Micromotor System Research Articles

Multi-Performance Degradation System Reliability Analysis with Varying Failure Threshold Based on Copulas

This paper investigated reliability modeling for systems subject to dependent competing risks considering that variation of the failure threshold is not considered in most studies on competing failure reliability. Firstly, the variation of degradation quantity under shocks was analyzed, and the variation of the threshold was considered on this basis. Secondly, the cumulative degradation under the influence of the random shock process was analyzed. The attractive property of Copula functions is symmetry. Then, a linear Wiener process model was applied to model performance degradation failure, and a multi-performance degradation correlated-competition model based on a Copula function was constructed, which considered the correlated competition between multi-performance degradation failures. Lastly, a micromotor system was used to analyze the applicability of the proposed model for bivariate instances, demonstrating the rationality and effectiveness of the proposed model.

Enzymatic Janus Liposome Micromotors

A liposome-based micromotor system that utilizes regional enzymatic conversion and gas generation to achieve directional motion in water is presented. Constituted mainly of a low-melting lipid and a high-melting lipid together with cholesterol, these liposomes maintain stable Janus configuration at room temperature as a result of lipid liquid-liquid phase separation. Local placement of enzymes such as horseradish peroxidase is realized via affinity binding between avidin and biotin, the latter as a lipid conjugate sorted specifically into one domain of these Janus liposomes as a minor component. In the presence of the substrate, hydrogen peroxide, these enzyme-decorated Janus liposomes undergo directional motion, yielding velocities exceeding thermal diffusion by three folds in some cases. Experimental details on liposome size control, motor assembly, and substrate distribution are presented; effects of key experimental factors on liposome motion, such as substrate concentration and liposome Janus ratio, are also examined. This work thus provides a viable approach to building asymmetrical lipid-assembled, enzyme-attached colloids and, in addition, stresses the importance of asymmetry in achieving particle directional motion.

Self-Propelled Initiative Collision at Microelectrodes with Vertically Mobile Micromotors.

Impact experiments enable single particle analysis for many applications. However, the effect of the trajectory of a particle to an electrode on impact signals still requires further exploration. Here, we investigate the particle impact measurements versus motion using micromotors with controllable vertical motion. With biocatalytic cascade reactions, the micromotor system utilizes buoyancy as the driving force, thus enabling more regulated interactions with the electrode. With the aid of numerical simulations, the dynamic interactions between the electrode and micromotors are categorized into four representative patterns: approaching, departing, approaching-and-departing, and departing-and-reapproaching, which correspond well with the experimentally observed impact signals. This study offers a possibility of exploring the dynamic interactions between the electrode and particles, shedding light on the design of new electrochemical sensors.

Self‐Propelled Initiative Collision at Microelectrodes with Vertically Mobile Micromotors

AbstractImpact experiments enable single particle analysis for many applications. However, the effect of the trajectory of a particle to an electrode on impact signals still requires further exploration. Here, we investigate the particle impact measurements versus motion using micromotors with controllable vertical motion. With biocatalytic cascade reactions, the micromotor system utilizes buoyancy as the driving force, thus enabling more regulated interactions with the electrode. With the aid of numerical simulations, the dynamic interactions between the electrode and micromotors are categorized into four representative patterns: approaching, departing, approaching‐and‐departing, and departing‐and‐reapproaching, which correspond well with the experimentally observed impact signals. This study offers a possibility of exploring the dynamic interactions between the electrode and particles, shedding light on the design of new electrochemical sensors.

Should new operating procedures arising from COVID-19 make us re-think our management of deep caries?

COVID-19 has impacted heavily on the delivery of dental services within the UK, particularly in regards to aerosol generating procedures (AGPs). However, it has created an opportunity to reflect on how operative dental procedures, such as the management of dental caries, are undertaken. In light of recent evidence in favour of speed increasing contra-angle handpieces in combination with an electric micromotor to eliminate the generation of aerosols at certain speeds while still allowing the cutting of hard tooth tissue, albeit at a slower rate than the traditional air-turbine, this article explores the evidence for partial caries removal using the electric micromotor system. Aspects of maintaing the health of the pulpal tissue using this system and adopting a logical approach to placing adhesive direct resin composites to faciliate an optimum outcome for the patient are also explored.

Control the Neural Stem Cell Fate with Biohybrid Piezoelectrical Magnetite Micromotors.

