Bubble Propulsion Research Articles

Making Mobile Nanotechnology Accessible: Is the Explicit Preparation of Janus Nanoparticle Necessary to Achieve Mobility?

This study compares the mobility behaviour, in a H2O2 environment, of three different geometries of hybrid particle made of silica core functionalized by gold (nanoparticles or layer). It is known that the decomposition of H2O2 on gold surfaces drives mobility; however, the link between mobility orientation and the organization of gold on silica surfaces is still questionable. While conventional wisdom posits that asymmetric designs are crucial for generating phoretic forces or localized bubble propulsion, recent research suggests that symmetrical particles may also exhibit motility. To address this debate, we developed a robust workflow for synthesizing gold grafted silica nanoparticles with precise control over size and shape, enabling the direct comparison of their motile behaviour by dynamic light scattering and particle tracking velocimetry. Our results indicate, first, that a combination of techniques is necessary to overcome their intrinsic limitation and, second, that the inherent asymmetry generated by isotropic gold nanoparticle deposition onto silica surfaces may enable particle motility.

Colloidal bubble propulsion mediated through viscous flows.

Bubble-propelled catalytic colloids stand out as a uniquely efficient design for artificial controllable micromachines, but so far lack a general theoretical framework that explains the physics of their propulsion. Here we develop a combined diffusive and hydrodynamic theory of bubble growth near a spherical catalytic colloid, that allows us to explain the underlying mechanism and the influence of environmental and material parameters. We identify two dimensionless groups, related to colloidal activity and the background fluid, that govern a saddle-node bifurcation of the bubble growth dynamics, and calculate the generated flows analytically for both slip and no slip boundary conditions on the bubble. We finish with a discussion of the assumptions and predictions of our model in the context of existing experimental results, and conclude that some of the observed behaviour, notably the ratchet-like gait, may stem from peculiarities of the experimental setup rather than fundamental physics of the propulsive mechanism.

Construction of Sustainable Biomass Bubble Propulsion Micromotor and Selective Recognition/Separation of Shikimic Acid with Open 3D Target Imprinting Cavity

Construction of Sustainable Biomass Bubble Propulsion Micromotor and Selective Recognition/Separation of Shikimic Acid with Open 3D Target Imprinting Cavity

Asymmetry-Enhanced Motion of Urease-Powered Micromotors from Double Emulsion-Templated Microcapsules.

Autonomous motion of enzyme-powered motors has important implications for drug delivery, cell-cell communication, and protocell engineering. Although many of these systems are inspired by the motion of biological cells, most of them lack key structural features, like micrometer-sized boundaries and aqueous compartments, and rely on bubble propulsion to generation motion. In this study, we use droplet microfluidics to generate large populations of cell-sized microcapsules with poly(lactic-co-glycolic acid) shells and functionalize their surfaces with the enzyme urease to drive their motion. We adjust the number of surface functional groups for urease conjugation by preparing microcapsules with two different surfactants, poly(vinyl alcohol) (PVA) and poly(ethylene-alt-maleic anhydride) (PEMA). We also tune the surface roughness of the microcapsules by varying the concentration of silica nanoparticles in the droplet middle phase. We find that PEMA plays a crucial role in increasing the grafting density of urease on the surface of smooth microcapsules, leading to active motion in the presence of urea. In addition, rough microcapsules prepared with PEMA and loaded with comparable amounts of urease move up to three times faster than their smooth counterparts, which we believe is due to an asymmetric distribution of urease on the surface, giving rise to a preferred direction of motion. Taken together, these results provide new insights into the role that various stabilizing agents play in the induction of motion by enzymatic motors prepared from microfluidics, which is a potentially powerful tool for future preparation of motile protocells in biomedicine.

Review of bubble and magnetically driven catalytic micro/nanomotors: Fabrication and characterization

Micro/nanomotors (MNMs) are very unique in performing tasks and performance according to their scale. These small and versatile motors are known as promising tools in various applications. The ultimate goal is the application of MNMs in various fields, which is considered an exciting technological challenge. Chemical fuel is reliable for the movement of MNMs. Among the various movement mechanisms that exist for these engines, bubble propulsion is one of the most important, and many engines have been investigated using this propulsion mechanism. Magnetic motors are another category of motors that move by applying a magnetic driving force and their direction of movement can be adjusted by the applied magnetic field. One of the most important challenges in the field of MNMs is the use of controlled and efficient engines, which requires the manufacturing and careful design of these engines. By incorporating of two engines, it is possible to benefit from the advantages of both, and at the same time, the limitations of each one are removed and the possibility of controlling the movement of the engine is provided. We will review the methods of manufacturing and characterizing MNMs which consume chemical fuel and move by bubble propulsion and also have magnetic properties and can propel by applying a magnetic field. These engines can reduce the common fuel used in chemical engines by applying magnetic driving force and switching their operation in response to changing conditions. Due to continuous innovations in this field, MNMs will profoundly impact the field of Nanorobotics.

