Light, as an external stimulus, is capable of driving the motion of micro/nanomotors (MNMs) with the advantages of reversible, wireless and remote manoeuvre on demand with excellent spatial and temporal resolution This review focuses on the state-of-the-art light-driven MNMs, which are able to move in liquids or on a substrate surface by converting light energy into mechanical work The general design strategies for constructing asymmetric fields around light-driven MNMs to propel themselves are introduced as well as the photoactive materials for light-driven MNMs, including photocatalytic materials, photothermal materials and photochromic materials Then, the propulsion mechanisms and motion behaviors of the so far developed light-driven MNMs are illustrated in detail involving light-induced phoretic propulsion, bubble recoil and interfacial tension gradient, followed by recent progress in the light-driven movement of liquid crystalline elastomers based on light-induced deformation An outlook is further presented on the future development of light-driven MNMs towards overcoming key challenges after summarizing the potential applications in biomedical, environmental and micro/nanoengineering fields

Light-driven micro/nanomotors: from fundamentals to applications.

Directed motion at the nanoscale is a central attribute of life, and chemically driven motor proteins are nature’s choice to accomplish it. Motivated and inspired by such bionanodevices, in the pas...

Photo- and Redox-Driven Artificial Molecular Motors

Precise control over molecular movement is of fundamental and practical importance in physics, biology, and chemistry. At nanoscale, the peculiar functioning principles and the synthesis of individual molecular actuators and machines has been the subject of intense investigations and debates over the past 60 years. In this review, we focus on the design of collective motions that are achieved by integrating, in space and time, several or many of these individual mechanical units together. In particular, we provide an in-depth look at the intermolecular couplings used to physically connect a number of artificial mechanically active molecular units such as photochromic molecular switches, nanomachines based on mechanical bonds, molecular rotors, and light-powered rotary motors. We highlight the various functioning principles that can lead to their collective motion at various length scales. We also emphasize how their synchronized, or desynchronized, mechanical behavior can lead to emerging functional properties and to their implementation into new active devices and materials.

Design of Collective Motions from Synthetic Molecular Switches, Rotors, and Motors

Manipulation and navigation of micro and nanoswimmers in different fluid environments can be achieved by chemicals, external fields, or even motile cells Many researchers have selected magnetic fields as the active external actuation source based on the advantageous features of this actuation strategy such as remote and spatiotemporal control, fuel-free, high degree of reconfigurability, programmability, recyclability, and versatility This review introduces fundamental concepts and advantages of magnetic micro/nanorobots (termed here as "MagRobots") as well as basic knowledge of magnetic fields and magnetic materials, setups for magnetic manipulation, magnetic field configurations, and symmetry-breaking strategies for effective movement These concepts are discussed to describe the interactions between micro/nanorobots and magnetic fields Actuation mechanisms of flagella-inspired MagRobots (ie, corkscrew-like motion and traveling-wave locomotion/ciliary stroke motion) and surface walkers (ie, surface-assisted motion), applications of magnetic fields in other propulsion approaches, and magnetic stimulation of micro/nanorobots beyond motion are provided followed by fabrication techniques for (quasi-)spherical, helical, flexible, wire-like, and biohybrid MagRobots Applications of MagRobots in targeted drug/gene delivery, cell manipulation, minimally invasive surgery, biopsy, biofilm disruption/eradication, imaging-guided delivery/therapy/surgery, pollution removal for environmental remediation, and (bio)sensing are also reviewed Finally, current challenges and future perspectives for the development of magnetically powered miniaturized motors are discussed

Magnetically Driven Micro and Nanorobots

Advances in medical robots promise to improve modern medicine and the quality of life. Miniaturization of these robotic platforms has led to numerous applications that leverages precision medicine. In this review, the current trends of medical micro and nanorobotics for therapy, surgery, diagnosis, and medical imaging are discussed. The use of micro and nanorobots in precision medicine still faces technical, regulatory, and market challenges for their widespread use in clinical settings. Nevertheless, recent translations from proof of concept to in vivo studies demonstrate their potential toward precision medicine.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/advs.202002203

Medical Micro/Nanorobots in Precision Medicine.

Stimuli-responsive hydrogel actuators have promising applications in various fields. However, the typical hydrogel actuation relies on the swelling and de-swelling process caused by osmotic-pressure changes, which is slow and normally requires the presence of water environment. Herein, we report a light-powered in-air hydrogel actuator with remarkable performances, including ultrafast motion speed (up to 1.6 m/s), rapid response (as fast as 800 ms) and high jumping height (~15 cm). The hydrogel is operated based on a fundamentally different mechanism that harnesses the synergetic interactions between the binary constituent parts, i.e. the elasticity of the poly(sodium acrylate) hydrogel, and the bubble caused by the photothermal effect of the embedded magnetic iron oxide nanoparticles. The current hydrogel actuator exhibits controlled motion velocity and direction, making it promising for a wide range of mobile robotics, soft robotics, sensors, controlled drug delivery and other miniature device applications. Actuation of hydrogel actuators relies on slow swelling and de-swelling process which hampers its application in many fields. Here the authors report a light-powered in-air hydrogel actuator with remarkable performances including fast motion, speed and rapid response time.

