Capillary-based, multifunctional manipulation of particles and fluids via focused surface acoustic waves.

Surface acoustic wave (SAW)-enabled acoustofluidic technologies have recently atttracted increasing attention for applications in biology, chemistry, biophysics, and medicine. Most SAW acoustofluidic devices generate acoustic energy which is then transmitted into custom microfabricated polymer-based channels. There are limited studies on delivering this acoustic energy into convenient commercially-available glass tubes for manipulating particles and fluids. Herein, we have constructed a capillary-based SAW acoustofluidic device for multifunctional fluidic and particle manipulation. This device integrates a converging interdigitated transducer to generate focused SAWs on a piezoelectric chip, as well as a glass capillary that transports particles and fluids. To understand the actuation mechanisms underlying this device, we performed finite element simulations by considering piezoelectric, solid mechanic, and pressure acoustic physics. This experimental study shows that the capillary-based SAW acoustofluidic device can perform multiple functions including enriching particles, patterning particles, transporting particles and fluids, as well as generating droplets with controlled sizes. Given the usefulness of these functions, we expect that this acoustofluidic device can be useful in applications such as pharmaceutical manufacturing, biofabrication, and bioanalysis.

Bipedal microwalkers actuated by oscillating magnetic fields.

Microrobots have attracted considerable attention due to their immense potential for biomedical and engineering applications in recent years. Inspired by human walks, a bipedal microwalker capable of standing and walking like humans regulated by external weak magnetic fields was reported in this paper. The walker has a submillimeter size and a simple arrowhead shape. Its standing and walking locomotion is controlled by external oscillating magnetic fields generated by orthogonal electromagnetic coil pairs. The walking speeds of the microwalker are controlled using magnetic fields with varying parameters. The walking speeds on a glass substrate immersed in water could reach up to 2.2 mm s-1. Designed walking paths of the microwalker on a horizontal substrate are also demonstrated. Besides walking on horizontal flat surfaces, the microwalker can climb up slopes and walk freely in circular microtubes. The microwalker is of interest in fundamental robotic gait research and for micromanipulation applications.

Extrusion printing for fabrication of spherical and cylindrical microlens arrays.

In this paper, we present an extrusion printing technique for producing spherical and cylindrical plano-convex microlens arrays with controllable feature dimensions. This technique employs a robotic adhesive dispenser for robotically controlled microextrusion of ultraviolet (UV) curable polymer onto a glass substrate surface to directly deposit the microlens arrays. It provides a simple and flexible alternative to fabricate both spherical and cylindrical microlens arrays.

In situ quantification of living cell adhesion forces: single cell force spectroscopy with a nanotweezer.

A novel method is presented for in situ quantification of living cell adhesion forces using a homemade nanorobotic system provided with two independently actuated probes that form a dual-probe nanotweezer capable of pick-and-place manipulation of a single living cell in an aqueous environment. Compared with single-cell force spectroscopy (SCFS) based on traditional atomic force microscopy (AFM), cell immobilization via chemical trapping is unnecessary and the test cell can be efficiently released using the nanotweezer to significantly enhance production of the SCFS. Benefiting from the accurate force sensing capability of AFM, the nanotweezer allows reliable force measurement ranging from picoNewtons to microNewtons and is sufficiently sensitive to characterize short- and long-term adhesion of cell-cell and cell-substrate adhesions. Capabilities of the nanotweezer have been validated through experimental qualification of cell-substrate and cell-cell adhesion events of C2C12 cells (mouse myoblast adherent) with different contact times.

Photothermal-Responsive Shape-Memory Magnetic Helical Microrobots with Programmable Addressable Shape Changes.

