Figure 6. Recent research and applications of acoustic control. A) Acoustic controlled RBC-PL-robot for removal of pathogenic bacteria and toxins.Reproduced with permission. [115] Copyright 2017, ACS. B) Acoustic controlled rotation of microbeads and oocytes. Reproduced with permission. [116] Copyright 2019, AIP. C) Acoustic controlled nanoswimmer for propulsion to maneuver micro-/nanosized objects. Reproduced with permission. [118] Copyright 2019, ACS. D) An untethered ultrasound-controlled actuator for targeted drug delivery. Reproduced with permission. [119] Copyright 2019, Springer Nature. E) Acoustic controlled micro rotor in PDMS channel for microelectromechanical systems. Reproduced with permission. [120]

Metastatic tumour recurrence caused by circulating tumour cells (CTCs) after surgery is responsible for more than 90% of tumour-related deaths. A postoperative evaluation system based on the long-term dynamic detection...

with efficient locomotion in fluids. Particularly, in fields that require biosafety, these robots need to be biofriendly, biocompatible, and multifunctional. In recent years, cell membrane-coated microrobots were designed, which provided new possibilities for researchers to easily harness native biological functions. [10,11] Additionally, biological template-based microrobots, such as bacterium-based robots, [12,13] sperm-based robots, [14] and cell-based motors, [15,16] have extraordinary properties while maintaining their original functionality. By providing these biological robots with new characteristics, they can be propelled by an external field to achieve various functions. For example, researchers have created cell-based delivery systems with the property of low toxicity and immunogenicity including the red blood cells, [17] platelets, [18] stem cells, [19] immune cells, [20] and tumor cells [21] that could be controlled to achieve precise site-specific delivery with better treatment efficacy. [22,23] Recently, magnetically propelled microrobots have gained particular attention in the bioengineering field, since magnetic fields are capable of penetrating most materials with minimal interaction and are nearly harmless. [24][25][26][27][28][29] Inspiringly, these magnetically actuated robots demonstrate flexible controllability to navigate mazes and could be used to manipulate cells precisely. [30,31] Exposed to a magnetic field, different magneticdriven microrobots can be controlled simultaneously and wirelessly with high precision. Therefore, microrobotic swarm behavior emerges when a large number of magnetic robots are activated by an external field. Although a single microrobot can achieve complex tasks, the power of an individual is always limited. In nature, swarm behavior appears everywhere. Specifically, bees collaborate to work efficiently, ant colonies work together to carry larger objects, and a school of fish swim together to resist predators. In the microworld, a magnetically driven robot swarm is promising because the swarm has a flexible morphology, [32] can travel through narrow channels, [33,34] and can even be observed in real organisms. [35] However, the implementation of biocompatible and biofriendly robot swarms is still a challenge.Immune cells are widely known as excellent carriers for targeted drug delivery, [36][37][38][39][40] owing to their capability to be decorated with functional nanoparticles. For robotics and cell manipulation, using a single cell robot to manipulate other Border-nearing microrobots with self-propelling and navigating capabilities have promising applications in micromanipulation and bioengineering, because they can stimulate the surrounding fluid flow for object transportation. However, ensuring the biosafety of microrobots is a concurrent challenge in bioengineering applications. Here, macrophage template-based microrobots (cell robots) that can be controlled individually or in chain-like swarms are proposed, which can transport various objects. The cell rob...

The capability to precisely rotate cells and other micrometer-sized biological samples is invaluable in biomedicine, bioengineering, and biophysics. We propose herein a novel on-chip cell rotation method using acoustic microstreaming generated by oscillating asymmetrical microstructures. When the vibration is applied to a microchip with our custom-designed microstructures, two different modes of highly localized microvortices are generated that are utilized to precisely achieve in-plane and out-of-plane rotational manipulation of microbeads and oocytes. The rotation mechanism is studied and verified using numerical simulations. Experiments of the microbeads are conducted to evaluate the claimed functions and investigate the effects of various parameters, such as the frequency and the driving voltage on the acoustically induced flows. Accordingly, it is shown that the rotational speed and direction can be effectively tuned on demand in single-cell studies. Finally, the rotation of swine oocytes is involved as further applications. By observing the maturation stages of M2 after the exclusion of the first polar body of operated oocytes, the proposed method is proved to be noninvasive. Compared with the conventional approaches, our acoustofluidic cell rotation approach can be simple-to-fabricate and easy-to-operate, thereby allowing rotations irrespective of the physical properties of the specimen under investigation.

The magnetically actuated robot has valuable potential in biomedicine, bioengineering, and biophysics for its capability to precisely manipulate particles or biological tissues. However, the deformability of rigid robots with predetermined shapes is limited, which constricts their functions and causes inconvenience for robots' movement in constricted space. In this study, we proposed a feasible and efficient ferrofluid-based robot for the transportation of tiny particles and blocks. In addition, a method to generate a patterned magnetic field is also introduced to model a ferrofluid-based robot with an adaptive shape. Benefiting from the paramagnetism and fluidity of the ferrofluid-based robot, it also demonstrates outstanding motion accuracy and output force on a superhydrophobic surface. Because of its excellent motion characteristics, high motion accuracy, and high measured output force, the proposed ferrofluid-based robot has great advantages in the field of microoperation. The correlation coefficient between the motion trajectory of the ferrofluid-based robot and the motion trajectory of the micro-stages is 0.9967. The position error is less than 1.5% of the total stroke.