Bioinspired Chemical Communication between Synthetic Nanomotors

While chemical communication plays a key role in diverse natural processes, the intelligent chemical communication between synthetic nanomotors remains unexplored. The design and operation of bioinspired synthetic nanomotors is presented. Chemical communication between nanomotors is possible and has an influence on propulsion behavior. A chemical “message” is sent from a moving activator motor to a nearby activated (receiver) motor by release of Ag⁺ ions from a Janus polystyrene/Ni/Au/Ag activator motor to the activated Janus SiO₂/Pt nanomotor. The transmitted silver signal is translated rapidly into a dramatic speed change associated with the enhanced catalytic activity of activated motors. Selective and successive activation of multiple nanomotors is achieved by sequential localized chemical communications. The concept of establishing chemical communication between different synthetic nanomotors paves the way to intelligent nanoscale robotic systems that are capable of cooperating with each other.     

Fuel‐Free Micro‐/Nanomotors as Intelligent Therapeutic Agents

There are many efficient biological motors in Nature that perform complex functions by converting chemical energy into mechanical motion. Inspired by this, the development of their synthetic counterparts has aroused tremendous research interest in the past decade. Among these man‐made motor systems, the fuel‐free (or light, magnet, ultrasound, or electric field driven) motors are advantageous in terms of controllability, lifespan, and biocompatibility concerning bioapplications, when compared with their chemically powered counterparts. Therefore, this review will highlight the latest biomedical applications in the versatile field of externally propelled micro‐/nanomotors, as well as elucidating their driving mechanisms. A perspective into the future of the micro‐/nanomotors field and a discussion of the challenges we need to face along the road towards practical clinical translation of external‐field‐propelled micro‐/nanomotors will be provided.     

Self‐Propelled Nanomotors for Thermomechanically Percolating Cell Membranes

We report a near‐infrared (NIR) light‐powered Janus mesoporous silica nanomotor (JMSNM) with macrophage cell membrane (MPCM) cloaking that can actively seek cancer cells and thermomechanically percolate cell membrane. Upon exposure to NIR light, a heat gradient across the Janus boundary of the JMSNMs is generated by the photothermal effect of the Au half‐shells, resulting in a self‐thermophoretic force that propels the JMSNMs. In biological medium, the MPCM camouflaging can not only prevent dissociative biological blocks from adhering to JMSNMs but also improve the seeking sensitivity of the nanomotors by specifically recognizing cancer cells. The biofriendly propulsion and recognition capability enable JMSNMs to achieve the active seeking and bind to the membrane of cancer cells. Subsequent illumination with NIR then triggers the photothermal effect of MPCM@JMSNMs to thermomechanically perforate the cytomembranes for guest molecular injection. This approach integrates the functions of active seeking, cytomembranes perforating, and thermomechanical therapy in nanomotors, which may pave the way to apply self‐propelled motors in biomedical fields.     

Fantastic voyage: designing self-powered nanorobots

The use of swarms of nanobots to perform seemingly miraculous tasks is a common trope in the annals of science fiction.1 Although several of these remarkable feats are still very much in the realm of fiction, scientists have recently overcome many of the physical challenges associated with operating on the small scale and have generated the first generation of autonomous self-powered nanomotors and pumps. The motors can be directed by chemical and light gradients, pick up and deliver cargo, and exhibit collective behavior.     

