Bidirectional transfer of particles across liquid-liquid interface under electric pulse

Motion of magnetic motors across liquid-liquid interface

HYPOTHESIS

In a number of applications related to chemical engineering and drug delivery, magnetic nanoparticles should move through a liquid-liquid interface in the presence of surfactant molecules. However, due to the action of capillary forces, this is not always possible. The mechanism of particle motion through the interface essentially depends on the intensity of the Marangoni flow, which is induced on the interface during its deformation.

EXPERIMENTS

In this paper we study the motion of nanoparticles Fe3O4 through the water-tridecane interface under the action of a nonuniform magnetic field when using different surfactants.

FINDINGS

If the linear size of the magnetic motor turns out to be less than a certain critical value, then it is not able to move between phases due to the action of capillary forces on the interface. Depending on the type and concentration of the surfactant used, various mechanisms for the motor motion through the liquid-liquid interface can be carried out. In one of them, a liquid phase is transferred through the interface along with a movable motor, while in the other, it is not.

Tunable particle/cell separation across aqueous two-phase system interface by electric pulse in microfluidics

HYPOTHESIS

Separations of particles and cells are indispensable in many microfluidic systems and have numerous applications in chemistry and biomedicine. The interface of aqueous two-phase system (ATPS) can act as a liquid filter. Under electric field stimuli, the selective transfer of targets across the liquid-liquid interface are expected for particles and cells separation.

EXPERIMENTS

The separations of particles and cells based on ATPS electrophoresis in a microfluidic chip were investigated. A systematical study of the mechanism of ATPS electrophoresis was performed first by employing polystyrene (PS) particles. Subsequently, the separations of particles and microalgae cells were demonstrated.

FINDINGS

The electrophoretic transfer of particles across the interface of ATPS is determined by multi-parameters, including the strength of electric pulse, particle size, zeta potential, and hydrophobicity of the particle. The continuous separations of particles/cells can be achieved through the controllable transfer of target particles/cells across the interface under electric pulses in a microfluidic chip. By simply turning the magnitude of the applied electric pulse, the technique is suitable for different purposes, for example, the separations of particles and cells, purification of cells, and viability identification of cells. This tunable separation approach opens opportunities in multidimensional particle and cell sorting for the fields of seed selection of microorganisms, environmental assessment, and biomedical research.

Magnetic field-mediated Janus particles with sustained driving capability for severe bleeding control in perforating and inflected wounds

Severe bleeding in perforating and inflected wounds with forky cavities or fine voids encountered during prehospital treatments and surgical procedures is a complex challenge. Therefore, we present a novel hemostatic strategy based on magnetic field-mediated guidance. The biphasic Janus magnetic particle (MSS@Fe₂O₃-T) comprised aggregates of α-Fe₂O₃ nanoparticles (Fe₂O₃ NPs) as the motion actuator, negatively modified microporous starch (MSS) as the base hemostatic substrate, and thrombin as the loaded hemostatic drug. Before application, the particles were first wrapped using NaHCO₃ and then doped with protonated tranexamic acid (TXA-NH₃⁺), which ensured their high self-dispersibility in liquids. During application, the particles promptly self-diffused in blood by bubble propulsion and travelled to deep bleeding sites against reverse rushing blood flow under magnetic guidance. In vivo tests confirmed the superior hemostatic performance of the particles in perforating and inflected wounds (“V”-shaped femoral artery and “J”-shaped liver bleeding models). The present strategy, for the first time, extends the range of magnetically guided drug carriers to address the challenges in the hemorrhage control of perforating and inflected wounds.

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A new Janus hemostat was developed for treating severe bleeding.

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The “J” shape bleeding model was proposed for hemostatic test.

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Magnetic field-mediated driving capacity was employed for hemostasis.

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Explosive self-dispersibility endowed to the hemostat largely enhanced the bleeding control capacity.

Interaction of proteins with phase boundaries in aqueous two-phase systems under electric fields

The electric-field driven transport of proteins across the liquid-liquid interface in an aqueous two-phase system (ATPS) is studied in a microfluidic device using fluorescence microscopy. An ATPS containing polyethylene glycol (PEG) and dextran is employed, and bovine serum albumin (BSA) and bovine γ-globulins (BγG) are considered as model proteins. It is shown that both proteins, initially in the dextran-rich phase, accumulate at the liquid-liquid interface, preferably close to the three-phase contact line between the two liquid phases and the microchannel wall. It is in these regions where the proteins penetrate into the PEG-rich phase. The transport resistance of the liquid-liquid interface is higher for BγG than for BSA, such that a much larger molar flux of BSA into the PEG phase is observed. This opens up the opportunity of separating different protein species by utilizing differences in the transport resistance at the interface. A mathematical model is developed, accounting for adsorption and desorption processes at the liquid-liquid interface. The underlying theoretical concept is that of an electrostatic potential minimum formed by superposing the applied electric field and the field due to the Donnan potential at the interface. A fit of the model parameters to the experimental data results in good agreement between theory and experiments, thereby corroborating the underlying picture.

Electrically controllable cargo delivery with dextran-rich droplets

The controllable delivery of cargo is of great importance in many areas, ranging from medicine and materials science to food and cosmetic industries. To fulfil the requirements in different areas, the development of new methods for cargo delivery in a controllable manner is always essential. A novel technique of cargo delivery controlled by electric pulse was developed in this paper. In an aqueous two-phase system, the dextran-rich droplets were fabricated as droplet carriers in a continuous polyethylene glycol-rich phase. The loading and releasing of model cargos (polystyrene particles) across the surface of the droplet carriers under electric pulses were demonstrated in microfluidic chips. By controlling the amplitude of the applied electric pulses, the cargos with designed sizes were sorted and loaded into the droplet carriers; hence, the targeted delivery of cargos by size can be achieved. The exchange of cargos between droplet carriers under reversed electric pulses was also investigated, and the results indicated the flexibility of this method in cargo delivery. Moreover, possible application of this method to biological cargos was demonstrated by controlling the loading and releasing of yeast cells under electric pulses. With the advantages of easy operation and fast response, this approach provides a novel route for controllable cargo delivery with droplets.