Analysis of 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, microchambers that have only one access point by which to interact with an external environment, are commonly used in centrifugal microfluidic chips. However, achieving void-free liquid filling of blind microchambers poses a significant challenge as the injection of liquid and the exhausting of air occurs simultaneously and thus interference leads to incomplete liquid filling with the presence of residual bubbles. 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 <i>via</i> high-speed camera analysis. According to the 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 a mechanism that 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, and therefore has the potential to benefit the microfluidics community.