Contactless Manipulation Research Articles

Hierarchical Nanostructures as Acoustically Manipulatable Multifunctional Agents in Dynamic Fluid Flow.

Acoustic waves provide a biocompatible and deep-tissue-penetrating tool suitable for contactless manipulation in in vivo environments. Despite the prevalence of dynamic fluids within the body, previous studies have primarily focused on static fluids, and manipulatable agents in dynamic fluids are limited to gaseous core-shell particles. However, these gas-filled particles face challenges in fast-flow manipulation, complex setups, design versatility, and practical medical imaging, underscoring the need for effective alternatives. In this study, flower-like hierarchical nanostructures (HNS) into microparticles (MPs) are incorporated, and demonstrated that various materials fabricated as HNS-MPs exhibit effective and reproducible acoustic trapping within high-velocity fluid flows. Through simulations, it is validated that the HNS-MPs are drawn to the focal point by acoustic streaming and form a trap through secondary acoustic streaming at the tips of the nanosheets comprising the HNS-MPs. Furthermore, the wide range of materials and modification options for HNS, combined with their high surface area and biocompatibility, enable them to serve as acoustically manipulatable multimodal imaging contrast agents and microrobots. They can perform intravascular multi-trap maneuvering with real-time imaging, purification of wastewater flow, and highly-loaded drug delivery. Given the diverse HNS materials developed to date, this study extends their applications to acoustofluidic and biomedical fields.

Contactless Manipulation and Raman Analysis of Cometary Analogs and Micrometeorites by Acoustic Levitation

Extraterrestrial material collected during space missions is highly exposed to contamination issues during on-Earth analysis. Although high-protection-level protocols were developed, to minimize the contamination due to sample manipulation and the substrate contribution an optimal strategy is to perform in situ analysis with contactless techniques. Optical and acoustic trapping represent ideal candidates for contactless manipulation and analysis of nanometer-to-millimeter-sized particles. Here, we show results of the manipulation of cometary analogs and micrometeorite samples using a single-axis acoustic levitator. The investigation of the particle dynamics in the trap allows the calculation of the trap spring constants that are found in the mN/m range. In addition, we collect the Raman spectra of two levitated fragments of Saratov meteorite, demonstrating that acoustic levitation can be effectively used for the contactless and low-contamination characterization of samples of interest in astrophysics.

Acousto-dielectric tweezers enable independent manipulation of multiple particles.

Acoustic tweezers have gained substantial interest in biology, engineering, and materials science for their label-free, precise, contactless, and programmable manipulation of small objects. However, acoustic tweezers cannot independently manipulate multiple microparticles simultaneously. This study introduces acousto-dielectric tweezers capable of independently manipulating multiple microparticles and precise control over intercellular distances and cyclical cell pairing and separation for detailed cell-cell interaction analysis. Our acousto-dielectric tweezers leverage the competition between acoustic radiation forces, generated by standing surface acoustic waves (SAWs), and dielectrophoretic (DEP) forces, induced by gradient electric fields. Modulating these fields allows for the precise positioning of individual microparticles at points where acoustic radiation and DEP forces are in equilibrium. This mechanism enables the simultaneous movement of multiple microparticles along specified paths as well as cyclical cell pairing and separation. We anticipate our acousto-dielectric tweezers to have enormous potential in colloidal assembly, cell-cell interaction studies, disease diagnostics, and tissue engineering.

Automated droplet manipulation enabled by a machine-vision-assisted acoustic tweezer

Automated droplet manipulation holds great significance for various biochemical applications, including but limited to heavy metal ions detection. Despite notable progress, contactless-acoustic-tweezer-based automated droplet manipulation on superhydrophobic surfaces is rarely reported. In this work, we introduce a machine-vision-assisted acoustic tweezer (MVAAT) for automated and contactless manipulation of droplets on a superhydrophobic surface. The MVAAT generates ultrasound standing waves between an ultrasonic transducer (UST) and a superhydrophobic surface, inducing acoustic radiation force to facilitate contactless droplet manipulation on the superhydrophobic surface. An industrial-camera-based machine vision system is employed for real-time detection and tracking of droplets, providing precise droplet positions for automated droplet transportation and merging via a UST equipped on a Cartesian robot. Experimental results demonstrate that the proposed MVAAT can transport droplets of various volumes on a superhydrophobic surface along planned paths at considerably high velocities exceeding one centimeter per second. Furthermore, with the vision feedback, the MVAAT can reliably and precisely transport a droplet to a target position, even if the droplet fails to follow the UST during its movement. Moreover, automated merging and patterning of multiple droplets are achieved, showcasing the versatility of the MVAAT. Last, the MVAAT is applied for fluorescence-based Cu2+ detection to showcase its potential for practical biochemical analyses. The proposed MVAAT significantly expands the capability of ultrasound for droplet manipulation on superhydrophobic surfaces, promising numerous practical applications in biology and chemistry.

