title: Design and implementation of fluidic micro-pulleys for flow control on centrifugal microfluidic platforms.
abstract: Microfluidic discs have been employed in a variety of applications for chemical analyses and biological diagnostics. These platforms offer a sophisticated fluidic toolbox, necessary to perform processes that involve sample preparation, purification, analysis, and detection. However, one of the weaknesses of such systems is the uni-directional movement of fluid from the disc center to its periphery due to the uni-directionality of the propelling centrifugal force. Here we demonstrate a mechanism for fluid movement from the periphery of a hydrophobic disc toward its center that does not rely on the energy supplied by any peripheral equipment. This method utilizes a ventless fluidic network that connects a column of working fluid to a sample fluid. As the working fluid is pushed by the centrifugal force to move toward the periphery of the disc, the sample fluid is pulled up toward the center of the disc analogous to a physical pulley where two weights are connected by a rope passed through a block. The ventless network is analogous to the rope in the pulley. As the working fluid descends, it creates a negative pressure that pulls the sample fluid up. The sample and working fluids do not come into direct contact and it allows the freedom to select a working fluid with physical properties markedly different from those of the sample. This article provides a demonstration of the "micro-pulley" on a disc, discusses underlying physical phenomena, provides design guidelines for fabrication of micro-pulleys on discs, and outlines a vision for future micro-pulley applications.
authors.affiliation: Department of Biomedical Engineering, University of California, Irvine, CA, 92697, USA.
authors.forename: Salar
authors.initials: S
authors.lastname: Soroori
authors.affiliation: Department of Mechanical & Aerospace Engineering, University of California, Irvine, CA, 92697, USA.
authors.forename: Lawrence
authors.initials: L
authors.lastname: Kulinsky
authors.affiliation: Department of Mechanical & Aerospace Engineering, University of California, Irvine, CA, 92697, USA ; RotaPrep, Inc., Tustin, CA, 92782, USA.
authors.forename: Horacio
authors.initials: H
authors.lastname: Kido
authors.affiliation: Department of Biomedical Engineering, University of California, Irvine, CA, 92697, USA ; Department of Mechanical & Aerospace Engineering, University of California, Irvine, CA, 92697, USA ; UNIST, World Class University (WCU), Ulsan, South Korea.
authors.forename: Marc
authors.initials: M
authors.lastname: Madou
keywords: Hydrophobic fluidics; centrifugal microfluidics; inward flow; micro-pulley; pressure change; siphon