Magnetically Modulated Pot‐Like MnFe2O4 Micromotors: Nanoparticle Assembly Fabrication and their Capability for Direct Oil Removal

This work demonstrates a simple‐structured, low‐cost magnetically modulated micromotor of MnFe₂O₄ pot‐like hollow microparticles as well as its facile, versatile, and large‐scale growing‐bubble‐templated nanoparticle (NP) assembly fabrication approach. In this approach, the hydrophobic MnFe₂O₄@oleic acid NPs in an oil droplet of chloroform and hexane assembled into a dense NP shell layer due to the hydrophobic interactions between the NP surfaces. With the encapsulated oil continuously vaporizing into high‐pressured gas bubbles, the dense MnFe₂O₄ NP shell layer then bursts, forming an asymmetric pot‐like MnFe₂O₄ micromotor by creating a single hole in it. For the as‐developed simple pot‐like MnFe₂O₄ micromotor, the catalytically generated O₂ molecules nucleate and grow into bubbles preferentially on the inner concave surface rather than on the outer convex surface, resulting in continuous ejection of O₂ bubbles from the open hole to propel it. Dexterously integrating the high catalytic activity for H₂O₂ decomposition to produce O₂ bubbles, excellent magnetic property with the instinctive surface hydrophobicity, the MnFe₂O₄ pot‐like micromotor not only can autonomously move in water media with both velocity and direction modulated by external magnetic field but also can directly serve for environmental oil removal without any further surface modification. The results here may inspire novel practical micromotors.     

Tailoring Metal/TiO2 Interface to Influence Motion of Light‐Activated Janus Micromotors

Catalytic light‐powered micromotors have become a major focus in current autonomous self‐propelled micromotors research. The attractiveness of such machines stems from the fact that these motors are “fuel‐free,” with their motion modulated by light irradiation. In order to study how different metals affect the velocities of metal/TiO₂ micromachines in the presence of UV irradiation in pure water, Pt/TiO₂, Cu/TiO₂, Fe/TiO₂, Ag/TiO₂, and Au/TiO₂ Janus micromotors are prepared. The metals have different chemical potentials and catalytic effects toward water splitting reaction, with both the effects expected to alter the photoelectrochemically‐induced reaction and propulsion rates. Analysis of structures, elemental compositions, motion patterns, velocities, and overall performances of different metals (Pt, Au, Ag, Fe, Cu) on TiO₂ are observed by scanning electron microscopy, energy dispersive X‐ray spectroscopy, and optical microscopy. Electrochemical Tafel analysis is performed for the different metal/TiO₂ structures and it is concluded that the effective velocity is a result of the synergistic effect of chemical potential and catalysis. It is found that the Pt/TiO₂ Janus micromotors exhibit the fastest motion compared to the rest of the prepared materials. Furthermore, after exposure to UV light, every fabricated micromotor shows high possibility of forming assembled chains which influence their velocity.     

Enzymatic Micromotors as a Mobile Photosensitizer Platform for Highly Efficient On‐Chip Targeted Antibacteria Photodynamic Therapy

Photodynamic therapy (PDT) functions when the light‐excited photosensitizers transfer energy to oxygen molecules (³O₂) to produce cytotoxic singlet oxygen (¹O₂) that can effectively kill cells or bacteria. However, the PDT efficacy is often reduced by the limited availability of ³O₂ surrounding the photosensitizer and extremely short diffusion range of the photoactivated ¹O₂. Herein, an enzymatic micromotor based on hollow mesoporous SiO₂ (mSiO₂) microspheres is constructed as a mobile and highly efficient photosensitizer platform. Carboxylated magnetic nanoparticles are connected with both hollow spheres and 5,10,15,20‐tetrakis(4‐aminophenyl)porphyrin molecules through covalent linkage between amino and carboxylic groups within a one‐step reaction. Due to the intrinsic asymmetry of the mSiO₂ spheres, the micromotors can be propelled by ionic diffusiophoresis induced by the enzymatic decomposition of urea. Via numerical simulation, the self‐propulsion mechanism is clarified and the movement direction is identified. By virtue of active self‐propulsion, the current system can overcome the long‐standing shortcomings of PDT and significantly enhance the PDT efficacy by improving the accessibility of the photosensitizer to ³O₂ and enlarging the diffusing range of ¹O₂. Therefore, by proposing a new solution to the bottleneck problems of PDT, this work provides insightful perspectives to the biomedical application of multifunctional micro/nanomotors.     