Airborne Acoustic Vortex End Effector‐Based Contactless, Multi‐Mode, Programmable Control of Object Surfing

AbstractTweezers based on optical, electric, magnetic, and acoustic fields have shown great potential for contactless object manipulation. However, current tweezers designed for manipulating millimeter‐sized objects such as droplets, particles, and small animals exhibit limitations in translation resolution, range, and path complexity. Here, a novel acoustic vortex tweezers system is introduced, which leverages a unique airborne acoustic vortex end effector integrated with a three‐degree‐of‐freedom (DoF) linear motion stage, for enabling contactless, multi‐mode, programmable manipulation of millimeter‐sized objects. The acoustic vortex end effector utilizes a cascaded circular acoustic array, which is portable and battery‐powered, to generate an acoustic vortex with a ring‐shaped energy pattern. The vortex applies acoustic radiation forces to trap and spin an object at its center, simultaneously protecting this object by repelling other materials away with its high‐energy ring. Moreover, The vortex tweezers system facilitates contactless, multi‐mode, programmable object surfing, as demonstrated in experiments involving trapping, repelling, and spinning particles, translating particles along complex paths, guiding particles around barriers, translating and rotating droplets containing zebrafish larvae, and merging droplets. With these capabilities, It is anticipated that the tweezers system will become a valuable tool for the automated, contactless handling of droplets, particles, and bio‐samples in biomedical and biochemical research.

Engineering free-standing electrospun PLLCL fibers on microfluidic platform for cell alignment

Here, a PLLCL-on-chip platform was developed by direct electrospinning of poly (L-lactide-co-ε-caprolactone) (PLLCL) on polymethyl methacrylate (PMMA) microfluidic chips. Designed microchip provides the electrospinning of free-standing aligned PLLCL fibers which eliminates limitations of conventional electrospinning. Besides, aligned fiber structure favors cell alignment through contactless manipulation. Average fiber diameter, and fiber alignment was evaluated by SEM analyses, then, leakage profile of microchip was investigated. 3D cell culture studies were conducted using HeLa and NIH-3T3 cells, and nearly 85% cell viability was observed in PLLCL-on-chip for 15 days, while cell viability of 2D control started to decrease after 7 days based on Live dead and Alamar Blue analyses. These findings emphasize biocompatibility of PLLCL-on-chip platform for 3D cell culture and its ability to mimic extracellular matrix (ECM). Immunostaining results prove that PLLCL-on-chip platform favors the secretion of ECM proteins compared to control groups, and cytoskeletons of cells were in aligned orientation in PLLCL-on-chip, while they were in random orientation in control groups. Overall, these results demonstrate that the developed platform is suitable for the formation of various 3D cell culture models and a potential candidate for cell alignment studies.Graphical

Selective Acoustic Trapping, Translating, Rotating, and Orienting of Organism From Heterogeneous Mixture.

Selective contactless manipulation of organisms with intrinsic mobility from heterogeneous mixture is essential for biomedical engineering and microbiology. Acoustic manipulation, compared to its optical, magnetic, and electrostatic counterparts, provides superior bio-compatibility and additive-free properties. In this study, we present an acoustic manipulation system capable of selectively trapping, translating, rotating, and orienting individual organisms from in-Petri dish organism mixture using a phased transducer array and microscope, by dynamically steering the acoustic field. Specifically, using brine shrimp and zebrafish populations as example, the to-be-manipulated organisms with different sizes or morphologies can be manually designated by the user in microscopic image and interactively localized. Thereafter, the selected organisms can be automatically trapped from the heterogeneous mixture using a multiple focal point-based acoustic field steering method. Finally, the trapped organisms can be translated, rotated, and oriented in regard to the user's distinct manipulation objectives in instant response. In different tasks, closed-loop positioning and real-time motion planning control are performed, highlighting the innovation in terms of automation and accuracy of our manipulation technique. The results demonstrate that our acoustic manipulation system and acoustic field steering method enable selective, stable, precision, real-time, and in-Petri dish manipulation of organisms from heterogeneous mixture.

