Autonomous Biohybrid Urchin‐Like Microperforator for Intracellular Payload Delivery

A magnetic urchin‐like microswimmer based on sunflower pollen grain (SPG) that can pierce the cancer cell membrane and actively deliver therapeutic drugs is reported. These drug loaded microperforators are fabricated on a large scale by sequentially treating the natural SPGs with acidolysis, sputtering, and vacuum loading. The microswimmers exhibit precise autonomous navigation and obstacle avoidance in complex environments via association with artificial intelligence. Assemblies of microswimmers can further enhance individual motion performance and adaptability to complicated environments. Additionally, the experimental results demonstrate that microswimmers with nanospikes can accomplish single‐cell perforation for direct delivery under an external rotating magnetic field. Drugs encapsulated in the inner cavity of the microperforators can be accurately delivered to a specific site via remote control. These dual‐action microswimmers demonstrate good biocompatibility, high intelligence, precision in single‐cell targeting, and sufficient drug loading, presenting a promising avenue for many varieties of biomedical applications.     

Magnetically Powered Shape‐Transformable Liquid Metal Micromotors

Shape‐transformable liquid metal (LM) micromachines have attracted the attention of the scientific community over the past 5 years, but the inconvenience of transfer routes and the use of corrosive fuels have limited their potential applications. In this work, a shape‐transformable LM micromotor that is fabricated by a simple, versatile ice‐assisted transfer printing method is demonstrated, in which an ice layer is employed as a “sacrificial” substrate that can enable the direct transfer of LM micromotors to arbitrary target substrates conveniently. The resulting LM microswimmers display efficient propulsion of over 60 µm s^?1 (≈3 bodylength s^?1) under elliptically polarized magnetic fields, comparable to that of the common magnetic micro/nanomotors with rigid bodies. Moreover, these LM micromotors can undergo dramatic morphological transformation in an aqueous environment under the irradiation of an alternating magnetic field. The ability to transform the shape and efficiently propel LM microswimmers holds great promise for chemical sensing, controlled cargo transport, materials science, and even artificial intelligence in ways that are not possible with rigid‐bodies microrobots.     

Light‐Activated,Multi‐Semiconductor Hybrid Microswimmers

Using a dynamic fabrication process, hybrid, photoactivated microswimmers made from two different semiconductors, titanium dioxide (TiO₂) and cuprous oxide (Cu₂O) are developed, where each material occupies a distinct portion of the multiconstituent particles. Structured light‐activated microswimmers made from only TiO₂ or Cu₂O are observed to be driven in hydrogen peroxide and water most vigorously under UV or blue light, respectively, whereas hybrid structures made from both of these materials exhibit wavelength‐dependent modes of motion due to the disparate responses of each photocatalyst. It is also found that the hybrid particles are activated in water alone, a behavior which is not observed in those made from a single semiconductor, and thus, the system may open up a new class of fuel‐free photoactive colloids that take advantage of semiconductor heterojunctions. The TiO₂/Cu₂O hybrid microswimmer presented here is but an example of a broader method for inducing different modes of motion in a single light‐activated particle, which is not limited to the specific geometries and materials presented in this study.     

Tuning the Solid Electrolyte Interphase for Selective Li‐ and Na‐Ion Storage in Hard Carbon

Solid‐electrolyte interphase (SEI) films with controllable properties are highly desirable for improving battery performance. In this paper, a combined experimental and theoretical approach is used to study SEI films formed on hard carbon in Li‐ and Na‐ion batteries. It is shown that a stable SEI layer can be designed by precycling an electrode in a desired Li‐ or Na‐based electrolyte, and that ionic transport can be kinetically controlled. Selective Li‐ and Na‐based SEI membranes are produced using Li‐ or Na‐based electrolytes, respectively. The Na‐based SEI allows easy transport of Li ions, while the Li‐based SEI shuts off Na‐ion transport. Na‐ion storage can be manipulated by tuning the SEI layer with film‐forming electrolyte additives, or by preforming an SEI layer on the electrode surface. The Na specific capacity can be controlled to < 25 mAh g^?1; ≈ 1/10 of the normal capacity (250 mAh g^?1). Unusual selective/preferential transport of Li ions is demonstrated by preforming an SEI layer on the electrode surface and corroborated with a mixed electrolyte. This work may provide new guidance for preparing good ion‐selective conductors using electrochemical approaches.     

