Multifunctional flexible magnetic drive gripper for target manipulation in complex constrained environments.

Soft actuators capable of remote-controlled guidance and manipulation within complex constrained spaces hold great promise in various fields, especially in medical fields such as minimally invasive surgery. However, most current magnetic drive soft actuators only have the functions of position control and guidance, and it is still challenging to achieve more flexible operations on different targets within constrained spaces. Herein, we propose a multifunctional flexible magnetic drive gripper that can be steered within complex constrained spaces and operate on targets of various shapes. On the one hand, changing the internal pressure of the magnetic gripper can achieve functions such as suction or injection of liquid and transportation of targets with smooth surfaces. On the other hand, with the help of slit structures in the constrained environment, by simply changing the position and orientation of the permanent magnet in the external environment, the magnetic gripper can be controlled to clamp and release targets of linear, flaked, and polyhedral shapes. The full flexibility and multifunctionality of the magnetic gripper suggest new possibilities for precise remote control and object transportation in constrained spaces, so it could serve as a direct contact operation tool for hazardous drugs in enclosed spaces or a surgical tool in human body cavities.

Wireless and Closed-Loop Smart Dressing for Exudate Management and On-Demand Treatment of Chronic Wounds.

Chronic wounds have become a significant threat to people's physical and mental health and have increased the burden of social medical care. Intelligent wound dressing (IWD) with wound condition monitoring and closed-loop on-demand drug therapy can shorten the healing process and alleviate patient suffering. However, single-function wound dressings cannot meet the current needs of chronic wound treatment. Here, a wearable IWD consisting of wound exudate management, sensor monitoring, closed-loop therapy, and flexible circuit modules is reported, which can achieve effective synergy between wound exudate management and on-demand wound therapy. The dressing is attached to the wound site, and the wound exudate is spontaneously pumped into the microfluidic channel for storage. Meanwhile, the IWD can detect the state of the wound through the temperature and humidity sensor, and use this as feedback to control the liquid metal (LM) heater through a smartphone, thereby realizing the on-demand drug release from the hydrogel. In a mouse model of infected wounds, IWD accelerates wound healing by reducing inflammatory responses, promoting angiogenesis and collagen deposition.

Portable general microfluidic device with complex electric field regulation functions for electrokinetic experiments.

Electrokinetic sample manipulation is a key step for many kinds of microfluidic chips to achieve various functions, such as particle focusing and separation, fluid pumping and material synthesis. But these microfluidic experiments usually rely on large-scale signal generators for power supply, microscopes for imaging and other instruments for analysis, which hampers the portable process of microfluidic technology. Inspired by this situation, we herein designed a portable general microfluidic device (PGMD) with complex electric field regulation functions, which can accurately regulate static or continuous fluid samples. Through the graphical user interface (GUI) and modular design, the PGMD can generate multiple different electrical signals, and the micro-flow of fluid can be pumped through the built-in micropump, which can meet the requirements of most microfluidic experiments. Photos or videos of the microfluidic chip captured by the built-in microscope are received and displayed by a smartphone. We carried out a variety of microfluidic experiments such as induced-charge electroosmosis (ICEO), particle beam exit switching, thermal buoyancy flow and dielectrophoresis (DEP) on the PGMD. In addition, the PGMD can perform rapid microalgae concentration estimation in an outdoor environment, which can be used to guide microalgae cultivation, further demonstrating the development potential of this device in the field of microbial applications. Numerous results show that the PGMD has a high degree of integration and strong reliability, which expands the application of microfluidic electrokinetic experiments and provides technical support for the integration and portability of microfluidic experimental devices.

Liquid metal droplet motion transferred from an alkaline solution by a robot arm.

The excellent motion performance of gallium-based liquid metals (LMs) upon the application of a modest electric field has provided a new opportunity for the development of autonomous soft robots. However, the locomotion of LMs often appears in an alkaline solution, which hampers the application under other different conditions. In this work, a novel robot arm is designed to transfer the motion of the LM from an alkaline solution in a synchronous drive mode. The liquid metal droplet (LMD) at the bottom of the robot arm is actuated using a DC voltage to provide the driving force for the system. By introducing an end effector at the center of the robot arm, the synchronous motion of the system is replicated and can be applied to different situations. The theoretical understanding of continuous electrowetting (CEW) at the LM interface is explained, and then the motion performance of the robot arm against the function of the applied voltage and driving direction is investigated. Moreover, several applications using this robot arm, such as pattern drawing, cargo transportation, and drug concentration detection, are demonstrated. The presented robot arm has the potential to observably expand the application fields of the LM.

Numerical investigation of field-effect control on hybrid electrokinetics for continuous and position-tunable nanoparticle concentration in microfluidics.

