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Mechanically programmable, reconfigurable micro/nanoscale materials that can dynamically change their mechanical properties or behaviors, or morph into distinct assemblies or swarms in response to stimuli have greatly piqued the interest of the science community due to their unprecedented potentials in both fundamental research and technological applications. To date, a variety of designs of hard and soft materials, as well as actuation schemes based on mechanisms including chemical reactions and magnetic, acoustic, optical, and electric stimuli, have been reported. Herein, state‐of‐the‐art micro/nanostructures and operation schemes for multimodal reconfigurable micro/nanomachines and swarms, as well as potential new materials and working principles, challenges, and future perspectives are discussed.

 

To develop active materials that can efficiently respond to external stimuli with designed mechanical motions is a major obstacle that have hindered the realization nanomachines and nanorobots. Here, we present our finding and investigation of an original working mechanism that allows multifold reconfigurable motion control in both rotation and alignment of semiconductor micromotors in an AC electric field with simple visible-light stimulation. In our previous work, we reported the instantly switchable electrorotation owing to the optically tunable imaginary part of electric polarization of a semiconductor nanowire in aqueous suspension[1]. Here we provide further experimental confirmation along with numerical simulation. Moreover, according to the Kramers-Kronig relation, the real part of the electric polarization should also be optically tunable, which can be experimentally verified with tests of electro-alignment of a nanowire. Here, we report our experimental study of light effect on electro-alignment along with theoretical simulation to complete the investigation of opto-tunable electric polarization of a semiconductor nanowire. Finally, we demonstrate a micromotor with periodically oscillating rotation with simple asymmetric exposure to a light pattern. This research could inspire development of a new class of micro/nanomachines with agile and spatially defined maneuverability. 

2D transition‐metal‐dichalcogenide materials, such as molybdenum disulfide (MoS₂) have received immense interest owing to their remarkable structure‐endowed electronic, catalytic, and mechanical properties for applications in optoelectronics, energy storage, and wearable devices. However, 2D materials have been rarely explored in the field of micro/nanomachines, motors, and robots. Here, MoS₂ with anatase TiO₂ is successfully integrated into an original one‐side‐open hollow micromachine, which demonstrates increased light absorption of TiO₂‐based micromachines to the visible region and the first observed motion acceleration in response to ionic media. Both experimentation and theoretical analysis suggest the unique type‐II bandgap alignment of MoS₂/TiO₂ heterojunction that accounts for the observed unique locomotion owing to a competing propulsion mechanism. Furthermore, by leveraging the chemical properties of MoS₂/TiO₂, the micromachines achieve sunlight‐powered water disinfection with 99.999% Escherichia coli lysed in an hour. This research suggests abundant opportunities offered by 2D materials in the creation of a new class of micro/nanomachines and robots.

 

To develop active nanomaterials that can instantly respond to external stimuli with designed mechanical motions is an important step towards the realization of nanorobots. Herein, we present our finding of a versatile working mechanism that allows instantaneous change of alignment direction and speed of semiconductor nanowires in an external electric field with simple visible-light exposure. The light induced alignment switch can be cycled over hundreds of times and programmed to express words in Morse code. With theoretical analysis and simulation, the working principle can be attributed to the optically tuned real-part (in-phase) electrical polarization of a semiconductor nanowire in aqueous suspension. The manipulation principle is exploited to create a new type of microscale stepper motor that can readily switch between in-phase and out-phase modes, and agilely operate independent of neighboring motors with patterned light. This work could inspire the development of new types of micro/nanomachines with individual and reconfigurable maneuverability for many applications.