Liquid Metal Swimming Nanorobots

ConspectusRoom temperature liquid metal gallium-based materials have received tremendous attention owing to their potential promises in various aspects including bioengineering and smart medicine, flexible circuits and electronic skins, transformable activators and triboelectric nanogenerators, etc. Particularly, the usage of gallium-based liquid metals to construct humanoid robots to accomplish diverse dangerous missions leads to the considerable focus on the development of gallium-based flexible robots. Unlike conventional metal materials with rigid properties and responsible mainly for the backbone, room temperature gallium-based liquid metals could serve as a new generation of smart flexible materials for robotic devices with its advantages, such as low toxicity, high fluidity, and plasticity at the micro/nanometer sizes. With the expectation in biomedicine, such as targeted drug delivery, the past decade has led to the scaling down of the swimming robot to the micro- and nanoscales. Swimming nanorobots, which are defined as devices that can convert chemical energy in the surrounding environment and externally physical field into their own kinetic energy at the micro/nanoscale and achieve self-propulsion, have shown widespread potential in the field of in vivo applications. Despite the great promises, gallium-based liquid metal robots are primarily limited to the millimeter and subcentimeter scales. Moving toward clinical medical practices, however, these gallium-based liquid metal swimming robots are facing the biocompatible problem caused by their large sizes and propulsion approaches. Particularly, the manufacture, self-propulsion, and navigation of nanoscale liquid metal swimming robots, ensuring the penetration though various tissues toward the disease area, is still challenging. Construction of gallium-based swimming nanorobots is of vital importance both for fundamental research, such as the dynamics of individual nanorobots and emergence of nanorobotic swarms, as well as for engineering and bioapplications, for instance, active target delivery. When applied as an in vivo surgical agent, the gallium-based liquid metal nanorobots will not only gather into the disease site at a higher targeting ratio but also behave in an emerged collective means that transform and infuse to destroy the lesion by photothermal and photodynamic therapy, and so on. Compared with the large-scale liquid metal robots, gallium-based swimming nanorobots offer the advantages in treatment of tumors with lower intensity, navigation with higher precision, and surgical therapies with minor invasion.In this Account, we will summarize our recent efforts and the outcome of others in the development of gallium-based liquid metal swimming nanorobots including the manufacture, self-propulsion, motion control, transformation, infusion, and collective emergence from the viewpoint of fundamental aspects. Also, the potential of gallium-based swimming nanorobots for active soft materials and systems with adaptive and interactive functions and biomedical applications will be illustrated.