A Force to Be Reckoned With: A Review of Synthetic Microswimmers Powered by Ultrasound

Synthetic microswimmers are a class of artificial nano‐ or microscale particle capable of converting external energy into motion. They are similar to natural microswimmers such as bacteria in behavior and are, therefore, of great interest to the study of active matter. Additionally, microswimmers show promise in applications ranging from bioanalytics and environmental monitoring to particle separation and drug delivery. However, since their sizes are on the nano‐/microscale and their speeds are in the μm s^?1 range, they fall into a low Reynolds number regime where viscosity dominates. Therefore, new propulsion schemes are needed for these microswimmers to be able to efficiently move. Furthermore, many of the hotly pursued applications call for innovations in the next phase of development of biocompatible microswimmers. In this review, the latest developments of microswimmers powered by ultrasound are presented. Ultrasound, especially at MHz frequencies, does little harm to biological samples and provides an advantageous and well‐controlled means to efficiently power microswimmers. By critically reviewing the recent progress in this research field, an introduction of how ultrasound propels colloidal particles into autonomous motion is presented, as well as how this propulsion can be used to achieve preliminary but promising applications.     

Template‐Assisted Electroforming of Fully Semi‐Hard‐Magnetic Helical Microactuators

The authors report on the fabrication of semi‐hard‐magnetic microhelices using template‐assisted electroforming. The method consists of electrodepositing a material on a sacrificial mandrel on which a pattern has been previously written. To electroform the helical microswimmers, a helical template on a polymer‐coated metallic mandrel is created using a laser, which precisely ablates the polymer coating and exposes the mandrel surface. Subsequently, the semi‐hard‐magnetic material is electrodeposited in the trenches produced by the laser. In this investigation, the helical structures are obtained from an electrolyte, which enables the production of hard‐magnetic CoPt alloys. The authors also show that electroformed semi‐hard‐magnetic helical microswimmers can propel in viscous environments such as silicon oil in three dimensions and against gravity. Their manufacturing approach can be used for the fabrication of more complex architectures for a wide range of applications and can be potentially extended to any electroplatable material.

     

A High‐Performance Top‐Gated Graphene Field‐Effect Transistor with Excellent Flexibility Enabled by an iCVD Copolymer Gate Dielectric

A high‐performance top‐gated graphene field‐effect transistor (FET) with excellent mechanical flexibility is demonstrated by implementing a surface‐energy‐engineered copolymer gate dielectric via a solvent‐free process called initiated chemical vapor deposition. The ultrathin, flexible copolymer dielectric is synthesized from two monomers composed of 1,3,5‐trimethyl‐1,3,5‐trivinyl cyclotrisiloxane and 1‐vinylimidazole (VIDZ). The copolymer dielectric enables the graphene device to exhibit excellent dielectric performance and substantially enhanced mechanical flexibility. The p‐doping level of the graphene can be tuned by varying the polar VIDZ fraction in the copolymer dielectric, and the Dirac voltage (V_Dirac) of the graphene FET can thus be systematically controlled. In particular, the V_Dirac approaches neutrality with higher VIDZ concentrations in the copolymer dielectric, which minimizes the carrier scattering and thereby improves the charge transport of the graphene device. As a result, the graphene FET with 20 nm thick copolymer dielectrics exhibits field‐effect hole and electron mobility values of over 7200 and 3800 cm² V^?1 s^?1, respectively, at room temperature. These electrical characteristics remain unchanged even at the 1 mm bending radius, corresponding to a tensile strain of 1.28%. The formed gate stack with the copolymer gate dielectric is further investigated for high‐frequency flexible device applications.     

