Manipulation Of Micro Research Articles

Acoustofluidics in an equilateral triangular channel

Acoustofluidics is of great interest in many fields, such as physics, biology, chemistry, medicine, and manufacturing. Numerous research has been conducted on the basic physics of acoustofluidics in common (e.g., rectangular and circular) fluid channels. Recently, it has been reported that the resonant acoustic field in a triangular channel can be applied for rapid acoustofluidic sedimentation of microparticles. In this paper, we examine in detail the fundamentals of acoustofluidics in triangular channels and show their potential for ultrasonic particle manipulation. The variations of acoustofluidic fields, including acoustic resonances, acoustic radiation force, and outer acoustic streaming, in an equilateral triangular channel are investigated both experimentally and numerically. We develop a generalized limiting velocity solution for predicting the outer acoustic streaming fields in triangular channels of arbitrary shape. We show that it can generate both symmetric and antisymmetric acoustic resonances in triangular channels, which lead to outer acoustic streaming fields that are similar or distinct to those seen in common fluid channels. Boundary vibration-dependent asymmetric standing wave profiles can typically be excited, where spatial separation of acoustic pressure and streaming patterns is observed, which is consistent with the recent prediction of acoustofluidics in asymmetric acoustic resonances. The results demonstrate the richness of acoustic resonances and boundary-driven acoustic streaming patterns that arise in standing acoustic wave fields and open perspectives for acoustomicrofluidic applications such as heat and mass transfer enhancement and dynamic manipulation of micro- and nanoparticles.

Deciphering viscoelastic cell manipulation in rectangular microchannels.

Viscoelastic focusing has emerged as a promising method for label-free and passive manipulation of micro and nanoscale bioparticles. However, the design of microfluidic devices for viscoelastic particle focusing requires a thorough comprehensive understanding of the flow condition and operational parameters that lead to the desired behavior of microparticles. While recent advancements have been made, viscoelastic focusing is not fully understood, particularly in straight microchannels with rectangular cross sections. In this work, we delve into inertial, elastic, and viscoelastic focusing of biological cells in rectangular cross-section microchannels. By systematically varying degrees of fluid elasticity and inertia, we investigate the underlying mechanisms behind cell focusing. Our approach involves injecting cells into devices with a fixed, non-unity aspect ratio and capturing their images from two orientations, enabling the extrapolation of cross-sectional equilibrium positions from two dimensional (2D) projections. We characterized the changes in hydrodynamic focusing behaviors of cells based on factors, such as cell size, flow rate, and fluid characteristics. These findings provide insights into the flow characteristics driving changes in equilibrium positions. Furthermore, they indicate that viscoelastic focusing can enhance the detection accuracy in flow cytometry and the sorting resolution for size-based particle sorting applications. By contributing to the advancement of understanding viscoelastic focusing in rectangular microchannels, this work provides valuable insight and design guidelines for the development of devices that harness viscoelastic focusing. The knowledge gained from this study can aid in the advancement of viscoelastic particle manipulation technique and their application in various fields.

Controllable experimental modulation of high-order Laguerre-Gaussian laser modes.

High-order helical and sinusoidal Laguerre-Gaussian (LG) laser modes have uneven energy distribution among their multiple concentric vortex core rings and lobes, respectively. Here, we explore an experimental method to reshuffle the optical energy among their multiple concentric vortex core rings and lobes of high-order LG modes in a controllable manner. We numerically designed a diffractive optical element displayed over a spatial light modulator to rearrange optical energy among multiple concentric vortex core rings. This changes outer low-intensity concentric vortex core rings into high-intensity vortex core rings of high-order helical LG modes at the Fourier plane. The precise generation of a high-order modulated helical LG laser mode has a maximum number of highly intense concentric vortex core rings compared to known standard helical LG modes. Further, this method is extended to high-order sinusoidal LG modes consisting of both low- and high-intensity lobes to realize modulated sinusoidal LG modes with a maximum number of highly intense lobes in a controllable manner. We envisage that the modulated helical and sinusoidal high-order LG modes may surpass standard LG modes in many applications where highly intense rings and lobes are crucial, as in particle manipulation of micro- and nanoparticles, and optical lithography.

