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.     

Coordination of contractility,adhesion and flow in migrating Physarum amoebae

This work examines the relationship between spatio-temporal coordination of intracellular flow and traction stress and the speed of amoeboid locomotion of microplasmodia of Physarum polycephalum. We simultaneously perform particle image velocimetry and traction stress microscopy to measure the velocity of cytoplasmic flow and the stresses applied to the substrate by migrating Physarum microamoebae. In parallel, we develop a mathematical model of a motile cell which includes forces from the viscous cytosol, a poro-elastic, contractile cytoskeleton and adhesive interactions with the substrate. Our experiments show that flow and traction stress exhibit back-to-front-directed waves with a distinct phase difference. The model demonstrates that the direction and speed of locomotion are determined by this coordination between contraction, flow and adhesion. Using the model, we identify forms of coordination that generate model predictions consistent with experiments. We demonstrate that this coordination produces near optimal migration speed and is insensitive to heterogeneity in substrate adhesiveness. While it is generally thought that amoeboid motility is robust to changes in extracellular geometry and the nature of extracellular adhesion, our results demonstrate that coordination of adhesive forces is essential to producing robust migration.     

Bioinspired Soft Microrobots with Precise Magneto-Collective Control for Microvascular Thrombolysis

New-era soft microrobots for biomedical applications need to mimic the essential structures and collective functions of creatures from nature. Biocompatible interfaces, intelligent functionalities, and precise locomotion control in a collective manner are the key parameters to design soft microrobots for the complex bio-environment. In this work, a biomimetic magnetic microrobot (BMM) inspired by magnetotactic bacteria (MTB) with speedy motion response and accurate positioning is developed for targeted thrombolysis. Similar to the magnetosome structure in MTB, the BMM is composed of aligned iron oxide nanoparticle (MNP) chains embedded in a non-swelling microgel shell. Linear chains in BMMs are achieved due to the interparticle dipolar interactions of MNPs under a static magnetic field. Simulation results show that, the degree and speed of assembly is proportional to the field strength. The BMM achieves the maximum speed of 161.7 µm s⁻¹ and accurate positioning control under a rotating magnetic field with less than 4% deviation. Importantly, the locomotion analyses of BMMs demonstrate the frequency-dependent synchronization under 8 Hz and asynchronization at higher frequencies due to the increased drag torque. The BMMs can deliver and release thrombolytic drugs via magneto-collective control, which is promising for ultra-minimal invasive thrombolysis.     

A Multidrug Delivery Microrobot for the Synergistic Treatment of Cancer

Multidrug combination therapy provides an effective strategy for malignant tumor treatment. This paper presents the development of a biodegradable microrobot for on-demand multidrug delivery. By combining magnetic targeting transportation with tumor therapy, it is hypothesized that loading multiple drugs on different regions of a single magnetic microrobot can enhance a synergistic effect for cancer treatment. The synergistic effect of using two drugs together is greater than that of using each drug separately. Here, a 3D-printed microrobot inspired by the fish structure with three hydrogel components: skeleton, head, and body structures is demonstrated. Made of iron oxide (Fe₃O₄) nanoparticles embedded in poly(ethylene glycol) diacrylate (PEGDA), the skeleton can respond to magnetic fields for microrobot actuation and drug-targeted delivery. The drug storage structures, head, and body, made by biodegradable gelatin methacryloyl (GelMA) exhibit enzyme-responsive cargo release. The multidrug delivery microrobots carrying acetylsalicylic acid (ASA) and doxorubicin (DOX) in drug storage structures, respectively, exhibit the excellent synergistic effects of ASA and DOX by accelerating HeLa cell apoptosis and inhibiting HeLa cell metastasis. In vivo studies indicate that the microrobots improve the efficiency of tumor inhibition and induce a response to anti-angiogenesis. The versatile multidrug delivery microrobot conceptualized here provides a way for developing effective combination therapy for cancer.     

