Nanoliter scale microbioreactor array for quantitative cell biology

High-Throughput Methods in the Discovery and Study of Biomaterials and Materiobiology

The complex interaction of cells with biomaterials (i.e., materiobiology) plays an increasingly pivotal role in the development of novel implants, biomedical devices, and tissue engineering scaffolds to treat diseases, aid in the restoration of bodily functions, construct healthy tissues, or regenerate diseased ones. However, the conventional approaches are incapable of screening the huge amount of potential material parameter combinations to identify the optimal cell responses and involve a combination of serendipity and many series of trial-and-error experiments. For advanced tissue engineering and regenerative medicine, highly efficient and complex bioanalysis platforms are expected to explore the complex interaction of cells with biomaterials using combinatorial approaches that offer desired complex microenvironments during healing, development, and homeostasis. In this review, we first introduce materiobiology and its high-throughput screening (HTS). Then we present an in-depth of the recent progress of 2D/3D HTS platforms (i.e., gradient and microarray) in the principle, preparation, screening for materiobiology, and combination with other advanced technologies. The Compendium for Biomaterial Transcriptomics and high content imaging, computational simulations, and their translation toward commercial and clinical uses are highlighted. In the final section, current challenges and future perspectives are discussed. High-throughput experimentation within the field of materiobiology enables the elucidation of the relationships between biomaterial properties and biological behavior and thereby serves as a potential tool for accelerating the development of high-performance biomaterials.

An Easily Accessible Microfluidic Chip for High-Throughput Microalgae Screening for Biofuel Production

Microalgae are important green energy resources. With high efficiency in fixing carbon dioxide, microalgae are broadly applied for biofuel production. Integrating various cultivation parameters, we applied ultraviolet (UV) mutagenesis, one of the most common approaches, to induce genomic mutation in microalgae and thus enhance the production of lipid content, but the screening process is convoluted and labor-intensive. In this study, we aimed to develop an accessible microfluidic platform to optimize the biofuel production of microalgae. Instead of traditional lithography, we designed hanging-drop microfluidic chips that were fabricated using a cheap computer numerical control (CNC) micro-milling technique. On each chip, we cultured in parallel Botryococcus braunii, one of the most common freshwater microalgae for biofuel production, in sets of ten separated hanging drops (~30 µL each); we monitored their growth in each individual drop for more than 14 days. To optimize the culturing conditions, using drops of varied diameter, we first identified the influence of cell density on algae growth and lipid production. After introducing UV-induced random mutations, we quantified the lipid content of the microalgae in situ; the optimized UV-C dosage was determined accordingly. In comparison with wild-type B. braunii, the results showed increased biomass growth (137%) and lipid content (149%) of the microalgae mutated with the desired UV process. Moreover, we showed a capacity to modulate the illumination on an addressed chip area. In summary, without using an external pump system, we developed a hanging-drop microfluidic system for long-term microalgae culturing, which can be easily operated using laboratory pipettes. This microfluidic system is expected to facilitate microalgae mutation breeding, and to be applied for algae cultivation optimization.

Novel external-loop-airlift milliliter scale bioreactors for cell growth studies: Low cost design, CFD analysis and experimental characterization

Many researchers have limited access to fully equipped laboratory-scale batch bioreactors and chemostats due to their relatively high cost. This becomes particularly prohibitive when multiple replicas of the same experiment are required, but not enough bioreactors are available to operate simultaneously. Additionally, experiments using shaken flasks are common but show significant limitations in terms of maintaining homogeneous conditions in liquid cultures or installing instrumentation for monitoring. Here, we proposed to tackle this significant hurdle by providing a route to make available the manufacture of low-cost, milliliter-scale bioreactors. This approach seems plausible for enabling proof-of-concept experiments before moving to a larger scale without significant investments. The conceptually designed systems were based on external-loop bioreactors due to their flexibility, simplicity, and ease of assembling and testing. Designs were initially evaluated in silico with the aid of COMSOL Multiphysics. The successfully evaluated systems were then constructed via additive manufacturing and assembled for hydrodynamics testing via tracer methods. This was enabled by a newly home-made optical absorbance sensor (OAS) for in-line and real-time measurements. Both the in silico and experimental results indicated close to ideal mixing conditions and low shear stress. Cell growth curves were prepared by culturing Escherichia coli and following its cell density in real-time. Our cell growth rate and maximum cell density were similar to those previously obtained in closely related systems. Therefore, the proposed bioreactors are an affordable alternative for batch and continuous cell growth studies rapidly and inexpensively.