Influence of electron beam irradiation on nanoscale adhesion during colloidal probe experiments inside the scanning electron microscope

Scanning electron microscope is not only a versatile visualization and characterization tool for nanomaterials, but it is also widely used for visual feedback during assembly and manipulation of micro- and nanoparticles, novel devices based on 2D and 1D materials, and microrobots. Due to increase in the surface-to-volume ratio, adhesion forces play a significant role in micro- and nanorobotic applications. We investigate the quantitative effect of electron beam irradiation on nanoscale adhesive interactions between different end effector types and plain substrates. For this purpose, we use an interferometry-based force measurement setup integrated into the chamber of a scanning electron microscope capable of a subnano Newton force resolution. We provide quantitative results for the influence of the electron beam on the adhesion forces depending on the exposure dose, geometrical configuration in which it is applied, as well as on the material of the end effector. Simulation results, atomic force microscope adhesion measurements, and measurements with piezoresistive cantilevers serve as references. Our findings indicate that the electron beam influences the adhesive interaction not only in the case of insulating probes but also for well-grounded conducting and semiconducting probes. Its influence can range from several 10% to several 100% in comparison to the adhesion values measured with an atomic force microscope in an ambient atmosphere and no charged particle beam is applied. Moreover, it is shown that the influence of a charged particle beam is a multidimensional phenomenon that depends on several factors such as end effector and substrate material, geometry and aspect ratio of the end effector, geometrical configuration between particle beam and probe–sample arrangement, as well as exposure dose and field of view. We provide recommendations for handling and characterization of micro- and nano-objects using end effectors under the influence of charged particle beams: not to rely on adhesion values acquired in different environmental and exposure conditions, not to expect the application of conductive materials and grounding to completely avoid the effect of charged particle beams, and to be aware that charged particle beams can lower or increase the adhesion force in vacuum depending on material properties, among others.

Enrichment and Selection of Particles through Parallel Induced-Charge Electro-osmotic Streaming for Detection of Low-Abundance Nanoparticles and Targeted Microalgae.

Manipulation of micro- and nanoscale objects is an essential procedure in many detection and sensing applications, including disease diagnosis and environmental monitoring. Induced-charge electro-osmotic (ICEO) vortices present excellent advantages in the enrichment and selection of micro/nanoscale particles for downstream detection due to gentle conditions and contactless operation, but the application of this method is currently constrained by the throughput. Double-layer charging at the ends of bipolar electrodes can maintain a continuous flow of electric current in the fluidically isolated channels, which provides a feasible method to manipulate particles using parallel ICEO vortices, promoting throughput of particle manipulation without compromising efficiency and overcoming the complicated ohmic contact of electrodes. Encouraged by these, we put forward a novel method with parallel ICEO vortices to manipulate micro/nanoscale samples for downstream detection. First, we study the extension regulation of the low-frequency electric field and mediating effect of the open BPEs on the extended electric field and characterize electric equilibrium states of microparticles and their voltage dependence. Afterward, we leverage this method to enrich nanoparticles for detection of low-abundance nanoparticles with about 20- and 40-fold fluorescence intensities by integrating with a simple fiber-optic sensor. Furthermore, this technique is engineered for the selection of targeted microalgae to continuously detect their proliferation behaviors by combining with a homemade electrical impedance spectroscopy device. This method can reinforce the throughput of ICEO vortices and enables it to integrate with simple and economical sensors to accomplish disease diagnosis and environmental monitoring.

Radiation and transition losses in curved waveguides for Bloch surface waves

One-dimensional photonic crystals that support the propagation of Bloch surface electromagnetic waves attract the interest of researchers as an alternative platform for integrated optics with potential applications in nanophotonics, sensing, and optical manipulation of micro- and nanoparticles. In this paper, we numerically study the properties of surface wave modes in curved waveguides on top of a one-dimensional photonic crystal. It is shown that, when the waveguide is bent, an additional channel of radiation losses appears, which is associated with light leakage from the surface wave mode into bulk modes of the photonic crystal, and the waveguide mode profile becomes asymmetric with respect to the middle of the waveguide. We also determine the conditions for minimizing transition losses, which occur at the junctions of waveguides with different curvatures, by transverse displacement of the waveguide facets relative to each other.

