Aqueous two-phase systems (ATPSs) have been recognized for their applications in extraction, separation, purification, and enrichment of (bio)molecules and cells. Recently, their unique ability to create aqueous-aqueous interfaces through phase separation and the characteristics of these interfaces have created new opportunities in biomedical applications. In this review, we summarize recent progress in understanding the dynamics at aqueous-aqueous interfaces, and in developing interface-assisted design of artificial cells and cyto-mimetic materials, fabrication of cyto- and bio-compatible microparticles, cell micropatterning, 3D bioprinting, and microfluidic separation of cells and biomolecules. We also discuss the challenges and perspectives to leverage the unique characteristics of ATPSs and their interfaces in broader applications.

Emerging aqueous two-phase systems: from fundamentals of interfaces to biomedical applications

This protocol describes the design of capillary microfluidics for spinning bioactive (cell-laden) microfibers for three-dimensional (3D) cell culture and tissue-engineering applications. We describe the assembly of three types of microfluidic systems: (i) simple injection capillary microfluidics for the spinning of uniform microfibers; (ii) hierarchical injection capillary microfluidics for the spinning of core–shell or spindle-knot structured microfibers; and (iii) multi-barrel injection capillary microfluidics for the spinning of microfibers with multiple components. The diverse morphologies of these bioactive microfibers can be further assembled into higher-order structures that are similar to the hierarchical structures in tissues. Thus, by using different types of capillary microfluidic devices, diverse styles of microfibers with different bioactive encapsulation can be generated. These bioactive microfibers have potential applications in 3D cell culture, the mimicking of vascular structures, the creation of synthetic tissues, and so on. The whole protocol for device fabrication and microfiber spinning takes ~1 d. This protocol describes how to produce cell-laden microfibers using capillary microfluidic devices. The devices enable spinning of increasingly complex microfibers, which can function as building blocks for 3D cell culture and tissue engineering.

Design of capillary microfluidics for spinning cell-laden microfibers.

Ferrofluids, also known as ferromagnetic particle suspensions, are materials with an excellent magnetic response, which have attracted increasing interest in both industrial production and scientific research areas. Because of their outstanding features, such as rapid magnetic reaction, flexible flowability, as well as tunable optical and thermal properties, ferrofluids have found applications in various fields, including material science, physics, chemistry, biology, medicine, and engineering. Here, a comprehensive, in-depth insight into the diverse applications of ferrofluids from material fabrication, droplet manipulation, and biomedicine to energy and machinery is provided. Design of ferrofluid-related devices, recent developments, as well as present challenges and future prospects are also outlined.

Flexible Ferrofluids: Design and Applications

The unprecedented demand for rapid diagnostics in response to the COVID-19 pandemic has brought the spotlight onto clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated systems (Cas)-assisted nucleic acid detection assays. Already benefitting from an elegant detection mechanism, fast assay time, and low reaction temperature, these assays can be further advanced via integration with powerful, digital-based detection. Thus motivated, the first digital CRISPR/Cas-assisted assay-coined digitization-enhanced CRISPR/Cas-assisted one-pot virus detection (deCOViD)-is developed and applied toward SARS-CoV-2 detection. deCOViD is realized through tuning and discretizing a one-step, fluorescence-based, CRISPR/Cas12a-assisted reverse transcription recombinase polymerase amplification assay into sub-nanoliter reaction wells within commercially available microfluidic digital chips. The uniformly elevated digital concentrations enable deCOViD to achieve qualitative detection in <15 min and quantitative detection in 30 min with high signal-to-background ratio, broad dynamic range, and high sensitivity-down to 1 genome equivalent (GE) µL-1 of SARS-CoV-2 RNA and 20 GE µL-1 of heat-inactivated SARS-CoV-2, which outstrips its benchtop-based counterpart and represents one of the fastest and most sensitive CRISPR/Cas-assisted SARS-CoV-2 detection to date. Moreover, deCOViD can detect RNA extracts from clinical samples. Taken together, deCOViD opens a new avenue for advancing CRISPR/Cas-assisted assays and combating the COVID-19 pandemic and beyond.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/advs.202003564

Digital CRISPR/Cas‐Assisted Assay for Rapid and Sensitive Detection of SARS‐CoV‐2

Living cells have evolved over billions of years to develop structural and functional complexity with numerous intracellular compartments that are formed due to liquid-liquid phase separation (LLPS). Discovery of the amazing and vital roles of cells in life has sparked tremendous efforts to investigate and replicate the intracellular LLPS. Among them, all-aqueous emulsions are a minimalistic liquid model that recapitulates the structural and functional features of membraneless organelles and protocells. Here, an emerging all-aqueous microfluidic technology derived from micrometer-scaled manipulation of LLPS is presented; the technology enables the state-of-art design of advanced biomaterials with exquisite structural proficiency and diversified biological functions. Moreover, a variety of emerging biomedical applications, including encapsulation and delivery of bioactive gradients, fabrication of artificial membraneless organelles, as well as printing and assembly of predesigned cell patterns and living tissues, are inspired by their cellular counterparts. Finally, the challenges and perspectives for further advancing the cell-inspired all-aqueous microfluidics toward a more powerful and versatile platform are discussed, particularly regarding new opportunities in multidisciplinary fundamental research and biomedical applications.