Separating mouse malignant cell line (EL4) from neonate spermatogonial stem cells utilizing microfluidic device in vitro

BACKGROUND

Some children who have survived cancer will be azoospermic in the future. Performing isolation and purification procedures for spermatogonial stem cells (SSC) is very critical. In this regard, performing the process of decontamination of cancerous cells is the initial step. The major objective of the present study is to separate the malignant EL4 cell line in mice and spermatogonial stem cells in vitro.

METHODS

The spermatogonial stem cells of sixty neonatal mice were isolated, and the procedure of co-culturing was carried out by EL4 which were classified into 2 major groups: (1) the control group (co-culture in a growth medium) and (2) the group of co-cultured cells which were separated using the microfluidic device. The percentage of cells was assessed using flow cytometry technique and common laboratory technique of immunocytochemistry and finally was confirmed through the laboratory technique of reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

The actual percentage of EL4 and SSC after isolation was collected at two outlets: the outputs for the smaller outlet were 0.12% for SSC and 42.14% for EL4, while in the larger outlet, the outputs were 80.38% for SSC and 0.32% for EL4; in the control group, the percentages of cells were 21.44% for SSC and 23.28% for EL4 (based on t test (p ≤ 0.05)).

CONCLUSIONS

The present study demonstrates that the use of the microfluidic device is effective in separating cancer cells from spermatogonial stem cells.

A Single-Layer PDMS Chamber for On-Chip Bacteria Culture

On-chip cell culture devices have been actively developed for both mammalian cells and bacteria. Most designs are based on PDMS multi-layer microfluidic valves, which require complicated fabrication and operation. In this work, single-layer PDMS microfluidic valves are introduced in the design of an on-chip culture chamber for E. coli bacteria. To enable the constant flow of culturing medium, we have developed a (semi-)always-closed single-layer microfluidic valve. As a result, the growth chamber can culture bacteria over long duration. The device is applied for the whole-cell detection of heavy metal ions with genetically modified E. coli. The platform is tested with culturing period of 3 h. It is found to achieve a limit-of-detection (LoD) of 44.8 ppb for Cadmium ions.

Liver Bioreactor Design Issues of Fluid Flow and Zonation, Fibrosis, and Mechanics: A Computational Perspective

Tissue engineering, with the goal of repairing or replacing damaged tissue and organs, has continued to make dramatic science-based advances since its origins in the late 1980’s and early 1990’s. Such advances are always multi-disciplinary in nature, from basic biology and chemistry through physics and mathematics to various engineering and computer fields. This review will focus its attention on two topics critical for tissue engineering liver development: (a) fluid flow, zonation, and drug screening, and (b) biomechanics, tissue stiffness, and fibrosis, all within the context of 3D structures. First, a general overview of various bioreactor designs developed to investigate fluid transport and tissue biomechanics is given. This includes a mention of computational fluid dynamic methods used to optimize and validate these designs. Thereafter, the perspective provided by computer simulations of flow, reactive transport, and biomechanics responses at the scale of the liver lobule and liver tissue is outlined, in addition to how bioreactor-measured properties can be utilized in these models. Here, the fundamental issues of tortuosity and upscaling are highlighted, as well as the role of disease and fibrosis in these issues. Some idealized simulations of the effects of fibrosis on lobule drug transport and mechanics responses are provided to further illustrate these concepts. This review concludes with an outline of some practical applications of tissue engineering advances and how efficient computational upscaling techniques, such as dual continuum modeling, might be used to quantify the transition of bioreactor results to the full liver scale.

Cell Seeding Technology for Microarray-Based Quantitative Human Primary Skeletal Muscle Cell Analysis

Pipetting techniques play a crucial role in obtaining reproducible and reliable results, especially when seeding cells on small target areas, such as on microarrays, biochips or microfabricated cell culture systems. For very rare cells, such as human primary skeletal muscle cells (skMCs), manual (freehand) cell seeding techniques invariably result in nonuniform cell spreading and heterogeneous cell densities, giving rise to undesirable variations in myogenesis and differentiation. To prevent such technique-dependent variation, we have designed and fabricated a simple, low-cost pipet guidance device (PGD), and holder that works with hand-held pipettes. This work validates the accuracy and reproducibility of the PGD platform and compares its effectiveness with manual and robotic seeding techniques. The PGD system ensures reproducibility of cell seeding, comparable to that of more expensive robotic dispensing systems, resulting in a high degree of cell uniformity and homogeneous cell densities, while also enabling cell community studies. As compared to freehand pipetting, PGD-assisted seeding of C2C12 mouse myoblasts showed 5.3 times more myotube formation and likewise myotubes derived from PGD-seeded human primary skMCs were 3.6 times thicker and 2.2 times longer. These results show that this novel, yet simple PGD-assisted pipetting technique provides precise cell seeding on small targets, ensuring reproducible and reliable high-throughput cell assays.