Gate‐Controlled Graphene–Silicon Schottky Junction Photodetector

Various photodetectors showing extremely high photoresponsivity have been frequently reported, but many of these photodetectors could not avoid the simultaneous amplification of dark current. A gate‐controlled graphene–silicon Schottky junction photodetector that exhibits a high on/off photoswitching ratio (≈10⁴), a very high photoresponsivity (≈70 A W⁻¹), and a low dark current in the order of µA cm⁻² in a wide wavelength range (395–850 nm) is demonstrated. The photoresponsivity is ≈100 times higher than that of existing commercial photodetectors, and 7000 times higher than that of graphene‐field‐effect transistor‐based photodetectors, while the dark current is similar to or lower than that of commercial photodetectors. This result can be explained by a unique gain mechanism originating from the difference in carrier transport characteristics of silicon and graphene.     

Magnetically Driven Undulatory Microswimmers Integrating Multiple Rigid Segments

Mimicking biological locomotion strategies offers important possibilities and motivations for robot design and control methods. Among bioinspired microrobots, flexible microrobots exhibit remarkable efficiency and agility. These microrobots traditionally rely on soft material components to achieve undulatory propulsion, which may encounter challenges in design and manufacture including the complex fabrication processes and the interfacing of rigid and soft components. Herein, a bioinspired magnetically driven microswimmer that mimics the undulatory propulsive mechanism is proposed. The designed microswimmer consists of four rigid segments, and each segment is connected to the succeeding segment by joints. The microswimmer is fabricated integrally by 3D laser lithography without further assembly, thereby simplifying microrobot fabrication while enhancing structural integrity. Experimental results show that the microswimmer can successfully swim forward along guided directions via undulatory locomotion in the low Reynolds number (Re) regime. This work demonstrates for the first time that the flexible characteristic of microswimmers can be emulated by 3D structures with multiple rigid segments, which broadens possibilities in microrobot design. The proposed magnetically driven microswimmer can potentially be used in biomedical applications, such as medical diagnosis and treatment in precision medicine.     

One‐Way Particle Transport Using Oscillatory Flow in Asymmetric Traps

One challenge of integrating of passive, microparticles manipulation techniques into multifunctional microfluidic devices is coupling the continuous‐flow format of most systems with the often batch‐type operation of particle separation systems. Here, a passive fluidic technique—one‐way particle transport—that can conduct microparticle operations in a closed fluidic circuit is presented. Exploiting pass/capture interactions between microparticles and asymmetric traps, this technique accomplishes a net displacement of particles in an oscillatory flow field. One‐way particle transport is achieved through four kinds of trap–particle interactions: mechanical capture of the particle, asymmetric interactions between the trap and the particle, physical collision of the particle with an obstacle, and lateral shift of the particle into a particle–trapping stream. The critical dimensions for those four conditions are found by numerically solving analytical mass balance equations formulated using the characteristics of the flow field in periodic obstacle arrays. Visual observation of experimental trap–particle dynamics in low Reynolds number flow (<0.01) confirms the validity of the theoretical predictions. This technique can transport hundreds of microparticles across trap rows in only a few fluid oscillations (<500 ms per oscillation) and separate particles by their size differences.     

One‐Step Fabrication of Triple‐Layered Polymeric Microparticles with Layer Localization of Drugs as a Novel Drug‐Delivery System

Particulate systems have tremendous potential to achieve controlled release and targeted delivery of drugs. However, conventional single‐layered particles have several inherent limitations, including initial burst release, the inability to provide zero‐order release, and a lack of time‐delayed or pulsatile release of therapeutic agents. Multilayered particles have the potential to overcome these disadvantages. Herein, it is shown how triple‐layered polymeric microparticles can be fabricated through a simple, economical, reliable, and versatile one‐step solvent evaporation technique. Particle morphologies and layer configurations are determined by scanning electron microscopy, polymer dissolution tests, and Raman mapping. Key fabrication parameters that affect the formation of triple‐layered polymeric microparticles comprising poly(DL ‐lactide‐co‐glycolide) (50:50), poly(L ‐lactide), and poly(ethylene‐co‐vinyl acetate) (40 wt% vinyl acetate) are discussed, along with their formation mechanisms. Layer thickness and the configurations of these microparticles are altered by changing the polymer mass ratios. Finally, it is shown that drugs can be localized in specific layers of the microparticles. This fabrication process can therefore be used to tailor microparticle designs, thus allowing such “designer” particulate drug‐delivery systems to function across a wide range of applications.     

