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Profiles of the hydrazine level and the motor speed within the motor droplet.: (A) Motor speeds at several radial distances from the center within the sample droplet after a one min exposure to the 20% hydrazine source droplet (the negative distance being closest to the source, and positive being furthest). Droplets (2.5 mm diameter, 1 μL) separated by 0.5 cm. (B) 3D simulated plot of the normalized hydrazine concentration within the sample droplet 1 min after exposure. (C) Normalized hydrazine concentration profile as a function of the radial position (ρ = r/R) within the sample droplet for different times after placing the hydrazine source: 0, 0.5, 1, 2.5, and 5 min (a–e).
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Chemically-powered micromotors offer exciting opportunities in diverse fields, including therapeutic delivery, environmental remediation, and nanoscale manufacturing. However, these nanovehicles require direct addition of high concentration of chemical fuel to the motor solution for their propulsion. We report the efficient vapor-powered propulsion...
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Context 1
... of hydrazine within the motor droplet is treated as a diffusion process within the hemisphere. We assume radial symmetry, which inherently captures the no-flux of hydrazine through the flat substrate, thus allowing us to solve the problem in spherical coordinates. The simulated hydrazine concentration profiles within the motor droplet, shown in Fig. 4(B,C) and SI Video 5, illustrate such decrease in the local hydrazine concentration from the droplet edges to the center. As time increases, the hydrazine concentration increases within the domain and asymptotically reaches the boundary concentration c m . Accordingly, motors closer to the motor-droplet boundary (ρ = r/R close to 1) are ...
Context 2
... concentration from the droplet edges to the center. As time increases, the hydrazine concentration increases within the domain and asymptotically reaches the boundary concentration c m . Accordingly, motors closer to the motor-droplet boundary (ρ = r/R close to 1) are expected to travel faster than those at the center. Overall, the data of Fig. 4A clearly illustrate that the partition of the fuel into the motor droplet, leads to distinct position-concentration dependent speed variations. In agreement with the theoretical predictions, we observed noticeably faster average motor speeds around the droplet edges compared to the center of the droplet (Fig. 4A). In addition, we found ...
Context 3
... at the center. Overall, the data of Fig. 4A clearly illustrate that the partition of the fuel into the motor droplet, leads to distinct position-concentration dependent speed variations. In agreement with the theoretical predictions, we observed noticeably faster average motor speeds around the droplet edges compared to the center of the droplet (Fig. 4A). In addition, we found that motors at equivalent radial distances moved at similar speeds over the range of experimental separation distances considered here. These experimental data are in good agreement with our model, where the hydrazine concentration immediately surrounding the small 2.5 mm droplet is assumed to be uniform on the ...
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Citations
... For instance, the ability of micromotors as a gas sensing platform was first demonstrated by Dong et al. using iridiumgold-based Janus microspheres to detect hydrazine vapor from the surrounding atmosphere. 99 Later, Liu et al. constructed metal-free noncorrosive hexagonal-shaped micromotors for the detection of HCl and NH 3 gas molecules with good precision and low detection limit. 58 They reported the preparation of a biodegradable polycaprolactone (PCL) and catalase (CAT)based fluorescent micromotor, which has the capacity to generate bubbles during propulsion in hydrogen peroxide solution and identify toxic gas molecules based on the change in their fluorescence signal. ...
The sensitive and rapid detection of a variety of hazardous environmental pollutants and bio-analytes such as microorganisms and biomolecules is of great importance for environmental and health care monitoring. Thus, significant progress has been made in the development of numerous sensor platforms for the quick and reliable sensitive detection of these analytes. However, most of the sensor platforms require complex technology, skillful personnel, prolonged operation, and laborious protocols, which limit their use worldwide, especially in low- and middle-income countries. Over the past few decades, the emergence and progress of nanotechnology have revolutionized the field of sensing. Particularly, the birth of self-propelled micro/nanomotors has become an area of interest in the current era owing to their versatility, ranging from environmental monitoring to biosensing. These are synthetic tiny multifunctional intelligent systems, capable of converting external energy such as light, magnetic field, ultrasound, electric field, and chemical fuel to kinetic energy and accomplishing tedious jobs. Among the external driving sources, chemically driven micromotors based on the bubble propulsion mechanism hold considerable promise in sensing on account of their greater propulsion rate, enhanced fluid mixing, and mass transfer. Employing this advantage, many leading research groups have focused on the fabrication of differently shaped bubble-propelled micromotors for the sensitive and selective detection of targets by functionalizing the motors with specific recognition units. In this review, we highlight the current progress in bubble-propelled micro/nanomotors for the detection of various environmental pollutants and bioanalytes such as microorganisms, cells, and biomolecules, and discuss their sensing mechanism. Finally, the challenges and limitations of these micromotors are presented together with their future direction.