Magnetically Powered Immunogenic Macrophage Microrobots for Targeted Multimodal Cancer Therapy (Small 42/2023)

Motile microrobots open a new realm for disease treatment. However, the concerns of possible immune elimination, targeted capability and limited therapeutic avenue of microrobots constrain its practical biomedical applications. Herein, a biogenic macrophage-based microrobot loaded with magnetic nanoparticles and bioengineered bacterial outer membrane vesicles (OMVs), capable of magnetic propulsion, tumor targeting, and multimodal cancer therapy is reported. Such cell robots preserve intrinsic properties of macrophages for tumor suppression and targeting, and bioengineered OMVs for antitumor immune regulation and fused anticancer peptides. Cell robots display efficient magnetic propulsion and directional migration in the confined space. In vivo tests show that cell robots can accumulate at the tumor site upon magnetic manipulation, coupling with tumor tropism of macrophages to greatly improve the efficacy of its multimodal therapy, including tumor inhibition of macrophages, immune stimulation, and antitumor peptides of OMVs. This technology offers an attractive avenue to design intelligent medical microrobots with remote manipulation and multifunctional therapy capabilities for practical precision treatment.     

Helical distributions of stokeslets

Helical distributions of stokeslets can valuably model microbial locomotion through a fluid, and also the flow field generated, wherever a flagellum actively executes helical undulations (as in many single-celled algae and protozoa) or where (as in many bacteria) the action of rotary motors causes a passive structure of helical shape (which may be a flagellum or else the cell body itself) to rotate. Here, previous biomechanical studies of such modes of locomotion are extended to include analyses of three-dimensional flow fields. In some cases, a rotlet field (curl of a stokeslet) needs to be incorporated in the models. For example, spirochete swimming is modelled by combined helical distributions of stokeslets and rotlets; the computed flow field being confined to within distances of less than twice the radius of the cell body's helical shape from its axis, while including a powerful jet-like interior flow through the coils of the swimming spirochete.     

Hybrid nanomotor: a catalytically/magnetically powered adaptive nanowire swimmer

A synthetic hybrid nanomotor, which combines chemically powered propulsion and magnetically driven locomotion, is described. The new catalytic-magnetic nanomotor consists of a flexible multisegment Pt-Au-Ag(flex)-Ni nanowire, with the Pt-Au and Au-Ag(flex)-Ni portions responsible for the catalytic and magnetic propulsion modes, respectively. The experimental data and theoretical considerations indicate that the hybrid design only minimally compromises the individual propulsion modes. Rapid and convenient switching from the catalytic to the magnetic mode is illustrated. The resulting catalytic-magnetic adaptive nanomotor can address the fuel depletion and salt limitation common to chemically powered motors by switching to magnetic propulsion. Reversal of the motion direction is also achieved upon applying the magnetic field. Such use of two sources to power a hybrid device offers a broader scope of operation and holds considerable promise for designing adaptive nanovehicles that reconfigure their operation in response to environmental changes or unexpected events.     

Moving Droplets in 3D Using Light

The emulation of the complex cellular and bacterial vesicles used to transport materials through fluids has the potential to add revolutionary capabilities to fluidic platforms. Although a number of artificial motile vesicles or microdroplets have been demonstrated previously, control over their movement in liquid in 3D has not been achieved. Here it is shown that by adding a chemical “fuel,” a photoactive material, to the droplet, it can be moved in any direction (3D) in water using simple light sources without the need for additives in the water. The droplets can be made up of a range of solvents and move with speeds as high as 10.4 mm s^?1 toward or away from the irradiation source as a result of a light‐induced isothermal change in interfacial tension (Marangoni flow). It is further demonstrated that more complex functions can be accomplished by merging a photoactive droplet with a droplet carrying a “cargo” and moving the new larger droplet to a “reactor” droplet where the cargo undergoes a chemical reaction. The control and versatility of this light‐activated, motile droplet system will open up new possibilities for fluidic chemical transport and applications.     

