could be used for sorting embryonic stem cells or in stem cell regenerative medicine research. 

Leanne Marle 

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