Simultaneous Trapping and Manipulation of Micro-Specimens Using an All-Dielectric One-Dimensional Photonic Crystal

We demonstrate a platform where optical evanescent vortex has been realized by focusing a laser beam with orbital angular momentum (OAM) onto an all-dielectric one-dimensional photonic crystal (1DPC). This platform can simultaneously trap and manipulate various micro-scale specimens (i.e., polymer microsphere, inorganic microwire, yeast cells and Escherichia coli cells). The working principle lies in the low loss of the excited Bloch surface waves (BSWs) that propagate on the dielectric 1DPC and form a virtual probe for trapping the specimens. The OAM encoded by the BSWs will then simultaneously manipulate the specimens, such as inducing the rotation or orbital motion. Both experimental and simulation results verify that the capability of this new platform is due to the two kinds of optical force induced by the BSWs, which presents a different mechanism from that by the commonly optical electric-field vortex. Optical trapping or manipulation of micro & nano specimens play important roles in physics, life and materials sciences, thus, this new platform will find applications in microscale assembly, cell-cell interaction, bioprinting and biosensing research, and also expand our understanding of the physics interaction between vector beam and BSWs.

Automated group motion control of magnetically actuated millirobots

Small-size robots offer access to spaces that are inaccessible to larger ones. This type of access is crucial in applications such as drug delivery, environmental detection, and collection of small samples. However, there are some tasks that are not possible to perform using only one robot including assembly and manufacturing at small scales, manipulation of micro- and nano- objects, and robot-based structuring of small-scale materials. In this article, we focus on tasks that can be achieved using a group of small-scale robots like pattern formation. These robots are typically externally actuated due to their size limitation. Yet, one faces the challenge of controlling a group of robots using a single global input. In this study, we propose a control algorithm to position individual members of a group in predefined positions. In our previous work, we presented a small-scaled magnetically actuated millirobot. An electromagnetic coil system applied external force and steered the millirobots in various modes of motion such as pivot walking and tumbling. In this paper, we propose two new designs of these millirobots. In the first design, the magnets are placed at the center of body to reduce the magnetic attraction force between the millirobots. In the second design, the millirobots are of identical length with two extra legs acting as the pivot points and varying pivot separation in design to take advantage of variable speed in pivot walking mode while keeping the speed constant in tumbling mode. This paper presents an algorithm for positional control of n millirobots with different lengths to move them from given initial positions to final desired ones. This method is based on choosing a leader that is fully controllable. Then, the motions of other millirobots are regulated by following the leader and determining their appropriate pivot separations in order to implement the intended group motion. Simulations and hardware experiments validate these results.

Tight Focusing Properties of Ring Pearcey Beams with a Cross Phase

We theoretically investigated the properties of tightly focused ring Pearcey beams with a cross phase (CPRPB). The expressions of the distributions of both electric field and magnetic field in the focal region of an objective were first derived from the vectorial Debye theory, and then numerical calculations were carried out to obtain the focused intensity distribution and the Poynting vector of CPRPB near the focus. Numerical calculations indicate that as CPRPB is focused on an objective of high numerical aperture (NA), two nonuniform self-focusing spots occur at both sides of the geometrical focus of the objective symmetrically, and the angle between their directions is 90 degrees. The stronger is the strength of cross-phase modulation, the flatter are the ellipses of the self-focusing spots, and the smaller is the intensity at the geometrical focus of the objective. Numerical calculations also demonstrate that the optical gradient force produced by tightly focused CPRPB in the focal region can be manipulated in magnitude and in direction by tuning the strength of cross-phase modulation. Due to these properties of tightly focused CPRPB, they might find applications in the manipulation of micro- and nanoparticles and so on.