Determination of Benzopyrene-Induced Lung Inflammatory and Cytotoxic Injury in a Chemical Gradient-Integrated Microfluidic Bronchial Epithelium System

Environmental pollution is one of the largest sources responsible for human diseases and premature death worldwide. However, the methodological development of a spatiotemporally controllable and high-throughput investigation of the environmental pollution-induced biological injury events is still being explored. In this study, we describe a chemical gradient generator-aided microfluidic cell system for the dynamic study of representative environmental pollutant-induced bronchial epithelium injury in a throughput manner. We demonstrated the stability and reliability of operation-optimized microfluidic system for precise and long-term chemical gradient production. We also performed a microenvironment-controlled microfluidic bronchial epithelium construction with high viability and structure integration. Moreover, on-chip investigation of bronchial epithelium injury by benzopyrene stimulation with various concentrations can be carried out in the single device. The varying bronchial inflammatory and cytotoxic responses were temporally monitored and measured based on the well-established system. The benzopyrene directionally led the bronchial epithelium to present observable cell shrinkage, cytoskeleton disintegration, Caspase-3 activation, overproduction of reactive oxygen species, and various inflammatory cytokine (TNF-α, IL-6, and IL-8) secretion, suggesting its significant inflammatory and cytotoxic effects on respiratory system. We believe the microfluidic advancement has potential applications in the fields of environmental monitoring, tissue engineering, and pharmaceutical development.

A microfluidic design to provide a stable and uniform in vitro microenvironment for cell culture inspired by the redundancy characteristic of leaf areoles

The leaf venation is considered to be an optimal transportation system with the mesophyll cells being divided by minor veins into small regions named areoles. The transpiration of water in different regions of a leaf fluctuates over time making the transportation of water in veins fluctuate as well. However, because of the existence of multiple paths provided by the leaf venation network and the pits on the walls of the vessels, the pressure field and nutrient concentration in the areoles that the mesophyll cells live in are almost uniform. Therefore, inspired by such structures, a microfluidic design of a novel cell culture chamber has been proposed to obtain a stable and uniform microenvironment. The device consists of a novel microchannel system imitating the vessels in the leaf venation to transport the culture medium, a cell culture chamber imitating the areole and microgaps imitating the pits. The effects of the areole and pit on flow fields in the cell culture chamber have been discussed. The results indicate that the bio-inspired microfluidic device is a robust platform to provide an in vivo like fluidic microenvironment.

Development and Characterization of a Parallelizable Perfusion Bioreactor for 3D Cell Culture

The three dimensional (3D) cultivation of stem cells in dynamic bioreactor systems is essential in the context of regenerative medicine. Still, there is a lack of bioreactor systems that allow the cultivation of multiple independent samples under different conditions while ensuring comprehensive control over the mechanical environment. Therefore, we developed a miniaturized, parallelizable perfusion bioreactor system with two different bioreactor chambers. Pressure sensors were also implemented to determine the permeability of biomaterials which allows us to approximate the shear stress conditions. To characterize the flow velocity and shear stress profile of a porous scaffold in both bioreactor chambers, a computational fluid dynamics analysis was performed. Furthermore, the mixing behavior was characterized by acquisition of the residence time distributions. Finally, the effects of the different flow and shear stress profiles of the bioreactor chambers on osteogenic differentiation of human mesenchymal stem cells were evaluated in a proof of concept study. In conclusion, the data from computational fluid dynamics and shear stress calculations were found to be predictable for relative comparison of the bioreactor geometries, but not for final determination of the optimal flow rate. However, we suggest that the system is beneficial for parallel dynamic cultivation of multiple samples for 3D cell culture processes.

A microfluidic platform for drug screening in a 3D cancer microenvironment

Development of resistance to chemotherapy treatments is a major challenge in the battle against cancer. Although a vast repertoire of chemotherapeutics is currently available for treating cancer, a technique for rapidly identifying the right drug based on the chemo-resistivity of the cancer cells is not available and it currently takes weeks to months to evaluate the response of cancer patients to a drug. A sensitive, low-cost diagnostic assay capable of rapidly evaluating the effect of a series of drugs on cancer cells can significantly change the paradigm in cancer treatment management. Integration of microfluidics and electrical sensing modality in a 3D tumour microenvironment may provide a powerful platform to tackle this issue. Here, we report a 3D microfluidic platform that could be potentially used for a real-time deterministic analysis of the success rate of a chemotherapeutic drug in less than 12h. The platform (66mm×50mm; L×W) is integrated with the microsensors (interdigitated gold electrodes with width and spacing 10µm) that can measure the change in the electrical response of cancer cells seeded in a 3D extra cellular matrix when a chemotherapeutic drug is flown next to the matrix. B16-F10 mouse melanoma, 4T1 mouse breast cancer, and DU 145 human prostate cancer cells were used as clinical models. The change in impedance magnitude on flowing chemotherapeutics drugs measured at 12h for drug-susceptible and drug tolerant breast cancer cells compared to control were 50,552±144 Ω and 28,786±233 Ω, respectively, while that of drug-susceptible melanoma cells were 40,197±222 Ω and 4069±79 Ω, respectively. In case of prostate cancer the impedance change between susceptible and resistant cells were 8971±1515 Ω and 3281±429 Ω, respectively, which demonstrated that the microfluidic platform was capable of delineating drug susceptible cells, drug tolerant, and drug resistant cells in less than 12h.

