Stimuli‐Responsive Microjets with Reconfigurable Shape

Flexible thermoresponsive polymeric microjets are formed by the self‐folding of polymeric layers containing a thin Pt film used as catalyst for self‐propulsion in solutions containing hydrogen peroxide. The flexible microjets can reversibly fold and unfold in an accurate manner by applying changes in temperature to the solution in which they are immersed. This effect allows microjets to rapidly start and stop multiple times by controlling the radius of curvature of the microjet. This work opens many possibilities in the field of artificial nanodevices, for fundamental studies on self‐propulsion at the microscale, and also for biorelated applications.     

Fusion-Induced Structural and Functional Evolution in Binary Emulsion Communities

The biomimetic dynamic behaviours of emulsions are receiving increasing attention from the broad scientific community; however, the spatiotemporal control and functionalization of emulsions based on simple fusion-induced method is rarely mentioned. A design for protein-stabilized oil-in-water droplets and phospholipid-stabilized oil-in-water droplets is described and a substance-diffusion-mediated fusion mechanism proposed within these two different emulsion communities. Significantly, a range of fusion-induced high-order behaviours were successfully demonstrated including competitive fusion, fusion-induced evolution in membrane complexity, and diversified structures with the formation of Janus or various patchy morphologies, fusion-induced membrane maturation, as well as fusion-induced multifunctionalization with a directional motility behaviour. These results highlight the fusion-induced diverse dynamic behaviours in complex emulsions communities and provide a platform for advancing versatile applications of emulsions.     

Reversible Speed Regulation of Self-Propelled Janus Micromotors via Thermoresponsive Bottle-Brush Polymers

This work reports a reversible braking system for micromotors that can be controlled by small temperature changes (≈5 °C). To achieve this, gated-mesoporous organosilica microparticles are internally loaded with metal catalysts (to form the motor) and the exterior (partially) grafted with thermosensitive bottle-brush polyphosphazenes to form Janus particles. When placed in an aqueous solution of H₂O₂ (the fuel), rapid forward propulsion of the motors ensues due to decomposition of the fuel. Conformational changes of the polymers at defined temperatures regulate the bubble formation rate and thus act as brakes with considerable deceleration/acceleration observed. As the components can be easily varied, this represents a versatile, modular platform for the exogenous velocity control of micromotors.     

Cargo Transportation and Methylene Blue Degradation by Using Fuel-Powered Micromotors

In the past two decades, micromotors have experienced rapid development, especially in environmental remediation, the biomedical field, and in cargo delivery. In this study micromotors have been synthesized from a variety of materials. Different functional layers and catalytic layers are formed through template electrodeposition (the bottom-up method). At the same time, the article analyzes the influence of hydrogen peroxide concentration, surfactant type and concentration on the speed of the micromotors. Cargo transportation through tubular micromotors has always been a problem that people are eager to solve. In this article, we electrodeposit a layer of Ni in the microtubes, which effectively guides the microtubular motors to complete the cargo transportation. The potential applications of micromotors are also being explored. We added the prepared micromotors to the methylene blue solution to effectively enhance the degradation.     

Graphdiyne Micromotors in Living Biomedia

Graphdiyne (GDY), a new kind of two-dimensional (2D) material, was combined with micromotor technology for “on-the-fly” operations in complex biomedia. Microtubular structures were prepared by template deposition on membrane templates, resulting in functional structures rich in sp and sp² carbons with highly conjugated π networks. This resulted in a highly increased surface area for a higher loading of anticancer drugs or enhanced quenching ability over other 2D based micromotors, such as graphene oxide (GO) or smooth tubular micromotors. High biocompatibility with almost 100 % cell viability was observed in cytotoxicity assays with moving micromotors in the presence of HeLa cells. On a first example, GDY micromotors loaded with doxorubicin (DOX) were used for pH responsive release and HeLa cancer cells killing. The use of affinity peptide engineered GDY micromotors was also illustrated for highly sensitive and selective fluorescent OFF–ON detection of cholera toxin B through specific recognition of the subunit B region of the target toxin. The new developments illustrated here offer considerable promise for the use of GDY as part of micromotors in living biosystems.     

