An integrated microfluidic culture device to regulate endothelial cell differentiation from embryonic stem cells

We developed an integrated microfluidic culture device to regulate embryonic stem (ES) cell fate. The integrated microfluidic culture device consists of an air control channel and a fluidic channel with 4×4 micropillar arrays. We hypothesized that the microscale posts within the micropillar arrays would enable the control of uniform cell docking and shear stress profiles. We demonstrated that ES cells cultured for 6 days in the integrated microfluidic culture device differentiated into endothelial cells. Therefore, our integrated microfluidic culture device is a potentially powerful tool for directing ES cell fate.     

用于细胞三维培养的集成微柱阵列的微流控芯片设计与验证

设计并验证了一种用于细胞三维培养的集成微柱阵列的微流控芯片.芯片由一片聚二甲基硅氧烷(PDMS)沟道片和一片玻璃盖片组成, 在PDMS沟道片上集成了一个由两排微柱阵列围成的细胞培养室和两条用于输送培养基的侧沟道.微柱间距直接影响了芯片的使用性能, 是整个芯片设计的关键.基于数值模拟和实验验证, 本研究对微柱间距进行了优化设计.优化后的微流控芯片可以很好地实现细胞与细胞外基质模拟材料混合液的稳定注入、培养基中营养物质向培养室内的快速扩散和细胞代谢物的及时排出.在芯片上进行了神经干细胞的三维培养, 证明了芯片上构建的细胞体外微环境的稳定性.     

Micropillar‐based microfluidic device to regulate neurite networks of uniform‐sized neurospheres

The inability of neurons to undergo mitosis renders damage to the central or peripheral nervous system. Neural stem cell therapy could provide a path for treating the neurodegenerative diseases. However, reliable and simple tools for the developing and testing neural stem cell therapy are still required. Here, we show the development of a micropillar‐based microfluidic device to trap the uniform‐sized neurospheres. The neurospheres trapped within micropillar arrays were largely differentiated into neuronal cells, and their neurite networks were observed in the microfluidic device. Compared to conventional cultures on glass slides, the neurite networks generated with this method have a higher reproducibility. Furthermore, we demonstrated the effect of thapsigargin on the neurite networks in the microfluidic device, demonstrating that neural networks exposed to thapsigargin were largely diminished and disconnected from each other. Therefore, this micropillar‐based microfluidic device could be a potential tool for screening of neurotoxins.     

Quantitative determination of dopamine in single rat pheochromocytoma cells by microchip electrophoresis with only one high‐voltage power supply

We developed a method for the direct identification of dopamine in single cultured rat pheochromocytoma cells by capillary electrophoresis using an end‐channel carbon fiber nanoelectrode amperometric detector. The operation mode was designed to achieve single‐cell injection and lysis in microfluidic chip electrophoresis with only one high‐voltage power supply. The separation and detection conditions were optimized. Four catecholamines were baseline‐separated and determined with this system, and the cell density and liquid height of the reservoirs were accommodated for single cell loading, docking and analysis. The microchip capillary electrophoresis system was successfully applied to determine dopamine in single cultured rat pheochromocytoma cells.     

Circular‐shaped microfluidic device to study the effect of shear stress on cellular orientation

Understanding the effects of shear stress on mammalian cells is a crucial factor for understanding a number of biological processes and diseases. Here, we show the development of a circular‐shaped microfluidic device for the facile generation of shear stress gradients. With this microfluidic device, the effect of shear stress on orientation of human umbilical vein endothelial cells was studied. This microfluidic device, which enables to control the alignment of human umbilical vein endothelial cells within a microchannel, can be a valuable tool to mimic blood vessels.     

