Controlling microbubble formation in microfluidic devices: Advancements in experimental, theoretical, and numerical strategies

Microfluidic devices are becoming increasingly popular for producing microbubbles, as these devices provide much greater control over microbubble size compared to traditional methods such as sonication and amalgamation. Recent developments in microfabrication technologies have prompted several modifications in conventional microfluidic devices, which allow one to “engineer” microbubbles relevant to specific biomedical applications. The pursuit of improvements in microbubble engineering requires a detailed understanding of fluid flow behavior in microfluidic systems, which is where the motivation for this work originates from. This work provides an extensive review of the theoretical, experimental, and numerical investigations reported in the literature to understand microbubbles formation using microfluidic devices. The evolution of gas-liquid interfaces during microbubble formation, the pinch-off mechanism, and the confinement effect on microbubble size and production rate have been discussed. The scaling laws for the prediction of microbubble diameter and microbubble formation regimes maps providing details about the interplay of different forces have also been reviewed. Furthermore, the developments in CFD simulations based on different interface tracking schemes for microbubble formation in microfluidic devices, along with the recent developments and strategies to upscale microbubble production rate in microfluidic devices, have also been discussed. We conclude this review by outlining the need for current modifications in microfluidic systems to produce microbubbles, which can pave the way to new research in the field of microfluidics for microbubble engineering.