Inducing neural stem cells to differentiate and replace degenerated functional neurons represents the most promising approach for neural degenerative diseases including Parkinson's disease, Alzheimer's disease, etc. While diverse strategies have been proposed in recent years, most of these are hindered due to uncontrollable cell fate and device invasiveness. Here, we report a minimally invasive micromotor platform with biodegradable helical Spirulina plantensis (S. platensis) as the framework and superparamagnetic Fe3O4 nanoparticles/piezoelectric BaTiO3 nanoparticles as the built-in function units. With a low-strength rotational magnetic field, this integrated micromotor system can perform precise navigation in biofluid and achieve single-neural stem cell targeting. Remarkably, by tuning ultrasound intensity, thus the local electrical output by the motor, directed differentiation of the neural stem cell into astrocytes, functional neurons (dopamine neurons, cholinergic neurons), and oligodendrocytes, can be achieved. This micromotor platform can serve as a highly controllable wireless tool for bioelectronics and neuronal regenerative therapy.

Energy Conversion Efficiency of a Micromotor System

The energy conversion efficiency of a micromotor system was quantified. The output of the micromotor system is the mechanical energy of the revolving and spinning motions of the spherical micromoto...

Energy consumption and conversion efficiency for a micromotor under DC voltage

A water droplet works as a novel kind of micromotor exhibiting back-and-forth motion between two needle-shaped electrodes in an oil phase under a stationary direct-current voltage. In the present study, a quantification method was adapted to estimate the kinetic energy output of back-and-forth motion of a water droplet, together with the electric energy input to this system. It was observed that the volume of the droplet gradually decreased accompanied by the periodic motion, which is attributed to electrolysis. Energy consumption owe to the electrolysis vs. the generation of kinetic energy of the moving droplet experimentally evaluated. The kinetic energy was deduced based on Stokes’ drag equation. Electric current was measured at the pA level. Then, the energy conversion efficiency of this micromotor system was able to be calculated. As far as we aware, this is the first report on the conversion efficiency for the autonomous motion under stationary DC voltage. Until now, various kinds of micromotor systems have been individually developed by different study group, and the comparison was difficult due to the lack of universal reliable index of the efficiency. The quantification method reported here evaluates micromotor system on its energy conversion efficiency, irrespective of experiment conditions. This quantification method can be a universal tool for micromotor system comparison, and is expected to play the role as the guidelines for future developments.

Enzyme-powered Janus platelet cell robots for active and targeted drug delivery.

Transforming natural cells into functional biocompatible robots capable of active movement is expected to enhance the functions of the cells and revolutionize the development of synthetic micromotors. However, present cell-based micromotor systems commonly require the propulsion capabilities of rigid motors, external fields, or harsh conditions, which may compromise biocompatibility and require complex actuation equipment. Here, we report on an endogenous enzyme-powered Janus platelet micromotor (JPL-motor) system prepared by immobilizing urease asymmetrically onto the surface of natural platelet cells. This Janus distribution of urease on platelet cells enables uneven decomposition of urea in biofluids to generate enhanced chemophoretic motion. The cell surface engineering with urease has negligible impact on the functional surface proteins of platelets, and hence, the resulting JPL-motors preserve the intrinsic biofunctionalities of platelets, including effective targeting of cancer cells and bacteria. The efficient propulsion of JPL-motors in the presence of the urea fuel greatly enhances their binding efficiency with these biological targets and improves their therapeutic efficacy when loaded with model anticancer or antibiotic drugs. Overall, asymmetric enzyme immobilization on the platelet surface leads to a biogenic microrobotic system capable of autonomous movement using biological fuel. The ability to impart self-propulsion onto biological cells, such as platelets, and to load these cellular robots with a variety of functional components holds considerable promise for developing multifunctional cell-based micromotors for a variety of biomedical applications.

