Magnetic-Driven Tubular Micromotors with Bases for Precise Positioning and Cargo Carrying

Nano/-micromotors self-assembling into static and dynamic clusters are of considerable promise to study smart, interactive, responsive, and adaptive nano/-micromaterials that can mimic spatio-temporal patterns, swarming, and collective behaviors widely observed in nature. Previously, the dynamic self-assembly of bubble-propelled catalytic micromotors initiated by capillary forces has been reported. This manuscript shows novel self-assembly modes of magnetic/catalytic Ti/FeNi/Pt tubular micromotors. When chemical fuel (hydrogen peroxide) is added it is decomposed on contact with Pt catalyst into oxygen and water. Here, the non-bubbling motion and autonomous assembly of catalytic/magnetic nanomembranes, i.e. without nucleation/generation of oxygen bubbles, are shown. Moreover, magnetic Ti/FeNi/Pt micromotors are spun using an external magnetic field and they form dynamic clusters balanced by attractive magnetic and repulsive hydrodynamic interactions. Micromotors form dynamic clusters, undergo precession and rapidly propagate through the solution.

Introduction. When heating with high-frequency currents (HFCs) at high speeds, more significant strengthening effects can be observed compared to using machine generators. Therefore, hardening at high frequencies is more efficient. However, the increase in the generator frequency results in a decrease in the depth of penetration of eddy currents and an increased unevenness of heating across the cross-section. The application of a constant external magnetic field during HFC hardening can increase the depth of eddy current penetration and create more uniform heating. Unfortunately, there is not enough information available on the effect of the external magnetic field on HFC heating processes and phase transformations in steel. Currently, there are no quantitative estimates for the impact of an external magnetic field on changes in the kinetics of electric heating and the penetration depth of eddy currents. In connection with the above, the aim of this paper is to investigate changes in the kinetics of high-frequency heating of iron-carbon alloys when an external constant magnetic field is applied and, and, based on this, to consider the potential for technological applications. Materials and Methods. Theoretical assessment of the influence of an external magnetic field on the change in the kinetics of electric heating and the penetration depth of eddy currents is based on the general theory of induction heating kinetics. An experimental study of the influence of a magnetic field on the kinetics of high-frequency current heating was performed on samples of 45 steel, pearlitic gray (SCh30), and ferritic malleable cast iron (KCh30-6). The temperature distribution over the cross-section of ferromagnetic materials during induction heating with an external magnetic field has been studied using special samples of iron, 45 steel, and SCh30 gray pearlitic cast iron. Electric tempering processes have been investigated on samples of U8A steel using a vacuum tube generator (heating temperature — 450℃, heating rate — 750℃/s). Changes in austenite grain size after high-speed heating with external magnetization have been examined on samples of reduced-hardenability 55PP steel. To study the processes of thermal treatment in a magnetic field during experiments involving heating samples using high-frequency currents, a specially designed electromagnet was created to apply an external constant magnetic field. Results. Theoretical curves were constructed for heating conditions with and without an external constant magnetic field. Experimental data on the effect of an external constant magnetic field on induction heating in the surface layer of various materials were summarized in kinetic diagrams. Evidence that the observed changes were due to increased depth of penetration of eddy currents came from experiments on cylindrical samples of 45 steel with different wall thicknesses. Kinetic curves were provided for estimating the temperature field (at 6 points at different depths) during high-frequency current heating with and without external magnetization. The paper presents experimental data on the micro-hardness distribution across the cross-section of a U8 steel sample after quenching, quenching and electric tempering, quenching and electric tempering with external magnetization, and quenching and bulk tempering. It also includes the results of the study of the austenite grain size of 55PP steel after high-speed heating with external magnetization and conventional (slow) deep heating. Discussion. The application of a high-intensity external constant magnetic field during the first quasi-stationary process resulted in a decrease in the rate of induction heating of the ferromagnetic material and an increase in the depth of its uniform heating. However, above the Curie point, the effect of the magnetic field was negligible due to the low magnetic susceptibility of the material, and the heating rate remained unchanged as if there was no field present. In addition, due to the insignificant difference in the values of magnetic permeability below and above the Curie point during heating in the field, the thermal curve did not exhibit the characteristic inflection typical of kinetic curves observed during the transition of the surface layer to a paramagnetic state. Experiments with electric tempering have demonstrated that by applying an external field, it was possible to temper a material to the desired depth and it could be done on a single high-frequency current setup. The size of the austenite grains after high-speed heating with magnetization was reduced compared to conventional deep heating of steel with low hardenability, eliminating the issue of induction heating for low-hardenability steel. Conclusion. The results of the study demonstrated that the use of an external magnetic field enabled the achievement of strengthening effects during heating at higher frequencies, thereby eliminating the drawbacks of such heating methods.