Cargo-towing synthetic nanomachines: towards active transport in microchip devices

This review article discusses the use of synthetic catalytic nano motors for cargo manipulations and for developing miniaturized lab-on-chip systems based on autonomous transport. The ability of using chemically-powered artificial nanomotors to capture, transport and release therapeutic payloads or nanostructured biomaterials represents one of the next major prospects for nanomotor development. The increased cargo-towing force of such self-propelled nanomotors, along with their precise motion control within microchannel networks, versatility and facile functionalization, pave the way to new integrated functional lab-on-a-chip powered by active transport and perform a series of tasks. Such use of cargo-towing artificial nanomotors has been inspired by on-chip kinesin molecular shuttles. Functionalized nano/microscale motors can thus be used to pick a selected nano/microscale chemical or biological payload target at the right place, transport and deliver them to a target location in a timely manner. Key challenges for using synthetic nanomachines for driving transport processes along microchannel networks are discussed, including loading and unloading of cargo and precise motion control, along with recent examples of related cargo manipulation processes and guided transport in lab-on-a-chip formats. The exciting research area of cargo-carrying catalytic man-made nanomachines is expected to grow rapidly, to lead to new lab-on-a-chip formats and to provide a wide range of future microchip opportunities.     

Supramolecular colloidal motors via chemical self-assembly

A colloidal motor can convert energy stored in the environment to achieve mechanical motion and exhibit dynamic behaviors in fluids. To overcome the challenges presented to a colloidal motor, controlled molecular self-assembly technology provides new opportunities for the precise fabrication of various nanoarchitectures and facilitates fundamental research on rational design, multifunctionalization, propulsion, and controlled movement of colloidal motors. These molecular assembled colloidal motors, also called supramolecular colloidal motors, can perform special tasks at the micro- and nanoscale in the fields of biomedicine, nanotechnology, and environmental remediation. In this feature article, we first introduce the recent progress of controllable self-assembly of spatially asymmetric supramolecular colloidal motors with variable sizes, structures, and functions and discuss the relationship between structure and propulsion. Next, we review the research progress of this type of colloidal motors in biomedical and environmental fields. Finally, we propose the challenges of the supramolecular colloidal motors and future development direction.     

Self‐Propelled Janus Mesoporous Silica Nanomotors with Sub‐100 nm Diameters for Drug Encapsulation and Delivery

The synthesis of an innovative self‐propelled Janus nanomotor with a diameter of about 75 nm that can be used as a drug carrier is described. The Janus nanomotor is based on mesoporous silica nanoparticles (MSNs) with chromium/platinum metallic caps and propelled by decomposing hydrogen peroxide to generate oxygen as a driving force with speeds up to 20.2 μm s^?1 (about 267 body lengths per second). The diffusion coefficient (D) of nanomotors with different H₂O₂ concentrations is calculated by tracking the movement of individual particles recorded by means of a self‐assembled fluorescence microscope and is significantly larger than free Brownian motion. The traction of a single Janus MSN nanomotor is estimated to be about 13.47×10^?15 N. Finally, intracellular localization and drug release in vitro shows that the amount of Janus MSN nanomotors entering the cells is more than MSNs with same culture time and particle concentrations, meanwhile anticancer drug doxorubicin hydrochloride loaded in Janus MSNs can be slowly released by biodegradation of lipid bilayers in cells.     

Tunable DNA Origami Motors Translocate Ballistically Over μm Distances at nm/s Speeds

Inspired by biological motor proteins, that efficiently convert chemical fuel to unidirectional motion, there has been considerable interest in developing synthetic analogues. Among the synthetic motors created thus far, DNA motors that undertake discrete steps on RNA tracks have shown the greatest promise. Nonetheless, DNA nanomotors lack intrinsic directionality, are low speed and take a limited number of steps prior to stalling or dissociation. Herein, we report the first example of a highly tunable DNA origami motor that moves linearly over micron distances at an average speed of 40 nm/min. Importantly, nanomotors move unidirectionally without intervention through an external force field or a patterned track. Because DNA origami enables precise testing of nanoscale structure-function relationships, we were able to experimentally study the role of motor shape, chassis flexibility, leg distribution, and total number of legs in tuning performance. An anisotropic rigid chassis coupled with a high density of legs maximizes nanomotor speed and endurance.     