Faced with complex and diverse tasks, researchers seek to introduce stimuli-responsive materials into the field of microrobots. Magnetic helical microrobots based on shape-memory polymers demonstrate excellent locomotion capability and programmable shape transformations. However, the stimulation method of shape changes is still dependent on the rising of ambient temperature and lacks the ability to address individuals among multiple microrobots. In this paper, magnetic helical microrobots were prepared based on polylactic acid and Fe3O4 nanoparticles, which demonstrated controlled locomotion under rotating magnetic fields and programmable shape changes in their length, diameter, and chirality. The transition temperature of shape recoveries was adjusted to a range above 37 °C. At 46 °C, helical microrobots had a fast shape change with a recovery ratio of 72% in a minute. The photothermal effect of Fe3O4 nanoparticles under near-infrared laser can actuate the shape recovery rapidly, with a recovery ratio of 77% in 15 s and 90% in a minute. The stimulation strategy also allows addressing among multiple microrobots, or even within a single microrobot, selectively stimulating one or a part to change its shape. Combined with the magnetic field, laser-addressed shape changes were used for precise deployment and individual control of microrobots. Multiple microrobots can be enriched at the targeted point, heating the ambient temperature over 46 °C. The shape changes of internal parts of microrobots help them to grasp and assemble objects. Such microrobots have great potential in biomedicine and micromanipulation.

Flexible Magnetic Micropartners for Micromanipulation at Interfaces.

Microrobots working at liquid surfaces have immense potential for micromanipulation in tight and enclosed spaces, whereas constructing agile and functional microrobots with simple structures at liquid surfaces is a great challenge. Herein, a pair of magnetic circular microdisks working as partners at ethylene glycol (EG) surfaces are proposed in order to accomplish flexible locomotion and in situ micromanipulation tasks. The microdisks can be controlled to connect and separate by modulating the orientation of the applied magnetic field. After the two disks connect as an entity, they are transformed into micropartners under an oscillating magnetic field in 3D space. By changing the vertical component of the oscillating field, the micropartners can obtain controllable propulsion through paddling and wriggling modes, and the locomotion speed can reach approximately two body lengths per second. They can also climb a meniscus, and even crawl on a solid surface in a liquid. Finally, this pair of micropartners is demonstrated as a flexible microgripper to implement manipulations at the liquid surfaces, including cargo capture, delivery along prescribed paths, and release.

Three-Dimensional Kelvin Probe Force Microscopy.

Traditional Kelvin probe force microscopy (KPFM) is mainly limited to the characterization of two-dimensional (2D) surfaces, and in situ surface potential (SP) imaging along 3D device surfaces remains a challenge. This paper presents a multimode 3D-KPFM based on an orthogonal cantilever probe (OCP) that can achieve SP mapping of 3D micronano structures. It integrates three working modes: a bending mode for 2D horizontal surface imaging, a torsion mode for vertical sidewall imaging, and a vector tracking-based 3D scanning mode. The customized OCP has a nanoscale tip protruding from the side and underside of the cantilever, rather than the front, and the extended tip makes the proposed approach universally applicable for 3D detection from the nanometer to micrometer scale. The spatial resolution of the proposed method is analyzed by simulation, which shows it can reduce the cantilever homogenization effect. Linearity and energy resolution measurements show that the proposed method has comparable performance to traditional methods. A comparative experiment using a gold-silicon interface verifies the accuracy of the reported method in its bending and torsion modes. Further, the imaging ability of the 3D scanning mode is confirmed in the 3D characterization of a step grating. This technique is applied to the in situ characterization of a microforce sensor with microcomb structures. The experiment results show that this method can excellently achieve the 3D quantitative characterization of topography and SP, including critical dimensions and SP along a 3D device surface. This novel 3D-KPFM technique has many potential applications in the further exploration of 3D micronano devices.

Study on the Manipulation Strategy of Metallic Microstructures Based on Electrochemical-Assisted Method.