Acoustofluidics for cell patterning and tissue engineering

• This review addresses the current developments and remaining challenges of advanced acoustofluidic techniques in bioengineering fields. • The fundamentals of acoustic manipulation and typical acoustofluidic devices are introduced. • This review provides an overall survey on the applications of cell and tissue engineering using acoustofluidic devices, such as 2D cell patterning for studying cell-cell interactions, and 3D tissue engineering for replicating multicellular developments. • This review presents an in-depth insight into the current difficulties and future prospects of acoustofluidics for future applications. Acoustofluidics has been a promising approach using sound waves to manipulate particles and actuate fluids in biomedical applications. It usually generates acoustic radiation force and acoustic streaming to initiate diffraction, reflection and interference, building up a pressure distribution to facilitate accurate manipulation of micro- or nano-scale particles and fluids. Owing to its remarkable contact-free and biocompatible advantages, acoustofluidics has been used in high-throughput cell analysis, size-controllable organoid structures, and functional tissue mimics. We enumerate the basic concepts and the sufficient research of acoustofluidics in precise patterning and tissue engineering in this review, including the design and function of four typical acoustofluidic devices, various forms of cell patterning and 3D tissue engineering. Meanwhile, we outlined current challenges and future directions of acoustofluidics in biomedicine and tissue engineering.

Rotational acoustofluidic fields induced by cross structures with asymmetric radiation surface arrangements

In this study, a novel strategy to generate sophisticated acoustic streaming vortices, which would be available for rotational manipulation of micro-/nano-scale objects, is proposed and simulated. All structural units in the microfluidic chamber are symmetric in design, and all radiation surfaces have the same settings of input frequency, oscillation amplitude, and initial phase. Different kinds of asymmetric acoustofluidic patterns can be generated in the originally static microfluidic chamber only because of the asymmetric arrangement of multiple radiation surfaces in space. The calculation results of kaleidoscopic acoustofluidic fields together with particle movement trajectories induced by cross structures with different radiation surface distributions further demonstrate the versatile particle manipulation capabilities of these functional microfluidic devices. In comparison to the existing oscillation modulation method, which requires multiple radiation surfaces with different initial phases, acoustofluidic devices with a same initial phase of all radiation surfaces can significantly reduce the required number of auxiliary signal generators and power amplifiers. The proposed generation method of acoustofluidic patterns is promising for microfluidic mixing without rotating machinery, driving operation of microrobots, and rotational manipulation of biological samples.

A composite electro-permanent magnetic actuator for microrobot manipulation

The properties of conventionally utilized magnetic cores limit the generation of a strong controllable magnetic force for the manipulation of micro-/nanorobots. This study proposes a novel electro-permanent magnetic actuator having a composite core structure that can significantly improve the magnetic field and field gradient. The core structure, called the composite electro-permanent magnetic actuator (CEPMA), consists of a hybrid permanent magnet sandwiched between an iron core and iron disk with a copper wire wound around it. . The CEPMA creates a strong magnetic field and enables the switching on/off of the magnetic field. A prototype of a magnetic actuator system using six CEPMAs was built with optimal parameters and was capable of 3-dimensional (3D) position control with a maximum achievable field and gradient field of 124 mT and 1.9 T/m, respectively, by utilizing a lower power consumption. We derived a mathematical model and control approach to address its hysteresis property and obtain a current input for the desired magnetic force for precise control of a microrobot. The theoretical analysis and experimental validation of CEPMA indicated that the proposed structure could enhance the controllable magnetic field and gradient field by up to 30% compared to the conventional iron core electromagnet. The system was also tested for 3D manipulating different microrobots in an in vitro environment with high accuracy. The experimental results demonstrate the potential of this newly developed platform for manipulating microrobots with high throughput.

Two-stage particle separation channel based on standing surface acoustic wave.