Tunable DNA Origami Motors Translocate Ballistically Over μm Distances at nm/s Speeds

Inspired by biological motor proteins, that efficiently convert chemical fuel to unidirectional motion, there has been considerable interest in developing synthetic analogues. Among the synthetic motors created thus far, DNA motors that undertake discrete steps on RNA tracks have shown the greatest promise. Nonetheless, DNA nanomotors lack intrinsic directionality, are low speed and take a limited number of steps prior to stalling or dissociation. Herein, we report the first example of a highly tunable DNA origami motor that moves linearly over micron distances at an average speed of 40 nm/min. Importantly, nanomotors move unidirectionally without intervention through an external force field or a patterned track. Because DNA origami enables precise testing of nanoscale structure‐function relationships, we were able to experimentally study the role of motor shape, chassis flexibility, leg distribution, and total number of legs in tuning performance. An anisotropic rigid chassis coupled with a high density of legs maximizes nanomotor speed and endurance.     

Core@Satellite Janus Nanomotors with pH-Responsive Multi-phoretic Propulsion

We report core@satellite Janus mesoporous silica-Pt@Au (JMPA) nanomotors with pH-responsive multi-phoretic propulsion. The JMPA nanomotors first undergo self-diffusiophoretic propulsion in 3.0 % H₂O₂ due to the isolation of the Au nanoparticles (AuNPs) from the PtNPs layer. Then the weak acidity of H₂O₂ can trigger the disassembly and reassembly of the AuNPs, resulting in the Janus distribution of large AuNPs aggregates. Such reconstruction of JMPA leads to the contact between PtNPs and AuNPs aggregates, thus changing the propulsion mechanism to self-electrophoresis. The asymmetric and aggregated AuNPs also enable the generation of a thermal gradient under laser irradiation, which propels the JMPA nanomotors by self-thermophoresis. Such multi-phoretic propulsion offers considerable promise for developing advanced nanomachines with a stimuli-responsive switch of propulsion modes in biomedical applications.     

Thermoresponsive Polymer Brush Modulation on the Direction of Motion of Phoretically Driven Janus Micromotors

We report a thermoresponsive poly(N‐isopropylacrylamide) (PNIPAM) brush functionalized Janus Au–Pt bimetallic micromotor capable of modulating the direction of motion with the change of the ambient temperature. The PNIPAM@Au–Pt micromotor moved along the Au–Pt direction with a speed of 8.5 μm s^?1 in 1.5 % H₂O₂ at 25 °C (below the lower critical solution temperature (LCST) of PNIPAM), whereas it changed the direction of motion (i.e., along the Pt–Au direction) and the speed decreased to 2.3 μm s^?1 at 35 °C (above LCST). Below LCST, PNIPAM brushes grafted on the Au side were hydrophilic and swelled, which permitted the electron transfer and proton diffusion on the Au side, and thus the motion is regarded as a self‐electrophoretic mechanism. However, PNIPAM brushes above LCST became hydrophobic and collapsed, and thus the driving mechanism switched to the self‐diffusiophoresis like that of Pt‐modified Janus silica motors. These motors could reversibly change the direction of motion with the transition of the hydrophobic and hydrophilic states of the grafted PNIPAM brushes. Such a thermoresponsive polymer brush functionalization method provides a new strategy for engineering the kinematic behavior of phoretically driven micro/nanomotors.     

Core@Satellite Janus Nanomotors with pH‐Responsive Multi‐phoretic Propulsion

We report core@satellite Janus mesoporous silica‐Pt@Au (JMPA) nanomotors with pH‐responsive multi‐phoretic propulsion. The JMPA nanomotors first undergo self‐diffusiophoretic propulsion in 3.0 % H₂O₂ due to the isolation of the Au nanoparticles (AuNPs) from the PtNPs layer. Then the weak acidity of H₂O₂ can trigger the disassembly and reassembly of the AuNPs, resulting in the Janus distribution of large AuNPs aggregates. Such reconstruction of JMPA leads to the contact between PtNPs and AuNPs aggregates, thus changing the propulsion mechanism to self‐electrophoresis. The asymmetric and aggregated AuNPs also enable the generation of a thermal gradient under laser irradiation, which propels the JMPA nanomotors by self‐thermophoresis. Such multi‐phoretic propulsion offers considerable promise for developing advanced nanomachines with a stimuli‐responsive switch of propulsion modes in biomedical applications.     

