Analysis and methods for void-free liquid filling of blind microchambers in centrifugal microfluidics

Centrifugal microfluidics are widely used in point-of-care testing applications. Blind microchambers, the microchambers that have only one access to interact with external environment, are commonly used in centrifugal microfluidic chips. However, achieving void-free liquid filling of blind microchambers poses a significant challenge since the injection of liquid and the exhausting of air occurs simultaneously thus interference leads to incomplete liquid filling with bubble residuals. To resolve this issue, we propose a strategy for achieving void-free liquid filling of blind microchambers by designing a tapered microchannel to modify the gas-liquid two-phase flow pattern, effectively preventing bubble formation. The liquid-gas two-phase flow pattern is analysed, and the corresponding inference is verified via high-speed camera. According to theoretical and experimental findings, tapered designs are implemented to the branch channels connected to the blind microchambers. By using tapered designs, the fluid velocity increases, leading to the transitions from Taylor flow to annular flow, thereby avoiding bubble generation during liquid injection. Our work reveals the mechanism and offers a simple path to achieve void-free liquid filling of blind microchambers in centrifugal microfluidics, without the need for complex surface treatments or external forces, therefore have potential to benefit the community.