https://onlinelibrary.wiley.com/doi/epdf/10.1002/advs.201903359

Cell-Inspired All-Aqueous Microfluidics: From Intracellular Liquid–Liquid Phase Separation toward Advanced Biomaterials

In this study, we develop a method to detect multiple DNAs of foodborne pathogens by encapsulating emulsion droplets for loop-mediated isothermal amplification (LAMP). In contrast to the traditional bulk-phase LAMP, which involves a labor-intensive mixing process, with our method, different primers are automatically mixed with DNA samples and LAMP buffers after picoinjection. By directly observing and analyzing the fluorescence intensity of the resultant droplets, one can detect DNA from different pathogens, with a detection limit 500 times lower than that obtained by bulk-phase LAMP. We further demonstrate the ability to quantify bacteria concentration by detecting bacterial DNA in practical samples, showing great potential in monitoring water resources and their contamination by pathogenic bacteria.

Picoinjection-Enabled Multitarget Loop-Mediated Isothermal Amplification for Detection of Foodborne Pathogens.

A model is proposed to simulate the generation and propagation of the shock wave (SW) produced by underwater electrical wire
explosion in microsecond timescale, with the assumption that the exploding wire instantly turns into uniform discharge plasma channel (DPC) after the onset of explosion. To describe the interaction between the DPC and the surrounding water medium, the initial temperature of DPC is obtained by fitting calculated pressures with experimental data, and the injected energy of DPC is provided by the measured discharge current after wire
explosion. To attenuate the high frequency oscillations generated by the discretization, the method with the double artificial viscosity parameters is proposed to calculate the SW propagation characteristics, and the input parameter is the above-calculated DPC boundary trajectory. Based on the proposed model, the DPC and SW properties of an underwater copper wire
explosion are analyzed. The results show that the estimated initial temperature of DPC is about 15 000 K, the attenuation of peak pressure can be characterized by a law of the radial propagation distance r to the power of −0.74, and the efficiency transferred from stored electrical energy to the exploding wire and the generated water flow are ∼71.5% and ∼10%, respectively.

Study of the shock waves characteristics generated by underwater electrical wire explosion

Shock waves in water have many applications, such as lithotripsy, sterilization, weapons, and so on. Underwater electrical wire explosion can be utilized to produce shock waves with fast front and short duration time efficiently. In order to amplify the energy of shock waves, energetic materials (EMs) were considered. In this paper, Al, Cu, Mo, and W wires with EM covers were designed and tested. The results showed that wire explosion ignited the EMs, which in turn affected the process of wire explosion. As a result, the duration time of shock waves was elongated.

Generation of Electrohydraulic Shock Waves by Plasma-Ignited Energetic Materials: I. Fundamental Mechanisms and Processes

Droplets containing ternary mixtures can spontaneously phase-separate into high-order structures upon a change in composition, which provides an alternative strategy to form multiphase droplets. However, existing strategies always involve nonaqueous solvents that limit the potential applications of the resulting multiple droplets, such as encapsulation of biomolecules. Here, a robust approach to achieve high-order emulsion drops with an all-aqueous nature from two aqueous phases by osmosis-induced phase separation on a microfluidic platform is presented. This technique is enabled by the existence of an interface of the two aqueous phases and phase separation caused by an osmolality difference between the two phases. The complexity of emulsion drops induced by phase separation could be controlled by varying the initial concentration of solutes and is systematically illustrated in a state diagram. In particular, this technique is utilized to successfully achieve high-order all-aqueous droplets in a different aqueous two-phase system. The proposed method is simple since it only requires two initial aqueous solutions for generating multilayered, organic-solvent-free all-aqueous emulsion drops, and thus these multiphase emulsion drops can be further tailored to serve as highly biocompatible material templates.

Youchuang Chao

Papers

Emerging aqueous two-phase systems: from fundamentals of interfaces to biomedical applications

Picoinjection-Enabled Multitarget Loop-Mediated Isothermal Amplification for Detection of Foodborne Pathogens.

Study of the shock waves characteristics generated by underwater electrical wire explosion

Generation of Electrohydraulic Shock Waves by Plasma-Ignited Energetic Materials: I. Fundamental Mechanisms and Processes

Generation of High-Order All-Aqueous Emulsion Drops by Osmosis-Driven Phase Separation.