Motion Control of Polymeric Nanomotors Based on Host–Guest Interactions

Controlling the motion of artificial self‐propelled micro‐ and nanomotors independent of the fuel concentration is still a great challenge. Here we describe the first report of speed manipulation of supramolecular nanomotors via blue light‐responsive valves, which can regulate the access of hydrogen peroxide fuel into the motors. Light‐sensitive polymeric nanomotors are built up via the self‐assembly of functional block copolymers, followed by bowl‐shaped stomatocyte formation and incorporation of platinum nanoparticles. Subsequent addition of β‐cyclodextrin (β‐CD) leads to the formation of inclusion complexes with the trans‐isomers of the azobenzene derivatives grafted from the surfaces of the stomatocytes. β‐CDs attachment decreases the diffusion rate of hydrogen peroxide into the cavities of the motors because of partly blocking of the openings of the stomatocyte. This results in a lowering of the speed of the nanomotors. Upon blue light irradiation, the trans‐azobenzene moieties isomerize to the cis‐form, which lead to the detachment of the β‐CDs due to their inability to form complexes with the cis‐isomer. As a result, the speed of the nanomotors increases accordingly. Such a conformational change provides us with the unique possibility to control the speed of the supramolecular nanomotor via light‐responsive host–guest complexation. We envision that such artificial responsive nano‐systems with controlled motion could have potential applications in drug delivery.     

Continuously Variable Regulation of the Speed of Bubble‐Propelled Janus Microcapsule Motors Based on Salt‐Responsive Polyelectrolyte Brushes

The engineering of self‐propelled micro‐/nanomotors (MNMs) with continuously variable speeds, akin to macroscopic automobiles equipped with a continuously variable transmission, is still a huge challenge. Herein, after grafting with salt‐responsive poly[2‐(methacryloyloxy)ethyltrimethylammonium chloride] (PMETAC) brushes, bubble‐propelled Janus microcapsule motors with polyelectrolyte multilayers exhibited adjustable speeds when the type and concentration of the counterion was changed. Reversible switching between low‐ and high‐speed states was achieved by modulating the PMETAC brushes between hydrophobic and hydrophilic configurations by ion exchange with ClO₄^? and polyphosphate anions. This continuously variable regulation enabled control of the speed in an accurate and predictable manner and an autonomous response to the local chemical environment. This study suggests that the integration of polymer brushes with precisely adjustable responsiveness offers a promising route for motion control of smart MNMs that act like their counterparts in living systems.     

Biocatalytic Micro- and Nanomotors

Enzyme-powered micro- and nanomotors are tiny devices inspired by nature that utilize enzyme-triggered chemical conversion to release energy stored in the chemical bonds of a substrate (fuel) to actuate it into active motion. Compared with conventional chemical micro-/nanomotors, these devices are particularly attractive because they self-propel by utilizing biocompatible fuels, such as glucose, urea, glycerides, and peptides. They have been designed with functional material constituents to efficiently perform tasks related to active targeting, drug delivery and release, biosensing, water remediation, and environmental monitoring. Because only a small number of enzymes have been exploited as bioengines to date, a new generation of multifunctional, enzyme-powered nanorobots will emerge in the near future to selectively search for and utilize water contaminants or disease-related metabolites as fuels. This Minireview highlights recent progress in enzyme-powered micro- and nanomachines.     