Multicompartment Tubular Micromotors Toward Enhanced Localized Active Delivery

A tubular micromotor with spatially resolved compartments is presented toward efficient site-specific cargo delivery, with a back-end zinc (Zn) propellant engine segment and an upfront cargo-loaded gelatin segment further protected by a pH-responsive cap. The multicompartment micromotors display strong gastric-powered propulsion with tunable lifetime depending on the Zn segment length. Such propulsion significantly enhances the motor distribution and retention in the gastric tissues, by pushing and impinging the front-end cargo segment onto the stomach wall. Once the micromotor penetrates the gastric mucosa (pH ≥ 6.0), its pH-responsive cap dissolves, promoting the autonomous localized cargo release. The fabrication process, physicochemical properties, and propulsion behavior are systematically tested and discussed. Using a mouse model, the multicompartment motors, loaded with a model cargo, demonstrate a homogeneous cargo distribution along with approximately four-fold enhanced retention in the gastric lining compared to monocompartment motors, while showing no apparent toxicity. Therapeutic payloads can also be loaded into the pH-responsive cap, in addition to the gelatin-based compartment, leading to concurrent delivery and sequential release of dual cargos toward combinatorial therapy. Overall, this multicompartment micromotor system provides unique features and advantages that will further advance the development of synthetic micromotors for active transport and localized delivery of biomedical cargos.

Micromotor-Based Biosensing Using Directed Transport of Functionalized Beads.

Previous micromotor-based biosensing studies used to functionalize the surface of the micromotor with specific molecular probes for binding of target analyte, thus limiting the use of the micromotor for the specific target. In contrast, here, we introduce a novel approach of using a nonfunctionalized micromotor as a generic cargo carrier being able to perform label-free and dynamic loading, transport, and release of functionalized beads. Hence, such an approach enables one to use the same micromotor system for sensing of varying targets via different commercially available functionalized beads, demonstrating the use of micromotors as a practical and versatile means for biosensing. We have also introduced a simplified microfluidic design that can be used for immunosensing or DNA binding tests without necessity for complicated fluid handling (buffer exchange, washing, etc.) steps. We expect this approach to open up new realizations of simplified and generic biosensing platforms.

Wireless Manipulation of Magnetic/Piezoelectric Micromotors for Precise Neural Stem‐Like Cell Stimulation

AbstractPrecise neural electrical stimulation, which is a means of promoting neuronal regeneration, is a promising solution for patients with neurotrauma and neurodegenerative diseases. In this study, wirelessly controllable targeted motion and precise stimulation at the single‐cell level using S.platensis@Fe3O4@tBaTiO3 micromotors are successfully demonstrated for the first time. A highly versatile and multifunctional biohybrid soft micromotor is fabricated via the integration of S.platensis with magnetic Fe3O4 nanoparticles and piezoelectric BaTiO3 nanoparticles. The results show that this micromotor system can achieve navigation in a highly controllable manner under a low‐strength rotating magnetic field. The as‐developed system can achieve single‐cell targeted motion and then precisely induce the differentiation of the targeted neural stem‐like cell by converting ultrasonic energy to an electrical signal in situ owing to the piezoelectric effect. This new approach toward the high‐precision stimulation of neural stem‐like cells opens up new applications for micromotors and has excellent potential for precise neuronal regenerative therapies.

ZnO/ZnO2/Pt Janus Micromotors Propulsion Mode Changes with Size and Interface Structure: Enhanced Nitroaromatic Explosives Degradation under Visible Light.

Self-motile mesoporous ZnO/Pt-based Janus micromotors accelerated by bubble propulsion that provide efficient removal of explosives and dye pollutants via photodegradation under visible light are presented. Decomposition of H2O2 (the fuel) is triggered by a platinum catalytic layer asymmetrically deposited on the nanosheets of the hierarchical and mesoporous ZnO microparticles. The size-dependent motion behavior of the mesoporous micromotors is studied; the micromotors with average size ∼1.5 μm exhibit enhanced self-diffusiophoretic motion, whereas the fast bubble propulsion is detected for micromotors larger than 5 μm. The bubble-propelled mesoporous ZnO/Pt Janus micromotors show remarkable speeds of over 350 μm s-1 at H2O2 concentrations lower than 5 wt %, which is unusual for Janus micromotors based on dense materials such as ZnO. This high speed is related to efficient bubble nucleation, pinning, and growth due to the highly active and rough surface area of these micromotors, whereas the ZnO/Pt particles with a smooth surface and low surface area are motionless. We discovered new atomic interfaces of ZnO2 introduced into the ZnO/Pt micromotor system, as revealed by X-ray diffraction (XRD), which contribute to enhance their photocatalytic activity under visible light. Such coupling of the rapid movement with the high catalytic performance of ZnO/Pt Janus micromotors provides efficient removal of nitroaromatic explosives and dye pollutants from contaminated water under visible light without the need for UV irradiation. This paves the way for real-world environmental remediation efforts using microrobots.