... MCs have also been employed as efficient vaccine, antibiotic, and probiotic carriers. [19][20][21] In contrast to passive MCs, MMs can autonomously propel themselves in certain environments and perform various functions leading to delivery of pharmaceutical compounds, [22] degradation of nitroaromatic explosives [23] and organic pollutants, [24] protein disaggregation, [25] photothermal therapy, [26] pH sensing, [27] vapor sensing, [28] and warfare agent removal. [29] The dynamic behavior allows MMs to become more readily engulfed in mucus and biofilms. ...
In the case of macromolecules and poorly permeable drugs, oral drug delivery features low bioavailability and low absorption across the intestinal wall. Intestinal absorption can be improved if the drug formulation could be transported close to the epithelium. To achieve this, a cascade delivery device comprising Magnesium‐based Janus micromotors (MMs) nesting inside a microscale containers (MCs) has been conceptualized. The device aims at facilitating targeted drug delivery mediated by MMs that can lodge inside the intestinal mucosa. Loading MMs into MCs can potentially enhance drug absorption through increased proximity and unidirectional release. The MMs will be provided with optimal conditions for ejection into any residual mucus layer that the MCs have not penetrated. MMS confined inside MCs propel faster in the mucus environment as compared to non‐confined MMs. Upon contact with a suitable fuel, the MM‐loaded MC itself can also move. An in vitro study shows fast release profiles and linear motion properties in porcine intestinal mucus compared to more complex motion in aqueous media. The concept of dual‐acting cascade devices holds great potential in applications where proximity to epithelium and deep mucus penetration are needed.
... One cannot be 100% sure that a micromotor self-propels faster/slower than the other because of the local availability/unavailability of the targeted analyte or because of intrinsic, but yet not well understood, heterogeneity from batch to batch, or even within the same batch, in the properties of the individual micromotors (see also Section 2), or for various other reasons related to the experimental setup. For example, it has been observed that hydrazine-fueled micromotors propel faster at the edges of a water droplet than in the middle of it, immediately after the droplet is exposed to hydrazine vapors [25]; this is so because in that setup the hydrazine vapors reach the micromotors faster through the shallow edges of the water droplet [25]. (v). ...
... One cannot be 100% sure that a micromotor self-propels faster/slower than the other because of the local availability/unavailability of the targeted analyte or because of intrinsic, but yet not well understood, heterogeneity from batch to batch, or even within the same batch, in the properties of the individual micromotors (see also Section 2), or for various other reasons related to the experimental setup. For example, it has been observed that hydrazine-fueled micromotors propel faster at the edges of a water droplet than in the middle of it, immediately after the droplet is exposed to hydrazine vapors [25]; this is so because in that setup the hydrazine vapors reach the micromotors faster through the shallow edges of the water droplet [25]. (v). ...
... The fascinating details of these two mechanisms are nicely presented in a review by Moran and Posner [40]. Vapors from a 2.5 mm diameter droplet containing 5-30 % hydrazine induced self-propulsion of motors found in a second 2.5 mm diameter droplet (at 0.5-3 cm from the first); [25] Urea ~2 µm diameter hollow silica microcapsules modified with urease; Selfdiffusiophoresis; ...
Catalytic micromotors can be used to detect molecules of interest in several ways. The straightforward approach is to use such motors as sensors of their “fuel” (i.e., of the species consumed for self-propulsion). Another way is in the detection of species which are not fuel but still modulate the catalytic processes facilitating self-propulsion. Both of these require analysis of the motion of the micromotors because the speed (or the diffusion coefficient) of the micromotors is the analytical signal. Alternatively, catalytic micromotors can be used as the means to enhance mass transport, and thus increase the probability of specific recognition events in the sample. This latter approach is based on “classic” (e.g., electrochemical) analytical signals and does not require an analysis of the motion of the micromotors. Together with a discussion of the current limitations faced by sensing concepts based on the speed (or diffusion coefficient) of catalytic micromotors, we review the findings of the studies devoted to the analytical performances of catalytic micromotor sensors. We conclude that the qualitative (rather than quantitative) analysis of small samples, in resource poor environments, is the most promising niche for the catalytic micromotors in analytical chemistry.