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In-air fast response and high speed jumping and rolling of a light-driven hydrogel actuator.

Bismuth oxychloride (BiOCl) was synthesized by a simple combustion method. The structures, morphologies, absorbance, optical, and photocatalytic properties of the samples were studied by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, ultraviolet–visible spectrophotometry, and photoluminescence. The experimental results show that BiOCl microsheet with high percentage of exposed {001} facets was obtained. It is interesting to note that the thickness of BiOCl sheets, in other words, the percentage of exposed {001} facets can be modulated through changing the added amount of ammonium chloride. The sample with the thinnest BiOCl sheets shows the best photodegradation performance of Rhodamine B under ultraviolet light irradiation, which can be attributed to the cooperative effect between the high percentage of exposed {001} facets and high-specific surface area. Moreover, the corresponding influencing mechanism on the percentage of exposed {001} facets of BiOCl was discussed.

Combustion Synthesis of BiOCl with Tunable Percentage of Exposed {001} Facets and Enhanced Photocatalytic Properties

Smart actuators have recently been widely studied due to their potential applications in the fields of wearable devices, artificial muscles and microrobots. However, it is still challenging to develop smart actuators with a fast response time, large deformation, multi-stimuli response ability and programmable shape-changing capability. Here, we report a novel smart actuator, which consists of polypyrrole and agar. Due to the water absorbing ability, the photothermal effect and the protonation behavior originating from polypyrrole and agar, the resulting actuator is responsive to a variety of stimuli, including humidity, light, temperature, HCl and NH3 gas. In addition, the actuator exhibits fast responsiveness, controllable actuation and large bending. Interestingly, two external stimuli can be combined to activate the actuator, leading to continuous shape changes in a programmable fashion. Multi-stimuli responsive actuators have opened up great opportunities in a variety of applications. As a proof-of-concept, we have demonstrated their application as a walking device with cargo transportation and delivery capabilities.

A multi-responsive bidirectional bending actuator based on polypyrrole and agar nanocomposites

In this paper, we report a fish-like enzymeless motor, which consists of a phenylboronic acid modified poly(N-isopropylacrylamide) hydrogel and a surfactant, i.e. sodium dodecyl sulfate. The motor is capable of moving autonomously upon exposure to the glucose molecule. This phenomenon originates from the complexation between glucose and phenylboronic acid, which leads to the swelling of the hydrogel and the release of the surfactant, thus propelling the whole structure based on the Marangoni effect. Interestingly, the motor's moving velocity is directly proportional to the glucose concentration. Through the introduction of a magnetically responsive material, the motion direction of the motor can be manipulated. More interestingly, the combination of the glucose-dependent motion and magnetically steerable motion allows us to directly visualize the glucose concentration in human serum or urine. We thus believe that the motor reported in the current study may have potential for application in the field of glucose sensing for the detection and monitoring of diabetes.

Motion-based glucose sensing based on a fish-like enzymeless motor

In this paper, we report a novel multi-responsive walnut-like micromotor consisting of polycaprolactone (PCL), iron oxide nanoparticles (Fe3O4 NPs), and catalase, which is constructed through a one-step electrospinning method. Based on the catalytic activity and photothermal and magnetic responsiveness originating from catalase and Fe3O4 NPs, respectively, the resulting micromotor exhibits an autonomous movement in the presence of hydrogen peroxide (H2O2) fuel, controlled motion velocity under light irradiation, and guided movement direction upon the application of an external magnetic field. Owing to the hydrophobic nature of the PCL polymer constituent inside the micromotor, the autonomous moving micromotor can collect spilled oil inside a solution once it collides with the oil droplet. Since the micromotor could be separated out using a magnetic field, we believe the current walnut-like micromotor holds great promise in the field of environmental remediation.

Mingtong Li

Papers

In-air fast response and high speed jumping and rolling of a light-driven hydrogel actuator.

Combustion Synthesis of BiOCl with Tunable Percentage of Exposed {001} Facets and Enhanced Photocatalytic Properties

A multi-responsive bidirectional bending actuator based on polypyrrole and agar nanocomposites

Motion-based glucose sensing based on a fish-like enzymeless motor

One-Step Fabrication of Dual Optically/Magnetically Modulated Walnut-like Micromotor.