Chemically Controlled Spatiotemporal Oscillations of Colloidal Assemblies

AbstractWe report an autonomous oscillatory micromotor system in which active colloidal particles form clusters, the size of which changes periodically. The system consists of an aqueous suspension of silver orthophosphate microparticles under UV illumination, in the presence of varying concentrations of hydrogen peroxide. The colloid particles first attract each other to form clusters. After a short delay, these clusters abruptly disperse and oscillation begins, alternating between clustering and dispersion of particles. After a cluster oscillation initiates, the oscillatory wave propagates to nearby clusters and eventually all the clusters oscillate in phase‐shifted synchrony. The oscillatory behavior is governed by an electrolytic self‐diffusiophoretic mechanism which involves alternating electric fields generated by the competing reduction and oxidation of silver. The oscillation frequency is tuned by changing the concentration of hydrogen peroxide. The addition of inert silica particles to the system results in hierarchical sorting and packing of clusters. Densely packed Ag3PO4 particles form a non‐oscillating core with an oscillating shell composed largely of silica microparticles.

Application of video microscopy in probing structures and dynamics of micromotor systems

Video microscopy has become an essential, real space experiment technique to study the structural and dynamical properties of microscopic particulate systems. On the one hand, video microcopy can be used to directly observe and record such particulate systems. On the other hand, combined with particle tracking technique, video microscopy enables quantitatively analysis of video data, and further calculation of the structures and dynamics of the studied microscopic systems. For example, video microscopy has been widely used in soft matter physics research. With the advantage of single particle resolution and the capability of longtime recording, video microscopy has led to great advances in our understudying of fundamental condensed matter physics phenomena such as crystallization, melting and glass transition. This paper reviews the applications of video microscopy in studying structures and dynamics of micromotor systems. Firstly, the experimental technique of the video microscopy is summarized. We introduce the hardware of video microscopy, which includes an optical microscope, a video camera and a personal computer. The video camera attached to the microscope records videos and the videos are stored in the computer for future image analysis. Then, the procedures of image analysis are detailed. Various methods to determine the positions of microscopic particles, i.e., particle tracking algorithms, are outlined. Suggestions on video acquisition are also discussed to enable better image analysis and particle tracking. The typical physical parameters to quantify the structures and dynamics of micromotor systems, such as radial distribution function g( r ) and mean square displacement (MSD), are introduced. Secondly, recent progress of the applications of video microscopy in micromotor systems are reviewed. Micromotors can move autonomously because they can convert chemical or other forms of energy (magnetic, electrical, photo- chemical, acoustic, thermal) to mechanical movement. Micromotors have attracted great attentions due to, (1) convenient experimental model of active matter in fundamental physics research; (2) great potential in applications such as chemical analysis and separations, repair of cracks in materials, pumping of fluids in microchannel, and prevention of membrane fouling. To review the applications of video microscopy in micromotor systems, we start with the investigation of the aggregation behavior of micromotors. The results show that both cluster and band phase exist in the micromotor system, and the formation of the cluster or band depends on the velocity of the micromotors. Then, the dynamics of micromotor in viscoelastic fluids are demonstrated. Of particular interest is the remarkable increase of rotational diffusion with increasing particle velocity for micromotor in viscoelastic fluids. The experimental studies of the dynamics of micromotor in confined environments are introduced. Two kinds of confined conditions are considered: A circle wall and an array of periodically arranged obstacles. For the first case, the probability of finding the micromotor at the confinement walls significantly increases compared to Brownian particles. For the second case, it is found that with increasing activity, the micromotor can steer to direction that is even perpendicular to the applied force. Finally, the application of video microscopy for the study of micromotor systems is summarized. The importance of the video microscopy for experimental study of the micromotor system is emphasized, and the limitations and the future of the video microscopy in micromotor research are also discussed.

Enteric Micromotor Can Selectively Position and Spontaneously Propel in the Gastrointestinal Tract.

The gastrointestinal (GI) tract, which hosts hundreds of bacteria species, becomes the most exciting organ for the emerging microbiome research. Some of these GI microbes are hostile and cause a variety of diseases. These bacteria colonize in different segments of the GI tract dependent on the local physicochemical and biological factors. Therefore, selectively locating therapeutic or imaging agents to specific GI segments is of significant importance for studying gut microbiome and treating various GI-related diseases. Herein, we demonstrate an enteric micromotor system capable of precise positioning and controllable retention in desired segments of the GI tract. These motors, consisting of magnesium-based tubular micromotors coated with an enteric polymer layer, act as a robust nanobiotechnology tool for site-specific GI delivery. The micromotors can deliver payload to a particular location via dissolution of their enteric coating to activate their propulsion at the target site toward localized tissue penetration and retention.

