Acoustic microstreaming and augmentation of gas exchange using an oscillating membrane towards microfluidic artificial lungs

This paper presents a novel configuration for generating acoustic microstreaming flows at audible frequencies within a microchannel utilizing a pinned oscillating membrane. The characterization and interactions of these acoustic streaming flows with the streamwise flow within the microchannel are investigated, along with their effects on gas exchange augmentation. Advanced characterization methods and computational fluid dynamics simulations show a similar pattern and magnitude in acoustic streaming, providing evidence that this flexural membrane oscillation is the driving mechanism of the time-averaged vortices. This method exhibits potential application to microfluidic artificial lungs, particularly due to the vertical orientation of the resulting mixing, which facilitates an augmentation of gas exchange across the permeable membrane. Furthermore, it eliminates any obstructions in the microchannel and ensures stability, as opposed to other acoustic streaming methods such as sharp edge and oscillating bubble methods. Successful augmentation of gas exchange by up to 3.7× is demonstrated as shown by characterization of CO₂ transferred into the channel. Scaling up of throughput is also demonstrated with a branching design, featuring a multilayer manifold to avoid undesirable interaction of the streaming flow with the channel geometry.