The dynamics of vertical coalescence of acoustically levitated droplets

Mobility manipulation of liquid droplets is an important task of digital imicrofluidics. Acoustic levitation has revolutionised the contactless manipulation of liquid droplets for various applications. Acoustic levitation technique can be effectively used to manipulate droplets to obtain their coalescence. This paper reports a unique, versatile, and material-independent approach for the vertical coalescence of the droplets suspended in an acoustic levitator. The acoustic power of the levitator is carefully engineered to obtain vertical coalescence of two liquid droplets. Water, 20% and 40% glycerol–water solutions are used as the working liquids. The results of the experiments revealed three outcomes during the coalescence. The outcomes are analysed and discussed.

Acoustic Actuators for the Manipulation of Micro/Nanorobots: State-of-the-Art and Future Outlooks.

Compared to other actuating methods, acoustic actuators offer the distinctive capability of the contactless manipulation of small objects, such as microscale and nanoscale robots. Furthermore, they have the ability to penetrate the skin, allowing for the trapping and manipulation of micro/nanorobots that carry therapeutic agents in diverse media. In this review, we summarize the current progress in using acoustic actuators for the manipulation of micro/nanorobots used in various biomedical applications. First, we introduce the actuating method of using acoustic waves to manipulate objects, including the principle of operation and different types of acoustic actuators that are usually employed. Then, applications involving manipulating different types of devices are reviewed, including bubble-based microrobots, bubble-free robots, biohybrid microrobots, and nanorobots. Finally, we discuss the challenges and future perspectives for the development of the field.

On-Demand, Contact-Less and Loss-Less Droplet Manipulation via Contact Electrification.

While there are many droplet manipulation techniques, all of them suffer from at least one of the following drawbacks - complex fabrication or complex equipment or liquid loss. In this work, a simple and portable technique is demonstrated that enables on-demand, contact-less and loss-less manipulation of liquid droplets through a combination of contact electrification and slipperiness. In conjunction with numerical simulations, a quantitative analysis is presented to explain the onset of droplet motion. Utilizing the contact electrification technique, contact-less and loss-less manipulation of polar and non-polar liquid droplets on different surface chemistries and geometries is demonstrated. It is envisioned that the technique can pave the way to simple, inexpensive, and portable lab on a chip and point of care devices.

Acoustic levitation as a tool for cell-driven self-organization of human cell spheroids during long-term 3D culture.

Acoustic levitation, which allows contactless manipulation of micro-objects with ultrasounds, is a promising technique for spheroids formation and culture. This acoustofluidic technique favors cell-cell interactions, away from the walls of the chip, which leads to the spontaneous self-organization of cells. Using this approach, we generated spheroids of mesenchymal stromal cells, hepatic and endothelial cells, and showed that long-term culture of cells in acoustic levitation is feasible. We also demonstrated that this self-organization and its dynamics depended weakly on the acoustic parameters but were strongly dependent on the levitated cell type. Moreover, spheroid organization was modified by actin cytoskeleton inhibitors or calcium-mediated interaction inhibitors. Our results confirmed that acoustic levitation is a rising technique for fundamental research and biotechnological industrial application in the rapidly growing field of microphysiological systems. It allowed easily obtaining spheroids of specific and predictable shape and size, which could be cultivated over several days, without requiring hydrogels or extracellular matrix.

Biopatterning of 3D Cellular Model by Contactless Magnetic Manipulation for Cardiotoxicity Screening.

Impact statement Contactless manipulation and cell patterning techniques provide rapid and cost-effective three-dimensional (3D) cell culture model formation for tissue engineering applications. The present study introduces a new methodology that comprised alginate-based bioink to pattern cells via contactless magnetic manipulation to fabricate 3D cardiac structures. The developed cardiac model was evaluated in terms of Doxorubicin-induced cardiotoxicity and biopatterned 3D cardiac structures were found more resistant to drug exposure compared to two-dimensional control.

Acoustically levitated whispering-gallery mode microlasers

Acoustic levitation has become a crucial technique for contactless manipulation in several fields, particularly in biological applications. However, its application in the photonics field remains largely unexplored. In this study, we implement an affordable and innovative phased-array levitator that enables stable trapping in the air of micrometer dye-doped droplets, thereby enabling the creation of microlasers. For the first time, this paper presents a detailed performance of the levitated microlaser cavity, supported by theoretical analysis concerning the hybrid technology based on the combination of whispering-gallery modes and acoustic fields. The pressure field distribution inside the acoustic cavity is numerically solved and qualitatively matched with the schlieren deflectometry technique. The optical lasing features of the levitated microlasers are highly comparable with those devices based On-a-Chip registering maximum Q-factors of ∼105, and minimum lasing thresholds ∼ 150 nJ cm−2. The emission comb is explained as a sum of multiple individual-supported whispering-gallery modes. The use of novel touchless micrometric lasers, produced with an acoustic levitator brings new technological opportunities based on photonic-acoustic technological platforms.

