Understanding Macrophage-Tumor Interactions: Insights from Single-Cell Behavior Monitoring in a Sessile Microdroplet System.

Interaction between tumor-associated macrophages and tumor cells is crucial for tumor development, metastasis, and the related immune process. However, the macrophages are highly heterogeneous spanning from anti-tumorigenic to pro-tumorigenic, which needs to be understood at the single-cell level. Herein, a sessile microdroplet system designed for monitoring cellular behavior and analyzing intercellular interaction, demonstrated with macrophage-tumor cell pairs is presented. An automatic procedure based on the inkjet printing method is utilized for the precise pairing and co-encapsulation of heterotypic cells within picoliter droplets. The sessile nature of microdroplets ensures controlled fusion and provides stable environments conducive to adherent cell culture. The nitric oxide generation and morphological changes over incubation are explored to reveal the complicated interactions from a single-cell perspective. The immune response of macrophages under distinct cellular microenvironments is recorded. The results demonstrate that the tumor microenvironment displays a modulating role in polarizing macrophages from anti-tumorigenic into pro-tumorigenic phenotype. The approach provides a versatile and compatible platform to investigate intercellular interaction at the single-cell level, showing promising potential for advancing single-cell behavior studies.

Evaluation of aconitine cardiotoxicity with a heart-on-a-particle prepared by a microfluidic device.

A heart-on-a-particle model based on multicompartmental microgel is proposed to simulate the heart microenvironment and study the cardiotoxicity of drugs. The relevant microgel was fabricated by a biocompatible microfluidic-based approach, where heart function-related HL-1 and HUVEC cells were arranged in separate compartments. Finally, the mechanism of aconitine-induced heart toxicity was elucidated using mass spectrometry and molecular biotechnology.

Gravity-Oriented Microfluidic Device for Biocompatible End-to-End Fabrication of Cell-Laden Microgels.

Droplet microfluidics are extensively utilized to generate monodisperse cell-laden microgels in biomedical applications. However, maintaining cell viability is still challenging due to overexposure to harsh conditions in subsequent procedures that recover the microgels from the oil phase. Here, a gravity-oriented microfluidic device for end-to-end fabrication of cell-laden microgels is reported, which integrates dispersion, gelation, and extraction into a continuous workflow. This innovative on-chip extraction, driven by native buoyancy and kinetically facilitated by pseudosurfactant, exhibits 100% retrieval efficiency for microgels with a wide range of sizes and stiffnesses. The viability of encapsulated cells is perfectly maintained at ≈98% with minimal variations within and between batches. The end-to-end fabrication remarkably enhances the biocompatibility and practicality of microfluidics-based cell encapsulation and is promising to be compatible with various applications ranging from single-cell analysis to clinical therapy.

Fabrication and Performance of Bubble-Containing Multicompartmental Particles: Novel Self-Orienting Carriers.

In this work, a class of bubble-containing multicompartmental particles with self-orienting capability is developed, where a single bubble is enclosed at the top of the super-segmented architecture. Such bubbles, driven by potential energy minimization, cause the particles to have a bubble-upward preferred orientation in liquid, enabling efficient decoding of their high-density signals in an interference-resistant manner. The particle preparation involves bubble encapsulation via the impact of a multicompartmental droplet on the liquid surface and overall stabilization via rational crosslinking. The conditions for obtaining these particles are systematically investigated. Methodological compatibility with materials is demonstrated by different hydrogel particles. Finally, by encapsulating cargoes of interest, these particles have found broad applications in actuators, multiplexed detection, barcodes, and multicellular systems.

Nanozyme-Mediated Catalytic Signal Amplification for Microfluidic Biosensing of Foodborne Bacteria.

Early detection of foodborne bacteria is urgently needed to ensure food quality and to avoid the outbreak of foodborne bacterial diseases. Here, a kind of metal-organic framework (Zr-MOF) modified with Pt nanoparticles (Pt-PCN-224) was designed as a peroxidase-like signal amplifier for microfluidic biosensing of foodborne bacteria. Taking Escherichia coli (E. coli) O157:H7 as a model, a linear range from 2.93 × 102 to 2.93 × 108 CFU/mL and a limit of detection of 2 CFU/mL were obtained. The whole detection procedure was integrated into a single microfluidic chip. Water, milk, and cabbage samples were successfully detected, showing consistency with the results of the standard culture method. Recoveries were in the range from 90 to 110% in spiked testing. The proposed microfluidic biosensor realized the specific and sensitive detection of E. coli O157:H7 within 1 h, implying broad prospects of MOF with biomimetic enzyme activities for biosensing.

