Dynamic self-assembly of micro-nanomotor

Intelligent micro/nanorobots based on biotemplates

Intelligent micro/nanorobots based on natural materials as biotemplates are considered to be some of the most promising robots in the future in the microscopic field. Due to the advantages of biotemplates such as unique structure, abundant resources, environmental friendliness, easy removal, low price, easy access, and renewability, intelligent micro/nanorobots based on biotemplates can be endowed with both excellent biomaterial activity and unique structural morphology through biotemplates themselves and specific functions through artificial micro/nanotechnology. Thus, intelligent micro/nanorobots show excellent application potential in various fields from biomedical applications to environmental remediation. In this review, we introduce the advantages of using natural biological materials as biotemplates to build intelligent micro/nanorobots, and then, classify the micro/nanorobots according to different types of biotemplates, systematically detail their preparation strategies and summarize their application prospects. Finally, in order to further advance the development of intelligent micro/nanorobots, we discuss the current challenges and future prospects of biotemplates. Intelligent micro/nanorobots based on biotemplates are a perfect combination of natural biotemplates and micro/nanotechnology, which is an important trend for the future development of micro/nanorobots. We hope this review can provide useful references for developing more intelligent, efficient and safe micro/nanorobots in the future.

Boosting the Efficiency of Photoactive Rod-Shaped Nanomotors via Magnetic Field-Induced Charge Separation

Photocatalytic nanomotors have attracted a lot of attention because of their unique capacity to simultaneously convert light and chemical energy into mechanical motion with a fast photoresponse. Recent discoveries demonstrate that the integration of optical and magnetic components within a single nanomotor platform offers novel advantages for precise motion control and enhanced photocatalytic performance. Despite these advancements, the impact of magnetic fields on energy transfer dynamics in photocatalytic nanomotors remains unexplored. Here, we introduce dual-responsive rod-like nanomotors, made of a TiO2/NiFe heterojunction, able to (i) self-propel upon irradiation, (ii) align with the direction of an external magnetic field, and (iii) exhibit enhanced photocatalytic performance. Consequently, when combining light irradiation with a homogeneous magnetic field, these nanomotors exhibit increased velocities attributed to their improved photoactivity. As a proof-of-concept, we investigated the ability of these nanomotors to generate phenol, a valuable chemical feedstock, from benzene under combined optical and magnetic fields. Remarkably, the application of an external magnetic field led to a 100% increase in the photocatalytic phenol generation in comparison with light activation alone. By using various state-of-the-art techniques such as photoelectrochemistry, electrochemical impedance spectroscopy, photoluminescence, and electron paramagnetic resonance, we characterized the charge transfer between the semiconductor and the alloy component, revealing that the magnetic field significantly improved charge pair separation and enhanced hydroxyl radical generation. Consequently, our work provides valuable insights into the role of magnetic fields in the mechanisms of light-driven photocatalytic nanomotors for designing more effective light-driven nanodevices for selective oxidations.

Active control of equilibrium, near-equilibrium, and far-from-equilibrium colloidal systems

The development of top-down active control over bottom-up colloidal assembly processes has the potential to produce materials, surfaces, and objects with applications in a wide range of fields spanning from computing to materials science to biomedical engineering. In this review, we summarize recent progress in the field using a taxonomy based on how active control is used to guide assembly. We find there are three distinct scenarios: (1) navigating kinetic pathways to reach a desirable equilibrium state, (2) the creation of a desirable metastable, kinetically trapped, or kinetically arrested state, and (3) the creation of a desirable far-from-equilibrium state through continuous energy input. We review seminal works within this framework, provide a summary of important application areas, and present a brief introduction to the fundamental concepts of control theory that are necessary for the soft materials community to understand this literature. In addition, we outline current and potential future applications of actively-controlled colloidal systems, and we highlight important open questions and future directions.