Formation of cell spheroids using Standing Surface Acoustic Wave (SSAW)

3D bioprinting becomes one of the popular approaches in the tissue engineering. In this emerging application, bioink is crucial for fabrication and functionality of constructed tissue. The use of cell spheroids as bioink can enhance the cell-cell interaction and subsequently the growth and differentiation of cells in the 3D printed construct with the minimum amount of other biomaterials. However, the conventional methods of preparing the cell spheroids have several limitations, such as long culture time, low-throughput, and medium modification. In this study, the formation of cell spheroids by SSAW was evaluated both numerically and experimentally in order to overcome the aforementioned limitations. The effects of excitation frequencies on the cell accumulation time, diameter of the formed cell spheroids, and subsequently, the growth and viability of cell spheroids in the culture medium over time were studied. Using the high-frequency (23.8 MHz) excitation, cell accumulation time to the pressure nodes could be reduced in comparison to that of the low-frequency (10.4 MHz) excitation, but in a smaller spheroid size. SSAW excitation at both frequencies does not affect the cell viability up to 7 days, > 90% with no statistical difference compared with the control group. In summary, SSAW can effectively prepare the cell spheroids as bioink for the future 3D bioprinting and various biotechnology applications (e.g., pharmaceutical drug screening and tissue engineering).

Concentration gradient generation methods based on microfluidic systems

Various concentration gradient generation methods based on microfluidic systems are summarized in this paper.

Microfluidic System for Automated Cell-based Assays

Microfluidic cell culture is a promising technology for applications in the drug screening industry. Key benefits include improved biological function, higher quality cell-based data, reduced reagent consumption, and lower cost. In this work, we demonstrate how a microfluidic cell culture design was adapted to be compatible with the standard 96-well plate format. Key design features include the elimination of tubing and connectors, the ability to maintain long term continuous perfusion cell culture using a passive gravity driven pump, and direct analysis on the outlet wells of the microfluidic plate. A single microfluidic culture plate contained 8 independent flow units, each with 10(4) cells at a flow rate of 50 μl/day (6 minute residence time). The cytotoxicity of the anti-cancer drug etoposide was measured on HeLa cells cultured in this format, using a commercial lactate dehydrogenase (LDH) plate reader assay. The integration of microfluidic cell culture methods with commercial automation capabilities offers an exciting opportunity for improved cell-based screening.

Microfluidic single-cell transcriptional analysis rationally identifies novel surface marker profiles to enhance cell-based therapies

Current progenitor cell therapies have only modest efficacy, which has limited their clinical adoption. This may be the result of a cellular heterogeneity that decreases the number of functional progenitors delivered to diseased tissue, and prevents correction of underlying pathologic cell population disruptions. Here, we develop a high-resolution method of identifying phenotypically distinct progenitor cell subpopulations via single-cell transcriptional analysis and advanced bioinformatics. When combined with high-throughput cell surface marker screening, this approach facilitates the rational selection of surface markers for prospective isolation of cell subpopulations with desired transcriptional profiles. We establish the usefulness of this platform in costly and highly morbid diabetic wounds by identifying a subpopulation of progenitor cells that is dysfunctional in the diabetic state, and normalizes diabetic wound healing rates following allogeneic application. We believe this work presents a logical framework for the development of targeted cell therapies that can be customized to any clinical application.

Unrecognized progenitor cell perturbations underlying a disease state may limit the efficacy of cell therapies. Here, the authors use high-throughput, single-cell transcriptional analysis to identify disease-specific cellular alterations and prospectively isolate restorative cell subpopulations.