Multicompartmental Hydrogel Microspheres as a Tool for Multicomponent Analysis.

Developing advanced tools for multicomponent analysis is an open challenge in engineering and life science. Herein, multicompartmental hydrogel microspheres with multi-material compatibility and structural scalability are developed as a tool for multicomponent analysis at a single-particle level. Microfluidic technology endows particles with adjustable sizes and super-segmented layouts that can be used to load various analyte probes. In order to perform multicomponent analysis, these microspheres are structurally divided into identifier regions for indicating reading direction and analyte regions for detecting target molecules. The multiplex detection ability of these particles is demonstrated in microRNA bioassays with high specificity and sensitivity. The multi-target analysis is performed on a single-particle level, and the bioassay is free of conventional labeling interference. We expect these particles to reach their potential in clinical diagnostics.

Multidimensional controllable fabrication of tumor spheroids based on a microfluidic device.

Multicellular tumor spheroids (MCTSs) are in vitro solid tumor models with physiological relevance. To achieve robust process control, a MCTS fabrication method that combines cell membrane engineering and droplet microfluidic techniques is designed. The fluidic control and the chemical interactions between biotin and streptavidin enable artificial cell aggregation to be accomplished in seconds. Then, spheroids with a uniform size are fabricated within alginate microcapsules. Microfluidic mixing-based cell aggregation regulates the cell aggregate size and the spheroid composition, and the microcapsules regulate the size of spheroids from 120 to 180 µm. The method shows applicability for various cancer cell lines, including HCT116, HepG2, and A549. In addition, composite colon cancer spheroids consisting of HCT116 and NIH3T3 with predetermined cell ratios and uniform distributions are produced. The generated MCTSs are assessed using the ELISA and UPLC-MS/MS techniques. The release of vascular endothelial growth factor (VEGF) and the 5-fluorouracil (5-FU) resistance differ in the monotypic and cocultured colon cancer models. Our method provides a robust way to produce consistent and customized MCTSs in cancer research and drug screening.

Functional Liquid Crystal Core/Hydrogel Shell Microcapsules for Monitoring Live Cells in a 3D Microenvironment.

Three-dimensional (3D) cell culture, even as a simple microspheroid model, can be used to recapitulate the native biological microenvironment of cells. Examining the biochemical characteristics of cells in multicellular hydrogel microspheroids using microsensors is usually limited to monitoring the medium around the microspheroids. Here, functional liquid crystal (LC) core/hydrogel shell microcapsules loaded with cells were prepared using droplet microfluidic technology for monitoring live cells in a 3D microenvironment. These microcapsules have a distinctive core/shell structure; cells can be cultured in the hydrogel shell of this 3D model. The functional LC core responds to the acidic microenvironment of cells, showing an axial-to-bipolar transfiguration. 3D cell culture and visual monitoring of the cell microenvironment can be simultaneously achieved in a single microcapsule. Therefore, this novel method may enable a standard approach for monitoring multiple ions or molecules in a 3D model of the cell microenvironment.

Microfluidic Engineering of Crater-Terrain Hydrogel Microparticles: Toward Novel Cell Carriers.

Fabrication and application of novel anisotropic microparticles are of wide interest. Herein, a new method for producing novel crater-terrain hydrogel microparticles is presented using a concept of droplet-aerosol impact and regional polymerization. The surface pattern of microparticles is similar to the widespread "crater" texture on the lunar surface and can be regulated by the impact morphology of aerosols on the droplet surface. Methodological applicability was demonstrated by producing ionic-cross-linked (alginate) and photo-cross-linked (poly(ethylene glycol) diacrylate, PEGDA) microparticles. Additionally, the crater-terrain microparticles (CTMs) can induce nonspecific protein absorption on their surface to acquire cell affinity, and they were exploited as cell carriers to load living cells. Cells could adhere and proliferate, and a special cellular adhesion fingerprint was observed on the novel cell carrier. Therefore, the scalable manufacturing method and biological potential make the engineered microparticles promising to open a new avenue for exploring cell-biomaterial crosstalk.

Ion Addition by Electrolysis to Improve the Quantitative Analysis of Bacteria with MALDI-TOF MS.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) is commonly applied to the identification of bacteria but rarely used for quantitative detection due to the inhomogeneous crystallization of the matrix leading to the unsatisfactory linear relationship between the sample amount and the mass spectrum signals. Herein, we proposed a noninterference ion addition (NIA) method by electrolysis to improve homogeneous crystallization during the evaporation progress of sample droplets on the target plates. The active metal wire was inserted in the droplet as the anode electrode, and metal ions were released through electrolysis. The directional migration of metal ions under the electric field can hinder the migration of matrix molecules to the boundary and homogenize the matrix crystals by forming spherical crystals. Simultaneously, trace cationic surfactant was added to the droplet for pinning the contact surface to define the circle crystallization region. The metal ions from the anode electrode wire were deposited on the surface of the target plates which served as the cathode. Therefore, ion addition has no interference effect on ionization during MALDI-MS detection. This NIA method benefits the homogeneous crystallization and so improves the quantitative analysis. NIA is suitable for biological samples with different matrices, and bacterial samples could be quantitatively analyzed.

