The driving and distribution of fluid is important for building integrated and functional microfluidic systems. This study presents a bidirectional micropump based on acoustically oscillating water droplet-shaped microbubbles. The micropump exploits the geometric asymmetry of the microbubbles along the pumping direction to generate asymmetric acoustic microstreaming actuated with acoustic waves, enabling directional fluid transport. Bidirectional pumping is achieved by adjusting the frequency of actuated acoustic waves, which switches the direction of the acoustic microstreaming. The prototypes were fabricated, and experimental tests were conducted. Experimental results show that water droplet-shaped microbubbles generate out-of-plane microstreaming near the base ends when the frequency of the actuated acoustic waves is between 11.85 and 13.11 kHz. As a result of that, the net flow from the base end to the tip of the water droplet-shaped microbubbles is formed by the superposition of the array of acoustic microstreaming. The micropump achieved its peak forward flow of 2658 nl/min at an acoustic frequency of 12.32 kHz and 60 Vpp. A reverse out-of-plane microstreaming is generated at the middle of the microbubbles when the frequency of acoustic waves is within the range of 18.22–19.35 kHz. A reverse flow from the tip to the base end is generated by the superposition of acoustic microstreaming produced by the microbubble array. A peak reverse flow of 1230 nl/min was achieved at 18.55 kHz and 140 Vpp. This study proposes a flexible bidirectional micropump, offering a solution for the dynamic regulation of flow direction in microfluidic systems.
Liu et al. (Mon,) studied this question.