Advancements in the research of finger-actuated POCT chips.

Microfluidic point-of-care testing (POCT) chips are used to enable the mixing and reaction of small sample volumes, facilitating target molecule detection. Traditional methods for actuating POCT chips rely on external pumps or power supplies, which are complex and non-portable. The development of finger-actuated chips has reduced operational difficulty and improved portability, promoting the development of POCT chips. This paper reviews the significance, developments, and potential applications of finger-actuated POCT chips. Three methods for controlling the flow accuracy of finger-actuated chips are summarized: direct push, indirect control, and sample injection control method, along with their respective advantages and disadvantages. Meanwhile, a comprehensive analysis of multi-fluid driving modes is provided, categorizing them into single-push multi-driving and multi-push multi-driving modes. Furthermore, recent research breakthroughs in finger-actuated chips are thoroughly summarized, and their structures, driving, and detection methods are discussed. Finally, this paper discusses the driving performance of finger-actuated chips, the suitability of detection scenarios, and the compatibility with existing detection technologies. It also provides prospects for the future development and application of finger-actuated POCT chips.

Three-dimensional microfluidic tumor-macrophage system for breast cancer cell invasion.

The recrudescence of breast cancer can partly be attributed to poor understanding of the early steps and the mechanisms involved in breast cancer metastasis, especially how tumor inflammatory cells including tumor-associated macrophages (TAM) affect invasion process. However, invasion-related biological studies in traditional in vitro assays or in vivo models are challenging due to the arduousness in establishing models that precisely reproduce the tumor invasion environment. To this end, we proposed a juxtaposed dual-layer cell-loaded hydrogels biomimetic microfluidic system and formed monolayer size-selective permeable vascular endothelial barriers besides the dual layer to mimic mammalian blood vessels. We clarified that in this system, TAM promoted the invasion of breast cancer cells, whereas breast cancer cells maintained the phenotype of TAM cells and promoted the differentiation of U937 cells into TAM. It formed a tumor-macrophage bidirectional crosstalk system. This system could be used for drug screening. So finally, through the calculation of the survival rate of breast cancer cells when cocultured with different macrophages under paclitaxel treatment, we analyzed the antagonism of tumor-macrophage bidirectional crosstalk on anticancer drugs.

Multi-step PDMS curing and a controlled separation method for mass manufacturing of high-performance and user-friendly micro-devices: valved micropumps.

Although valved micropumps have powerful performance, their popularized application is limited by high technical barriers and high costs brought by complex microstructures. Herein, we propose a multi-step PDMS curing method and a local PDMS separation strategy to achieve mass, standardized, and low-cost manufacturing of valved micropumps, solving their popularized problems by promoting role separation between manufacturers and users. The multi-step curing and the centralized structural layout enable a volume 20 times smaller than other valved micropumps. The lithography mold quality is the main reason for only 74% yield, and using metal molds would be a better alternative. Theoretical analysis shows that the thickness and diameter of the pump membrane are the main factors in designing different driving capabilities of the micropump. By driving the micropump through periodic fluid pressure, the results show that the flow rate is positively related to the input pressure and exhibits two flow rate formation mechanisms at high and low frequencies. Its powerful back pressure generating ability also indicates that the micropump has wide application prospects as injection pumps. The micropump also demonstrates tremendous flexibility and convenience in integration, driving, and application. The multi-step PDMS curing and controlled separating ideas show popularization value for other microfluidic components, such as one-way valves, hoping to innovate the microfluidics field.

Research of restricted migration evaluation of MDA-MB-231 cells in 2D and 3D co-culture models.

The restricted migration evaluation is conducive to more complex tumor migration research because of the conformity with in vivo tumors. However, the differences between restricted and unrestricted cell migration and the distinction between different evaluation methods have not been systematically studied, hindering related research. In this study, by constructing the restricted environments on chips, the influence of co-culture conditions on the cancer cell migration capacity was studied. The results showed that the restricted channels can discriminate the influence of weak tumor environmental factors on complex tumor migration behaviors by limiting the free growth instinct of tumor cells. Through the comparison of 2D and 3D restricted migration methods, the extracellular matrix (ECM) restriction was also helpful in distinguishing the influence of the weak tumor environmental factor. However, the 3D ECM can better reflect the tortuosity of the cell migration process and the cooperative behavior among cancer cells. In the anticancer drug evaluation, 3D ECM can more accurately reflect the cytotoxicity of drugs and is more consistent with the drug resistance in the human body. In conclusion, the research will help to distinguish different evaluation methods of cancer cell migration, help researchers select appropriate evaluation models, and promote the research of tumor metastasis.

Long-term cultured microvascular networks on chip for tumor vascularization research and drug testing.

