Tubular Micro/Nanomachines: From the Basics to Recent Advances

Inspired by the machines that have changed the world through their autonomous functions, scientists have focused their attention on performing similar functions at the micro/nanoscale. The motility of these micro/nanomachines (micro/nanomotors) offers enormous opportunities for cargo delivery, biodetection, and environmental and biomedical applications. Among the various geometries of micro/nanomotors, a tubular shape provides asymmetric inner and outer surfaces, where the inner wall hosts chemical reactions that supply the moving power and the outer wall can be modified for specific chemical and biological functions. This review describes the concept of tubular micro/nanomotors, including their basic principles, fabrication methods and control over their motion. With the assistance of catalytic reactions, tubular micro/nanomotors can generate a powerful thrust force to navigate in complex natural and in vitro environments. Modification of the tubular micro/nanomotors allows the motors to capture, transport, and release selected cargos on demand. In addition, their application in sensing and decontamination benefits from their collection behavior and self-mixing effect. Furthermore, noncatalytic reaction-driven tubular micro/nanomotors, such as redox-based and biohybrid tubular micro/nanomotors, provide new possibilities for practical in vivo applications. The state-of-the-art tubular micro/nanomotors could offer a promising platform for various applications, e.g., lab-on-chip devices and in vivo theranostics.