A pumpless cell culture chip with the constant medium perfusion-rate maintained by balanced droplet dispensing

A flux-adaptable pump-free microfluidics-based self-contained platform for multiplex cancer biomarker detection

Microfluidics drives technological advancement in point-of-care (POC) bioanalytical diagnostics towards portability, fast response and low cost. In most microfluidic bioanalytical applications, flowing antigen/antibody reacts with immobilized antibody/antigen at a constant flux; it is difficult to reach a compromise to simultaneously realize sufficient time for the antigen-antibody interaction and short time for the entire assay. Here, we present a pump-free microfluidic chip, in which flow is self-initialized by capillary pumping and continued by imbibition of a filter paper. Microfluidic units in teardrop shape ensure that flow passes through the reaction areas at a reduced flux to facilitate the association between antigen and antibody and speeds up after the reaction areas. By spotting different antibodies into the reaction area, four types of biomarkers can be measured simultaneously in one microfluidic chip. Moreover, a small-sized instrument was developed for chemiluminescence detection and signal analysis. The system was validated by testing four biomarkers of colorectal cancer using plasma samples from patients. The assay took about 20 minutes. The limit of detection is 0.89 ng mL^-1, 1.72 ng mL^-1, 3.62 U mL^-1 and 1.05 U mL^-1 for the assays of carcinoembryonic antigen, alpha-fetoprotein, carbohydrate antigen 125 and carbohydrate antigen 19-9, respectively. This flux-adaptable and self-contained microfluidic platform is expected to be useful in various POC disease-monitoring applications.

Pumpless platform for high-throughput dynamic multicellular culture and chemosensitivity evaluation

We report here a novel pumpless, 96-well plate-based platform for high-throughput dynamic multicellular culture and chemosensitivity evaluation. A gravity-driven flow strategy was developed to generate and sustain the flow rate of culture medium within 10% in the platform's 20 culture chambers. The ability of the platform to generate and sustain the medium flow was demonstrated by computational simulation, flow visualization, and ascertaining the previously known effect of flow-induced shear stress on the stimulated osteogenic differentiation of osteoblasts. The high-throughput utility of the platform was demonstrated by in situ cell staining and high content screening of chemosensitivity assays of multiple myeloma and osteoblast co-cultures. Endpoint characterization and data analyses for all 20 culture chambers required less than 1 hour.

Closed-loop feedback control for microfluidic systems through automated capacitive fluid height sensing

Precise fluid height sensing in open-channel microfluidics has long been a desirable feature for a wide range of applications. However, performing accurate measurements of the fluid level in small-scale reservoirs (<1 mL) has proven to be an elusive goal, especially if direct fluid-sensor contact needs to be avoided. In particular, gravity-driven systems used in several microfluidic applications to establish pressure gradients and impose flow remain open-loop and largely unmonitored due to these sensing limitations. Here we present an optimized self-shielded coplanar capacitive sensor design and automated control system to provide submillimeter fluid-height resolution (∼250 μm) and control of small-scale open reservoirs without the need for direct fluid contact. Results from testing and validation of our optimized sensor and system also suggest that accurate fluid height information can be used to robustly characterize, calibrate and dynamically control a range of microfluidic systems with complex pumping mechanisms, even in cell culture conditions. Capacitive sensing technology provides a scalable and cost-effective way to enable continuous monitoring and closed-loop feedback control of fluid volumes in small-scale gravity-dominated wells in a variety of microfluidic applications.

Pumpless microfluidic system driven by hydrostatic pressure induces and maintains mouse spermatogenesis in vitro

Three-dimensional aggregation and organ culture methods are critical for recreating in vivo cellular phenomena outside the body. Previously, we used the conventional gas liquid interphase organ culture method to induce complete mouse spermatogenesis. After incorporating microfluidic systems, we achieved a significant increase in efficiency and duration of spermatogenesis. One of the major drawbacks preventing the popularization of microfluidics, however, is the use of a power-pump to generate medium flow. In this study, we produced a pumpless microfluidic device using hydrostatic pressure and a resistance circuit to facilitate slow, longer lasting medium flow. During three months of culture, results in induction and maintenance of spermatogenesis showed no difference between pumpless and pump-driven devices. Correspondingly, the spermatogonial population was favorably maintained in the pumpless device compared to the conventional method. These results show the advantage of using microfluidic systems for organ culture experiments. Our pumpless device could be applied to a variety of other tissues and organs, and may revolutionize organ culture methods as a whole.