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.

Propulsion at the microscale has attracted significant research interest. In this work, a numerical simulation to explain the speed boost of up to 34 % experienced by transition metal dichalcogenides (TMD) based micromotors under the effect of applied magnetic fields is described. The simulations show that, when an external magnetic field is applied, the flow regime changes from turbulent to laminar. This causes an increase in the residence time of the fuel over the catalyst surface, which enhances the oxygen production. The more efficient generation and growth of the bubbles lead to an increase of the capillary force exerted by them. Interestingly, the effect is more pronounced as the level of fuel decrease. The validity of the model is also proven by comparing both theoretical and experimental results. Interestingly, the speed enhancement in magnetic mode depends on geometrical factors only, as a similar phenomenon was observed in a variety of microjets with a variable surface roughness. The understanding of such phenomena will open new avenues for understanding and controlling the motion behavior of high-towing-force catalytic micromotors.

The application of micro/nanomotors as active cleaners for environmental remediation including pollutant degradation has been an ongoing scientific frontier. However, most of previous studies were conducted by using simulated sewage configured in the laboratory rather than real sewage discharged from industries. In this work, we prepared classical bubble‐propelled SiO2−Pt tubular micromotors and for the first time studied their motion behaviours in real sewage. We clarified the effect of the pollutants in sewage on the movement performance of the micromotors. Besides, the SiO2−Pt tubular micromotors were functionalized with Fe3O4 to result in SiO2−Pt−Fe3O4, whose ability to degrade typical pollutant (methylene blue) in sewage solution was accessed. The results show that the degrading ability of the SiO2−Pt−Fe3O4 micromotors in sewage solution is far weaker than that in deionized water. This work will provide an important reference for further exploration on using MNMs for environmental applications in realistic scenarios.

This article deals with magnetohydrodynamic (MHD) flows of a thin rotating layer of astrophysical plasma in external magnetic field. We use the shallow water approximation to describe thin rotating plasma layer with a free surface in a vertical external magnetic field. The MHD shallow water equations with external vertical magnetic field are revised by supplementing them with the equations that are consequences of the magnetic field divergence-free conditions and reveal the existence of third component of the magnetic field in such approximation providing its relation with the horizontal magnetic field. It is shown that the presence of a vertical magnetic field significantly changes the dynamics of the wave processes in astrophysical plasma compared to the neutral fluid and plasma layer in a toroidal magnetic field. The equations for the nonlinear wave packets interactions are derived using the asymptotic multiscale method. The equations for three magneto-Poincare waves interactions, for three magnetostrophic waves interactions, for the interactions of two magneto-Poincare waves and for one magnetostrophic wave and two magnetostrophic wave and one magneto-Poincare wave interactions are obtained. The existence of parametric decay and parametric amplifications is predicted. We found following four types of parametric decay instabilities: magneto-Poincare wave decays into two magneto-Poincare waves, magnetostrophic wave decays into two magnetostrophic waves, magneto-Poincare wave decays into one magneto-Poincare wave and one magnetostrophic wave, magnetostrophic wave decays into one magnetostrophic wave and one magneto-Poincare wave. Following mechanisms of parametric amplifications are found: parametric amplification of magneto-Poincare waves, parametric amplification of magnetostrophic waves, magneto-Poincare wave amplification in magnetostrophic wave presence and magnetostrophic wave amplification in magneto-Poincare wave presence. The instabilities growth rates are obtained respectively.