Microcomponent manipulation (MCM) technology plays a decisive role in assembling complex systems at the micro- and nanoscale. However, the existing micromanipulation methods are difficult to widely apply in the manufacturing of microelectromechanical systems (MEMSs) due to the limited manipulation space and complex application objects, and the manipulation efficiency is relatively low, which makes it difficult to industrialize these micromanipulating systems. To solve the above problems, this paper proposes an efficient metal MCM strategy based on the electrochemical method. To verify the feasibility and repeatability of the strategy, the finite element model (FEM) incorporating the hydrodynamic and electrochemical theories is used to calculate the local stress distribution of the contact position during the dynamic pick-up process. Based on the simulation results, we defined the relationship between the parameters, such as the optimal manipulating position and angle for picking, transferring and releasing. The failure behaviors of pick-up are built to realize the efficient three-dimensional manipulation of microcopper wire of 300 µm. By establishing a theoretical model and experimental verification, it was concluded that the middle point was the best manipulating position when picking up the microcopper wire, the most efficient picking angle was between 45 and 60 degrees for the pipette, and the average time was 480 s in three sets of picking-release manipulation experiments. This paper provides an achievable idea for different types of micro-object manipulations and promotes the rapid application of micromanipulation techniques in MEMSs.

Study of Microscale Meniscus Confined Electrodeposition Based on COMSOL.

The rate and quality of microscale meniscus confined electrodeposition represent the key to micromanipulation based on electrochemistry and are extremely susceptible to the ambient relative humidity, electrolyte concentration, and applied voltage. To solve this problem, based on a neural network and genetic algorithm approach, this paper optimizes the process parameters of the microscale meniscus confined electrodeposition to achieve high-efficiency and -quality deposition. First, with the COMSOL Multiphysics, the influence factors of electrodeposition were analyzed and the range of high efficiency and quality electrodeposition parameters were discovered. Second, based on the back propagation (BP) neural network, the relationships between influence factors and the rate of microscale meniscus confined electrodeposition were established. Then, in order to achieve effective electrodeposition, the determined electrodeposition rate of 5 × 10-8 m/s was set as the target value, and the genetic algorithm was used to optimize each parameter. Finally, based on the optimization parameters obtained, we proceeded with simulations and experiments. The results indicate that the deposition rate maximum error is only 2.0% in experiments. The feasibility and accuracy of the method proposed in this paper were verified.

Cooperative Self-Assembled Magnetic Micropaddles at Liquid Surfaces.

Cooperative controls of magnetic microswimmers are desired for complex micromanipulation and microassembly tasks. Self-assembled magnetic micropaddles as microswimmers that can locomote freely and cooperate at liquid surfaces are proposed inspired by the paddling motion. The micropaddles are self-assembled with metallic disks under a rotating magnetic field, and they are endowed with controlled propulsion in the precessing field. The micropaddles can locomote freely with a maximum speed of approximately 3.3 mm/s and manipulate objects at the liquid surface. It is found that the micropaddles reverse moving directions at high frequencies and that those with different lengths can locomote in opposite directions under the same precessing magnetic field. Based on the distinctive motion properties, not only could several micropaddles combine into the longer ones but a single micropaddle could also be disassembled into two cooperative partners. Assemblies of different parts based on their cooperation are realized in this study, which is challenging for other types of magnetic microswimmers. Micropaddles with adjustable length, flexible locomotion, and cooperative capability present a promising avenue for various micromanipulation applications.

Vertical distance from shading in the SEM.

Vertical data collected by Scanning Electron Microscopy (SEM) are important for sample characterization, 3D reconstruction, and flex manipulation. Traditional methods are limited by the extent to which the probe obstructs the view of the sample along the vertical axis. Herein, we propose a novel SEM microprobe for measuring the vertical distance between the probe and substrate. To form a semi-transparent hole that is set as the objective regions in processing of the SEM images, an epoxy film was embedded in the through-hole at the tip of the microforce probe with 3D printing. The film can be modified with a focused ion beam (FIB) system. The motion of the modified probe along the vertical axis is controlled by a nanopositioner and the process is recorded by taking a real-time SEM video. The change in gray contrast caused by the semi-transparent epoxy is corrected during the SEM image processing of the video. By comparing the gray contrast with the nanopositioner motion data, we find that the change in gray contrast can provide feedback for adjusting the displacement between the probe and the substrate, and the resolution can be up to 100 nm. We propose a novel and simple method for measuring vertical distances in the SEM, which is useful for in-situ measurements and nanomanipulations.