Superassembled Biocatalytic Porous Framework Micromotors with Reversible and Sensitive pH‐Speed Regulation at Ultralow Physiological H2O2 Concentration

Synthetic nano/micromotors are a burgeoning class of materials with vast promise for applications ranging from environmental remediation to nanomedicine. The motility of these motors is generally controlled by the concentration of accessible fuel, and therefore, engineering speed‐regulation mechanisms, particularly using biological triggers, remains a continuing challenge. Here, control over the movement of superassembled porous framework micromotors via a reversible, biological‐relevant pH‐responsive regulatory mechanism is demonstrated. Succinylated β‐lactoglobulin and catalase are superassembled in porous framework particles, where the β‐lactoglobulin is permeable at neutral pH. This permeability allows the fuel (H₂O₂) to access catalase, leading to autonomous movement of the micromotors. However, at mild acidic pH, succinylated β‐lactoglobulin undergoes a reversible gelation process, preventing the access of fuel into the micromotors where the catalase resides. To one's knowledge, this study represents the first example of chemically driven motors with rapid, reversible pH‐responsive motility. Furthermore, the porous framework significantly enhances the biocatalytic activity of catalase, allowing ultralow H₂O₂ concentrations to be exploited at physiological conditions. It is envisioned that the simultaneous exploitation of pH and chemical potential of such nanosystems could have potential applications as stimulus‐responsive drug delivery vehicles that benefit from the complex biological environment.     

A Microfluidic Tool for Fine‐Tuning Motion of Soft Micromotors

Microfluidics is an ideal tool for the design of self‐assembled micromotors. It allows for easy change of solutions, catalysts, and flow rates, which affect shape, structure, and motion of the resulting micromotors. A microfluidic tool generating aqueous‐two‐phase‐separating droplets of UV‐polymerizable poly(ethylene glycol)diacrylate (PEGDA) and an inert phase, salt, or polysaccharide, is utilized to fabricate asymmetric microbeads. Different molecular weights and branching of polysaccharides are used to study the effect on shape, surface roughness, and motion of the particles. The molecular weight of the polysaccharide determines the roughness of the motors inner surface. Smooth openings are obtained by low molecular weight dextran, while high surface roughness is obtained with a high molecular weight branched polysaccharide. Since roughness plays an important role in bubble pinning, it influences both speed and trajectory. Increasing speeds are obtained with increasing roughness and trajectories ranging from linear, circular to tumble‐and‐run depending on the nature of bubble pinning. This microfluidic tool allows for fine‐tuning shape, structure, and motion by easy change of solutions, catalysts, and flow rates.     

Real‐Time IR Tracking of Single Reflective Micromotors through Scattering Tissues

Medical micromotors have the potential to lead to a paradigm shift in future biomedicine, as they may perform active drug delivery, microsurgery, tissue engineering, or assisted fertilization in a minimally invasive manner. However, the translation to clinical treatment is challenging, as many applications of single or few micromotors require real‐time tracking and control at high spatiotemporal resolution in deep tissue. Although optical techniques are a popular choice for this task, absorption and strong light scattering lead to a pronounced decrease of the signal‐to‐noise ratio with increasing penetration depth. Here, a highly reflective micromotor is introduced which reflects more than tenfold the light intensity of simple gold particles and can be precisely navigated by external magnetic fields. A customized optical IR imaging setup and an image correlation technique are implemented to track single micromotors in real‐time and label‐free underneath phantom and ex vivo mouse skull tissues. As a potential application, the micromotors speed is recorded when moving through different viscous fluids to determine the viscosity of diverse physiological fluids toward remote cardiovascular disease diagnosis. Moreover, the micromotors are loaded with a model drug to demonstrate their cargo‐transport capability. The proposed reflective micromotor is suitable as theranostic tool for sub‐skin or organ‐on‐a‐chip applications.     

平面电磁型微电机定转子制作工艺

为了在平面微电机有限大尺寸的定子上制作大深宽比结构的绕组线圈,对大深宽比微结构的制作工艺进行了研究,综合比较各方面因素,从中找出了成品率高、可重复性好、工艺步骤简单的平面线圈的制作工艺,即在Si沟槽里通过微电铸得到大深宽比平面铜线圈的深刻蚀成型电铸工艺;分析了光刻工艺关键参数之间的关系及对后续工艺的影响。通过该工艺制作的直径10mm定子线圈深宽比较大(宽40μm、深80μm),且无空洞。该工艺有很大的深宽比挖掘潜力,也可应用在其他需要较大深宽比平面线圈的微执行器的制作中。