Photo‐crosslinkable hydrogel‐based 3D microfluidic culture device

We developed the photo‐crosslinkable hydrogel‐based 3D microfluidic device to culture neural stem cells (NSCs) and tumors. The photo‐crosslinkable gelatin methacrylate (GelMA) polymer was used as a physical barrier in the microfluidic device and collagen type I gel was employed to culture NSCs in a 3D manner. We demonstrated that the pore size was inversely proportional to concentrations of GelMA hydrogels, showing the pore sizes of 5 and 25 w/v% GelMA hydrogels were 34 and 4 μm, respectively. It also revealed that the morphology of pores in 5 w/v% GelMA hydrogels was elliptical shape, whereas we observed circular‐shaped pores in 25 w/v% GelMA hydrogels. To culture NSCs and tumors in the 3D microfluidic device, we investigated the molecular diffusion properties across GelMA hydrogels, indicating that 25 w/v% GelMA hydrogels inhibited the molecular diffusion for 6 days in the 3D microfluidic device. In contrast, the chemicals were diffused in 5 w/v% GelMA hydrogels. Finally, we cultured NSCs and tumors in the hydrogel‐based 3D microfluidic device, showing that 53–75% NSCs differentiated into neurons, while tumors were cultured in the collagen gels. Therefore, this photo‐crosslinkable hydrogel‐based 3D microfluidic culture device could be a potentially powerful tool for regenerative tissue engineering applications.     

Epithelial‐to‐mesenchymal transition of human lung alveolar epithelial cells in a microfluidic gradient device

Epithelial‐to‐mesenchymal transition (EMT), a process in which epithelial cells undergo phenotypic transitions to fibrotic cells, is induced by stimulants including transforming growth factor‐beta1 (TGF‐β1). In the present study, we developed a microfluidic gradient device to reproduce EMT in A549 human lung alveolar epithelial cells in response to TGF‐β1 gradients. The device was directly mounted on the cells that had grown in cell culture plates and produced a stable concentration gradient of TGF‐β1 with negligible shear stress, thereby providing a favorable environment for the anchorage‐dependent cells. A549 cells elongated with the characteristic spindle‐shaped morphological changes with upregulation of alpha‐smooth muscle actin, a mesenchyme marker, in a gradient‐dependent manner, suggestive of EMT progression. We observed that at higher TGF‐β1 concentrations ranging from 5 to 10 ng/mL, the cultures in the microfluidic device allowed to quantitatively pick up subtle differences in the EMT cellular response as compared with plate cultures. These results suggest that the microfluidic gradient device would accurately determine the optimal concentrations of TGF‐β1, given that epithelial cells of different tissue origins greatly vary their responses to TGF‐β1. Therefore, this microfluidic device could be a powerful tool to monitor EMT induced by a variety of environmental stresses including cigarette smoke with high sensitivity.     

High‐Throughput Isolation of Cell Protrusions with Single‐Cell Precision for Profiling Subcellular Gene Expression

Invading cancer cells extend cell protrusions, which guide cancer‐cell migration and invasion, eventually leading to metastasis. The formation and activity of cell protrusions involve the localization of molecules and organelles at the cell front; however, it is challenging to precisely isolate these subcellular structures at the single‐cell level for molecular analysis. Here, we describe a newly developed microfluidic platform capable of high‐throughput isolation of cell protrusions at single‐cell precision for profiling subcellular gene expression. Using this microfluidic platform, we demonstrate the efficient generation of uniform cell‐protrusion arrays (more than 5000 cells with protrusions) for a series of cell types. We show precise isolation of cell protrusions with high purity at single‐cell precision for subsequent RNA‐Seq analysis, which was further validated by RT‐qPCR and RNA FISH. Our highly controlled protrusion isolation method opens a new avenue for the study of subcellular functional mechanisms and signaling pathways in metastasis.     

In Situ Single‐Cell Western Blot on Adherent Cell Culture

Integrating 2D culture of adherent mammalian cells with single‐cell western blotting (in situ scWB) uses microfluidic design to eliminate the requirement for trypsin release of cells to suspension, prior to single‐cell isolation and protein analysis. To assay HeLa cells from an attached starting state, we culture adherent cells in fibronectin‐functionalized microwells formed in a thin layer of polyacrylamide gel. To integrate the culture, lysis, and assay workflow, we introduce a one‐step copolymerization process that creates protein‐decorated microwells. After single‐cell culture, we lyse each cell in the microwell and perform western blotting on each resultant lysate. We observe cell spreading after overnight microwell‐based culture. scWB reports increased phosphorylation of MAP kinases (ERK1/2, p38) under hypertonic conditions. We validate the in situ scWB with slab‐gel western blot, while revealing cell‐to‐cell heterogeneity in stress responses.     