Controllable High‐Speed Electrostatic Manipulation of Water Droplets on a Superhydrophobic Surface

Biological processes and technological applications cannot work without liquid control, where versatile water droplet manipulation is a significant issue. Droplet motion is conventionally manipulated by functionalizing the target surface or by utilizing additives in the droplet, still, with uncontrolled limitation on superhydrophobic surfaces since droplets are either unable to move fast or are difficult to stop while moving. A controllable high‐speed “all‐in‐one” no‐loss droplet manipulation, that is, in‐plane moving and stopping/pinning in any direction on a superhydrophobic surface, with electrostatic charging is demonstrated. The experimental results reveal that the transport speed can vary from zero to several hundreds of millimeters per second. Controlled dynamic switching between the onset moving state and the offset pinning state of a water droplet can be achieved by out‐of‐plane electrostatic charging. This work opens the possibility of droplet control techniques in various applications, such as combinatory chemistry, biochemical, and medical detection.     

Length Scale Selects Directionality of Droplets on Vibrating Pillar Ratchet

Directional control of droplet motion at room temperature is of interest for applications such as microfluidic devices, self‐cleaning coatings, and directional adhesives. Here, arrays of tilted pillars ranging in height from the nanoscale to the microscale are used as structural ratchets to directionally transport water at room temperature. Water droplets deposited onto vibrating chips with a nanostructured ratchet move preferentially in the direction of the feature tilt while the opposite directionality is observed in the case of microstructured ratchets. This remarkable switch in directionality is consistent with changes in the contact angle hysteresis. To glean further insights into the length scale dependent asymmetric contact angle hysteresis, the contact lines formed by a nonvolatile room temperature ionic liquid placed onto the tilted pillar arrays were visualized and analyzed in situ in a scanning electron microscope. The ability to tune droplet directionality by merely changing the length scale of surface features all etched at the same tilt angle would be a versatile tool for manipulating multiphase flows and for selecting droplet directionality in other lap‐on‐chip applications.     

Mechanics of peristaltic locomotion and role of anchoring

Limbless crawling is a fundamental form of biological locomotion adopted by a wide variety of species, including the amoeba, earthworm and snake. An interesting question from a biomechanics perspective is how limbless crawlers control their flexible bodies in order to realize directional migration. In this paper, we discuss the simple but instructive problem of peristalsis-like locomotion driven by elongation–contraction waves that propagate along the body axis, a process frequently observed in slender species such as the earthworm. We show that the basic equation describing this type of locomotion is a linear, one-dimensional diffusion equation with a time–space-dependent diffusion coefficient and a source term, both of which express the biological action that drives the locomotion. A perturbation analysis of the equation reveals that adequate control of friction with the substrate on which locomotion occurs is indispensable in order to translate the internal motion (propagation of the elongation–contraction wave) into directional migration. Both the locomotion speed and its direction (relative to the wave propagation) can be changed by the control of friction. The biological relevance of this mechanism is discussed.     

Friction and Wetting Transitions of Magnetic Droplets on Micropillared Superhydrophobic Surfaces

Reliable characterization of wetting properties is essential for the development and optimization of superhydrophobic surfaces. Here, the dynamics of superhydrophobicity is studied including droplet friction and wetting transitions by using droplet oscillations on micropillared surfaces. Analyzing droplet oscillations by high‐speed camera makes it possible to obtain energy dissipation parameters such as contact angle hysteresis force and viscous damping coefficients, which indicate pinning and viscous losses, respectively. It is shown that the dissipative forces increase with increasing solid fraction and magnetic force. For 10 µm diameter pillars, the solid fraction range within which droplet oscillations are possible is between 0.97% and 2.18%. Beyond the upper limit, the oscillations become heavily damped due to high friction force. Below the lower limit, the droplet is no longer supported by the pillar tops and undergoes a Cassie–Wenzel transition. This transition is found to occur at lower pressure for a moving droplet than for a static droplet. The findings can help to optimize micropillared surfaces for low‐friction droplet transport.     