The vascular structure of the tumor microenvironment (TME) plays an essential role in the process of metastasis. In vitro microvascular structures that can be maintained for a long time will greatly promote metastasis research. In this study, we constructed a mimicking breast cancer invasion model based on a microfluidic chip platform, and the maintenance time of the self-assembled microvascular networks significantly improved by culturing with fibroblasts (up to 13 days). Using this model, we quantified the invasion ability of breast cancer cells and angiogenesis sprouts caused by cancer cells, and the intravasation behavior of cancer cells was also observed in sprouts. We found that cancer cells could significantly cause angiogenesis by promoting sprouting behaviors of the self-assembled human umbilical vein endothelial cells, which, in turn, promoted the invasion behavior of cancer cells. The drug test results showed that the drug resistance of the widely used anti-cancer drugs 5-Fluorouracil (5-FU) and Doxorubicin (DOX) in the 3D model was higher than that in the 2D model. Meanwhile, we also proved that 5-FU and DOX had the effect of destroying tumor blood vessels. The anti-angiogenic drug Apatinib (VEGFR inhibitor) enhanced the drug effect of DOX on MDA-MB-231 cells, further proving the promoting effect of angiogenesis on the invasion ability of cancer cells. These results indicate that our model is of great value in reconstructing TME and drug testing in vitro.

An integrated microchannel biosensor platform to analyse low density lactate metabolism in HepG2 cells in vitro.

In this study, we developed an electrochemical microchannel biosensor platform to analyse lactate metabolism in cells. This biosensor platform was fabricated by photolithography, thin-film deposition and microfluidic technology. A kind of functional biomaterial was prepared by mixing lactate oxidase, single-walled carbon nanotubes and chitosan, and platinum as working and blank electrodes of the biosensor was modified by a thin Prussian blue layer. The lactate biosensor was obtained by dropping functional biomaterials on the electrode. The results demonstrated that the sensitivity of the electrochemical biosensor was up to 567 nA mM-1 mm-2 and the limit of detection was 4.5 µM (vs. Ag/AgCl as the counter/reference electrode). The biosensor used to quantitatively detect metabolic lactate concentrations in HepG2 cells cultured with cancer drugs showed high sensitivity, selectivity and stability, and has potential applications in organ-on-a-chip and tissue engineering technologies, which typically involve low concentrations of metabolites.

A Novel Controllable Cell Array Printing Technique on Microfluidic Chips.

GOAL: The construction of single-cell array is known as the challenging technology to manipulate cell position and number and accomplish cell analysis in biomedical engineering. METHODS: We put forward a novel controllable cell printing technique for rapid, precise, convenient, high cell viability, multicellular, and high-throughput printing. We also proposed a novel microfluidic device to verify the effectiveness of the printing and study the migration ability and anti-cancer drug responses of cancer cell as important applications. RESULTS: This technique offered a minimum process time of 5 min, a maximum positional accuracy of 10 µm, 0.1 nL liquid volume level per droplet, above 87% cell viability after seven days and the ability to print different multicellular arrays. We found that the cell compared to cell culture in petri dish after 48 h. In addition, there was a significant different inhibition on cancer cells migration ability and cell drug activities with different concentrations of paclitaxel. CONCLUSION: This novel controllable cell array printing technique on the microfluidic platforms provides a useful method with high-quality printing and cell viability for the applications of single-cell analysis and high-throughput drug screening. SIGNIFICANCE: The controllable cell printing technique could apply in many biological processes and biomedical engineering applications, such as cell analysis, cancer development, and drug screening and metabolism. Combined with the microfluidic chips, tissue engineering, and sensors, this technique will be widely used for the construction and analysis of biological and biomedical model.

The crossing and integration between microfluidic technology and 3D printing for organ-on-chips.

Organ-on-chips were designed to simulate the real tissue or organ microenvironment by precise control of the cells, the extracellular matrix and other micro-environmental factors to clarify physiological or pathological mechanisms. The organ chip is mainly based on the poly(dimethylsiloxane) (PDMS) microfluidic devices, whereas the conventional soft lithography requires a cumbersome manufacturing process, and the complex on-chip tissue or organ chip also depends on the complicated loading process of the cells and biomaterials. 3D printing can efficiently design and automatically print micrometre-scale devices, while bio-printing can also precisely manipulate cells and biomaterials to create complex organ or tissue structures. In recent years, the popularization of 3D printing has provided more possibilities for its application to 3D printed organ-on-chips. The combination of 3D printing and microfluidic technology in organ-on-chips provides a more efficient choice for building complex flow channels or chambers, as well as the ability to create biological structures with a 3D cell distribution, heterogeneity and tissue-specific function. The fabrication of complex, heterogeneous 3D printable biomaterials based on microfluidics also provides new assistance for building complex organ-on-chips. Here, we discuss the recent advances and potential applications of 3D printing in combination with microfluidics to organ-on-chips and provide outlooks on the integration of the two technologies in building efficient, automated, modularly integrated, and customizable organ-on-chips.

Construction of a liver sinusoid based on the laminar flow on chip and self-assembly of endothelial cells.