High‐Mobility Helical Tellurium Field‐Effect Transistors Enabled by Transfer‐Free,Low‐Temperature Direct Growth

The transfer‐free direct growth of high‐performance materials and devices can enable transformative new technologies. Here, room‐temperature field‐effect hole mobilities as high as 707 cm² V^?1 s^?1 are reported, achieved using transfer‐free, low‐temperature (≤120 °C) direct growth of helical tellurium (Te) nanostructure devices on SiO₂/Si. The Te nanostructures exhibit significantly higher device performance than other low‐temperature grown semiconductors, and it is demonstrated that through careful control of the growth process, high‐performance Te can be grown on other technologically relevant substrates including flexible plastics like polyethylene terephthalate and graphene in addition to amorphous oxides like SiO₂/Si and HfO₂. The morphology of the Te films can be tailored by the growth temperature, and different carrier scattering mechanisms are identified for films with different morphologies. The transfer‐free direct growth of high‐mobility Te devices can enable major technological breakthroughs, as the low‐temperature growth and fabrication is compatible with the severe thermal budget constraints of emerging applications. For example, vertical integration of novel devices atop a silicon complementary metal oxide semiconductor platform (thermal budget <450 °C) has been theoretically shown to provide a 10× systems level performance improvement, while flexible and wearable electronics (thermal budget <200 °C) can revolutionize defense and medical applications.     

Thread‐Like Radical‐Polymerization via Autonomously Propelled (TRAP) Bots

Micromotor‐mediated synthesis of thread‐like hydrogel microstructures in an aqueous environment is presented. The study utilizes a catalytic micromotor assembly (owing to the presence of a Pt layer), with an on‐board chemical reservoir (i.e., polymerization mixture), toward thread‐like radical‐polymerization via autonomously propelled bots (i.e., TRAP bots). Synergistic coupling of catalytically active Pt layer, together with radical initiators (H₂O₂ and FeCl₃ (III)), and PEGDA monomers preloaded into the TRAP bot, results in the polymerization of monomeric units into elongated thread‐like hydrogel polymers coupled with self‐propulsion. Interestingly, polymer generation via TRAP bots can also be triggered in the absence of hydrogen peroxide for cellular/biomedical application. The resulting polymeric hydrogel microstructures are able to entrap living cells (NIH 3T3 fibroblast cells), and are easily separable via a centrifugation or magnetic separation (owing to the presence of a Ni layer). The cellular biocompatibility of TRAP bots is established via a LIVE/DEAD assay and MTS cell proliferation assay (7 days observation). This is the first study demonstrating real‐time in situ hydrogel polymerization via an artificial microswimmer, capable of enmeshing biotic/abiotic microobjects in its reaction environment, and lays a strong foundation for advanced applications in cell/tissue engineering, drug delivery, and cleaner technologies.     

Microwave Energy Drives “On–Off–On” Spin‐Switch Behavior in Nitrogen‐Doped Graphene

The established application of graphene in organic/inorganic spin‐valve spintronic assemblies is as a spin‐transport channel for spin‐polarized electrons injected from ferromagnetic substrates. To generate and control spin injection without such substrates, the graphene backbone must be imprinted with spin‐polarized states and itinerant‐like spins. Computations suggest that such states should emerge in graphene derivatives incorporating pyridinic nitrogen. The synthesis and electronic properties of nitrogen‐doped graphene (N content: 9.8%), featuring both localized spin centers and spin‐containing sites with itinerant electron properties, are reported. This material exhibits spin‐switch behavior (on–off–on) controlled by microwave irradiation at X‐band frequency. This phenomenon may enable the creation of novel types of switches, filters, and spintronic devices using sp²‐only 2D systems.     