Enhanced photocatalytic activity of TiO2/UiO-67 under visible-light for aflatoxin B1 degradation.

TiO2 has great potential in photocatalytic degradation of organic pollutants, but poor visible light response and low separation efficiency of photogenerated electron-hole pairs limit its wide applications. In this study, we have successfully prepared TiO2/UiO-67 photocatalyst through an in situ solvothermal method. The degradation rate of aflatoxin B1 (AFB1) is 98.9% in only 80 min, which is superior to the commercial P25, commercial TiO2 and most of reported photocatalysts under visible light irradiation. In addition, the TiO2/UiO-67 photocatalyst showed excellent recyclability. We demonstrated that the enhanced photocatalytic mechanism was owing to the heterojunction between TiO2 and UiO-67, which enhanced effectively the separation photogenerated charge carriers and visible light response. The free radical trapping tests demonstrated that superoxide radicals (˙O2 -), holes (h+) and hydroxyl radicals (˙OH) were the main active species and then oxidized AFB1 to some small molecules.

Nickel Coated Polyester Sponge for Delaying the Specific Aggregation of Fine Particles Induced by Negative Air Ions.

Negative air ions (NAIs) produced by corona discharge is often used for indoor air purification; however, the specific aggregation of suspended particles caused by NAIs, especially fine particles (FPs), needs to be considered. Here, a nickel coated conductive sponge (NCCS) was used as the main adsorption interface for delaying the obstinate aggregation caused by NAIs on another surface. The specific aggregation of FPs is caused by the directional transfer of electric charge, and the oxidation characteristic of NAIs results in the surface reaction of FPs simultaneously. The conductivity and roughness of the adsorption interface determine the migration direction and enrichment number of FPs, respectively. Nickel coated conductive sponge with high conductivity and high specific surface area can effectively adsorb the FPs affected by NAIs and can effectively delay the specific aggregation on the surface of indoor objects.

Microfluidic droplet-based functional materials for cell manipulation.

Functional materials from the microfluidic-based droplet community are emerging as enabling tools for various applications in tissue engineering and cell biology. The innovative micro- and nano-scale materials with diverse sizes, shapes and components can be fabricated without the use of complicated devices, allowing unprecedented control over the cells that interact with them. Here, we review the current development of microfluidic-based droplet techniques for creation of functional materials (i.e., liquid droplet, microcapsule, and microparticle). We also describe their various applications for manipulating cell fate and function.

Inhibition Effect of Negative Air Ions on Adsorption between Volatile Organic Compounds and Environmental Particulate Matter.

This work focused on the chemisorption of volatile organic compounds (VOCs) on particulate matter of less than 2.5 µm (PM2.5). The detection results illustrated that VOCs on PM2.5 containing hydroxyl, carbonyl, and ester groups and CxHy on PM2.5 were sequentially decreased as 70.02, 21.35, 6.42, and 2.21%, respectively. The chemisorption mechanism showed that the stronger the electronegativity of oxygen-containing functional groups of VOCs, the easier it is to adsorb them on the silicate PM2.5 due to hydrogen bond formation. Strong electronegative oxygen-containing functional groups readily interacted through hydrogen bonds with silanol groups, which was the main component of PM2.5, resulting in VOC adsorption on PM2.5. Negative air ions (NAIs) can weaken the offset ability of the lone pair of electrons in oxygen-containing functional groups in VOCs, which could significantly weaken the possibility of forming hydrogen bonds with silanol groups. Therefore, NAIs can effectively inhibit the adsorption between VOCs and PM2.5, leading to a significant reduction in VOCs on the surface of PM2.5.

Monitoring H2 O2 on the Surface of Single Cells with Liquid Crystal Elastomer Microspheres.

