Flipping: A Valve-Free Strategy to Control Fluid Flow in Centrifugal Microfluidic Systems

Centrifugal microfluidics has emerged as a technology to automate fluid handling at the microliter scale in bioassays. It has been mostly developed for point-of-care diagnostic applications, where assays involve a well-defined workflow. By contrast, this study introduces a microfluidic strategy that allows multiple workflows within the same device, thereby addressing the requirements of sample preparation steps in R&D settings. The corresponding device is a microfluidic chip that can be inserted either in a lab-on-a-disk or in the swinging-bucket of a commercial centrifuge. The control of liquid transfers from one chamber to the next is achieved by flipping the chip, thereby reorienting it in the centrifugal force field. The present experimental study describes the fluid instability that triggers the transfer upon flipping. A semi-empirical physical model is developed that predicts the acceleration threshold of the instability as a function of design parameters. By contrast to most existing control strategies in centrifugal microfluidics, the present strategy does not involve any valve. Consequently, it is robust to variations of material and sample properties, and it yields minimal fabrication constraints. Designing appropriately sized chambers enables flexible implementation of complex workflows. This strategy brings the miniaturization benefits of centrifugal microfluidics to sample preparation workflows.