Binary coding metasurface for broadband and flexible generation of acoustic vortex beams

Considerable efforts have recently focused on sound vortices imprinted with orbital angular momentum (OAM) yet whose generation generally relies on sophisticated phase modulation, whether through traditional phased arrays or emerging metamaterial methods. Here, we propose and numerically demonstrate a mechanism for broadband generation of acoustic vortices in a simple, flexible, and high-efficiency way through binary-phase-based chirality modulation enabled by building a binary coding metasurface. The metasurface with a theoretically derived phase profile that is implemented with two types of meta-structures is capable of twisting the incident plane wave into a vortex beam with a desired order in a broad band and at the same time enables steering the vortices' propagation direction freewheelingly. The effectiveness of our proposed mechanism is verified by numerically demonstrating the broadband generation of vortex beams carrying different OAMs through a monolayered binary coding metasurface. We further demonstrate the generality and flexibility of our mechanism for generating the multiplexed vortex beams as well as modulating the propagation direction of the output beam by judiciously designing the 1-bit coding sequences of the metasurface. We anticipate our design with capability and simplicity to have far-reaching implications in OAM-enabled applications ranging from high-capacity acoustic communication to contactless particle manipulation.

Superhydrophobic and magnetic Fe3O4/RGO/SA composite membranes for oil-water separation

The iron tetroxide/reduced graphene oxide/stearic acid (Fe3O4/RGO/SA) composite membrane with a micro-nano-graded rough structure is fabricated on cotton cloth. Surface morphology, crystal structure, infrared spectra, and contact angle are tested to analyze the microstructure and wettability properties of the composite membrane. Compared with the original cotton, the composite membrane is changed from superhydrophilic to superhydrophobic, the water contact angle reached 156.1°, and it has stable superhydrophobicity at different pH values (pH = 5, 6, 7, 8, 9). A series of oil-water separation experiments show that the separation efficiency of composite membrane for four oil-water mixtures is higher than 98.4%, the results of the cycle separation test show that the separation efficiency and flux test for 10 cycles did not appear measurably fluctuations, the separation efficiency has always been maintained above 98%. In addition, the membrane can absorb oil slick on the water surface by magnetic drive, which provides a new idea for contactless manipulation of oil removal.

Modular Drug-Loaded Nanocapsules with Metal Dome Layers as a Platform for Obtaining Synergistic Therapeutic Biological Activities.

Multifunctional drug-loaded polymer-metal nanocapsules have attracted increasing attention in drug delivery due to their multifunctional potential endowed by drug activity and response to physicochemical stimuli. Current chemical synthesis methods of polymer/metal capsules require specific optimization of the different components to produce particles with precise properties, being particularly complex for Janus structures combining polymers and ferromagnetic and highly reactive metals. With the aim to generate tunable synergistic nanotherapeutic actuation with enhanced drug effects, here we demonstrate a versatile hybrid chemical/physical fabrication strategy to incorporate different functional metals with tailored magnetic, optical, or chemical properties on solid drug-loaded polymer nanoparticles. As archetypical examples, we present poly(lactic-co-glycolic acid) (PLGA) nanoparticles (diameters 100-150 nm) loaded with paclitaxel, indocyanine green, or erythromycin that are half-capped by either Fe, Au, or Cu layers, respectively, with application in three biomedical models. The Fe coating on paclitaxel-loaded nanocapsules permitted efficient magnetic enhancement of the cancer spheroid assembly, with 40% reduction of the cross-section area after 24 h, as well as a higher paclitaxel effect. In addition, the Fe-PLGA nanocapsules enabled external contactless manipulation of multicellular cancer spheroids with a speed of 150 μm/s. The Au-coated and indocyanine green-loaded nanocapsules demonstrated theranostic potential and enhanced anticancer activity in vitro and in vivo due to noninvasive fluorescence imaging with long penetration near-infrared (NIR) light and simultaneous photothermal-photodynamic actuation, showing a 3.5-fold reduction in the tumor volume growth with only 5 min of NIR illumination. Finally, the Cu-coated erythromycin-loaded nanocapsules exhibited enhanced antibacterial activity with a 2.5-fold reduction in the MIC50 concentration with respect to the free or encapsulated drug. Altogether, this technology can extend a nearly unlimited combination of metals, polymers, and drugs, thus enabling the integration of magnetic, optical, and electrochemical properties in drug-loaded nanoparticles to externally control and improve a wide range of biomedical applications.