RBC micromotors carrying multiple cargos towards potential theranostic applications.

Red blood cell (RBC)-based micromotors containing both therapeutic and diagnostic modalities are described as a means for potential theranostic applications. In this natural RBC-based multicargo-loaded micromotor system, quantum dots (QDs), anti-cancer drug doxorubicin (DOX), and magnetic nanoparticles (MNPs), were co-encapsulated into RBC micromotors. The fluorescent emission of both QDs and DOX provides direct visualization of their loading inside the RBC motors at two distinct wavelengths. The presence of MNPs within the RBCs allows for efficient magnetic guidance under ultrasound propulsion along with providing the potential for magnetic resonance imaging. The simultaneous encapsulation of the imaging nanoparticles and therapeutic payloads within the same RBC micromotor has a minimal effect upon its propulsion behavior. The ability of the RBC micromotors to transport imaging and therapeutic agents at high speed and spatial precision through a complex microchannel network is also demonstrated. Such ability to load and transport diagnostic imaging agents and therapeutic drugs within a single cell-based motor, in addition to a lower toxicity observed once the drug is encapsulated within the multicargo RBC motor, opens the door to the development of theranostic micromotors that may simultaneously treat and monitor diseases.

Triple Degree-of-Freedom Piezoelectric Ultrasonic Micromotor via Flexural-Axial

Actuators remain a limiting factor in robotics, especially in microrobotics where the power density of actuators is a problem. A 3 x 3 x 8.7 mm 3-axis piezoelectric ultrasonic micromotor system is described here in an effort to help solve this problem. Formed from 4 bulk lead zirconate titanate (PZT) thickness-polarized elements placed around the periphery of a rectangular rod, the stator is designed to combine axial and flexural vibrations in a way that permits rotation of a hardened steel ball as a rotor about an arbitrary axis. A simple prototype of the micromotor was found to produce at least a rotation speed of 10.4 rad/s with 4 microN-m torque about all 3 orthogonal directions at an excitation frequency of about 221 kHz, demonstrating the feasibility of a 3 degree-of-freedom millimeter-scale piezoelectric motor.

Design and implementation of an H ∞ controller for a micropermanent-magnet synchronous motor position control system

Design and implementation of an H∞ controller for a micropermanent- magnet synchronous motor position control system is proposed. The diameter of the micromotor is only 6 mm. In addition, the weighting functions of the H∞ controller are selected using the genetic algorithms. A state-space H∞ controller, obtained using a systematic design procedure, is incorporated in a closed-loop position control micromotor system. The system has good performance, including fast transient responses and good load disturbance rejection responses, although its encoder is only 100 pulses/revolution. A digital signal processor, TMS320F2407, is used to execute the position control algorithms. Experimental results validate the theoretical analysis and show the correctness and feasibility of the proposed method. An advanced controller design is proposed for a micromotor.

An ultrasonic linear motor using ridge-mode traveling waves

A new type of ultrasonic linear motor is presented using traveling waves excited along a ridge atop a substrate. The ridge cross section was designed to permit only the fundamental mode to be excited during operation of the motor, with a Langevin transducer used as the source of vibration in this study. The ridge waveguide was first made of lossy media to avoid reflecting vibration energy back toward the vibration source, forming a traveling wave. A 5-mm-wide, 15-mm-tall rectangular acrylic ridge was used to move a slider placed upon it toward the vibration source, in opposition to the direction of the traveling wave transmitted along the waveguide ridge. Using a low-loss 3 x 6-mm aluminum rectangular ridge combined with a damper clamped onto the far end of the waveguide, similar results were obtained. To obtain bidirectional operation, the damper was replaced with a second Langevin transducer, giving a pair of transducers located perpendicularly to the ends of the ridge and driven with an appropriate phase difference. The moving direction of the slider was reversed by shifting this phase difference by about 180 degrees. With this simple configuration, it may soon be possible to fabricate a linear micromotor system on a silicon substrate or other semiconductor wafer adjacent to other electronic and optoelectronic devices.