The liver is one of the main metabolic organs, and nearly all ingested drugs will be metabolized by the liver. Only a small fraction of drugs are able to come onto the market during drug development, and hepatic toxicity is a major cause for drug failure. Since drug development is costly in both time and materials, an in vitro liver model that can accelerate bioreactions in the liver and reduce drug consumption is imperative in the pharmaceutical industry. The liver on a chip is an ideal alternative for its controllable environment and tiny size, which means constructing a more biomimetic model, reducing material consumption as well as promoting drug diffusion and reaction. In this study, taking advantage of the laminar flow on chips and using natural degradable gel rat tail Collagen-I, we constructed a liver sinusoid on a chip. By synchronously injecting two kinds of cell-laden collagen, HepG2-laden collagen and HUVEC-laden collagen, we formed two collagen layers with a clear borderline. By controlling the HUVEC density and injection of growth factors, HUVECs in collagen formed a monolayer through self-assembly. Thus, a liver sinusoid on a chip was achieved in a more biomimetic environment with a more controllable and uniform distribution of discrete HUVECs. Viability, album secretion and urea synthesis of the live sinusoid on a chip were analysed on days 3, 5 and 7 after collagen injection with acetaminophen treatment at 0 (control), 10 and 20 mM. The results indicated that our liver sinusoid on a chip was able to maintain bioactivity and function for at least 7 d and was beneficial for hepatotoxic drug screening.

Microfluidic system for modelling 3D tumour invasion into surrounding stroma and drug screening.

Tumour invasion into the surrounding stroma is a critical step in metastasis, and it is necessary to clarify the role of microenvironmental factors in tumour invasion. We present a microfluidic system that simulated and controlled multi-factors of the tumour microenvironment for three-dimensional (3D) assessment of tumour invasion into the stroma. The simultaneous, precise and continuous arrangement of two 3D matrices was visualised to observe the migration of cancer cell populations or single cells by transfecting cells with a fluorescent protein. A vascular endothelial layer was formed to simulate transendothelial transport of nutrients, and its endothelial barrier function was verified by the diffusion of 70 kDa fluorescein isothiocyanate (FITC)-Dextran in 3D matrices. Through high-throughput cell migration tracking observation and statistic evaluation, we clarified that cell density of the tumour directly determined its invasiveness. The results suggested that increased secretion of IL-6 among both cancer cells (MDA-MB-231) and noncancerous cells (MCF-10A or HDF-n) after co-culture contributes to cancer cell invasiveness, and this was verified by an IL-6 inhibitor assay. Finally, the drug efficacy of paclitaxel was reflected as changes in cancer cell migration ability, viability, and morphology. Together, our microfluidic devices could be a useful tool to study the mechanism of tumour invasion into the stroma and to screen anti-metastatic drugs.

An AC electrothermal self-circulating system with a minimalist process to construct a biomimetic liver lobule model for drug testing.

Liver-on-chip, due to its precision and low cost for constructing in vitro models, has tremendous potential for drug toxicity testing and pathological studies. By applying APAP (acetaminophen) treatment of different concentrations, a dynamic self-circulating liver lobule model for drug testing was proven useful for emulating the human physiological system. However, the demand for a dynamic system of on-chip organs is difficult to fulfil due to the relatively cumbersome fabrication processes. In this paper, the design and fabrication of an AC electrothermal self-circulating system combined with a 3D biomimetic liver lobule is described. The system was fabricated using a low-cost ITO laser etching process within a few seconds. A large number of interdigital electrodes were arranged in a limited space to increase the fluid flow-driven efficiency. The liver lobule consists of two parts, a hepatocyte cell-laden layer and an endothelial layer, which exhibit a sandwich radial shaped pattern that is more bionic in structure and function. By evaluating the velocity and temperature in the self-circulating system at various voltages and frequencies, we obtained a set of reliable input parameters to provide an adequate supply of culture fluid without cell damage. The metabolism of the liver lobule in dynamic culture and static culture was compared based on cell viability, albumin secretion and urea synthesis.

Microfluidic co-culture system for cancer migratory analysis and anti-metastatic drugs screening.

Tumour metastasis is an important reason for cancer death, and cancer cell migration is an important step in the process of tumour metastasis. Studying cancer cell migration is of great significance. Here, we present a novel microfluidic co-culture system and establish mild, moderate and severe cancer models by using HMEpiC and MDA-MB-231 cells to study cancer cell migration and anti-cancer drug screening. Using this device, we achieved high cell viability (over 90%) and a stable analysis of the migration ability of cancer cells. We observed that the density of the cancer cells determined the probability of the occurrence of metastatic cells and that the induction of normal cells affected the metastatic velocity of each cancer cell. We verified that the increase in the migration ability of MDA-MB-231 cells co-cultured with HMEpiC cells was relative to the increased secretion of IL-6 and that this was verified by an IL-6 inhibitor assay. This co-culture also led to decreased CK-14 secretion and morphological changes in HMEpiC cells. Finally, significant inhibition of paclitaxel and tamoxifen on cancer migration was observed. Taken together, our microfluidic device could be a useful tool for the quantitation of the migratory capability and anti-metastatic drug screening.