Micro-Nano Motors with Taxis Behavior: Principles, Designs, and Biomedical Applications

As a novel mobile nanodevice, micro-nano motors (MNMs) can convert the energy of the surrounding environment into mechanical motion. With this unique ability, they promise revolutionary potential in bio-applications including precise drug delivery, bio-sensing, and noninvasive surgery. Yet for practically reaching the target and fulfilling these tasks in dynamically changing bio-environment, environment adaptivity beyond propulsion is important yet challenging. MNMs with taxis behavior/autonomous target-seeking ability offer a desirable solution. These motors can adaptively move to the target location and complete the task. Thanks to the persistent efforts of researchers, tactic MNMs have shown automatic navigation to target under various energy fields, not only in static environments, but also in shear rheological conditions that simulate blood flow. Therefore, tactic motors with self-targeting capability lay a concrete foundation for targeted drug delivery, cell transplantation, and thrombus ablation. This review systematically presents the moving principle, design, and biological applications of tactic MNMs under different energy fields. Through in-depth analysis of state-of-art progress, the obstacles of the field and possible solutions are discussed. With the continuous innovation and breakthroughs of multi-disciplinary researchers, MNMs with taxis behavior are expected to provide a revolutionary solution for cancer and other major diseases in the biomedical field.

Construction of Nanomotors with Replaceable Engines by Supramolecular Machine-Based Host-Guest Assembly and Disassembly

Micro/nanomotors (MNMs) are miniaturized devices capable of performing self-propelled motion and on-demand tasks, which have brought revolutionary renovations in nanomedicine, environmental remediation, biochemical sensing, etc. Numerous methods of either chemical synthesis or physical fabrications have been extensively investigated to prepare MNMs of various shapes and functions. However, MNMs with replaceable engines that can be flexibly assembled and disassembled, resembling that of a macroscopic machine, have not been achieved. Here, for the first time, we report a demonstration of control over the engine replacement of self-propelled nanomotors based on hollow mesoporous silica nanoparticles (HMSNPs) via supramolecular machine-based host-guest assembly and disassembly between azobenzene (Azo) and β-cyclodextrin (β-CD). Nanomotors with different driving mechanisms can be rapidly constructed by selecting corresponding β-CD-modified nanoengines of urease, Pt, or Fe₃O₄, to assemble with the azobenzene-modified HMSNPs (HMSNPs-Azo). In virtue of photoresponsive cis/trans isomer conversion of azobenzene molecules, engine switching can be accomplished by remote light triggered host-guest assembly or disassembly between HMSNPs-Azo and β-CD-modified engines. Moreover, this method can quickly include multiple engines on the surface of the HMSNPs-Azo to prepare a hybrid MNM with enhanced motion capability. This strategy not only is cost-effective for the rapid and convenient preparation of nanomotors with different propulsion mechanism but also paves a new path to future multiple functionalization of MNMs for on-demand task assignment.

Catalytic/magnetic assemblies of rolled-up tubular nanomembrane-based micromotors

Nano/-micromotors self-assembling into static and dynamic clusters are of considerable promise to study smart, interactive, responsive, and adaptive nano/-micromaterials that can mimic spatio-temporal patterns, swarming, and collective behaviors widely observed in nature. Previously, the dynamic self-assembly of bubble-propelled catalytic micromotors initiated by capillary forces has been reported. This manuscript shows novel self-assembly modes of magnetic/catalytic Ti/FeNi/Pt tubular micromotors. When chemical fuel (hydrogen peroxide) is added it is decomposed on contact with Pt catalyst into oxygen and water. Here, the non-bubbling motion and autonomous assembly of catalytic/magnetic nanomembranes, i.e. without nucleation/generation of oxygen bubbles, are shown. Moreover, magnetic Ti/FeNi/Pt micromotors are spun using an external magnetic field and they form dynamic clusters balanced by attractive magnetic and repulsive hydrodynamic interactions. Micromotors form dynamic clusters, undergo precession and rapidly propagate through the solution.

Ti/FeNi/Pt tubular micromotors self-assemble into static and dynamic clusters during catalytic decomposition of hydrogen peroxide and using an external rotational magnetic field.

Spatial control over catalyst positioning on biodegradable polymeric nanomotors

Scientists over the world are inspired by biological nanomotors and try to mimic these complex structures. In recent years multiple nanomotors have been created for various fields, such as biomedical applications or environmental remediation, which require a different design both in terms of size and shape, as well as material properties. So far, only relatively simple designs for synthetic nanomotors have been reported. Herein, we report an approach to create biodegradable polymeric nanomotors with a multivalent design. PEG-PDLLA (poly(ethylene glycol)-b-poly(D,L-lactide)) stomatocytes with azide handles were created that were selectively reduced on the outside surface by TCEP (tris(2-carboxyethyl)phosphine) functionalized beads. Thereby, two different functional handles were created, both on the inner and outer surface of the stomatocytes, providing spatial control for catalyst positioning. Enzymes were coupled on the inside of the stomatocyte to induce motion in the presence of fuel, while fluorophores and other molecules can be attached on the outside.