Rapid and Multimaterial 4D Printing of Shape-Morphing Micromachines for Narrow Micronetworks Traversing.

Micromachines with high environmental adaptability have the potential to deliver targeted drugs in complex biological networks, such as digestive, neural, and vascular networks. However, the low processing efficiency and single processing material of current 4D printing methods often limit the development and application of shape-morphing micromachines (SMMs). Here, two 4D printing strategies are proposed to fabricate SMMs with pH-responsive hydrogels for complex micro-networks traversing. On the one hand, the 3Dvortex light single exposure technique can rapidly fabricate a tubular SMM with controllable size and geometry within 0.1 s. On the other hand, the asymmetric multimaterial direct laser writing (DLW)method is used to fabricate SMMs with designable 3D structures composed of hydrogel and platinum nanoparticles (Pt NPs). Based on the presence of ferroferric oxide (Fe3 O4 ) and Pt NPs in the SMMs, efficient magnetic, bubble, and hybrid propulsion modes are achieved. Finally, it is demonstrated that the spatial shape conversion capabilities of these SMMs can be used for narrow micronetworks traversing, which will find potential applications in targeted cargo delivery in microcapillaries.

3D inkjet printed self-propelled motors for micro-stirring

HypothesisMicroscopic self-propelled motors (SPMs) are an area of active research, but very little investigation has been conducted on millimetre-scale or macroscopic SPMs and exploring their potential in biomedical research. In this study, we tested if 3D reactive inkjet (RIJ) printing could be used for precise fabrication of millimetre-scale self-propelled motors (SPMs) with well-defined shapes from regenerated silk fibroin (RSF) by converting water soluble RSF (silk I) to insoluble silk fibroin (silk II). Secondly, we compared the different propulsion behaviour of the SPMs to put forward the best geometry and propulsion mechanism for potential applications in enhancing the sensitivity of diffusion-rate limited biomedical assays by inducing fluid flow. ExperimentsSPMs with four different geometric shapes and propelled by two different mechanisms (catalysis and surface tension gradient) were fabricated by 3D RIJ printing and compared. For bubble propulsion, the structures were selectively doped in specific regions with the enzyme catalase in order to produce motion via bubble generation and detachment in hydrogen peroxide solutions. For surface tension propulsion, PEG400-doped structures were propelled through surface tension gradients caused by leaching of PEG400 surfactant in deionized water. FindingsThe results demonstrated the ability of 3D inkjet printing to fabricate SPMs with desired propulsion mechanism and fine-tune the propulsion by precisely fabricating the different geometric shapes. The resulting 3D structures were capable of generating motion without external actuation, thereby enabling applications in biomedicine such as micro-stirring small fluid volumes to enhance biological assay sensitivity. The surface tension gradient caused by the leaching of surfactant led to faster propulsion velocities with smooth deceleration, whereas, in comparison, catalysis-induced bubble propulsion tended to be jerky and uneven in deceleration, and therefore less suitable for aforementioned applications. Computational fluid dynamic simulations were used to compare the various experimental SPMs ability to enhance mixing when deployed within 96-well plate microwells, to reveal the effect of both SPM shape and motion character on performance, and show viability for small scale mixing applications.

Prussian Blue/Chitosan Micromotors with Intrinsic Enzyme-like Activity for (bio)-Sensing Assays

Prussian Blue (PB)/chitosan enzyme mimetic tubular micromotors are used here for on-the-fly (bio)-sensing assays. The micromotors are easily prepared by direct deposition of chitosan into the pores of a membrane template and in situ PB synthesis during hydrogel deposition. Under judicious pH control, PB micromotors display enzyme mimetic capabilities with three key functions on board: the autonomous oxygen bubble propulsion (with PB acting as a catalase mimic for hydrogen peroxide decomposition), 3,3′,5,5′-tetramethylbenzidine (TMB) oxidation (with PB acting as a peroxidase mimic for analyte detection), and as a magnetic material (to simplify the (bio)-sensing steps). In connection with chitosan capabilities, these unique enzyme mimetic micromotors are further functionalized with acetylthiocholinesterase enzyme (ATChE) to be explored in fast inhibition assays (20 min) for the colorimetric determination of the nerve agent neostigmine, with excellent analytical performance in terms of quantification limit (0.30 μM) and concentration linear range (up to 500 μM), without compromising efficient micromotor propulsion. The new concept illustrated holds considerable potential for a myriad of (bio)-sensing applications, including forensics, where this conceptual approach remains to be explored. Micromotor-based tests to be used in crime scenes are also envisioned due to the reliable neostigmine determination in unpretreated samples.