We introduce herein an effective way for continuous delivery and position-switchable trapping of nanoparticles via field-effect control on hybrid electrokinetics (HEK). Flow field-effect transistor exploiting HEK delicately combines horizontal linear electroosmosis and transversal nonlinear electroosmosis of a shiftable flow stagnation line (FSL) on gate terminals under DC-biased AC forcing. The microfluidic nanoparticle concentrator proposed herein makes use of a simple device geometry, in which an individual or a series of planar metal strips serving as gate electrode (GE) are subjected to a hybrid gate voltage signal and arranged in parallel between a pair of 3D driving electrodes. On the application of a DC-biased AC electric field across channel length direction, all the GE are electrochemically polarized, and the action of imposed hybrid electric field on the multiple-frequency bipolar counterions within the composite-induced double layer generates two counter-rotating induced-charge electroosmotic (ICEO) micro-vortices on top of each GE. Symmetry breaking in ICEO flow profile occurs once the gate voltage deviates from natural floating potential of corresponding GE. The gate voltage offset not only results in an additional pump motion of working fluid for enhanced electroosmotic transport but also directly changes the location of FSL where nanoparticles are preferentially collected by field-effect HEK. Our results of field-effect control on HEK are supposed to guide an elaborate design of flexible electrokinetic frameworks embedding coplanar metal strips for a high degree of freedom analyte manipulation in modern micro-total-analytical systems.

Numerical characterization of inter-core coalescence by AC dielectrophoresis in double-emulsion droplets.

The utilization of an alternating current electric field provides a good means to achieve controlled coalescence between paired inner cores encapsulated in water-in-oil-in-water double-emulsion (DE) droplets. Although previous studies have experimentally determined the conditions under which inter-core electrokinetic fusion occurs, the transient interfacial dielectrophoretic (DEP) dynamics key to understand the underlying fluid mechanics is still unclear from a physical point of view. By coupling DEP motion of two-phase flow to phase-field formulation, bulk-coupled numerical simulations are conducted to characterize the spatial-temporal evolution of the surface charge wave and the resulting nonlinear electrical force induced at both the core/shell and medium/shell oil/water interfaces. The effect of interfacial charge relaxation and droplet geometry on inter-core attractive dipolar interaction is investigated within a wide parametric space, and four distinct device operation modes, including normal inter-core fusion, shell elongation, partial core leakage, and complete core release, are well distinguished from one another by flow regime argumentation. Our results herein reveal for the first time the hitherto unknown transient electrohydrodynamic fluid motion of DE droplet driven by Maxwell-Wagner structural polarization. The dynamic simulation method proposed in present study points out an effective outlet to predict the nonlinear electrokinetic behavior of multicore DE droplets for realizing a more controlled triggering of microscale reactions for a wide range of applications in drug discovery, skin care, and food industry.

Desktop-level small automatic guided vehicle driven by a liquid metal droplet.

Gallium-based liquid metals (LMs) are a new type of intelligent material, and their ability to move under the action of an electric field provides new opportunities for the design of small flexible vehicles. However, due to the extremely high fluidity of LMs and the poor automatic control ability of LM vehicles, it's still a huge challenge to control the movement of LMs flexibly and accurately. Therefore, in this paper, a small traction vehicle is designed by putting the flexible LM in rigid armor to make the movement more controllable. Moreover, a desktop-level small automatic guided vehicle (sAGV) system is built by using an external control circuit to follow a predetermined trajectory. Firstly, the basic characteristics of the vehicles driven by a LM droplet are simulated and analyzed. Then the effects of different factors on the movement velocity of the vehicles are measured by experiment. Finally, as a preliminary application test, the sAGV system is used to control the vehicles following a specific trajectory and realize the targeted transportation of cargos. The sAGV system designed in this paper can realize the automatic and precise control of the movement of the small vehicle. The current findings will inspire the further construction of complex small operating systems and the realization of accurate control.

DC electric field-driven heartbeat phenomenon of gallium-based liquid metal on a floating electrode.

The heart beating phenomenon of room temperature liquid metal (LM) mercury has attracted much attention in the past years, but its research and application are limited because of the low vapor pressure and high toxicity. Here, a fundamental scientific finding is reported that the non-toxic eutectic gallium indium (EGaIn) alloy droplets beat periodically at a certain frequency based on a floating electrode under the stimulation of the direct current (DC) field. The essential characteristics of heart beating are the displacement and the projected area change of the LM droplet. The mechanism of this phenomenon is the self-regulation of interfacial tension caused by chemical oxidation, chemical corrosion, and continuous electrowetting. In this article, a series of experiments are also carried out to examine the effects of different factors on the heartbeat, such as voltage, the volume of the droplet, the droplet immersion depth, the electrolyte solution concentration, the distance of electrodes, and the type of floating electrode. Finally, the heartbeat state and application boundary of the LM droplet under different conditions are summarized by imitating the human life process. The periodic changes of the LM droplet under an external DC electric field provide a new method to simulate the beating of the heart artificially, and can be applied to the research of organ chip fluid pumping in the future.