... Micro-and nanorobots have shown characteristic behaviors, such as geotaxis (Boiteau & MacKinley, 2014), chemotaxis (Mei et al., 2011;Jurado-Sanchez et al., 2015;Xu et al., 2015;Xing et al., 2019;Mou et al., 2021), phonotaxis (Ding et al., 2012;Wang et al., 2014;Melde et al., 2016), magnetotaxis (Peyer, Zhang, & Nelson, 2013;Jurado-Sanchez et al., 2017;Jin et al., 2019;Xu et al., 2020), galvanotaxis (Klapper et al., 2010;Prusa & Cifra, 2019), phototaxis (Eelkema et al., 2006;Wu et al., 2014;Dai et al., 2016;Dai et al., 2016;Dong et al., 2016;Mou et al., 2016;Zhou et al., 2018;Mou et al., 2019), and thermotaxis (Cai et al., 2017;Zhu et al., 2020). They have been widely used in targeted drug delivery, cell manipulation and separation, and environmental remediation (Jang et al., 2014;Dong et al., 2015;Ma et al., 2016;Wang et al., 2016;Chang et al., 2019a;Chang et al., 2019b;Ramos-Docampo et al., 2019;Wu et al., 2019;Yin et al., 2019;Xie et al., 2020). Because of their autonomous propulsion and versatile functions, magnetically propelled micromotors present great potential in aqueous environments Lin et al., 2018;Wang et al., 2018;Yu et al., 2019;Ji et al., 2021). ...
In this study, we propose a highly efficient robot platform for pollutant adsorption. This robot system consists of a flapping-wing micro aircraft (FWMA) for long-distance transportation and delivery and cost-effective multifunctional Janus microrobots for pollutant purification. The flapping-wing micro air vehicle can hover for 11.3 km with a flapping frequency of approximately 15 Hz, fly forward up to 31.6 km/h, and drop microrobots to a targeted destination. The Janus microrobot, which is composed of a silica microsphere, nickel layer, and hydrophobic layer, is used to absorb the oil and process organic pollutants. These Janus microrobots can be propelled fast up to 9.6 body lengths per second, and on-demand speed regulation and remote navigation are manageable. These Janus microrobots can continuously carry oil droplets in aqueous environments under the control of a uniform rotating magnetic field. Because of the fluid dynamics induced by the Janus microrobots, a highly efficient removal of Rhodamine B is accomplished. This smart robot system may open a door for pollutant purification.
... [36] Utilizing this property, Wang group prepared a remotely triggered Janus micromotor that exhibited sensitive "On-Off" responsive to fuel molecules from the surrounding atmosphere. [145] This vapor-powered micromotor offered new opportunities in threat detection and gas sensing. The specific binding of targeted biomolecules allows the motion-based MNMs to selectively detect the targets. ...
Artificial micro-/nanomotors (MNMs) are tiny apparatuses that can autonomously navigate and perform specific tasks at micro-/nanoscale. The continuous movement characteristics of MNMs and related motion-induced micromixing effect enable these devices to act as “on-the-move” cleaners, sensors, and reactors to facilitate corresponding chemical/physical processes. With reasonable design and specific surface functionalization, MNMs show great promise in environmental, sensing, and chemical applications. This review conveys the current propulsion strategies of MNMs, with specific focus on their capabilities of accelerating chemical/physical processes. Representative applications of MNMs in environmental remediation, detection, and chemical conversion are discussed, emphasizing and highlighting the role of these moving MNMs in chemical aspects. Finally, the main challenges and existing limitations to translating the potential of MNMs into real-world applications are discussed, along with the future opportunities of this field.
... Magnetic microrobots are widely applied in biomedicine [29], sensing [30][31][32], environmental remediation [33], and nanofabrication [34][35][36][37]. Magnetic field can be safely applied to biological systems without obvious side effects [29]. ...
Recent strides in microfabrication technologies offer important possibilities for developing microscale robotic systems with enhanced power, functionality and versatility. Previous microrobots fabricated by lithographic techniques usually lack the ability to adaptively deform in confined and constricted spaces and navigate through, therefore hindering their applications in complex biological environments. Here, a microfluidic strategy is combined with a dip-coating process for continuous fabrication of soft helical structures with controllable mechanical property as magnetically propelled microrobots, capable of actively propelling through narrow and sinuous microchannels. Because of their self-adaptive deformation capability, the magnetically propelled soft microrobots can actively navigate through a narrow opening, 2.21 times smaller than the sectional area of the microrobot, and a U-shape-bent capillary, directed by a programmed magnetic field. Additionally, the soft microrobot demonstrates increased swimming speed in a fluid of high viscosity, because of the adaptive tightening deformation of the helix when swimming. This new magnetically propelled soft microrobot and its attractive performance will open up new possibilities for biomedical operation at the micro and nanoscale.
