A microfluidic device that separates plasma from blood could be used to monitor patients during cardiac surgery, according to scientists in the US. Sung Yang at Pennsylvania State University, and colleagues, have designed a simple microfluidic network to separate blood cells and plasma.

Yang's device is based on a fluid separation principle called the Zweifach-Fung effect. Applied to blood travelling through a capillary, this means that when a red blood cell meets a bifurcating region (a region that divides in two) it will tend to move into the outlet with the faster flow rate. Yang's device uses several bifurcating regions to separate blood from one inlet channel into two outlet channels, containing purified plasma and concentrated blood cells.

Yang said that the challenge in the future will be to couple the plasma separation device to a heart-lung (cardiopulmonary bypass) machine. The use of a heart-lung machine during cardiac surgery can induce inflammatory responses in the body. These responses may cause serious postoperative complications, said Yang. 'There is an unmet need to be able to separate blood plasma directly from the cardiopulmonary bypass circuit and analyze it for inflammation markers,' he explained. These measurements are not usually available for hours or days after surgery, according to Yang. 

Developing the plasma separation technology for measuring inflammation markers is a further challenge, said Yang. A microanalytical module is now being designed and tested to enable continuous, real time measurement of clinically relevant proteins seen during an inflammatory response. 

Jan Lichtenberg of the Swiss Federal Institute of Technology (ETH) in Zurich said of the team's work: 'Microfluidics is all about re-thinking the laws of nature in the micro domain. This research project illustrates how a straightforward and easy-to-fabricate microstructure can do an excellent job, if the right principle is chosen.'

Katherine Davies