Development and Characterization of In Vitro Microvessel Network and Quantitative Measurements of Endothelial [Ca2+]i and Nitric Oxide Production

Endothelial cells (ECs) lining the blood vessel walls in vivo are constantly exposed to flow, but cultured ECs are often grown under static conditions and exhibit a pro-inflammatory phenotype. Although the development of microfluidic devices has been embraced by engineers over two decades, their biological applications remain limited. A more physiologically relevant in vitro microvessel model validated by biological applications is important to advance the field and bridge the gaps between in vivo and in vitro studies. Here, we present detailed procedures for the development of cultured microvessel network using a microfluidic device with a long-term perfusion capability. We also demonstrate its applications for quantitative measurements of agonist-induced changes in EC [Ca(2+)]i and nitric oxide (NO) production in real time using confocal and conventional fluorescence microscopy. The formed microvessel network with continuous perfusion showed well-developed junctions between ECs. VE-cadherin distribution was closer to that observed in intact microvessels than statically cultured EC monolayers. ATP-induced transient increases in EC [Ca(2+)]i and NO production were quantitatively measured at individual cell levels, which validated the functionality of the cultured microvessels. This microfluidic device allows ECs to grow under a well-controlled, physiologically relevant flow, which makes the cell culture environment closer to in vivo than that in the conventional, static 2D cultures. The microchannel network design is highly versatile, and the fabrication process is simple and repeatable. The device can be easily integrated to the confocal or conventional microscopic system enabling high resolution imaging. Most importantly, because the cultured microvessel network can be formed by primary human ECs, this approach will serve as a useful tool to investigate how pathologically altered blood components from patient samples affect human ECs and provide insight into clinical issues. It also can be developed as a platform for drug screening.

Microfluidic cell chips for high-throughput drug screening

The current state of screening methods for drug discovery is still riddled with several inefficiencies. Although some widely used high-throughput screening platforms may enhance the drug screening process, their cost and oversimplification of cell-drug interactions pose a translational difficulty. Microfluidic cell-chips resolve many issues found in conventional HTS technology, providing benefits such as reduced sample quantity and integration of 3D cell culture physically more representative of the physiological/pathological microenvironment. In this review, we introduce the advantages of microfluidic devices in drug screening, and outline the critical factors which influence device design, highlighting recent innovations and advances in the field including a summary of commercialization efforts on microfluidic cell chips. Future perspectives of microfluidic cell devices are also provided based on considerations of present technological limitations and translational barriers.

Multiple Subsets of Brain Tumor Initiating Cells Coexist in Glioblastoma

Brain tumor-initiating cells (BTICs) are self-renewing multipotent cells critical for tumor maintenance and growth. Using single-cell microfluidic profiling, we identified multiple subpopulations of BTICs coexisting in human glioblastoma, characterized by distinct surface marker expression and single-cell molecular profiles relating to divergent bulk tissue molecular subtypes. These data suggest BTIC subpopulation heterogeneity as an underlying source of intra-tumoral bulk tissue molecular heterogeneity, and will support future studies into BTIC subpopulation-specific therapies. Stem Cells 2016;34:1702-1707.

High-Resolution Microfluidic Single-Cell Transcriptional Profiling Reveals Clinically Relevant Subtypes among Human Stem Cell Populations Commonly Utilized in Cell-Based Therapies

Stem cell therapies can promote neural repair and regeneration, yet controversy regarding optimal cell source and mechanism of action has slowed clinical translation, potentially due to undefined cellular heterogeneity. Single-cell resolution is needed to identify clinically relevant subpopulations with the highest therapeutic relevance. We combine single-cell microfluidic analysis with advanced computational modeling to study for the first time two common sources for cell-based therapies, human NSCs and MSCs. This methodology has the potential to logically inform cell source decisions for any clinical application.

Screening applications in drug discovery based on microfluidic technology

Microfluidics has been the focus of interest for the last two decades for all the advantages such as low chemical consumption, reduced analysis time, high throughput, better control of mass and heat transfer, downsizing a bench-top laboratory to a chip, i.e., lab-on-a-chip, and many others it has offered. Microfluidic technology quickly found applications in the pharmaceutical industry, which demands working with leading edge scientific and technological breakthroughs, as drug screening and commercialization are very long and expensive processes and require many tests due to unpredictable results. This review paper is on drug candidate screening methods with microfluidic technology and focuses specifically on fabrication techniques and materials for the microchip, types of flow such as continuous or discrete and their advantages, determination of kinetic parameters and their comparison with conventional systems, assessment of toxicities and cytotoxicities, concentration generations for high throughput, and the computational methods that were employed. An important conclusion of this review is that even though microfluidic technology has been in this field for around 20 years there is still room for research and development, as this cutting edge technology requires ingenuity to design and find solutions for each individual case. Recent extensions of these microsystems are microengineered organs-on-chips and organ arrays.