... The driving technology and the biocompatibility problem are the essential challenges faced by the design and manufacture of micro-nanorobots for medical applications [1,2]. Micronanorobots can have various driving methods, including electric field driving, magnetic field driving [3,4], chemical energy driving [5,6], and so on [7][8][9][10][11][12]. These driving modes control the motion of the micro-nanorobots through external equipment such as the light, magnetic, and electric fields and other physical environments. ...
... Similarly, the movement speed of the micro-nanorobot, whose length was 4.13 μm and 4.96 μm, could be calculated. According to the kinematic calculation model of the Pt/CNT micro-nanorobot, the Stokes viscous force of the cylinder is shown in equation (5). The micro-nanorobot was exposed to the concentration of 30% glucose solution, whose dynamic viscosity was 2:23 × 10 −3 Pa · s. ...
... The diameter of the anodic aluminum oxide template (AAO) was about 90 nm. The length of the micro-nanorobot is 3.32 μm, 4.13 μm, and 4.96 μm, whose movement speed was about 0.46 μm/s, 0.37 μm/s, and 0.34 μm/s, respectively, and then the calculated size of the viscous force was 1:02 × 10 −14 N, 0:92 × 10 −14 N, and 0:87 × 10 −14 N by equation (5). According to the video sequence, it could be observed that the motion of the micro-nanorobot was basically at a constant speed, and the acceleration of the micro-nanorobot was tiny. ...
Swimming micro-nanorobots have attracted researchers’ interest in potential medical applications on target therapy, biosensor, drug carrier, and others. At present, the experimental setting of the swimming micro-nanorobots was mainly studied in pure water or H 2 O 2 solution. This paper presents a micro-nanorobot that applied glucose in human body fluid as driving fuel. Based on the catalytic properties of the anode and cathode materials of the glucose fuel cell, platinum (Pt) and carbon nanotube (CNT) were selected as the anode and cathode materials, respectively, for the micro-nanorobot. The innovative design adopted the method of template electrochemical and chemical vapor deposition to manufacture the Pt/CNT micro-nanorobot structure. Both the scanning electron microscope (SEM) and transmission electron microscope (TEM) were employed to observe the morphology of the sample, and its elements were analyzed by energy-dispersive X-ray spectroscopy (EDX). Through a large number of experiments in a glucose solution and according to Stoker’s law of viscous force and Newton’s second law, we calculated the driving force of the fabricated micro-nanorobot. It was concluded that the structure of the Pt/CNT micro-nanorobot satisfied the required characteristics of both biocompatibility and motion.
... Janus particles have at least two different surfaces referred to one structural unit [58]. Interest in Janus capsules is associated with a combination of delivery [12,59] for various therapies and selfpropelled micro-/nanomotor approaches [60][61][62]. Applied to the encapsulation process, Janus particles combine different properties and provide a range of functions such as delivery, recognition, release of therapeutics, enzymatic activity, physical and chemical sensing [63,64]. In particular, drug delivery is focused on: (i) encapsulation of active chemicals [65], (ii) targeted delivery [66], and (iii) stimuli-responsive release [12]. ...
... Janus particles have at least two different surfaces referred to one structural unit [58]. Interest in Janus capsules is associated with a combination of delivery [12,59] for various therapies and self-propelled micro-/nanomotor approaches [60][61][62]. Applied to the encapsulation process, Janus particles combine different properties and provide a range of functions such as delivery, recognition, release of therapeutics, enzymatic activity, physical and chemical sensing [63,64]. In particular, drug delivery is focused on: (i) encapsulation of active chemicals [65], (ii) targeted delivery [66], and (iii) stimuli-responsive release [12]. ...
Originally regarded as auxiliary additives, nanoparticles have become important constituents of polyelectrolyte multilayers. They represent the key components to enhance mechanical properties, enable activation by laser light or ultrasound, construct anisotropic and multicompartment structures, and facilitate the development of novel sensors and movable particles. Here, we discuss an increasingly important role of inorganic nanoparticles in the layer-by-layer assembly—effectively leading to the construction of the so-called hybrid coatings. The principles of assembly are discussed together with the properties of nanoparticles and layer-by-layer polymeric assembly essential in building hybrid coatings. Applications and emerging trends in development of such novel materials are also identified.