Interfacial Superassembly of Light-Responsive Mechanism-Switchable Nanomotors with Tunable Mobility and Directionality.

Mechanism-switchable nanomotors are expected to exhibit high adaptability and wide applicability. Herein, for the first time, we report a flask-shaped carbon@Pt@fatty-acid nanomotor with a light-induced switch between nonionic self-diffusiophoresis and bubble propulsion. This nanomotor is fabricated through superassembly of platinum nanoparticles on the surface of carbon nanobottles, and fatty acids are infused into the cavity of carbon nanobottles to serve as a light-sensitive switch. Such a nanomotor can be propelled via catalytic decomposition of H2O2 by platinum nanoparticles, exhibiting self-diffusiophoresis with opening-forward migration. Upon 980 nm laser irradiation, the fatty acids melt due to the photothermal effect and are released from the cavity, switching the dominant operational mechanism to bubble propulsion with bottom-forward migration. Compared with self-diffusiophoresis, bubble propulsion shows higher mobility and better directionality due to the hindered self-rotation. Simulation results further reveal that the confinement effect of the cavity, which facilitates the nucleation of nanobubbles, leads to the switch to bubble propulsion. This study offers an insight into the relationship between nanostructures, fundamental nanomotor operational mechanisms, and apparent propulsion performance, as well as provides a novel strategy for the regulation of movement, which is instructive for both the design and applications of nanomotors.

Acoustics-Actuated Microrobots.

Microrobots can operate in tiny areas that traditional bulk robots cannot reach. The combination of acoustic actuation with microrobots extensively expands the application areas of microrobots due to their desirable miniaturization, flexibility, and biocompatibility features. Herein, an overview of the research and development of acoustics-actuated microrobots is provided. We first introduce the currently established manufacturing methods (3D printing and photolithography). Then, according to their different working principles, we divide acoustics-actuated microrobots into three categories including bubble propulsion, sharp-edge propulsion, and in-situ microrotor. Next, we summarize their established applications from targeted drug delivery to microfluidics operation to microsurgery. Finally, we illustrate current challenges and future perspectives to guide research in this field. This work not only gives a comprehensive overview of the latest technology of acoustics-actuated microrobots, but also provides an in-depth understanding of acoustic actuation for inspiring the next generation of advanced robotic devices.

Metal‐Organic‐Framework based Catalytic Micromotor for Enhanced Water Decontamination

AbstractThis work demonstrates the application of a Fe3O4/zeolitic imidazolate framework 67 (ZIF67) micromotor for improved catalytic degradation of organic pollutants. The micromotors were fabricated by simple adsorption of Fe3O4 nanoparticles on the surface of ZIF67 microparticles, which were synthesized by wet chemistry method. Both Fe3O4 and ZIF67 perform asymmetric decomposition of H2O2 to achieve bubble propulsion of the micromotors. The ferromagnetism of Fe3O4 enables easy directional control of the micromotor. The porous structure of ZIF67 benefits the enrichment of pollutant molecules around the micromotors, facilitating the efficient catalytic degradation. With intensified interaction between active sites and pollutant molecules due to self‐propelled motion and synergistic catalysis of iron in Fe3O4 and zinc ions in ZIF67, the micromotors exhibit enhanced degradation activity of methylene blue as compared to the pure Fe3O4 or ZIF67 counterparts without autonomous motion. This research can be extended to developing other metal‐organic frameworks (MOF)‐integrated micromotors for the environmental applications.

Propulsion Mechanisms of Light‐Driven Plasmonic Colloidal Micromotors

Colloidal micromotors are important candidates for a wide spectrum of applications, ranging from medicine to environmental remediation. Thus far, the propulsion force determination has been obtained from the colloidal motor motion speed and surrounding viscosity via the Stokes drag. Herein, a precise force measurement method and detailed analysis of the fundamental propulsion mechanisms of colloidal Janus micromotors propelled by thermophoretic and steam bubble force vectors, revealing findings uninvestigated to date, are presented. Optical tweezers provide fast and high‐precision force measurements in all three orthogonal dimensions simultaneously. Colloidal Janus micromotors are compared with isotropic hot Brownian reference microparticles, which have no defined force vector that propels them perpendicular to the direction of the laser beam. Janus micromotors display a defined laser power intensity‐dependent thermophoretic propulsion, as well as bubble force‐based propulsion, after surpassing the threshold value for the water boiling. The steam bubble propulsion force vector and the thermophorethic force vectors sum up for the Janus micromotor propulsion direction. On the contrary, the bubble force counteracts photophoretic force in propagation direction of light. Moreover, the thermal‐based reduction of viscosity around the Janus colloidal motor contributes significantly to its speed and guidance abilities.