GISAXS studies of self-assembling of colloidal Co nanoparticles

In this work we report on the formation of ordered monolayers (2-D) and arrays of rods (3-D) of magnetic Co nanoparticles in magnetic field perpendicular to the substrate surface. Samples were prepared by drying a droplet of colloidal solution of Co nanoparticles (10 nm diameter) on Si/Si₃N₄ substrates in magnetic field between 0.2 and 0.9 T. The samples were characterized by high resolution scanning electron microscopy (SEM), atomic and magnetic force microscopy (AFM/MFM) and grazing incidence small angle X-ray scattering (GISAXS). SEM studies of monolayers show well-ordered 2-D arrays with hexagonal symmetry of 200 nm × 500 nm in size forming a mosaic structure. Rods, about 500 nm in diameter, aligned with the field direction and forming a hexagonal pattern were obtained when higher concentration of colloid and low evaporation rate of the solvent were used. The ordering of nanoparticles in the monolayer analyzed by GISAXS is described by the local order with hexagonal symmetry. The model of close packing of hard spheres is used for ordering of particles inside the rods. Magnetic features corresponding to the 3-D arrays have been observed by MFM pointing out that all magnetic moments in the rod are oriented along the field direction.     

Microalgae-Based Biohybrid Microrobot for Accelerated Diabetic Wound Healing

A variety of wound healing platforms have been proposed to alleviate the hypoxic condition and/or to modulate the immune responses for the treatment of chronic wounds in diabetes. However, these platforms with the passive diffusion of therapeutic agents through the blood clot result in the relatively low delivery efficiency into the deep wound site. Here, a microalgae-based biohybrid microrobot for accelerated diabetic wound healing is developed. The biohybrid microrobot autonomously moves at velocity of 33.3 µm s⁻¹ and generates oxygen for the alleviation of hypoxic condition. In addition, the microrobot efficiently bound with inflammatory chemokines of interleukin-8 (IL-8) and monocyte chemoattractant protein-1 (MCP-1) for modulating the immune responses. The enhanced penetration of microrobot is corroborated by measuring fibrin clots in biomimetic wound using microfluidic devices and the enhanced retention of microrobot is confirmed in the real wounded mouse skin tissue. After deposition on the chronic wound in diabetic mice without wound dressing, the wounds treated with microrobots are completely healed after 9 days with the significant decrease of inflammatory cytokines below 31% of the control level and the upregulated angiogenesis above 20 times of CD31⁺ cells. These results confirm the feasibility of microrobots as a next-generation platform for diabetic wound healing.     

Rainbow refractometry: simultaneous measurement of temperature, refractive index, and size of droplets

The capabilities and limitations of rainbow refractometry, specifically the minimum measurable droplet size and the errors in the refractive index (temperature), have been studied. We evaluate what we believe is a new method of indirectly applying the Lorenz-Mie theory to rainbow refractometry. The results show that this new method reduces the errors and eliminates the biases that may occur if the Airy theory is used. A more precise method to filter the high-frequency oscillations associated with the measurement signals was developed. Finally, it was discovered that the errors associated with rainbow refractometry are such that a single droplet measurement is unreliable. A mean refractive index should be determined on the basis of multiple droplet measurements.     

