Efficient liquid manipulation is a fundamental requirement in chemical engineering, biological research, clinical practice, and materials processing, where performance is largely determined by the ability to achieve rapid mixing and effective mass transfer across multiple length scales. Although bubbles have long been exploited for transport enhancement because of their distinctive hydrodynamic behaviors, conventional bubble-based systems often fail to simultaneously provide large-scale coverage and efficient local mass transfer, particularly in high-viscosity media. "Bulk mixing approaches such as mechanical stirring and bubble-column reactors can generate macroscopic agitation, but remain ineffective for microscale transport under low-Reynolds-number conditions; by contrast, microfluidic and acoustofluidic approaches can enhance localized mixing, yet are often constrained by limited throughput, confined operating space, and poor scalability." said the author Chenhao Bai, a researcher at Beijing Institute of Technology, "Against this background, there is a clear need for a liquid-manipulation strategy that can couple buoyancy-driven large-scale convection with localized acoustic microstreaming while maintaining low energy consumption and scalability."
In this study, the authors established an acoustically actuated rising-microbubble platform in which microbubbles with an average diameter of approximately 120 μm were generated by a high-precision syringe pump through a glass capillary with an inner diameter of 10 μm, while a piezoelectric transducer fixed to the outer bottom of the liquid container applied a low-frequency acoustic field near resonance to induce coupled bubble oscillation and buoyant ascent. Orthogonal microscopic imaging, high-speed recording, micro-particle image velocimetry, and computational fluid dynamics simulations were combined to characterize the localized acoustic microstreaming around the bubble, the macroscopic convection generated during bubble rise, and their superimposed transport effect, with driving voltage and frequency treated as the principal control variables for evaluating mixing intensity and mass-transfer performance. On this basis, the method was further examined in high-viscosity fluid mixing, bubble-array-based workspace expansion, gas–liquid and saponification reaction enhancement, as well as HeLa cell transfection, thrombus clearance, and red blood cell lysis, thereby validating its applicability across both chemical and biomedical settings.
The results show that acoustically actuated rising microbubbles enhance both macroscopic mixing and microscopic mass transfer through the coupling of buoyancy-driven convection and localized acoustic microstreaming. Relative to acoustic microstreaming alone, the effective coverage area increased by more than 3.5-fold, and the mean flow velocity amplitude was enhanced by approximately 12–15 times, yielding pronounced advantages in high-viscosity media. Specifically, a single-column microbubble configuration achieved a mixing index of 88.4% ± 3.2% within 20 s, corresponding to a 55% reduction in mixing time relative to the passive control, whereas a triple-column array reached 92.7% ± 2.5% within 8 s, representing a 100% improvement in efficiency compared with robot-assisted stirring. The method also produced clear gains in chemical processing: in the CO₂–Ca(OH)₂ system, it increased the mass-transfer coefficient by approximately 3.2-fold and shortened reaction time by 45%, while in triglyceride saponification it achieved a conversion rate of 93.2% within 4 min, compared with 6 min for the control. In biomedical applications, acoustic rising microbubbles enabled gene delivery with ~68% transfection efficiency while maintaining cell viability above 85% at 7.5–10 Vpp; at higher voltages (≥15 Vpp), they substantially promoted thrombus clearance and induced rapid red blood cell lysis, indicating a tunable bio-interaction window and broad application potential.
In summary, this study shows that acoustically actuated rising microbubbles can couple buoyancy-driven macroscopic convection with localized acoustic microstreaming, thereby enabling large-area liquid agitation and microscale mass-transfer enhancement within a single platform. In this sense, the proposed method provides a low-energy, tunable, and scalable route for liquid operations involving high-viscosity mixing, accelerated gas–liquid and liquid-phase reactions, and cell-level manipulation. More importantly, by overcoming the limited spatial reach of conventional acoustofluidic approaches and the insufficient microscale transport efficiency of traditional bubble-driven mixing, and by demonstrating effectiveness in chemical synthesis, gene delivery, thrombus clearance, and cell lysis, this work positions acoustic rising microbubbles as a broadly applicable platform with substantial potential for both engineering-scale liquid processing and biomedical applications.
Authors of the paper include Chenhao Bai, Zhuo Chen, Yunsheng Li, Yan Chen, Qing Shi, Qiang Huang, Toshio Fukuda, Tatsuo Arai, and Xiaoming Liu.
This research was supported in part by the Prevention and Control of Emerging and Major Infectious Diseases-National Science and Technology Major Project (Grant 2025ZD01901603 to Y.L.), the National Natural Science Foundation of China (Grant 62273052 to X.L.), the National Natural Science Foundation of China (Grant W2431050 to T.A.), the Beijing Natural Science Foundation (Grant L248102 to X.L.), the Beijing Natural Science Foundation (Grant IS23062 to T.A.), and in part by the Grant-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology of Japan (Grant 23K22712 to T.A.).
The paper, "Acoustic Rising Microbubbles for Efficient Liquid Operations" was published in the journal Cyborg and Bionic Systems on Mar 9, 2026, at https://doi.org/10.34133/cbsystems.0449.