Microfluidic geometric metering-based multi-reagent mixture generator for robust live cell screening array

Microfluidic live cell arrays with integrated concentration gradient or mixture generators have been utilized in screening cellular responses to various biomolecular cues. Microfluidic network-based gradient generators that can create concentration gradients by repeatedly splitting and mixing different solutions using networks of serpentine channels are commonly used. However, in this method the generation of concentration gradients relies on the continuous flow of sample solutions at optimized flow rates, which poses challenges in maintaining the pressure and flow stability throughout the entire assay period. Here we present a microfluidic live cell screening array with an on-demand multi-reagent mixture generator where the mixing ratios, thus generated concentrations, are hard-wired into the chip itself through a geometric metering method. This platform showed significantly improved robustness and repeatability in generating concentration gradients of fluorescent dyes (average coefficient of variance C.V. = 9 %) compared to the conventional network-based gradient generators (average C.V. = 21 %). In studying the concentration dependent effects of the environmental toxicant 3-methylcholanthrene (3MC) on the activation of cytochrome P450 1A1 (Cyp 1A1) enzyme in H4IIE rat hepatoma cells, statistical variation of the Cyp 1A1 response was significantly lower (C.V. = 5 %) when using the developed mixture generator compared to that using the conventional gradient generator (C.V. = 12 %). Reduction in reagent consumption by 12-times was also achieved. This robust, accurate, and scalable multi-reagent mixture generator integrated with a cell culture array as a live cell assay platform can be readily implemented into various screening applications where repeatability, robustness, and low reagent consumptions over long periods of assay time are of importance.

Cancer Associated Fibroblast-Derived Hepatocyte Growth Factor Inhibits the Paclitaxel-Induced Apoptosis of Lung Cancer A549 Cells by Up-Regulating the PI3K/Akt and GRP78 Signaling on a Microfluidic Platform

Tumor stroma and growth factors provide a survival environment to tumor cells and can modulate their chemoresistance by dysregulating several signal pathways. In this study, we fabricated a three-dimensional (3D) microfluidic chip using polydimethylsiloxane (PDMS) to investigate the impact of hepatocyte growth factor (HGF) from cancer-associated fibroblasts (CAF) on the Met/PI3K/AKT activation, glucose regulatory protein (GRP78) expression and the paclitaxel-induced A549 cell apoptosis. With a concentration gradient generator, the assembled chip was able to reconstruct a tumor microenvironment in vitro. We found high levels of HGF in the supernatants of CAF and the CAF matrix from the supernatants of activated HFL1 fibroblasts or HGF enhanced the levels of Met, PI3K and AKT phosphorylation and GRP78 expression in A549 cells cultured in a 3D cell chamber, which was abrogated by anti-HGF. Inhibition of Met attenuated the CAF matrix-enhanced PI3K/AKT phosphorylation and GRP78 expression while inhibition of PI3K reduced GRP78 expression, but not Met phosphorylation in A549 cells. Inhibition of GRP78 failed to modulate the CAF matrix-enhanced Met/PI3K/AKT phosphorylation in A549 cells. Furthermore, inhibition of PI3K or GRP78 enhanced spontaneous and paclitaxel-induced A549 cell apoptosis. Moreover, treatment with the CAF matrix inhibited spontaneous and medium or high dose of paclitaxel-induced A549 cell apoptosis. Inhibition of PI3K or GRP78 attenuated the CAF matrix-mediated inhibition on paclitaxel-induced A549 cell apoptosis. Our data indicated that HGF in the CAF matrix activated the Met/PI3K/AKT and up-regulated GRP78 expression, promoting chemoresistance to paclitaxel-mediated apoptosis in A549 cells. Our findings suggest that the microfluidic system may represent an ideal platform for signaling research and drug screening.

Aging disrupts cell subpopulation dynamics and diminishes the function of mesenchymal stem cells

Advanced age is associated with an increased risk of vascular morbidity, attributable in part to impairments in new blood vessel formation. Mesenchymal stem cells (MSCs) have previously been shown to play an important role in neovascularization and deficiencies in these cells have been described in aged patients. Here we utilize single cell transcriptional analysis to determine the effect of aging on MSC population dynamics. We identify an age-related depletion of a subpopulation of MSCs characterized by a pro-vascular transcriptional profile. Supporting this finding, we demonstrate that aged MSCs are also significantly compromised in their ability to support vascular network formation in vitro and in vivo. Finally, aged MSCs are unable to rescue age-associated impairments in cutaneous wound healing. Taken together, these data suggest that age-related changes in MSC population dynamics result in impaired therapeutic potential of aged progenitor cells. These findings have critical implications for therapeutic cell source decisions (autologous versus allogeneic) and indicate the necessity of strategies to improve functionality of aged MSCs.