探讨电弧离子镀中“大颗粒”净化方法

传统电弧离子镀存在着大颗粒污染、沉积温度相对较高和易引发微弧击穿效应等诸多不足,制约其在精细薄膜、低温沉积和功能薄膜等方面的应用。本文简要介绍了电弧离子镀中大颗粒的形成机理,旨在探讨用磁场控制、脉冲电弧、磁过滤及脉冲偏压等方法来减少大微粒污染及其作用机理。     

环境设计中的人工智能视角

人工智能在环境设计中的应用已经进入了快速发展的阶段,人工智能在环境设计的工具、方法、表达,以及设计内容的扩充、设计语言的丰富性等方面都产生了广泛的变革。本文从环境设计中的人工智能视角出发,探讨了在环境设计中人工智能发展的未来趋势及可能出现的革命性变化。对环境设计中人工智能的应用情况进行梳理,对具有广泛影响力的设计作品进行分析,探讨人工智能在应用环境设计中的价值和意义,以及其未来可能的发展趋势。人工智能在环境设计中的应用是从设计手段到设计内容的一次重大变革。从互动能力、虚拟能力,到大数据的整合等,都是人工智能所具有的能力给环境设计带来的新的机遇和挑战。环境艺术设计从业者在应对这样的变革时,应建立更加系统化、立体化、数据化的设计活动体系及更加宽泛的设计理论体系。     

Magnetophoretic velocimetry of manganese(II) in a single emulsion droplet at the femtomole level.

We developed a new experimental technique named magnetophoretic velocimetry to determine a small amount of paramagnetic species in a single microdroplet. The magnetophoretic velocity of an aqueous droplet containing paramagnetic metal ion dispersed in an organic medium could response to a very small amount of the metal ion under an inhomogeneous magnetic field. The paramagnetic droplet (2 approximately 8 microm diam) used as a test sample in this study was the aqueous droplet of manganese(II) chloride dispersed in ethylbenzoate whose density was nearly equal to water. A pair of small Nd-Fe-B magnets placed with a gap of 400 microm generated an inhomogeneous magnetic field between the edges, at which the product of the magnetic flux density and the gradient, B(dB/dx), was as high as 410 T2 m(-1). When a silica capillary containing the emulsion was inserted into the gap between the magnets, the magnetophoretic migration of the droplets was observed with a video microscope. The magnetophoretic velocity divided by the squared radius of the droplet was proportional to the MnCl2 concentration in the droplet, as predicted by a theoretical calculation. The estimated detection limit in this simple method was lower than 10(-16) mol for manganese(II).     

Angular diagram of broadband emission of millimeter-sized water droplets exposed to gigawatt femtosecond laser pulses

We report on the experiments on the interaction of gigawatt femtosecond laser pulses with suspended millimeter-sized water droplets. The transparent droplets experienced laser-induced breakdown and explosive boiling up and emitted a broadband radiation. This radiation covers the spectral range from 450 to 1100?nm and consists of the spectrum of laser pulse scattered and transformed by the droplet due to self-phase modulation and plasma emission produced in water during photoionization. The droplet emission spectrum showed remarkable broadening at all viewing angles and is maximal in the direction of the laser exit from the droplet. The enlargement of the droplet results in additional spectral spreading of the emitted radiation. The depth and amount of laser pulse spectral self-transformations upon propagation through the water droplet are simulated by means of numerical calculations.     

Nanodiamonds That Swim

Nanodiamonds are emerging as nanoscale quantum probes for bio‐sensing and imaging. This necessitates the development of new methods to accurately manipulate their position and orientation in aqueous solutions. The realization of an “active” nanodiamond (ND) swimmer in fluids, composed of a ND crystal containing nitrogen vacancy centers and a light‐driven self‐thermophoretic micromotor, is reported. The swimmer is propelled by a local temperature gradient created by laser illumination on its metal‐coated side. Its locomotion—from translational to rotational motion—is successfully controlled by shape‐dependent hydrodynamic interactions. The precise engineering of the swimmer's geometry is achieved by self‐assembly combined with physical vapor shadow growth. The optical addressability of the suspended ND swimmers is demonstrated by observing the electron spin resonance in the presence of magnetic fields. Active motion at the nanoscale enables new sensing capabilities combined with active transport including, potentially, in living organisms.