Online monitoring of hepatic rat metabolism by coupling a liver biochip and a mass spectrometer

A microfluidic liver biochip was coupled with a mass spectrometer to detect in real time the drug metabolism of hepatocytes.

Self-driven perfusion culture system using a paper-based double-layered scaffold

Shear stress caused by fluid flow is known to promote tissue development from cells in vivo. Therefore, perfusion cultures have been studied to investigate the mechanisms involved and to fabricate engineered tissues in vitro, particularly those that include blood vessels. Microfluidic devices, which function with fine machinery of chambers and microsyringes for fluid flow and have small culture areas, are conventionally used for perfusion culture. In contrast, we have developed a self-driven perfusion culture system by using a paper-based double-layered scaffold as the fundamental component. Gelatin microfibers were electrospun onto a paper material to prepare the scaffold system, in which the constant perfusion of the medium and the scaffold for cell adhesion/proliferation were functionally divided into a paper and a gelatin microfiber layer, respectively. By applying both the capillary action and siphon phenomenon of the paper-based scaffold, which bridged two medium chambers at different height levels, a self-driven medium flow was achieved and the flow rate was also stable, constant, and quantitatively controllable. Moreover, the culture area was enlargeable to the cm(2) scale. The endothelial cells cultivated on this system oriented along the medium-flow direction, suggesting that the shear stress caused by medium flow was effectively applied. This perfusion culture system is expected to be useful for fabricating three-dimensional and large engineered tissues in the future.

Modelling the Human Respiratory System: Approaches for in Vitro Safety Testing and Drug Discovery

Respiratory research can be broken down into two main areas: (i) exposure to airborne substances (basic toxicology assessment); and (ii) respiratory diseases (understanding disease mechanisms and development of new therapeutics, including toxicological assessment). Both have suffered from inadequate and inaccurate models used to predict human toxicological end points. A growing need therefore exists for accurate in vitro models of the respiratory system, which accurately reflect the human lung situation in vivo. Advances in cell culture techniques and accessibility of human cells/tissues have resulted in the development of increasingly in vivo-like respiratory models. This chapter will focus on the development, advantages and disadvantages of these models and what the future holds for in vitro lung toxicology.

Migration and vascular lumen formation of endothelial cells in cancer cell spheroids of various sizes

We developed a microfluidic device to culture cellular spheroids of controlled sizes and suitable for live cell imaging by selective plane illumination microscopy (SPIM). We cocultured human umbilical vein endothelial cells (HUVECs) within the spheroids formed by hepatocellular carcinoma cells, and studied the distributions of the HUVECs over time. We observed that the migration of HUVECs depended on the size of spheroids. In the spheroids of ∼200 μm diameters, HUVECs migrated outwards to the edges within 48 h; while in the spheroids of ∼250 μm diameters, there was no outward migration of the HUVECs up to 72 h. In addition, we studied the effects of pro-angiogenic factors, namely, vascular endothelial growth factor (VEGF) and fibroblast growth factor (β-FGF), on the migration of HUVECs in the carcinoma cell spheroid. The outward migration of HUVECs in 200 μm spheroids was hindered by the treatment with VEGF and β-FGF. Moreover, some of the HUVECs formed hollow lumen within 72 h under VEGF and β-FGF treatment. The combination of SPIM and microfluidic devices gives high resolution in both spatial and temporal domains. The observation of HUVECs in spheroids provides us insight on tumor vascularization, an ideal disease model for drug screening and fundamental studies.