Self-Propelled Nanojets for Fenton Catalysts Based on Halloysite with Embedded Pt and Outside-Grafted Fe3O4.

Taking inspirations from nature, we endeavor to develop catalytically self-propelled nanojets from a type of tubular clay minerals, halloysite nanotubes (HNTs), and utilize them as catalysts targeted for catalysis where the traditional means of mechanical agitation cannot be implemented. Nanojets of Fe3O4@HNTs/Pt were prepared by impregnating platinum nanoparticles (Pt NPs) in lumens of HNTs and selective grafting of magnetite (Fe3O4) particles on the external surface. The HNT-based nanojets were validated to be highly suitable both in free bulk solution and in microfluidic flow. An example of Fenton degradation catalyzed by these jets was demonstrated. The powerful movement of Fe3O4@HNTs/Pt (368 ± 50 μm·s-1) fueled by 5.0% wt. H2O2 was found to follow a bubble propulsion mechanism, and the motion exhibits collective behavior as swarms. The clay tubes were for the first time observed to self-assemble into fish-like aggregates during swimming, reflecting natural occurrence of motion-evolution philosophy. Guided motion was realized by employing magnetic manipulation which makes jets feasible for reactors with complex microchannels/reactors.

Magnetic field-mediated Janus particles with sustained driving capability for severe bleeding control in perforating and inflected wounds

Severe bleeding in perforating and inflected wounds with forky cavities or fine voids encountered during prehospital treatments and surgical procedures is a complex challenge. Therefore, we present a novel hemostatic strategy based on magnetic field-mediated guidance. The biphasic Janus magnetic particle (MSS@Fe2O3-T) comprised aggregates of α-Fe2O3 nanoparticles (Fe2O3 NPs) as the motion actuator, negatively modified microporous starch (MSS) as the base hemostatic substrate, and thrombin as the loaded hemostatic drug. Before application, the particles were first wrapped using NaHCO3 and then doped with protonated tranexamic acid (TXA-NH3+), which ensured their high self-dispersibility in liquids. During application, the particles promptly self-diffused in blood by bubble propulsion and travelled to deep bleeding sites against reverse rushing blood flow under magnetic guidance. In vivo tests confirmed the superior hemostatic performance of the particles in perforating and inflected wounds (“V”-shaped femoral artery and “J”-shaped liver bleeding models). The present strategy, for the first time, extends the range of magnetically guided drug carriers to address the challenges in the hemorrhage control of perforating and inflected wounds.

Sulfur-encapsulated zeolite micromotors for the selective removal of cesium from high-salt water with accelerated cleanup times

Bubble-propelled sulfur-encapsulated NaX zeolite (S-NaX) micromotors were developed for the selective removal of cesium from high-salt conditions with accelerated cleanup times. NaX was first modified with sulfur to provide additional Lewis acid−base interactions with Cs+ for enhanced Cs+ selectivity, and then Pt was half-deposited on S-NaX for bubble propulsion via the catalytic decomposition of H2O2. The average velocity of the resulting S-NaX/Pt micromotors in 5 wt% H2O2 is 39.7 ± 17.1 μm/s, which is higher than that of a previously reported Cs adsorbent micromotor (35.4 μm/s). The Cs+ ion-exchange kinetics of the S-NaX micromotor is 1.32 times higher than that of the NaX micromotor in a 5 wt% H2O2 solution where the molar ratio of Na+ to Cs+ is 200, even though the sulfur in the S-NaX micromotor causes an adverse effect on the propulsion speed due to the sulfur poisoning effect. Moreover, the S-NaX micromotor in simulated groundwater also exhibited excellent Cs+ removal performance with distribution coefficient (Kd) values at least 3.2 times higher than those of the nonpropelled S-NaX and NaX micromotor, demonstrating the great potential for the treatment of radioactive Cs+-contaminated water.

Dual-Propelled Lanbiotic Based Janus Micromotors for Selective Inactivation of Bacterial Biofilms.

