Ultrasound-Powered Micro-/Nanorobots: Fundamentals and Biomedical Applications

Micro-/nanorobots are miniaturized devices that convert energy stored in the environment into motion and are envisioned to revolutionize applications of biomedicine, environmental remediation, sensing, and micro-manufacturing. Among the various ways to power micro-/nanorobots, ultrasound is particularly advantageous because of its biocompatibility and thus wide adoption in hospitals and clinics. In this chapter, we review the recent development of ultrasound-powered micro-/nanorobots, highlighting their usefulness in biomedical applications as well as challenges ahead. We begin with a brief introduction to the operating principles of acoustic radiation forces and acoustic streaming, two concepts critical for ultrasonic propulsion. This is followed by a thorough description of four major types of ultrasound micro-/nanomotors, namely, microrod streamers, bubble streamers, flagella streamers, and acoustic jets. Their future prospects in biomedical applications are discussed in the last section. This book chapter is particularly useful for readers interested in biomedical applications but new to the field of micro-/nanorobots. It is also useful for experienced readers looking for expanding their toolbox or improving their understanding of operating mechanisms.