Ultrasound‐Controlled Swarmbots Under Physiological Flow Conditions

Abstract

Navigation of microrobots in living vasculatures is essential in realizing targeted drug delivery and advancing non‐invasive surgeries. Acoustically‐controlled “swarmbots” are developed based on the self‐assembly of clinically‐approved microbubbles (MBs). Ultrasound is noninvasive, penetrates deeply into the human body, and is well‐developed in clinical settings. This propulsion strategy relies on two forces: the primary radiation force and the secondary Bjerknes force. Upon ultrasound activation, the MBs self‐assemble into microswarms, which migrate toward and anchor at the containing vessel's wall. A second transducer, which produces an acoustic field parallel to the channel, propels the swarms along the wall. Noting that human arteries have a blood flow 5–19 cm s−1, powerful features of cross‐ and upstream swarmbot navigation are demonstrated against physiologically‐relevant flow rates that reach 16.7 cm s−1. Additionally, controlled navigation of swarmbots is shown within mice blood and under pulsatile flow conditions of 100 beats per minute (bpm); an adult human heart at rest executes between 60 and 100 bpm. This capability represents a much‐needed pathway for advancing preclinical research.

Micro/Nanorobotic Swarms: From Fundamentals to Functionalities

“…To date, most of the medical micro/nanorobotic swarms reported result in zero-flow and 2D environments. To yield promising efficacy for clinical use, the capability for swarms to maintain their structural integrity and motion in physiological environments, such as pulsatile biofluid flow and organ motion, must be considered. ,,,, The navigation of micro/nanorobotic swarms in 3D environments must also be taken into considerations (Figure A). ,,, Microrobotic swarms have been shown to be capable of rolling up circular channels [Figure A­(i)] and performing adaptive locomotion in 3D environments, such as climbing up stairs and crossing gaps [Figure A­(ii)] . However, swarm navigation in a 3D environment without relying on interfaces or solid boundaries requires further research.…”

“…The technique was demonstrated to be applicable to living cell manipulation. Moreover, swarms of microbubbles have been trapped and navigated in the physiological flow conditions by tailoring the acoustic waves. , A mobile transducer was designed to create a vortexlike acoustic well for the attraction and trapping of microbubbles . Through adjustment of the position of the transducer, the navigated motion of the microbubble swarms was achieved in in vivo murine blood flow (Figure D).…”

Ultrasound Microrobots with Reinforcement Learning

“…Recently, ultrasoundbased propulsion has elicited considerable interest as an alternate means to generate propulsion and manoeuvre micro-and nanosized objects. [26][27][28][29][30][31][32][33][34][35][36][37] A brief overview of research in this area follows.…”

A robot-assisted acoustofluidic end effector

“…Such acoustic fields are generated with commercially-available piezo transducers, which have limited bandwidth, and so the acoustic microtraps can only be operated over limited distances 18,36 . Additionally, three-dimensional (3D) manipulation 4,37 and selective trapping 38,39 and manipulation of microparticles 40,41 via acoustic methods have all proven extremely difficult to implement. Dynamic manipulation in a large working environment has recently been achieved by connecting acoustic devices to a manipulation stage.…”