A valve‐based microfluidic device for on‐chip single cell treatments

Assays toward single‐cell analysis have attracted the attention in biological and biomedical researches to reveal cellular mechanisms as well as heterogeneity. Yet nowadays microfluidic devices for single‐cell analysis have several drawbacks: some would cause cell damage due to the hydraulic forces directly acting on cells, while others could not implement biological assays since they could not immobilize cells while manipulating the reagents at the same time. In this work, we presented a two‐layer pneumatic valve‐based platform to implement cell immobilization and treatment on‐chip simultaneously, and cells after treatment could be collected non‐destructively for further analysis. Target cells could be encapsulated in sodium alginate droplets which solidified into hydrogel when reacted with Ca²⁺. The size of hydrogel beads could be precisely controlled by modulating flow rates of continuous/disperse phases. While regulating fluid resistance between the main channel and passages by the integrated pneumatic valves, on‐chip capture and release of hydrogel beads was implemented. As a proof of concept for on‐chip single‐cell treatments, we showed cellular live/dead staining based on our devices. This method would have potential in single cell manipulation for biochemical cellular assays.     

Isolation,Detection, and Antigen‐Based Profiling of Circulating Tumor Cells Using a Size‐Dictated Immunocapture Chip

Even though the diagnostic and prognostic value of circulating tumor cells (CTCs) has been demonstrated, their clinical utility and widespread adoption have been limited. Herein, we describe a new device, size‐dictated immunocapture chip (SDI‐Chip), for efficient, sensitive, and spatially resolved capture and detection of CTCs. SDI‐Chip enables selective, frequent, and extended interaction of CTCs with hydrodynamically optimized immunocoated micropillar surfaces. CTCs with different antigen expression levels can be efficiently captured and spatially resolved around the micropillars. Capture efficiency greater than 92 % with a purity of 82 % was achieved with blood samples. CTCs were detected in non‐metastasis colorectal (CRC) patients, while none was detected from healthy volunteers. We believe that SDI‐Chip will facilitate the transition of tumor diagnosis from anatomical pathology to molecular pathology in localized CRC patients.     

Isolation,Detection, and Antigen‐Based Profiling of Circulating Tumor Cells Using a Size‐Dictated Immunocapture Chip

Even though the diagnostic and prognostic value of circulating tumor cells (CTCs) has been demonstrated, their clinical utility and widespread adoption have been limited. Herein, we describe a new device, size‐dictated immunocapture chip (SDI‐Chip), for efficient, sensitive, and spatially resolved capture and detection of CTCs. SDI‐Chip enables selective, frequent, and extended interaction of CTCs with hydrodynamically optimized immunocoated micropillar surfaces. CTCs with different antigen expression levels can be efficiently captured and spatially resolved around the micropillars. Capture efficiency greater than 92 % with a purity of 82 % was achieved with blood samples. CTCs were detected in non‐metastasis colorectal (CRC) patients, while none was detected from healthy volunteers. We believe that SDI‐Chip will facilitate the transition of tumor diagnosis from anatomical pathology to molecular pathology in localized CRC patients.     

A Concentric Ring Electrode for a Wall‐jet Cell in a Microfluidic Device

A concentric ring array electrode that amplifies the current signal without redox cycling has been developed for highly sensitive electrochemical detection at a single potential in a microfluidic platform. Herein, the effect of ring‐electrode width on the current and current density was examined. A ring‐array electrode with widths that decrease from the inner to the outer ring was shown to exhibit the highest sensitivity. This electrode delivered a current density that was approximately 50 % higher than that of a conventionally used disc electrode. We used numerical simulations to further optimize this type of array electrode, which led to a limit of detection for catechol of 6.2 nmol/L. This ring array electrode has great potential for use in a variety of applications because it can be used to detect irreversible targets with a simple apparatus at a single potential and requires no electrode modification to achieve high sensitivity.     

