Microfluidic counterflow centrifugal elutriation system for sedimentation-based cell separation

We present a centrifugal microfluidic system for precise cell/particle sorting using the concept of counterflow centrifugal elutriation (CCE). A conventional CCE system uses a rotor device incorporating a flow-through separation chamber, in which the balance of centrifugal and counterflow drag forces exerted on particles is gradually shifted by changing the flow rate and/or the rotation speed. In the present system, both the centrifugal and the fluid forces are generated through microdevice rotation in order to significantly simplify the setup of the conventional CCE. In addition, the density gradient of the medium is employed to elute particles/cells of different sedimentation velocities stepwise from the separation chamber instead of changing the rotation speed. We successfully separated polymer particles with diameters of 1.0-5.0 mu m using a branched loading channel for focusing particles to the center of the separation chamber. We also demonstrated the sorting of blood cells for biological applications. This system may provide a versatile means for cell/particle sorting in a general biological laboratory and function as a unit operation in various centrifugal microfluidic platforms for biochemical experiments and clinical diagnosis.