Microfluidic System Based High Throughput Drug Screening System for Curcumin/TRAIL Combinational Chemotherapy in Human Prostate Cancer PC3 Cells

We have developed a fully automated high throughput drug screening (HTDS) system based on the microfluidic cell culture array to perform combinational chemotherapy. This system has 64 individually addressable cell culture chambers where the sequential combinatorial concentrations of two different drugs can be generated by two microfluidic diffusive mixers. Each diffusive mixer has two integrated micropumps connected to the media and the drug reservoirs respectively for generating the desired combination without the need for any extra equipment to perfuse the solution such as syringe pumps. The cell array is periodically exposed to the drug combination with the programmed LabVIEW system during a couple of days without extra handling after seeding the cells into the microfluidic device and also, this device does not require the continuous generation of solutions compared to the previous systems. Therefore, the total amount of drug being consumed per experiment is less than a few hundred micro liters in each reservoir. The utility of this system is demonstrated through investigating the viability of the prostate cancer PC3 cell line with the combinational treatments of curcumin and tumor necrosis factor-alpha related apoptosis inducing ligand (TRAIL). Our results suggest that the system can be used for screening and optimizing drug combination with a small amount of reagent for combinatorial chemotherapy against cancer cells.

Microfluidic perfusion culture

Microfluidic perfusion culture is a novel technique to culture animal cells in a small-scale microchamber with medium perfusion. Polydimethylsiloxane (PDMS) is the most popular material to fabricate a microfluidic perfusion culture chip. Photolithography and replica molding techniques are generally used for fabrication of a microfluidic perfusion culture chip. Pressure-driven perfusion culture system is convenient technique to carry out the perfusion culture of animal cells in a microfluidic device. Here, we describe a general theory on microfluid network design, microfabrication technique, and experimental technique for pressure-driven perfusion culture in an 8 × 8 microchamber array on a glass slide-sized microchip made out of PDMS.

Advantages and challenges of microfluidic cell culture in polydimethylsiloxane devices

Culture of cells using various microfluidic devices is becoming more common within experimental cell biology. At the same time, a technological radiation of microfluidic cell culture device designs is currently in progress. Ultimately, the utility of microfluidic cell culture will be determined by its capacity to permit new insights into cellular function. Especially insights that would otherwise be difficult or impossible to obtain with macroscopic cell culture in traditional polystyrene dishes, flasks or well-plates. Many decades of heuristic optimization have gone into perfecting conventional cell culture devices and protocols. In comparison, even for the most commonly used microfluidic cell culture devices, such as those fabricated from polydimethylsiloxane (PDMS), collective understanding of the differences in cellular behavior between microfluidic and macroscopic culture is still developing. Moving in vitro culture from macroscopic culture to PDMS based devices can come with unforeseen challenges. Changes in device material, surface coating, cell number per unit surface area or per unit media volume may all affect the outcome of otherwise standard protocols. In this review, we outline some of the advantages and challenges that may accompany a transition from macroscopic to microfluidic cell culture. We focus on decisive factors that distinguish macroscopic from microfluidic cell culture to encourage a reconsideration of how macroscopic cell culture principles might apply to microfluidic cell culture.

Three dimensional microfluidic cell arrays for ex vivo drug screening with mimicked vascular flow

Currently, there are no reliable ex vivo models that predict anticancer drug responses in human tumors accurately. A comprehensive method of mimicking a 3D microenvironment to study effects of anticancer drugs on specific cancer types is essential. Here, we report the development of a three-dimensional microfluidic cell array (3D μFCA), which reconstructs a 3D tumor microenvironment with cancer cells and microvascular endothelial cells. To mimic the in vivo spatial relationship between microvessels and nonendothelial cells embedded in extracellular matrix, three polydimethylsiloxane (PDMS) layers were built into this array. The multilayer property of the device enabled the imitation of the drug delivery in a microtissue array with simulated blood circulation. This 3D μFCA system may provide better predictions of drug responses and identification of a suitable treatment for a specific patient if biopsy samples are used. To the pharmaceutical industry, the scaling-up of our 3D μFCA system may offer a novel high throughput screening tool.

New tools and new biology: recent miniaturized systems for molecular and cellular biology

Recent advances in applied physics and chemistry have led to the development of novel microfluidic systems. Microfluidic systems allow minute amounts of reagents to be processed using μm-scale channels and offer several advantages over conventional analytical devices for use in biological sciences: faster, more accurate and more reproducible analytical performance, reduced cell and reagent consumption, portability, and integration of functional components in a single chip. In this review, we introduce how microfluidics has been applied to biological sciences. We first present an overview of the fabrication of microfluidic systems and describe the distinct technologies available for biological research. We then present examples of microsystems used in biological sciences, focusing on applications in molecular and cellular biology.