A microfluidic generator of dynamic shear stress and biochemical signals based on autonomously oscillatory flow

Biological cells in vivo typically reside in a dynamic flowing microenvironment with extensive biomechanical and biochemical cues varying in time and space. These dynamic biomechanical and biochemical signals together act to regulate cellular behaviors and functions. Microfluidic technology is an important experimental platform for mimicking extracellular flowing microenvironment in vitro. However, most existing microfluidic chips for generating dynamic shear stress and biochemical signals require expensive, large peripheral pumps and external control systems, unsuitable for being placed inside cell incubators to conduct cell biology experiments. This study has developed a microfluidic generator of dynamic shear stress and biochemical signals based on autonomously oscillatory flow. Further, based on the lumped-parameter and distributed-parameter models of multiscale fluid dynamics, the oscillatory flow field and the concentration field of biochemical factors has been simulated at the cell culture region within the designed microfluidic chip. Using the constructed experimental system, the feasibility of the designed microfluidic chip has been validated by simulating biochemical factors with red dye. The simulation results demonstrate that dynamic shear stress and biochemical signals with adjustable period and amplitude can be generated at the cell culture chamber within the microfluidic chip. The amplitudes of dynamic shear stress and biochemical signals is proportional to the pressure difference and inversely proportional to the flow resistance, while their periods are correlated positively with the flow capacity and the flow resistance. The experimental results reveal the feasibility of the designed microfluidic chip. Conclusively, the proposed microfluidic generator based on autonomously oscillatory flow can generate dynamic shear stress and biochemical signals without peripheral pumps and external control systems. In addition to reducing the experimental cost, due to the tiny volume, it is beneficial to be integrated into cell incubators for cell biology experiments. Thus, the proposed microfluidic chip provides a novel experimental platform for cell biology investigations.     

Microcirculation within grooved substrates regulates cell positioning and cell docking inside microfluidic channels

Immobilization of cells inside microfluidic devices is a promising approach for enabling studies related to drug screening and cell biology. Despite extensive studies in using grooved substrates for immobilizing cells inside channels, a systematic study of the effects of various parameters that influence cell docking and retention within grooved substrates has not been performed. We demonstrate using computational simulations that the fluid dynamic environment within microgrooves significantly varies with groove width, generating microcirculation areas in smaller microgrooves. Wall shear stress simulation predicted that shear stresses were in the opposite direction in smaller grooves (25 and 50 microm wide) in comparison to those in wider grooves (75 and 100 microm wide). To validate the simulations, cells were seeded within microfluidic devices, where microgrooves of different widths were aligned perpendicularly to the direction of the flow. Experimental results showed that, as predicted, the inversion of the local direction of shear stress within the smaller grooves resulted in alignment of cells on two opposite sides of the grooves under the same flow conditions. Also, the amplitude of shear stress within microgrooved channels significantly influenced cell retainment in the channels. Therefore, our studies suggest that microscale shear stresses greatly influence cellular docking, immobilization, and retention in fluidic systems and should be considered for the design of cell-based microdevices.     

Microfluidic Cell Deformability Assay for Rapid and Efficient Kinase Screening with the CRISPR‐Cas9 System

Herein we report a CRISPR‐Cas9‐mediated loss‐of‐function kinase screen for cancer cell deformability and invasive potential in a high‐throughput microfluidic chip. In this microfluidic cell separation platform, flexible cells with high deformability and metastatic propensity flowed out, while stiff cells remained trapped. Through deep sequencing, we found that loss of certain kinases resulted in cells becoming more deformable and invasive. High‐ranking candidates identified included well‐reported tumor suppressor kinases, such as chk2, IKK‐α, p38 MAPKs, and DAPK2. A high‐ranking candidate STK4 was chosen for functional validation and identified to play an important role in the regulation of cell deformability and tumor suppression. Collectively, we have demonstrated that CRISPR‐based on‐chip mechanical screening is a potentially powerful strategy to facilitate systematic genetic analyses.     