Live-imaging of signaling molecules released from living cells is a fundamental challenge in life sciences. Herein, we synthesized liquid crystal elastomer microspheres functionalized with horse-radish peroxidase (LCEM-HRP), which can be immobilized directly on the cell membrane to monitor real-time release of H2 O2 at the single-cell level. LCEM-HRP could report H2 O2 through a concentric-to-radial (C-R) transfiguration, which is due to the deprotonation of LCEM-HRP and the break of inter or intra-chain hydrogen bonding in LCEM-HRP caused by HRP-catalyzed reduction of H2 O2 . The level of transfiguration of LCEM-HRP revealed the different amounts of H2 O2 released from cells. The estimated detection sensitivity was ≈2.2×10-7  µm for 10 min of detection time. The cell lines and cell-cell heterogeneity was explored from different configurations. LCEM-HRP presents a new approach for in situ real-time imaging of H2 O2 release from living cells and can be the basis for seeking more advanced chemical probes for imaging of various signaling molecules in the cellular microenvironment.

ATP-responsive mitochondrial probes for monitoring metabolic processes of glioma stem cells in a 3D model.

The metastatic cascade of cancer stem cells (CSCs) is always accompanied by elevated levels of adenosine triphosphate (ATP) as well as the alterntion of energy metabolism to support their differentiation and migration. Here we propose a 3D microfluidic tumor model coupled with an ATP-responsive mitochondrial probe (AMP) for investigation of metabolic processes of glioma stem cells (GSCs). The 3D tumor model has a middle matrix gel microchannel mimicking the extracellular matrix (ECM), which is sandwiched between a GSC culture chamber and a stimulation chamber. The AMPs consist of structure-switching ATP aptamers and triphenylphosphonium (TPP)-conjugated peptide nucleic acids (PNAs). Under TGF-ß stimulation, invasive migration of GSCs accompanied by a high ATP level and spindle mesenchymal morphologies is observed due to the epithelial-to-mesenchymal transition (EMT). Moreover, acidic stress can keep GSCs in a low-energy state, while long-term low pH stimulation screens out more malignant glioma cells. This AMP-assisted 3D microfluidic tumor model provides a tremendous opportunity for studying the biological properties of CSCs.

Hydrated negative air ions generated by air-water collision with TiO2 photocatalytic materials.

Photocatalytic materials are often used in the field of electrolysis of water for its competitive performance and low cost. This study describes the use of TiO2 for providing free electrons to prepare hydrated negative air ions together with the Lenard effect caused by air-water collision. The lifetime of HNAIs increased by 47.62% in comparison with the traditional corona discharge method; both the stability and the actual yield of the HNAIs increased significantly. The stability of HNAIs has a correlative relationship with the molecular weight and relative humidity. Lower mobility of the HNAIs with larger molecular weight results in low probability of collision with other air particles, making it relatively stable. Water molecules could form a water shell around the cluster ions in a high relative humidity environment, which can protect the ions, avoiding physical collision to extend the lifetime.

Controllable Synthesis of Multicompartmental Particles Using 3D Microfluidics.

A microfluidic assembly method based on a microfluidic chip and capillary device was developed to create multicompartmental particles. The microfluidic chip design endows the particles with regulable internal structure. By adjusting the microstructure of the chip, the diameter of the capillary, the gap length between the two microfluidic components, and the flow rates, the size of the particles and the number or the ratio of different regions within the particle could be widely varied. As a proof of concept, we have produced some complicated particles that even contain 20 compartments. Furthermore, the potential applications of the anisotropic particles are explored by encapsulating magnetic beads, fluorescent nanoparticles, and the cells into different compartments of the microparticles. We believe that this method will open new avenues for the design and application of multicompartmental particles.

Multifunctional Regulation of 3D Cell-Laden Microsphere Culture on an Integrated Microfluidic Device.

Three-dimensional (3D) hydrogel microspheres have aroused increasing attention as an in vitro cell culture model. Yet the preservation of cells' original biological properties has been overlooked during model construction. Here we present an integrated microfluidic device to accomplish the overall process including cell-laden microsphere generation, online extraction, and dynamic-culture. The method extends the noninvasive and nonsuppression capabilities of the droplet preparation system and provides a constant microenvironment, which reduces intracellular oxidative stress damage and the accumulation of mitochondria. Compared to the conventional preparation method, the coculture model of tumor-endothelial construction on an integrated platform displays high-level angiogenic protein expression. We believe that this versatile and biocompatible platform will provide a more reliable analysis tool for tissue engineering and cancer therapy.

A tumor microenvironment model coupled with a mass spectrometry system to probe the metabolism of drug-loaded nanoparticles.

This study describes a novel integrated microfluidic platform with microvessel network channels which are connected to an electrospray ionization-mass spectrometer (ESI-MS), allowing real-time probing of nanoparticle (NP) drug delivery in vascular niche around tumors and understanding the drug delivery efficacy in a realistic tumor microenvironment.