Enzyme-powered micro- and nano-motors: key parameters for an application-oriented design

Nature has inspired the creation of artificial micro- and nanomotors that self-propel converting chemical energy into mechanical action. These tiny machines have appeared as promising biomedical tools for treatment and diagnosis and have also been used for environmental, antimicrobial or sensing applications. Among the possible catalytic engines, enzymes have emerged as an alternative to inorganic catalysts due to their biocompatibility and the variety and bioavailability of fuels. Although the field of enzyme-powered micro- and nano-motors has a trajectory of more than a decade, a comprehensive framework on how to rationally design, control and optimize their motion is still missing. With this purpose, herein we performed a thorough bibliographic study on the key parameters governing the propulsion of these enzyme-powered devices, namely the chassis shape, the material composition, the motor size, the enzyme type, the method used to incorporate enzymes, the distribution of the product released, the motion mechanism, the motion media and the technique used for motion detection. In conclusion, from the library of options that each parameter offers there needs to be a rational selection and intelligent design of enzymatic motors based on the specific application envisioned.

Nature has inspired the creation of artificial micro- and nano-motors that self-propel converting chemical energy into mechanical action.     

Enhancing the stability of kinesin motors for microscale transport applications

Biomolecular motors, such as kinesins, have great potential for micro-actuation and micro- or nanoscale active transport when integrated into microscale devices. However, the stability and limited shelf life of these motor proteins and their associated protein filaments is a barrier to their implementation. Here we demonstrate that freeze-drying or critical point-drying kinesins adsorbed to glass surfaces extends their lifetime from days to more than four months. Further, photoresist deposition and removal can be carried out on these motor-adsorbed surfaces without loss of motor function. The methods developed here are an important step towards realizing the integration of biological motors into practical devices, and these approaches can be extended to patterning and preserving other proteins immobilized on surfaces.     

Catalysis‐Driven Self‐Thermophoresis of Janus Plasmonic Nanomotors

It is highly demanding to design active nanomotors that can move in response to specific signals with controllable rate and direction. A catalysis‐driven nanomotor was constructed by designing catalytically and plasmonically active Janus gold nanoparticles (Au NPs), which generate an asymmetric temperature gradient of local solvent surrounding NPs in catalytic reactions. The self‐thermophoresis behavior of the Janus nanomotor is monitored from its inherent plasmonic response. The diffusion coefficient of the self‐thermophoresis motion is linearly dependent on chemical reaction rate, as described by a stochastic model.     

面向疾病应用的微纳米马达

微纳米马达是能将环境中的化学反应或外场(光、声、磁场、电场等)提供的能量转化为推进力,从而产生自主运动的微纳米级人造机器。由于具有集群效应、比表面积大、运动可控等多种特征,微纳米马达在环境修复、药物递送、微纳手术、抗感染、重金属清除等诸多领域受到关注。在一定条件下,微纳米马达能主动运动并聚集到病灶,将治疗或诊断药物递送到靶部位,有望在人体复杂环境中进行精细化的工作。因此,微纳米马达在疾病预防、诊断、治疗以及预后中具有巨大的发展空间。在此,本综述首先对微纳米马达进行简要介绍,包括其结构设计、驱动方式。其次,详细介绍微纳米马达在不同类型的疾病中的研究进展。最后,提出目前该技术面临的挑战与未来发展方向。     

Strictly Biphasic Soft and Hard Janus Structures: Synthesis,Properties, and Applications

Janus structures, named after the ancient two‐faced Roman god Janus, comprise two hemistructures (e.g. hemispheres) with different compositions and functionalities. Much research has been carried out over the past few years on Janus structures because of the intriguing properties and promising potential applications of these unusually shaped materials. This Review discusses recent progress made in the synthesis, properties, and applications of strictly biphasic Janus structures possessing symmetrical structures but made of disparate materials. Depending on the chemical compositions, such biphasic structures can be categorized into soft, hard, and hybrid soft/hard Janus structures of different architectures, including spheres, rodlike, disclike, or any other shape. The main synthetic routes to soft, hard, and hybrid soft/hard Janus structures are summarized and their unique properties and applications are introduced. The perspectives for future research and development are also described.