Small universal mechanical module driven by a liquid metal droplet.

Gallium-based liquid metal droplets (LMDs) from micro-electromechanical systems (MEMS) have gained much attention due to their precise and sensitive controllability under an electric field. Considerable research progress has been made in the field of actuators by taking advantage of the continuous electrowetting (CEW) present within the solution. However, the motion generated is confined within the specific liquid environment and is lacking a way to transmit its motion outwardly, which undoubtedly serves as the greatest obstacle restricting any further development. Therefore, a driving module is proposed to generate rotational motion outside the solution for universality. Its performance can be easily tuned by adjusting the applied voltage. As an example of further application, the module is designed in the form of a pump that realizes the continuous/intermittent propulsion to mimic the veins/arteries of the human body without the problem in the previous LMD-based pumps. The feasibility of this pump in the on-chip in vitro analysis is proved by preparing a dynamic cell culture to simulate the movement of biofluids within human bodies. This study proposes an optional solution with an LMD-based motor for generating rotational motion and to expand current research on soft materials in actuators.

Pumping of electrolyte with mobile liquid metal droplets driven by continuous electrowetting: A full-scaled simulation study considering surface-coupled electrocapillary two-phase flow.

With the excellent merits of both solid conductors and rheological fluids, liquid metal (LM) provides new opportunities to serve as flexible building blocks of miniaturized electronic and fluidic devices. The phenomenon of continuous electrowetting (CEW) has been long utilized for actuating LM contents in buffer medium, wherein an externally imposed voltage difference is responsible of manipulating the interfacial tension of deformable LM droplets. CEW effectively lowers the surface tension at the LM/electrolyte interface by driving bipolar counterions to the surface of conducting droplet. Since surface tension coefficient relies sensitively on the local voltage drop across the induced double layer, an electric-analogy Marangoni effect occurs even under a rather weak electric field in the presence of a surface gradient of the interfacial tension. CEW of LM routinely induces unidirectional pumping of electrolyte in the direction of applied electric field, with LM droplet translating oppositely within the device channel. Although this subject has received great attention from the microfluidic society in the past decade, previous reports concerned either the individual delivery of the suspension medium or the transport of LM droplet. Starting from this point, we offer herein a fully coupled physical description of two-phase flow dynamics occurring in CEW. The proposed simulation model successfully incorporates the synergy of the interfacial electrokinetic momentum transfer, surface tension on a curved surface, contact angle at the three-phase contact line as well as the gravity force density. The spatial-temporal motion of the contact interface is traced instantly with a moving mesh approach. By direct numerical simulation, the importance of the direct-current bias, additional alternating-current forcing, droplet size, initial ion adsorption in the process of CEW is addressed. Additionally, it is discovered that increasing the number of LM droplet is more cost-effective than enhancing the volume of a single drop in terms of achieving an improvement of the resulted electrocapillary pump performance, while the translational speed of the discrete droplet carrier does not make an observable change in response to a variation in the drop number. These results prove invaluable in terms of an elaborate design of smart on-chip electrokinetic frameworks embedding flexible LM contents in modern micro-total-analytical systems.

A Numerical Investigation of Enhancing Microfluidic Heterogeneous Immunoassay on Bipolar Electrodes Driven by Induced-Charge Electroosmosis in Rotating Electric Fields.

A unique approach is proposed to boost on-chip immuno-sensors, for instance, immunoassays, wherein an antibody immobilized on the walls of a microfluidic channel binds specifically to an antigen suspended freely within a working fluid. The performance of these sensors can be limited in both susceptibility and response speed by the slow diffusive mass transfer of the analyte to the binding surface. Under appropriate conditions, the binding reaction of these heterogeneous immuno-assays may be enhanced by electroconvective stirring driven by external AC electric fields to accelerate the translating motion of antigens towards immobilized antibodies. To be specific, the phenomenon of induced-charge electroosmosis in a rotating electric field (ROT-ICEO) is fully utilized to stir analyte in the vicinity of the functionalized surface of an ideally polarizable floating electrode in all directions inside a tri-dimensional space. ROT-ICEO appears as a consequence of the action of a circularly-polarized traveling wave signal on its own induced rotary Debye screening charge within a bipolar induced double layer formed on the central floating electrode, and thereby the pertinent electrokinetic streamlines exhibit a radially converging pattern that greatly facilitates the convective transport of receptor towards the ligand. Numerical simulations indicate that ROT-ICEO can enhance the antigen-antibody binding reaction more effectively than convectional nonlinear electroosmosis driven by standing wave AC signals. The effectiveness of ROT-ICEO micro-stirring is strongly dependent on the Damkohler number as well as the Peclet number if the antigens are carried by a continuous base flow. Our results provide a promising way for achieving a highly efficient heterogeneous immunoassay in modern micro-total-analytical systems.