3D Motion Manipulation for Micro- and Nanomachines: Progress and Future Directions.

In the past decade, micro- and nanomachines (MNMs) have made outstanding achievements in the fields of targeted drug delivery, tumor therapy, microsurgery, biological detection, and environmental monitoring and remediation. Researchers have made significant efforts to accelerate the rapid development of MNMs capable of moving through fluids by means of different energy sources (chemical reactions, ultrasound, light, electricity, magnetism, heat, or their combinations). However, the motion of MNMs is primarily investigated in confined two-dimensional (2D) horizontal setups. Furthermore, three-dimensional (3D) motion control remains challenging, especially for vertical movement and control, significantly limiting its potential applications in cargo transportation, environmental remediation, and biotherapy. Hence, an urgent need is to develop MNMs that can overcome self-gravity and controllably move in 3D spaces. This review will delve into the latest progress made in MNMs with 3D motion capabilities under different manipulation approaches, discuss the underlying motion mechanisms, explore potential design concepts inspired by nature for controllable 3D motion in MNMs, and present the available 3D observation and tracking systems. This article is protected by copyright. All rights reserved.