Versatile bubble maneuvering on photopyroelectric slippery surfaces

Contactless bubble manipulation with a high spatiotemporal resolution brings a qualitative leap forward in a variety of applications. Despite considerable advances, light-induced bubble maneuvering remains challenging in terms of robust transportation, splitting and detachment. Here, a photopyroelectric slippery surface (PESS) with a sandwich structure is constructed to achieve the versatile bubble manipulation. Due to the generated dielectric wetting and nonuniform electric field under the irradiation of near infrared (NIR) light, a bubble is subject to both the Laplace force and dielectrophoresis force, enabling a high-efficiency bubble steering. We demonstrate that the splitting, merging and detachment of underwater bubbles can be achieved with high flexibility and precision, high velocity and agile direction maneuverability. We further extend the capability of bubble control to microrobots for cargo transportation, micropart assembly and transmission of gear structures. We envision this robust bubble manipulation strategy on the PESS would provide a valuable platform for various bubble-involved processes, ranging from microfluidic devices to soft robotics.

Synergistic Inclusion Effects of Hard Magnetic Nanorods on the Magnetomechanical Actuation of Soft Magnetic Microsphere-Based Polymer Composites.

The magnetomechanical actuation of micropillars is developed for the contactless manipulation of miniaturized actuators and microtextured surfaces. Anisotropic geometry of micropillars can significantly enhance the magnetic actuation compared with their isotropic counterparts by directional stress distributions. However, this strategy is not viable for triangular micropillars owing to insufficient anisotropy. In this study, a significant improvement in the magnetic actuation of triangular micropillars using composite magnetic particles is reported. A minute and optimal amount of hard magnetic gamma-ferrite nanorods are hybridized with soft magnetic iron microspheres to generate synergistic effects of magnetic coupling and percolation phenomenon on the magnetic actuation of polymer composites. The addition of 1wt% face-centered cubic-phased gamma-ferrite nanorods suppresses the magnetic coupling interference of body-centered cubic-phased iron microspheres. Furthermore, the nanorods reduce the percolation threshold by participating in the percolation of the microspheres. A systematic compositional study on the magnetization and magnetorheological properties reveals that the coupling effect dominates the percolation effect at a low magnetic field, whereas the percolation effect governs the magnetic actuation at a high magnetic field. This hybrid approach can help in designing material constituents for effective magnetic actuators and robotic systems that can sensitively respond to an external magnetic field.

Calibration of the axial stiffness of a single-beam acoustic tweezers.

Single-beam acoustic tweezers have recently been demonstrated to be capable of selective three-dimensional trapping. This new contactless manipulation modality has great potential for many scientific applications. Its development as a scientific tool requires precise calibration of its radiation force, specifically its axial component. The lack of calibration for this force is mainly due to its weak magnitude compared to competing effects such as weight. We investigate an experimental method for the calibration of the axial stiffness of the radiation force by observing the axial oscillations of a trapped bead in a microgravity environment. The stiffness exhibits a linear relationship with the acoustic intensity and is of the mN/m order. Then, a predictive model, loaded with the experimental acoustic field, is compared to the measured stiffness with very good agreement, within a single amplitude coefficient. This study paves the way for the development of calibrated acoustic tweezers.

Study of micro-scale flow characteristics under surface acoustic waves

As an effective tool for contactless manipulation of submicrometer scale objects, the controllability of acoustic streaming velocity and flow field morphology determines the accuracy of object migration and the completeness of three dimensional (3D) imaging. This paper proposes an equivalent acoustic streaming driving force model that is applicable to both two dimensional (2D) and 3D calculations and constructs a numerical method for submicrometer microsphere migration and rotation velocity in acoustic streaming. The results show that the relationship between the peripheral vortex size Lp/wc and the relative acoustic streaming velocity vas/vf satisfies Lp/wc = 0.125vas/vf0.36 under certain geometrical conditions. Reducing the spatial confinement and increasing the inter-vortex distance will increase the energy release efficiency, reduce the pressure gradient distribution and convective dissipation rates, increase the vortex intensity and radiation range, and consequently, increase the vortex characteristic size. In complex 3D vortex flow fields, suspended objects are affected by velocity distributions and exhibit motions such as cross-flow lines and rotation. For larger vortex structure sizes, full 3D imaging is more favorable due to the increased rotation speed and period of motion along the orbit of the submicrometer microspheres. This study helps us to reveal the modulation mechanism of acoustic streaming field flow characteristics, enrich the basic theory of alternating orbital motion and forces on objects in vortex structures, and provide guidance for acoustic flow-based contactless object manipulation.