Simulation of Picking Up Metal Microcomponents Based on Electrochemistry.

The technology of picking up microcomponents plays a decisive role in the assembly of complex systems in micro- and nanoscale. The traditional method of picking up microcomponents with a mechanical manipulation tool can easily cause irreversible damage to the object, and only one object can be manipulated at a time. Furthermore, it is difficult to release the object with this method, and the release location is not accurate. With the aim of solving the above problems, the present study proposes an electrochemistry-based method for picking up metal microcomponents. First, the effect of ambient relative humidity on pickup was analyzed, and the effect of current density and electrolyte concentration on the deposition was examined. Then, a force analysis in the process of manipulation was carried out. Through the analysis of influence factors, the ideal experimental parameters were obtained theoretically. Finally, a simulation was carried out with COMSOL Multiphysics based on the above analysis. Copper microwires with a diameter of 60 µm and lengths of 300, 500, and 700 µm were successfully picked up and released using a pipette with a nozzle diameter of 15 µm. Compared with the traditional method, this method is simple to manipulate. Furthermore, it has a high success rate, causes less damage to the object, and good releasing accuracy.

Construction and evaluation of a wavelet-based focus measure for microscopy imaging.

Microscopy imaging can not achieve both high resolution and wide image space simultaneously. Autofocusing is of fundamental importance to automated micromanipulation. This article proposes a new wavelet-based focus measure, which is defined as a ratio of high frequency coefficients and low frequency coefficients. 8 series of 49 microscope images each acquired under five magnifications are used to comprehensively compare the performance of our focus measure with the classic and popular focus measures, including Normalized Variance, Entropy, Energy Laplace and wavelet-based high frequency focus measures. The robustness of these focus measures is evaluated using noisy image sequences corrupted by Gaussian white noise with standard deviations (STD) 5 and 15. An evaluation methodology is proposed, based on which these 5 focus measures are ranked. Experimental results show that the proposed focus measure can provide significantly the best overall performance and robustness. This focus measure can be widely applied to the automated biological and biomedical applications.

A single-step lithography system based on an enhanced robotic adhesive dispenser.

In the paper, we present a single-step lithography system whereby the robotically controlled micro-extrusion of resist adhesive onto a substrate surface to directly create resist adhesive patterns of interest. This system is modified from a robotic adhesive dispenser by shrinking the aperture of the nozzle to a few micrometers aiming to realize patterns at microscale. From experimental investigation, it is found that working factors including writing speed, working time, and applied pressure can be adopted to conveniently regulate the feature size (the width of the line features and the diameter of the dot features). To test its functionality, the system was used to pattern line features on silicon dioxide (SiO2) and generate an array of square-like silicon microstructure by combining with wet etching. It provides a simple and flexible alternative tool to facilitate the development of microfabrication.

A vacuum microgripping tool with integrated vibration releasing capability.

Pick-and-place of micro-objects is a basic task in various micromanipulation demands. Reliable releasing of micro-objects is usually disturbed due to strong scale effects. This paper focuses on a vacuum micro-gripper with vibration releasing functionality, which was designed and assembled for reliable micromanipulation tasks. Accordingly, a vibration releasing strategy of implementing a piezoelectric actuator on the vacuum microgripping tool is presented to address the releasing problem. The releasing mechanism was illustrated using a dynamic micro contact model. This model was developed via theoretical analysis, simulations and pull-off force measurement using atomic force microscopy. Micromanipulation experiments were conducted to verify the performance of the vacuum micro-gripper. The results show that, with the assistance of the vibration releasing, the vacuum microgripping tool can achieve reliable release of micro-objects. A releasing location accuracy of 4.5±0.5 µm and a successful releasing rate of around 100% (which is based on 110 trials) were achieved for manipulating polystyrene microspheres with radius of 35-100 µm.