Liquid‐Crystalline Dynamic Networks Doped with Gold Nanorods Showing Enhanced Photocontrol of Actuation

A near‐infrared‐light (NIR)‐ and UV‐light‐responsive polymer nanocomposite is synthesized by doping polymer‐grafted gold nanorods into azobenzene liquid‐crystalline dynamic networks (AuNR‐ALCNs). The effects of the two different photoresponsive mechanisms, i.e., the photochemical reaction of azobenzene and the photothermal effect from the surface plasmon resonance of the AuNRs, are investigated by monitoring both the NIR‐ and UV‐light‐induced contraction forces of the oriented AuNR‐ALCNs. By taking advantage of the material's easy processability, bilayer‐structured actuators can be fabricated to display photocontrollable bending/unbending directions, as well as localized actuations through programmed alignment of azobenzene mesogens in selected regions. Versatile and complex motions enabled by the enhanced photocontrol of actuation are demonstrated, including plastic “athletes” that can execute light‐controlled push‐ups or sit‐ups, and a light‐driven caterpillar‐inspired walker that can crawl forward on a ratcheted substrate at a speed of about 13 mm min^‐1. Moreover, the photomechanical effects arising from the two types of light‐triggered molecular motion, i.e., the trans–cis photoisomerization and a liquid‐crystalline–isotropic phase transition of the azobenzene mesogens, are added up to design a polymer “crane” that is capable of performing light‐controlled, robot‐like, concerted macroscopic motions including grasping, lifting up, lowering down, and releasing an object.     

Unraveling the Solution‐State Supramolecular Structures of Donor–Acceptor Polymers and their Influence on Solid‐State Morphology and Charge‐Transport Properties

Polymer self‐assembly in solution prior to film fabrication makes solution‐state structures critical for their solid‐state packing and optoelectronic properties. However, unraveling the solution‐state supramolecular structures is challenging, not to mention establishing a clear relationship between the solution‐state structure and the charge‐transport properties in field‐effect transistors. Here, for the first time, it is revealed that the thin‐film morphology of a conjugated polymer inherits the features of its solution‐state supramolecular structures. A “solution‐state supramolecular structure control” strategy is proposed to increase the electron mobility of a benzodifurandione‐based oligo(p‐ phenylene vinylene) (BDOPV)‐based polymer. It is shown that the solution‐state structures of the BDOPV‐based conjugated polymer can be tuned such that it forms a 1D rod‐like structure in good solvent and a 2D lamellar structure in poor solvent. By tuning the solution‐state structure, films with high crystallinity and good interdomain connectivity are obtained. The electron mobility significantly increases from the original value of 1.8 to 3.2 cm² V^?1 s^?1. This work demonstrates that “solution‐state supramolecular structure” control is critical for understanding and optimization of the thin‐film morphology and charge‐transport properties of conjugated polymers.     

From Strong Dichroic Nanomotor to Polarotactic Microswimmer

Light‐driven micro/nanomotors are promising candidates for long‐envisioned next‐generation nanorobotics for targeted drug delivery, noninvasive surgery, nanofabrication, and beyond. To achieve these fantastic applications, effective control of the micro/nanomotor is essential. Light has been proved as the most versatile method for microswimmer manipulation, while the light propagation direction, intensity, and wavelength have been explored as controlling signals for light‐responsive nanomotors. Here, the controlling method is expanded to the polarization state of the light, and a nanomotor with a significant dichroic ratio is demonstrated. Due to the anisotropic crystal structure, light polarized parallel to the Sb₂Se₃ nanowires is preferentially absorbed. The core–shell Sb₂Se₃/ZnO nanomotor exhibits strong dichroic swimming behavior: the swimming speed is ≈3 times faster when illuminated with parallel polarized light than perpendicular polarized light. Furthermore, by incorporating two cross‐aligned dichroic nanomotors, a polarotactic artificial microswimmer is achieved, which can be navigated by controlling the polarization direction of the incident light. Compared to the well‐studied light‐driven rotary motors based on optical tweezers, this dichroic microswimmer offers eight orders of magnitude light‐intensity reduction, which may enable large‐scale nanomanipulation as well as other heat‐sensitive applications.     

