Bjerknes Forces in Motion: Long‐Range Translational Motion and Chiral Directionality Switching in Bubble‐Propelled Micromotors via an Ultrasonic Pathway

Moo, James Guo Sheng; Mayorga‐Martinez, Carmen C.; Hong, Wang; Teo, Wei Zhe; Tan, Beng Hau; Luong, Trung-Dung; Gonzalez-Avila, Silvestre Roberto; Ohl, Claus‐Dieter; Pumera, Martin

doi:10.1002/adfm.201702618

Cited by 47 publications

(24 citation statements)

References 61 publications

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“…On the other hand, the assembly and disassembly of the acoustic microrobots would be possible, due to the mutual multibubble interactions resulting from the secondary order Bjerknes force (34,50). In addition to the actuation and control strategies, the real-time imaging of the microscopic swimmers presents a grand challenge in the microrobotics field.…”

Section: Discussionmentioning

confidence: 99%

Acoustically powered surface-slipping mobile microrobots

Aghakhani

Yaşa

Wrede

et al. 2020

Proc. Natl. Acad. Sci. U.S.A.

222

215

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Untethered synthetic microrobots have significant potential to revolutionize minimally invasive medical interventions in the future. However, their relatively slow speed and low controllability near surfaces typically are some of the barriers standing in the way of their medical applications. Here, we introduce acoustically powered microrobots with a fast, unidirectional surface-slipping locomotion on both flat and curved surfaces. The proposed threedimensionally printed, bullet-shaped microrobot contains a spherical air bubble trapped inside its internal body cavity, where the bubble is resonated using acoustic waves. The net fluidic flow due to the bubble oscillation orients the microrobot's axisymmetric axis perpendicular to the wall and then propels it laterally at very high speeds (up to 90 body lengths per second with a body length of 25 μm) while inducing an attractive force toward the wall. To achieve unidirectional locomotion, a small fin is added to the microrobot's cylindrical body surface, which biases the propulsion direction. For motion direction control, the microrobots are coated anisotropically with a soft magnetic nanofilm layer, allowing steering under a uniform magnetic field. Finally, surface locomotion capability of the microrobots is demonstrated inside a threedimensional circular cross-sectional microchannel under acoustic actuation. Overall, the combination of acoustic powering and magnetic steering can be effectively utilized to actuate and navigate these microrobots in confined and hard-to-reach body location areas in a minimally invasive fashion. microrobots | acoustic actuation | magnetic control | microswimmers | bubble oscillation U ntethered synthetic microrobots have been recently investigated for their potential applications in targeted drug delivery, detoxification, and noninvasive surgeries (1-4). The existing microswimmers are powered by different external energy sources, such as light (5-7), electrical (8,9), magnetic (10, 11), and acoustic (12, 13) fields, or fueled by chemicals in the environment (14, 15). Among these actuation schemes, magnetic and acoustic field-based powering methods are the most prevalent in the biomedical context thanks to their deep-tissue penetration and high-energy-density capabilities. While the acoustic waves can deliver strong propulsion forces (16), the magnetic field can provide controlled steering of the microswimmers (17, 18). For example, acoustically excited bubbles can generate high streaming forces (16,19), and when employed in the robot's body they can act as an engine for the propulsion (12,20).Up to now, a few studies have used two-dimensional (2D) microfabrication (20, 21) and ultraviolet light-based polymerization techniques (12,22) to fabricate around 100-to 300-μm microrobots with cylindrical or conical cavities for bubble entrapment. As the bubble diameter scales down to the 10-to 30-μm range, the cylindrical cavity geometry would require advanced hydrophobic treatment to hold a microbubble stable due to the increased surface tens...

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Section: Discussionmentioning

confidence: 99%

Acoustically powered surface-slipping mobile microrobots

Aghakhani

Yaşa

Wrede

et al. 2020

Proc. Natl. Acad. Sci. U.S.A.

222

215

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“…Furthermore, unlike thermal or optical stimuli, this approach does not affect the fuel or reaction rate allowing for maintaining chemical propulsion integrity. More recent studies have shown that apart from ON/OFF motion, the ultrasound fields can induce oscillations of bubble aggregates and hinder the bubble forming phenomena of the microrocket, resulting in change of directionality …”

Section: Multistimuli‐enabled Advanced Motion Controlmentioning

confidence: 99%

Hybrid Nanovehicles: One Machine, Two Engines

Chen

Soto

Karshalev

et al. 2018

Adv Funct Materials

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Nanomotors have emerged as promising and versatile nanorobotic tools in a variety of medical, sensing, decontamination, and manufacturing applications due to their unique ability to operate and perform task at small scales. This review focuses on the current progress and future perspectives of hybrid nanomotors based on two power sources, with a special highlight on their distinct advantages, unique propulsion behaviors, adaptive operation, and potential applications. Such incorporation of multiple engines into a single nanoscale vehicle addresses certain limitations of nanomotors based on a single propulsion mode and adds new dimensions for advanced motion management. These attractive capabilities of hybrid nanoscale vehicles are discussed along with the challenges and opportunities when coupling several propulsion modes into a single device. With continuous innovations, it is expected that hybrid nanomotors will have a profound impact upon the field of nanorobotics.

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“…This situation might correspond to a situation observed experimentally, where the bubble exits from both the rear and front openings, spoiling a robust unidirectional motion [15,29]. This mechanism might even be exploited to achieve complex bidirectional motions, as described in [30] as an alternative strategy to the ultrasound control [31]. In fact, when the bubble exits from the front opening, the micro-rocket displaces from left to right while it displaces from right to left when the bubble exits from the rear opening.…”

Section: Critical Threshold For Sustained Bubble Ejectionmentioning

confidence: 81%

The Hydrodynamics of a Micro-Rocket Propelled by a Deformable Bubble

Gallino

Zhu

Gallaire

2019

Fluids

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We perform simulations to study the hydrodynamics of a conical-shaped swimming micro-robot that ejects catalytically produced bubbles from its inside. We underline the nontrivial dependency of the swimming velocity on the bubble deformability and on the geometry of the swimmer. We identify three distinct phases during the bubble evolution: immediately after nucleation the bubble is spherical and its inflation barely affects the swimming speed; then the bubble starts to deform due to the confinement gradient generating a force that propels the swimmer; while in the last phase, the bubble exits the cone, resulting in an increase in the swimmer velocity. Our results shed light on the fundamental hydrodynamics of the propulsion of catalytic conical swimmers and may help to improve the efficiency of these micro-machines.

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Bjerknes Forces in Motion: Long‐Range Translational Motion and Chiral Directionality Switching in Bubble‐Propelled Micromotors via an Ultrasonic Pathway

Cited by 47 publications

References 61 publications

Acoustically powered surface-slipping mobile microrobots

Acoustically powered surface-slipping mobile microrobots

Hybrid Nanovehicles: One Machine, Two Engines

The Hydrodynamics of a Micro-Rocket Propelled by a Deformable Bubble

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