Microfluidic technology has great advantages in the precise manipulation of micro and nano particles, and the collection method of micro and nano particles based on ultrasonic standing waves has attracted much attention for its high efficiency and simplicity of structure. This article proposes a two-stage particle separation channel using ultrasound. In the microfluidic channel, two different sound pressure regions are used to achieve the separation of particles with positive acoustic contrast factors. Through numerical simulation, the performance of three common piezoelectric substrate materials was compared qualitatively and quantitatively, and it was found that the output sound pressure intensity of 128°YX-LiNbO3 was high and the output was stable. At the same time, the influence of the number of electrode pairs of the interdigital transducer and the electrode voltage on the output sound wave is studied. Finally, 15 pairs of electrode pairs are selected, and the electrode voltages of the two sound pressure regions are 2.0 V and 3.0 V, respectively. After selecting the corresponding parameters, the separation process was numerically simulated, and the separation of three kinds of particles was successfully achieved. This work has laid a certain theoretical foundation for rapid disease diagnosis and real-time monitoring of the environment in practical applications.

Insights into a deterministic lateral displacement sorting chip with new cross-section micropillars

Microfluidic technology has great advantages in the precise manipulation of micro and nanoparticles, and the separation method based on deterministic lateral displacement separation technology has attracted much attention due to its high resolution, high throughput, and strong size dependence. In this paper, starting from the principle of deterministic lateral displacement sorting and taking control of the flow velocity distribution and pressure difference in the gap as the key points, a new shape of inverted heart-shaped micro-columns with a smaller critical size was designed to separate white blood cells and red blood cells. Under the premise of considering the two-way coupling, the trajectory of the particles was simulated, the critical size of the array was determined, and the influence of the flow velocity particle sorting was discussed. Finally, the separation process of the two kinds of cells was simulated, and the separation of the two kinds of cells was successfully realized. This work has laid a certain theoretical foundation for the rapid diagnosis of diseases in practical applications.

Rotational manipulation of massive particles in a 2D acoustofluidic chamber constituted by multiple nonlinear vibration sources

Rotational manipulation of massive particles and biological samples is essential for the development of miniaturized lab-on-a-chip platforms in the fields of chemical, medical, and biological applications. In this paper, a device concept of a two-dimensional acoustofluidic chamber actuated by multiple nonlinear vibration sources is proposed. The functional chamber enables the generation of acoustic streaming vortices for potential applications that include strong mixing of multi-phase flows and rotational manipulation of micro-/nano-scale objects without any rotating component. Using numerical simulations, we find that diversified acoustofluidic fields can be generated in the chamber under various actuations, and massive polystyrene beads inside can experience different acoustophoretic motions under the combined effect of an acoustic radiation force and acoustic streaming. Moreover, we investigate and clarify the effects of structural design on modulation of the acoustofluidic fields in the chamber. We believe the presented study could not only provide a promising potential tool for rotational acoustofluidic manipulation, but could also bring this community some useful design insights into the achievement of desired acoustofluidic fields for assorted microfluidic applications.

Effect of geometry on dielectrophoretic trap stiffness in microparticle trapping.

Dielectrophoresis, an electrokinetic technique, can be used for contactless manipulation of micro- and nano-size particles suspended in a fluid. We present a 3-D microfluidic DEP device with an orthogonal electrode configuration that uses negative dielectrophoresis to trap spherical polystyrene micro-particles. Traps with three different basic geometric shapes, i.e. triangular, square, and circular, and a fixed trap area of around 900 μm2 were investigated to determine the effect of trap shape on dynamics and strength of particle trapping. Effects of trap geometry were quantitatively investigated by means of trap stiffness, with applied electric potentials from 6 VP-P to 10 VP-P at 1MHz. Analyzing the trap stiffness with a trapped 4.42μm spherical particle showed that the triangular trap is the strongest, while the square shape trap is the weakest. The trap stiffness grew more than eight times in triangular traps and six times in both square and circular traps when the potential of the applied electric field was increased from 6 VP-P to 10 VP-P at 1MHz. With the maximum applied potential, i.e. 10 VP-P at 1MHz, the stiffness of the triangular trap was 60% and 26% stronger than the square and circular trap, respectively. A finite element model of the microfluidic DEP device was developed to numerically compute the DEP force for these trap shapes. The findings from the numerical computation demonstrate good agreement with the experimental analysis. The analysis of three different trap shapes provides important insights to predict trapping location, strength of the trapping zone, and optimized geometry for high throughput particle trapping.

