Efficient liquid manipulation is crucial in chemical engineering, biological research, clinical applications, and materials science. Bubbles, such as boiling, rising, and cavitating bubbles, have been widely employed to enhance mixing and mass transfer through their unique hydrodynamic behaviors. Yet, conventional bubble-based approaches often face limited scalability and poor performance in high-viscosity environments. Here, we introduce a strategy that employs low-energy acoustic excitation of rising microbubbles to achieve scalable and efficient mass transfer across macroscale and microscale domains. By coupling buoyancy-driven convection with localized acoustic microstreaming, acoustic rising microbubbles simultaneously extend the operational workspace and intensify local mass transfer. Particle image velocimetry and computational fluid dynamics analyses characterize the distinct contributions of buoyancy-induced flows, acoustically induced microstreaming, and their superimposed effects. Various chemical and biomedical applications, including efficient high-viscosity mixing, accelerated chemical material synthesis, altered cell membrane permeability, promoted cell lysis, and thrombus clearance, demonstrate the great potential of the proposed acoustic rising bubbles for efficient mass transfer in laboratory and industrial liquid manipulations.

Microrobots driven by magnetic and acoustic fields have shown great potential in multiple biomedical applications due to their excellent biocompatibility, wireless actuation, access to confined environments, and tissue penetration. A single physical actuation method often meets inevitable limitations and complications, such as the limited propulsion of the magnetic actuation and difficult direction control of the acoustic actuation. This review summarizes the current progress of hybrid magneto-acoustic actuation to address the limitations of single magnetic or acoustic actuation. First, we review the research on microrobots driven by single magnetic and acoustic fields and clarify the properties of each physical actuation. Then, we summarize 2 forms of hybrid magnetic-acoustic actuation: (a) magnetic steering and acoustic propulsion and (b) magnetic propulsion and acoustic manipulation. The state-of-the-art applications of magneto-acoustic microrobots, including targeted drug delivery, minimally invasive surgery, and medical imaging, are presented to demonstrate their great potential in biology and clinics. This article finally discusses current challenges and potential developments in magneto-acoustic robotics to provide a reliable path for designing and applying hybrid magneto-acoustic actuation methods.

Magnetic soft microrobots have great potential to access narrow spaces and conduct multiple tasks in the biomedical field. Until now, drug delivery, microsurgery, disease diagnosis, and dredging the blocked blood vessel have been realized by magnetic soft microrobots in vivo or in vitro. However, as the tasks become more and more complex, more functional units have been embedded in the body of the developed magnetic microrobots. These magnetic soft microrobots with complex designed geometries, mechanisms, and magnetic orientation are now greatly challenging the fabrication of the magnetic microrobots. In this paper, we propose a new method combining photopolymerization and assembly for the fabrication of magnetic soft microrobots. Utilizing the micro-hand assembly system, magnetic modules with different shapes and materials are firstly arrayed with precise position and orientation control. Then, the developed photopolymerization system is employed to fix and link these modules with soft materials. Based on the proposed fabrication method, 3 kinds of soft magnetic microrobots were fabricated, and the fundamental locomotion was presented. We believe that the presented fabrication strategy could help accelerate the clinical application of magnetic microrobots.

Field-controlled microrobots have attracted extensive research in the biological and medical fields due to the prominent characteristics including high flexibility, small size, strong controllability, remote manipulation, and minimal damage to living organisms. However, the fabrication of these field-controlled microrobots with complex and high-precision 2- or 3-dimensional structures remains challenging. The photopolymerization technology is often chosen to fabricate field-controlled microrobots due to its fast-printing velocity, high accuracy, and high surface quality. This review categorizes the photopolymerization technologies utilized in the fabrication of field-controlled microrobots into stereolithography, digital light processing, and 2-photon polymerization. Furthermore, the photopolymerized microrobots actuated by different field forces and their functions are introduced. Finally, we conclude the future development and potential applications of photopolymerization for the fabrication of field-controlled microrobots.