BSCCO/Ag tapes are being developed for electrical power applications at liquid nitrogen temperatures. In these applications, conductors are exposed to an alternating magnetic field and fed simultaneously with an alternating transport current. In this contribution the influence of an external alternating magnetic field on the transport current loss of a single tape is studied experimentally. Special attention is paid to the loss as a function of the orientation of the external magnetic field. The transport current loss in a DC external magnetic field can be described well by the decrease of the critical current due to the magnetic field. In the case of an AC external magnetic field this is only a minor effect. Effects responsible for the increase of the transport current loss in external AC magnetic field are investigated with respect to their angle dependency. A model based on a 1 dimensional modelling of the conductor and an average critical current density during the magnetic field cycle is presented. This model describes the measured results reasonably well below the critical current.

A new system was developed for measuring AC current distributions in high T/sub c/ superconducting tapes under an external AC magnetic field. In our measurement the current distributions are indirectly found from the results of the self-field distributions measured by an array of pickup coils located around the tape. For improved measurement accuracy under the external magnetic field, a compensation coil was used to cancel the component of the external magnetic field from the signal of pickup coil. In order to confirm the validity of this system, measurement of current distributions in a test conductor composed of insulated copper wires was carried out under an external AC magnetic field. Using this system, we measured the current distributions in multifilamentary Ag alloy sheathed Bi-2223 tape as a function of the angle of the external AC magnetic field at 77 K. Further, we investigated the characteristics of the current distributions for the case of a simultaneous application of AC transport current and transverse AC magnetic field. On the basis of the obtained results the practicality of our measurement system is discussed.

We investigate collision of two atoms in an external magnetic field and in the field of laser radiation with formation of Fano-Feshbach resonances. At one-photon resonance of laser radiation with two discrete vibrational states of molecule the dressed states are formed (Autler-Townes effect) which form Fano-Feshbach resonances in interaction with the external magnetic field. In addition, the lower molecular vibrational state is coupled with the continuum of the elastic channel via also LICS (laser-induced continuum structure) forming laser-induced resonance. We obtain cross-sections of elastic and inelastic resonant scattering and expression for the scattering length depending on the external magnetic and laser radiation fields.

Small-scale robots have great potential in minimally invasive surgery (MIS). In this paper, we propose an untethered magnetic gripper with small scale and build a double-magnet model for it. The gripper is 4.3mm long and its maximum width is 4mm. It contains a spindle and two magnets, which can achieve precise control of orientation, position and open angle with external magnetic driven field. As a result, it can perform operations such as transporting medicines in confined and constrained environments. Modeling and analysis of the magnetic gripper have been carried out. Relationship between the open angle and external magnetic field has been established. Kinematics model of the gripper has been built. A 3-axis Helmholtz-Maxwell coil system has been established to generate the magnetic field, in which orientation and open angle can be controlled with uniform magnetic field while position can be controlled with gradient field. The proposed gripper have been validated with phantom experiments. An opened angle control error of 0.63° and direction control error of 1.1° have been obtained.

Magnetic hydrogel soft robots have shown great potential in various fields. However, their contact dynamic behaviors are complex, considering stick-slip motion at the contact interface, and lack accurate computational models to analyze them. This paper improves the numerical computational method for hydrogel materials with magneto-mechanical coupling effect, analyses the inchworm-like contact motion of the biomimetic bipedal magnetic hydrogel soft robot, and designs and optimizes the robot's structure. In the constitutive model, a correction factor representing the influence of the direction of magnetic flux density on the domain density has been introduced. The magnetic part of the Helmholtz free energy has been redefined as the magnetic potential energy, which can be used to explain the phenomenon that the material will still deform when the magnetic flux density is parallel to the external magnetic field. The accuracy of the simulation is verified by comparing numerical solutions with experimental results for a magnetic hydrogel cantilever beam. Furthermore, employing the present methods, the locomotion of a magnetic hydrogel soft robot modeled after the inchworm's gait is simulated, and the influence of the coefficient of friction on its movement is discussed. The numerical results clearly display the control effect of the external magnetic field on the robot's motion.