Incoherent Optical Tweezers on Black Titanium.

Optical tweezers enable the manipulation of micro- and nanodielectric particles through entrapment using a tightly focused laser. Generally, optical trapping of submicron size particles requires high-intensity light in the order of MW/cm2. Here, we demonstrate a technique of stable optical trapping of submicron polymeric beads on nanostructured titanium surfaces (black-Ti) without the use of lasers. Fluorescent polystyrene beads with a diameter d = 20-500 nm were successfully trapped on black-Ti by low-intensity focused illumination of incoherent light at λ = 370 m from a Hg lamp. Light intensity was 5.5 W/cm2, corresponding to a reduced light intensity of 6 orders of magnitude. Upon switching off illumination, trapped particles were released from the illuminated area, indicating that trapping was optically driven and reversible. Such trapping behavior was not observed on nonstructured Ti surfaces or on nanostructured silicon surfaces. Thus, the Ti nanostructures were demonstrated to play a key role.

Particle separation in microfluidics using different modal ultrasonic standing waves

Microfluidic technology has great advantages in the precise manipulation of micro and nano particles, and the separation of micro and nano particles based on ultrasonic standing waves has attracted much attention for its high efficiency and simplicity of structure. This paper proposes a device that uses three modes of ultrasonic standing waves to continuously separate particles with positive acoustic contrast factor in microfluidics. Three modes of acoustic standing waves are used simultaneously in different parts of the microchannel. According to the different acoustic radiation force received by the particles, the particles are finally separated to the pressure node lines on both sides and the center of the microchannel. In this separation method, initial hydrodynamic focusing and satisfying various equilibrium constraints during the separation process are the key. Through numerical simulation, the resonance frequency of the interdigital transducer, the distribution of sound pressure in the liquid, and the relationship between the interdigital electrode voltage and the output sound pressure are obtained. Finally, the entire separation process in the microchannel was simulated, and the separation of the two particles was successfully achieved. This work has laid a certain theoretical foundation for the rapid diagnosis of diseases in practical applications.

Nature of trapping forces in optically induced electrothermal vortex based tweezers

Precise manipulation of micro and nanosized particles has enabled investigations into various applications ranging from mechanobiology of biomolecules and cells to self-assembly of two-dimensional colloids. This work is focussed on studying the nature of a noninvasive electrothermal vortex based micro-manipulation tool called rapid electrokinetic patterning (REP). Using the equipartition method, we show that a REP trap is Hookean in nature and has an ultralow trap stiffness on the order of femtonewtons/\ensuremath{\mu}m. The dynamic tunability of an optically induced REP trap makes it a versatile tool for various biophysical applications.

Bessel beam approach for photovoltaic trapping of micro- and nanoparticles on Fe-doped lithium niobate crystal

The non-diffracting Bessel beam approach was used for the first time for the elaboration of photovoltaic tweezers. We report the trapping of dielectric microparticles of chalk (CaCO3), as well as silver nanoparticles in glycerin suspension via dielectrophoretic forces on the surface of Fe doped LiNbO3 (LN:Fe) crystal with recorded volume holographic grating by the non-diffracting Bessel beam technique. The photorefractive Y-cut LN:Fe crystal was illuminated by 20–40 mW power Bessel beam at 532 nm wavelength which generates refractive Bessel lattice with ~40 μm periodicity via induction of photovoltaic space-charge fields. The Bessel beam approach provides the induction of high contrast 2D quasi-periodic distribution of space-charge electric field in the crystal volume and proximity of the crystal surface and high quality 2D patterning of the particles. Experiments showed that CaCO3 microparticles are trapped by attractive forces on the crystal surface in the areas of refractive index maxima of the Bessel lattice, while the trapping of Ag nanoparticles dispersed in glycerin takes places at the borderlines of lattice rings due to the repulsive forces. A physical model was developed to explain the experimental results. The photovoltaic approach of trapping and manipulation of micro- and nanoparticles is promising for applications in photonics, integrated optics and biotechnology.