In Situ Scatheless Cell Detachment Reveals Correlation between Adhesion Strength and Viability at Single‐Cell Resolution

Single‐cell biology provides insights into some of the most fundamental processes in biology and promotes the understanding of life's mysteries. As the technologies to study single‐cells expand, they will require sophisticated analytical tools to make sense of various behaviors and components of single‐cells as well as their relations in the adherent tissue culture. In this paper, we revealed cell heterogeneity and uncovered the connections between cell adhesion strength and cell viability at single‐cell resolution by extracting single adherent cells of interest from a standard tissue culture by using a microfluidic chip‐based live single‐cell extractor (LSCE). We believe that this method will provide a valuable new tool for single‐cell biology.     

A novel 3D mammalian cell perfusion-culture system in microfluidic channels

Mammalian cells cultured on 2D surfaces in microfluidic channels are increasingly used in drug development and biological research applications. These systems would have more biological or clinical relevance if the cells exhibit 3D phenotypes similar to the cells in vivo. We have developed a microfluidic channel based system that allows cells to be perfusion-cultured in 3D by supporting them with adequate 3D cell-cell and cell-matrix interactions. The maximal cell-cell interaction was achieved by perfusion-seeding cells through an array of micropillars; and 3D cell-matrix interactions were achieved by a polyelectrolyte complex coacervation process to form a thin layer of matrix conforming to the 3D cell shapes. Carcinoma cell lines (HepG2, MCF7), primary differentiated (hepatocytes) and primary progenitor cells (bone marrow mesenchymal stem cells) were perfusion-cultured for 72 hours to 1 week in the microfluidic channel, which preserved their 3D cyto-architecture and cell-specific functions or differentiation competence. This transparent 3D microfluidic channel-based cell culture system also allows direct optical monitoring of cellular events for a wide range of applications.     

Microfluidic‐Printed Microcarrier for In Vitro Expansion of Adherent Stem Cells in 3D Culture Platform

Microcarrier‐based stem cell expansion cultures can increase the dimensions of in vitro stem cell cultures from 2D to 3D. The culture handling process then becomes more efficient compared with conventional 2D cultures. However, the use of spherical plastic microcarriers complicates the monitoring of cell culture. To facilitate monitoring, transparent disc‐shaped microcarriers are manufactured using a light‐initiated microfluidic printing system and the obtained microcarriers are named as 2.5D microcarrier. The 2.5D microcarriers (diameter/height ≈ 5) enable us to use conventional monitoring tools in 2D‐based platform during the in vitro expansion on a 3D culture platform. Surface modification via a 1 h‐long poly‐dopamine (PDA) reaction can maintain the transparent nature of the microcarriers while optimizing the cell attachment. The surface marker expression and differentiation potential of the 2.5D microcarrier‐expanded stem cells reveal that the characteristics and functionalities preserved during expansion. The 2.5D microcarrier is readily integrated into an on‐bead assay to conserve reagents and permit a high number (n = 9) of repeated measurements with reliable results. These results demonstrate that the 2.5D microcarrier‐based scale‐up culture provides a valuable tool for the in vitro expansion of adherent stem cells, especially if repetitive monitoring is required.     

Magnetothermal Microfluidic‐Assisted Hierarchical Microfibers for Ultrahigh‐Energy‐Density Supercapacitors

Chemical architectures with an ordered porous backbone and high charge transfer are significant for fiber‐shaped supercapacitors (FSCs). However, owing to the sluggish ion kinetic diffusion and storage in compacted fibers, achieving high energy density remains a challenge. An innovative magnetothermal microfluidic method is now proposed to design hierarchical carbon polyhedrons/holey graphene (CP/HG) core–shell microfibers. Owing to highly magnetothermal etching and microfluidic reactions, the CP/HG fibers maintain an open inner‐linked ionic pathway, large specific surface area, and moderate nitrogen active site, facilitating more rapid ionic dynamic transportation and accommodation. The CP/HG FSCs show an ultrahigh energy density (335.8 μWh cm^?2) and large areal capacitance (2760 mF cm^?2). A self‐powered endurance application with the integration of chip‐based FSCs is designed to profoundly drive the durable motions of an electric car and walking robot.