Fusion‐Induced Structural and Functional Evolution in Binary Emulsion Communities

The biomimetic dynamic behaviours of emulsions are receiving increasing attention from the broad scientific community; however, the spatiotemporal control and functionalization of emulsions based on simple fusion‐induced method is rarely mentioned. A design for protein‐stabilized oil‐in‐water droplets and phospholipid‐stabilized oil‐in‐water droplets is described and a substance‐diffusion‐mediated fusion mechanism proposed within these two different emulsion communities. Significantly, a range of fusion‐induced high‐order behaviours were successfully demonstrated including competitive fusion, fusion‐induced evolution in membrane complexity, and diversified structures with the formation of Janus or various patchy morphologies, fusion‐induced membrane maturation, as well as fusion‐induced multifunctionalization with a directional motility behaviour. These results highlight the fusion‐induced diverse dynamic behaviours in complex emulsions communities and provide a platform for advancing versatile applications of emulsions.     

Micromotors from Microfluidics

Inspired by the motions of natural objects, attention and efforts have been paid and devoted to fabricate micromotors of spherical, tubular, helical or other shapes for applications in emerging fields including delivery, remediation, and other biomedical applications. Among the proposed methods, the microfluidic technology offers an opportunity to fabricate micromotors with different microstructures. This review presents research progress on micromotors, especially those from microfluidics. The morphologies of the micromotors were firstly outlined. Then, the microfluidic technology used to fabricate different micromotors was discussed. Finally, the applications of these micromotors were briefly introduced, followed by their challenges and future developments.     

Colloidal Motors 101: A Beginner's Guide to Colloidal Motor Research

The research progress in colloidal motors, synthetic colloids that convert environmental energy and swim in water, has attracted much attention in recent years. Yet, its rapid development and interdisciplinary nature has created a hurdle for beginners, especially students and postdocs. In light of this challenge, this tutorial review gives a bird's eye overview of the research field of colloidal motors, presenting in a beginner‐friendly manner subjects including the definition and significance of colloidal motors, physical challenges associated with their motion at the microscale, their fabrication and propulsion mechanisms, functionalities that enable their applications, and essential tools and techniques useful for beginners. Emphasis on each aspect is placed on elucidating and connecting important concepts and ideas, rather than on details and individual references. An appendix of recent review articles grouped by subjects on colloidal motors is given in the Supporting Information. This article equips beginners with a clear big picture and essential knowledge that will facilitate future explorations.     

Highly Acid‐Resistant,Magnetically Steerable Acoustic Micromotors Prepared by Coating Gold Microrods with Fe3O4 Nanoparticles via pH Adjustment

There is mounting interest in designing magnetically steerable nano‐ and micromotors for next generation medical nanorobotics, which requires biocompatibility for each individual component. Although various magnetic materials (e.g., Ni, Co, and Fe₃O₄) have been incorporated into micromotors, their acid resistance remains largely unexplored. In this article, a simple one‐step method to prepare magnetic microrods via electrostatic attraction between paramagnetic magnetite nanoparticles (Fe₃O₄ NPs) and gold microrods at appropriate pH values is reported. The as‐prepared Fe₃O₄‐coated micromotors can be powered by MHz ultrasound and easily steered by external magnetic fields, and perform well in harsh working conditions such as high acidity, high viscosity, and high ionic strength. In particular, extended exposure to solution of pH as low as 0.9 has a minimal effect on the speed, steerability, or cargo‐transporting capability of micromotors coated with Fe₃O₄ NPs, in stark contrast with those containing Ni segments. Considering the many challenges of biomedical applications, acid‐resistant, magnetically steerable Fe₃O₄‐coated micromotors powered by MHz ultrasound can be a promising prototype for the future development of medical nano‐ and microrobotics.     

Magnetic Fields Enhanced the Performance of Tubular Dichalcogenide Micromotors at Low Hydrogen Peroxide Levels

Propulsion at the microscale has attracted significant research interest. In this work, a numerical simulation to explain the speed boost of up to 34 % experienced by transition metal dichalcogenides (TMD) based micromotors under the effect of applied magnetic fields is described. The simulations show that, when an external magnetic field is applied, the flow regime changes from turbulent to laminar. This causes an increase in the residence time of the fuel over the catalyst surface, which enhances the oxygen production. The more efficient generation and growth of the bubbles lead to an increase of the capillary force exerted by them. Interestingly, the effect is more pronounced as the level of fuel decrease. The validity of the model is also proven by comparing both theoretical and experimental results. Interestingly, the speed enhancement in magnetic mode depends on geometrical factors only, as a similar phenomenon was observed in a variety of microjets with a variable surface roughness. The understanding of such phenomena will open new avenues for understanding and controlling the motion behavior of high-towing-force catalytic micromotors.