Alteration of Inertial Focusing Positions in Triangular Channels Using Flexible PDMS Microfluidics

Inertial focusing offers passive manipulation techniques of cells or microparticles with extremely high throughput. We devised a 3D-curved triangular channel using a flexible, thin PDMS microfluidic device to control inertial focusing positions. The flexible PDMS channel is coiled to form 3D spiral channels, which can provide a convenient route to control the structural parameters including 3D curvature and curving direction. We investigated the changes in focusing positions of the 3D spiral channels depending on Re, De, particle size, and the curving direction. The Dean flows induced by 3D curvature alter the focusing positions of the straight triangular channel, which is solely determined by inertial lift forces. We found the Dean drag force not only resulted in shifting of the focusing positions but also unstabilized some of the focusing positions and changed the number of focusing positions at specific configurations. These changes in the inertial focusing positions can lead to applications, such as single-cell analysis and rare cell separation. We demonstrated that the inertial focusing position in the 3D curved triangular channel could be easily tuned to achieve single-stream focusing and size-based separations of micro particles and cells.