A continuous perfusion microplate for cell culture

We describe a 96-well microplate with fluidically connected wells that enables the continuous fluid perfusion between wells without the need for external pumping. A single unit in such a perfusion microplate consists of three wells: a source well, a sample (cell culture) well in the middle and a waste well. Fluid perfusion is achieved using a combination of the hydrostatic pressure generated by different liquid levels in the wells and the fluid wicking through narrow strips of a cellulose membrane connecting the wells. There is an excellent correspondence between the observed perfusion flow dynamics and the flow simulations based on Darcy's Law. Hepatocytes (C3A cells) cultured for 4 days in the perfusion microplate with no media exchange in the cell culture well had the same viability as hepatocytes exposed to a daily exchange of media. EOC 20 cells that require media conditioned by LADMAC cells were shown to be equally viable in the adjacent cell culture well of the perfusion microplate with LADMAC cells cultured in the source well. Tegafur, a prodrug, when added to primary human hepatocytes in the source well, was metabolized into a cytotoxic metabolite that kills colon cancer cells (HCT 116) cultured in the adjacent cell culture well; no toxicity was observed when only medium was in the source well. These results suggest that the perfusion microplate is a useful tool for a variety of cell culture applications with benefits ranging from labor savings to enabling in vivo-like toxicity studies.

A microfluidic device for uniform-sized cell spheroids formation, culture, harvesting and flow cytometry analysis

Culture of cells as three-dimensional (3D) aggregates, named spheroids, possesses great potential to improve in vitro cell models for basic biomedical research. However, such cell spheroid models are often complicated, cumbersome, and expensive compared to conventional Petri-dish cell cultures. In this work, we developed a simple microfluidic device for cell spheroid formation, culture, and harvesting. Using this device, cells could form uniformly sized spheroids due to strong cell-cell interactions and the spatial confinement of microfluidic culture chambers. We demonstrated cell spheroid formation and culture in the designed devices using embryonic stem cells, carcinoma cells, and fibroblasts. We further scaled up the device capable of simultaneously forming and culturing 5000 spheroids in a single chip. Finally, we demonstrated harvesting of the cultured spheroids from the device with a simple setup. The harvested spheroids possess great integrity, and the cells can be exploited for further flow cytometry assays due to the ample cell numbers.

On-chip three-dimensional tumor spheroid formation and pump-less perfusion culture using gravity-driven cell aggregation and balanced droplet dispensing

This paper presents a spheroid chip in which three-dimensional (3D) tumor spheroids are not only formed by gravity-driven cell aggregation but also cultured at the perfusion rates controlled by balanced droplet dispensing without fluidic pumps. The previous spheroid chips require additional off-chip processes of spheroid formation and extraction as well as bulky components of fluidic pumps. However, the present spheroid chip, where autonomous medium droplet dispensers are integrated on a well array, achieves the on-chip 3D tumor spheroid formation and perfusion culture using simple structure without bulky fluidic pumps. In the experimental study, we demonstrated that the spheroid chip successfully forms 3D tumor spheroids in the wide diameter range of 220 μm-3.2 mm (uniformity > 90%) using H358, H23, and A549 non-small cell lung cancer cells. At the pump-less perfusion culture (Q = 0.1-0.3 μl/min) of spheroids, the number of H358 cells in the spheroid increased up to 50% from the static culture (Q = 0 μl/min) and the viability of the cultured cells also increased about 10%. Therefore, we experimentally verified that the perfusion environment created by the spheroid chip offers a favourable condition to the spheroids with high increase rate and viability. The present chip achieves on-chip 3D tumor spheroid formation and pump-less perfusion culture with simple structure, thereby exhibiting potential for use in integrated in-vivo-like cell culture systems.

Design of pressure-driven microfluidic networks using electric circuit analogy

This article reviews the application of electric circuit methods for the analysis of pressure-driven microfluidic networks with an emphasis on concentration- and flow-dependent systems. The application of circuit methods to microfluidics is based on the analogous behaviour of hydraulic and electric circuits with correlations of pressure to voltage, volumetric flow rate to current, and hydraulic to electric resistance. Circuit analysis enables rapid predictions of pressure-driven laminar flow in microchannels and is very useful for designing complex microfluidic networks in advance of fabrication. This article provides a comprehensive overview of the physics of pressure-driven laminar flow, the formal analogy between electric and hydraulic circuits, applications of circuit theory to microfluidic network-based devices, recent development and applications of concentration- and flow-dependent microfluidic networks, and promising future applications. The lab-on-a-chip (LOC) and microfluidics community will gain insightful ideas and practical design strategies for developing unique microfluidic network-based devices to address a broad range of biological, chemical, pharmaceutical, and other scientific and technical challenges.