... Synthetic micromotors are a hot field of basic and applied research since they are able to convert environmental energy into autonomous motion. [1] Owing to their tiny sizes, distinct motion and lineless actuation, micromotors have potential application in the fields of targeted drug delivery, [2] microsurgery, [3] assisted fertilization, [4] chemical detection, [5] pumping, [6] particle separation, [7] environmental remediation, [8] and nanolithography. [9] Although great progress has been made, these potential applications of synthetic micromotors are still in a proof-of-concept stage. ...
of main observation and conclusion
Biocompatible micromotors have received increasing attention, due to their powerful motion, diverse functionalities and autonomous navigation in the field of biomedical applications. Herein, we report an acoustically‐propelled, magnetic‐guided, erythrocyte‐mimicking hemoglobin micromotor with oxygen‐carrying capability. These hemoglobin micromotors were fabricated by encapsulating magnetic nanoparticles in hybrid hemoglobin/calcium carbonate microparticles, followed by covalently layer‐by‐layer assembly of hemoglobin multilayers. The asymmetric distribution of magnetic nanoparticles enables these micromotors to move rapidly under the propulsion of an acoustic field. The velocity of acoustophoretic motion of hemoglobin micromotors increases with the increase of input voltage of acoustic field, up to 58.2 μm s‐1 at 10 V. The hemoglobin micromotors are directionally navigated by applying an externally magnetic field, and also could pass through microchannels toward the targeted region. Moreover, such hemoglobin micromotors show effective oxygen loading and releasing capability, holding considerable promise as a new platform for oxygen delivery applications.
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... 8,9 The mesoscopic motors exploit the catalytic reaction 10 and/or external stimuli, including surface tension gradients, 11,12 light, 13,14 ultrasound, 15,16 heat, 17 pH gradients, 18,19 and electric 20,21 and magnetic fields 22,23 for their self-propulsion under various fluidic atmospheres. The propulsive thrust of these motors is mostly generated from the chemical reaction between the catalytic motor surface and the surrounding fuel, such as hydrogen peroxide (H 2 O 2 ), 24−26 water, 27,28 acid, 29,30 alkali, 29 alcohols, 31 acetylene, 32 urea, 33 hydrazine, 34 sodium borohydride, 35 and halogens, 36 resulting in continuous locomotion inside the aqueous medium over a prolonged time period. ...
Multifunctional chemically-powered micromotors were fabricated from the airborne contaminant carbon soot (CS) for environmental remediation following two approaches - firstly, by physical deposition of catalytic platinum (Pt) and magnetic nickel (Ni) nanoscale films of ~ 110 nm and ~ 100 nm respectively, on CS, namely CARBOts, and secondly, by chemical deposition of magneto-catalytic iron nanoparticles (FeNPs) of ~ 30 nm or less in size on CS surface, namely iCARBOts. The chemical synthesis of magneto-catalytic iron nanoparticles (FeNPs)-based iCARBOts provides an economical alternative to the synthesis of CARBOts by physical method. The hydrophobic soot contained agglomerates of high-density carbon nanospheres of ~ 40 nm or less in size, generated form the incomplete combustion of a hydrocarbon source. The catalytic component (Pt nanofilm or FeNPs) on the nanostructures on the CS surface allowed rapid catalytic decomposition of aqueous peroxide fuel (H2O2) to generate chemical propulsion. The issuance of O2 microbubbles from the motor surface imparted required thrust for active bubble propulsion. Integration of a magnetic component (Ni nanofilm or FeNPs) facilitated a remote magnetic control on the micromotor navigation. These magneto-catalytic micromotors demonstrated efficient catalytic degradation of methylene blue (MB) dye in presence of 10% (v/v) H2O2 fuel under ambient conditions. The CARBOts completely decolourized the non-biodegradable MB dye pollutant within 40 min of treatment. The magnetic sensitivity of motors facilitated ease of retrieval and reusability after the execution of the remediation tasks, thereby, increased the feasibility of water detoxification process. In addition, with the help of remote magnetic guidance, micromotors were employed for removal of freely floating and surfactant-stabilized oil droplets in seawater without any further surface modification. The intrinsic super-oleophilic nature of the micromotors owing to the presence of nanostructured soot surface facilitated an enhanced oil-motor interaction, which led to efficient on-the-fly capturing of oil droplets with remote magnetic guidance.