Magnetorheological (MR) gels consist of micron sized magnetic particles inside a gel matrix. Before physical cross-linking, the suspension is subjected to a small magnetic field which creates a particle string structure. After cross-linking, the string is kept within the gel at room temperature. Under an external homogeneous magnetic field and mechanical deformation, the soft swollen gel matrix allows the string to largely rearrange at microscopic scales. With the help of two homemade magneto cells mounted on an optical microscope, we were able to follow the conformational change and instabilities of a single magnetic particle string under the combined influence of shear (or stretch) and the magnetic field. In the absence of mechanical deformation, an external magnetic field, applied in the perpendicular direction to the string, breaks it into small pieces generating periodic structures like sawteeth. When an external magnetic field is applied parallel to the pre-aligned string, it exhibits a length contraction. However, under shear strain perpendicular to the original pre-structured string (and magnetic field), the string breaks and short string segments tilt, making an angle with the original direction that is smaller than that of the applied shear (non-affine). The difference in tilt angle scales with the inverse length of the small segments L-1 and the magnetic flux density B, reflecting the ability of the gel matrix to expel solvents under local stress.

Fabrication and characterization of cobalt ferrite magnetic hydrogel combined with static magnetic field as a potential bio-composite for bone tissue engineering

In this work propagation of a high frequency electromagnetic wave in underdense plasma in presence of an external magnetic field is investigated. When a constant magnetic field perpendicular to the motion of electrons is applied, then the electrons rotate around the magnetic field lines and generate electromagnetic part in the wake with a nonzero group velocity. By using of the Maxwell equations and nonlinear differential equation for the electric field a direct one-dimensional (1D) procedure for calculating hydrodynamic equations are developed and the electric and magnetic field profiles in the plasma are investigated. It is shown that by using the external (dc) magnetic field in constant laser intensity, the magnetic field profile in plasma deviates from the sinusoidal structure. It is found that the wavelength of electric and magnetic field oscillations increases by increasing the external magnetic field and the density distribution of electrons also increases in comparison to the unmagnetized underdense plasma. We noticed that by the increase in electron temperature in the unmagnetized and magnetized plasmas the electron density distribution ratio δn/n0e increases and the wavelength of electric and magnetic fields increase where in the magnetized system it becomes positive in some regions.

Moonlighting proteins are multifunctional proteins widely present in organisms, playing crucial roles in various physiological activities. Drawing inspiration from the moonlight proteins, we developed a cerium (Ce)-based nanozyme CF, featuring multiple enzymatic activities along with robust cargo-loading and transport capabilities. The CF was synthesized through a one-step assembly between Ce3+ and a phosphorylated amino acid derivative, achieving high biostability through a simple heat treatment. The nanozyme possesses both superoxide dismutase (SOD) and catalase (CAT) activities, enabling scavenging of reactive oxygen species (ROS) and modulation of inflammation by inhibiting NF-κB pathway activation. Besides its enzymatic activities, CF can also serve as a versatile nanocarrier for various cargoes through one-pot co-assembly. Herein, the CF-based nanoassembly loaded with a near infrared fluorescent dye was demonstrated to work well for the diagnosis of atherosclerotic plaques. The nanoassembly co-assembled with probucol exhibited superior ROS-scavenging and anti-inflammatory effects compared to either CF nanozyme or probucol, attributed to the synergy of the nanozyme and the drug, thus facilitating a highly efficient treatment of atherosclerosis. This work introduces a novel Ce-based nanozyme with multifunctional properties, providing a promising approach to endow nanozymes with moonlighting protein-like characteristics, thereby enhancing their functional capabilities and broadening their application potential in various fields.