Smart Chemistry, Smart Motors

Abstract

In the Editorial for this special issue, Guest Editor Yongfeng Mei gives, together with Yimeng Chen and Borui Xu, a brief overview of the field of micro- and nanomotors. They furthermore highlight the state-of-the-art contributions in this research field featured in this special issue. Micro- and nanomotors that use various kinds of energy from their surrounding environment and convert it to kinetic motion are a prominent part of emerging nanotechnology, which could improve all aspects of human life.1 These tiny devices capable of artificial autonomous motion can be chemically and biologically functionalized and designed to perform complex and specific tasks, such as drug delivery, cargo transport, environmental monitoring and remediation.2 From the accessible energy supply for conversion to the application stage in reality, diverse aspects of micro/nanomotors need to be considered and interweaved around chemistry, which plays an important role in the majority of micro- and nanomotors within this field.3 Nowadays, numerous smart devices with intelligent functions were realized spanning from the macroscale4 to the microworld.5 With the development of nanotechnology, “smart” motors were also developed that hold great potential for unprecedented applications.6 Consequently, current micro- and nanomotors will enter the next stage of evolution in which these devices are integrated with smart systems, holding considerable promise for executing a series of more complicated and challenging tasks from biological and medical technology to bioinspired robots. To this end, precisely designed and accurately regulated micro- and nanomotors are desired for more groundbreaking research. As a result, this special issue highlights contributions of chemists and materials scientists to make smart micro/nanomotors and looks forward to more achievable applications by smart motors. It is of critical importance in this area of research to understand the motion behaviors of micro/nanomotors with different structures and find out where their energy input comes from.7 In this special issue, a tutorial review from Wang et al. gives a brief introduction on colloidal motors containing the elucidation of important concepts, which can equip the beginners with a core knowledge in a friendly and convenient way. Li et al. focused on the interaction behaviors of micro/nanomotors and showcased the recent progress regarding interaction capabilities, providing inspiration for the design of nanomachines cooperating with each other for more attractive and smart applications. Moreover, Peng et al. summarized the driving mechanism of fuel-free micro/nanomotors beyond chemically-propelled counterparts and reviewed recent advances pertaining to biomedical applications. A reviews by Lu et al. concentrated on the development of micro/nanomotors driven by ultrasound power sources. With advanced microfabrication methods, micro/nanomotors were designed and processed into distinct geometries to transform energy for their autonomous movement with the goal of functional micro/nanomachines including tubes, Janus spheres, rods, helices and other novel structural shapes.8 In this special issue, micro/nanomotors with diverse morphologies, impelled using the pioneered bubble propulsion mechanism,9 are presented in several articles. Ma et al. reported on Pt-based catalytic helix micro/nanomotors capable of being driven by the decomposition of hydrogen peroxide, of which the motion behaviors were closely related with helical turn numbers. The influence of the micro/nanomotor's size on the motion was investigated by Wu et al. with enzyme-powered microshells; they comply with a size-dependent locomotion mechanism. Furthermore, an updated strategy for fabricating micro/nanomotors with 3D lithography was proposed by Mei et al. They exemplified an advanced rocket-shape micro/nanomotor with enhanced moving speed compared with that of normal tubular micro/nanomotors. Additionally, in the cont