Graphene oxide/PtNPs/Fe2 O3 "dual-propelled" catalytic and fuel-free rotary actuated magnetic Janus micromotors modified with the lanbiotic Nisin are used for highly selective capture/inactivation of gram-positive bacteria units and biofilms. Specific interaction of Nisin with the Lipid II unit of Staphylococcus Aureus bacteria in connection with the enhanced micromotor movement and generated fluid flow result in a 2-fold increase of the capture/killing ability (both in bubble and magnetic propulsion modes) as compared with free peptide and static counterparts. The high stability of Nisin along with the high towing force of the micromotors allow for efficient operation in untreated raw media (tap water, juice and serum) and even in blood and in flowing blood in magnetic mode. The high selectivity of the approach is illustrated by the dramatically lower interaction with gram-negative bacteria (Escherichia Coli). The double-propulsion (catalytic or fuel-free magnetic) mode of the micromotors and the high biocompatibility holds considerable promise to design micromotors with tailored lanbiotics that can response to the changes that make the bacteria resistant in a myriad of clinical, environmental remediation or food safety applications.

Dual‐Propelled Lanbiotic Based Janus Micromotors for Selective Inactivation of Bacterial Biofilms

AbstractGraphene oxide/PtNPs/Fe2O3 “dual‐propelled” catalytic and fuel‐free rotary actuated magnetic Janus micromotors modified with the lanbiotic Nisin are used for highly selective capture/inactivation of gram‐positive bacteria units and biofilms. Specific interaction of Nisin with the Lipid II unit of Staphylococcus Aureus bacteria in connection with the enhanced micromotor movement and generated fluid flow result in a 2‐fold increase of the capture/killing ability (both in bubble and magnetic propulsion modes) as compared with free peptide and static counterparts. The high stability of Nisin along with the high towing force of the micromotors allow for efficient operation in untreated raw media (tap water, juice and serum) and even in blood and in flowing blood in magnetic mode. The high selectivity of the approach is illustrated by the dramatically lower interaction with gram‐negative bacteria (Escherichia Coli). The double‐propulsion (catalytic or fuel‐free magnetic) mode of the micromotors and the high biocompatibility holds considerable promise to design micromotors with tailored lanbiotics that can response to the changes that make the bacteria resistant in a myriad of clinical, environmental remediation or food safety applications.

A near-infrared light-responsive upconversion nanoparticle micromotor propelled by oxygen bubbles.

Light-responsive micromotors using photosensitizer-decorated upconversion nanoparticles (UCNPs) are described. The UCNP motors converting near-infrared light into visible emission were propelled by oxygen bubble propulsion. The micromotor can be easily controlled by adjusting the light intensity, solution pH, and concentration of H2O2 and UCNPs.

Photosynthesis Drives the Motion of Bio‐nanomotors

Bio-nanomotors The photosynthesis process has been studied widely for mimicking water splitting reaction but has never been utilized for powering supramolecular assemblies. In article number 2000028, Daniela A. Wilson and Motilal Mathesh demonstrate a bio-nanomotor fabrication by encapsulating thylakoid nanoparticles that can carry out the water-splitting reaction using visible light. The propulsion mechanism is based on bubble propulsion and photophoresis with complete control over motion and directionality.

Self-propelled cellulose nanocrystal based catalytic nanomotors for targeted hyperthermia and pollutant remediation applications

Inspired from biological motors, cellulose nanocrystals (CNCs) are strategically modified to induce self-propulsion behavior with the capabilities to catalytically degrade pollutants along with magnetic hyperthermia to clean arterial plaques during its course of propulsion. CNCs derived from renewable biomass, are decorated with catalytically active, magneto-responsive nanomaterials (Fe2O3/Pd nanoparticles) through sustainable routes. CNC nanomotors show improved propulsion at lowered peroxide concentrations with remotely controlled trajectory through chemo-magnetic field gradients and ideal surface-wettability characteristics, overcoming the requirement of surfactants, as with traditional nanomotors. We observed that nanomotors undergo motion through heterogeneous bubble propulsion mechanism, with capability to in situ degrade pollutants and generate local heat through hyperthermia, enhancing the rate of degradation process in real time. As proof of concept, we demonstrate that the dynamics of nanomotors can be controlled in a microfluidic channel through site-directed magnetic field and induction of pH gradient, mimicking the chemotaxis in cell-like environment and as swarm of nano-surgeons removes plaques from clogged arteries. Our study shows that strategic modification of CNCs results in fabrication of nanomotors with efficient propulsion system infused with multi-functional characteristics of high catalytic activity and magnetic hyperthermia which opens up new avenues for utilization of bio-based nanomotors derived from lignocellulose for myriad applications.