Investigation of the Dynamics of Cavitation Bubbles in a Microfluidic Channel with Actuations

Air trap and removal on a pressure driven PDMS-based microfluidic device

With the development of microfluidic technology, microfluidic chips have played a positive role in applications such as cell culture, microfluidic PCR, and nanopore gene sequencing. However, the presence of bubbles interferes with fluid flow and has a significant impact on experimental results. There are many reasons for the generation of bubbles in microfluidic chips, such as pressure changes inside the chip, air vibration inside the chip, and the open chip guiding air into the chip when driving fluid. This study designed and prepared a microfluidic device based on polydimethylsiloxane. First, air was actively introduced into the microfluidic chip, and bubbles were captured through the microfluidic device to simulate the presence of bubbles inside the chip in biological experiments. To remove bubbles trapped in the microfluidic chip, distilled water, distilled water containing surfactants, and mineral oil were pumped into the microfluidic chip. We compared and discussed the bubble removal efficiency under different driving fluids, driving pressures, and open/closed channel configurations. This study helps to understand the mechanism of bubble formation and removal in microfluidic devices, optimize chip structure design and experimental reagent selection, prevent or eliminate bubbles, and reduce the impact of bubbles on experiments.

Study on the Motion Characteristics of Solid Particles in Fine Flow Channels by Ultrasonic Cavitation

Microjets caused by the cavitation effect in microchannels can affect the motion trajectory of solid particles in microchannels under ultrasonic conditions. The optimal parameters for an observation experiment were obtained through simulations, and an experiment was designed to verify these parameters. When the cavitation bubbles collapse in the near-wall area, the solid particles in the microchannel can be displaced along the expected motion trajectory. Using fluent software to simulate the bubble collapse process, it can be seen that, when an ultrasonic sound pressure acts on a bubble near the wall, the pressure causes the top of the bubble wall to sink inward and eventually penetrate the bottom of the bubble wall, forming a high-speed microjet. The maximum speed of the jet can reach nearly 28 m/s, and the liquid near the top of the bubble also moves at a high speed, driving the particles in the liquid towards the wall. A high-speed camera was used to observe the ultrasonic cavitation process of bubbles in the water to verify the simulation results. A comparison of particle motion with and without ultrasonic waves proved the feasibility of using the ultrasonic cavitation effect to guide small particles towards the wall. This method provides a novel experimental basis for changing the fluid layer state in the microchannel and improving precision machining.