Rotating‐Electric‐Field‐Induced Carbon‐Nanotube‐Based Nanomotor in Water: A Molecular Dynamics Study

Using molecular dynamics simulations, it is shown that a carbon nanotube (CNT) suspended in water and subjected to a rotating electric field of proper magnitude and angular speed can be rotated with the aid of water dipole orientations. Based on this principle, a rotational nanomotor structure is designed and the system is simulated in water. Use of the fast responsiveness of electric‐field‐induced CNT orientation in water is employed and its operation at ultrahigh‐speed (over 10¹¹ r.p.m.) is shown. To explain the basic mechanism, the behavior of the rotational actuation, originated from the water dipole orientation, is also analyzed . The proposed nanomotor is capable of rotating an attached load (such as CNT) at a precise angle as well as nanogear‐based complex structures. The findings suggest a potential way of using the electric‐field‐induced CNT rotation in polarizable fluids as a novel tool to operate nanodevices and systems.     

A New Approach to In‐Situ “Micromanufacturing”: Microfluidic Fabrication of Magnetic and Fluorescent Chains Using Chitosan Microparticles as Building Blocks

An in situ microfluidic assembly approach is described that can both produce microsized building blocks and assemble them into complex multiparticle configurations in the same microfluidic device. The building blocks are microparticles of the biopolymer chitosan, which is intentionally selected because its chemistry allows for simultaneous intraparticle and interparticle linking. Monodisperse chitosan‐bearing droplets are created by shearing off a chitosan solution at a microfluidic T‐junction with a stream of hexadecane containing a nonionic detergent. These droplets are then interfacially crosslinked into stable microparticles by a downstream flow of glutaraldehyde (GA). The functional properties of these robust microparticles can be easily varied by introducing various payloads, such as magnetic nanoparticles and/or fluorescent dyes, into the chitosan solution. The on‐chip connection of such individual particles into well‐defined microchains is demonstrated using GA again as the chemical “glue” and microchannel confinement as the spatial template. Chain flexibility can be tuned by adjusting the crosslinking conditions: both rigid chains and semiflexible chains are created. Additionally, the arrangement of particles within a chain can also be controlled, for example, to generate chains with alternating fluorescent and nonfluorescent microparticles. Such microassembled chains could find applications as microfluidic mixers, delivery vehicles, microscale sensors, or miniature biomimetic robots.     

Rapid,Controllable Fabrication of Regular Complex Microarchitectures by Capillary Assembly of Micropillars and Their Application in Selectively Trapping/Releasing Microparticles

A simple strategy to realize new controllable 3D microstructures and a novel method to reversibly trapping and releasing microparticles are reported. This technique controls the height, shape, width, and arrangement of pillar arrays and realizes a series of special microstructures from 2‐pillar‐cell to 12 cell arrays, S‐shape, chain‐shape and triangle 3‐cell arrays by a combined top down/bottom up method: laser interference lithography and capillary force‐induced assembly. Due to the inherent features of this method, the whole time is less than 3 min and the fabricated area determined by the size of the laser beam can reach as much as 1 cm², which shows this method is very simple, rapid, and high‐throughput. It is further demonstrated that the ‘mechanical hand’‐like 4‐cell arrays could be used to selectively trap/release microparticles with different sizes, e.g., 1.5, 2, or 3.5 μm, which are controlled by the period of the microstructures from 2.5 to 4 μm, and 6 μm. Finally, the ‘mechanical hand’‐like 4‐cell arrays are integrated into 100 μm‐width microfluidic channels prepared by ultraviolet photolithography, which shows that this technique is compatible with conventional microfabrication methods for on‐chip applications.