High-Throughput Single-Cell Analysis for Wound Healing Applications

SIGNIFICANCE

Wound repair is a complex biological process that integrates multiple physiologic pathways to restore skin homeostasis after a wide array of gross and anatomical insults. As such, a scientific examination of the wound typically requires broad sampling of numerous factors and is commonly achieved through DNA microarray analysis.

CRITICAL ISSUES

In the last several years, it has become increasingly evident that the granularity afforded by such traditional population-based assays may be insufficient to capture the complex relationships in heterogeneous processes such as those associated with wound healing and stem cell biology.

RECENT ADVANCES

Several emerging technologies have recently become available that permit high-throughput single-cell gene expression analysis in a manner which provides novel insights into the relationships of complex tissue. The most prominent among these employs microfluidic-based devices to achieve a high-resolution analysis of tissue samples.

FUTURE DIRECTIONS

The intrinsically heterogeneous nature of injured tissue, in conjunction with its temporal dynamics, makes wound repair and tissue regeneration an attractive target for high-throughput single-cell analysis. Given the staggering costs associated with chronic and non-healing wounds, the development of predictive and diagnostic tools using this technology would likely be attractive to healthcare providers.

An integrated microfluidic device for the high-throughput screening of microalgal cell culture conditions that induce high growth rate and lipid content

This study describes the development of a microfluidic device for the high-throughput screening of culture conditions, such as the optimum sodium acetate concentration for promoting rapid growth and high lipid accumulation of Chlamydomonas reinhardtii. An analysis of the microalgal growth on the microfluidic device revealed an optimum sodium acetate concentration of 5.72 g L(-1). The lipid content, determined by the 4,4-Difluoro-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene (BODIPY® 505/515) staining method, increased with the sodium acetate concentration. The results were found to be statistically reproducible with respect to cell growth and lipid production. Other nutrient conditions, including the nitrogen and phosphorus concentrations, can also be optimized on the same microfluidic platform. The microfluidic device performance results agreed well with the results obtained from the flask-scale experiments, validating that the culture conditions were scalable. Finally, we, for the first time, established a method for the absolute quantification of the microalgal lipid content in the picoliter culture volumes by comparing the on-chip and off-chip data. In conclusion, we successfully demonstrated the high-throughput screening of sodium acetate concentrations that induced high growth rates and high lipid contents in C. reinhardtii cells on the microfluidic device.

Regeneration-on-a-chip? The perspectives on use of microfluidics in regenerative medicine

The aim of regenerative medicine is to restore or establish normal function of damaged tissues or organs. Tremendous efforts are placed into development of novel regenerative strategies, involving (stem) cells, soluble factors, biomaterials or combinations thereof, as a result of the growing need caused by continuous population aging. To satisfy this need, fast and reliable assessment of (biological) performance is sought, not only to select the potentially interesting candidates, but also to rule out poor ones at an early stage of development. Microfluidics may provide a new avenue to accelerate research and development in the field of regenerative medicine as it has proven its maturity for the realization of high-throughput screening platforms. In addition, microfluidic systems offer other advantages such as the possibility to create in vivo-like microenvironments. Besides the complexity of organs or tissues that need to be regenerated, regenerative medicine brings additional challenges of complex regeneration processes and strategies. The question therefore arises whether so much complexity can be integrated into microfluidic systems without compromising reliability and throughput of assays. With this review, we aim to investigate whether microfluidics can become widely applied in regenerative medicine research and/or strategies.

Fabricated micro-nano devices for in vivo and in vitro biomedical applications

In recent years, the innovative use of microelectromechanical systems (MEMSs) and nanoelectromechanical systems (NEMSs) in biomedical applications has opened wide opportunities for precise and accurate human diagnostics and therapeutics. The introduction of nanotechnology in biomedical applications has facilitated the exact control and regulation of biological environments. This ability is derived from the small size of the devices and their multifunctional capabilities to operate at specific sites for selected durations of time. Researchers have developed wide varieties of unique and multifunctional MEMS/NEMS devices with micro and nano features for biomedical applications (BioMEMS/NEMS) using the state of the art microfabrication techniques and biocompatible materials. However, the integration of devices with the biological milieu is still a fundamental issue to be addressed. Devices often fail to operate due to loss of functionality, or generate adverse toxic effects inside the body. The in vitro and in vivo performance of implantable BioMEMS such as biosensors, smart stents, drug delivery systems, and actuation systems are researched extensively to understand the interaction of the BioMEMS devices with physiological environments. BioMEMS developed for drug delivery applications include microneedles, microreservoirs, and micropumps to achieve targeted drug delivery. The biocompatibility of BioMEMS is further enhanced through the application of tissue and smart surface engineering. This involves the application of nanotechnology, which includes the modification of surfaces with polymers or the self-assembly of monolayers of molecules. Thereby, the adverse effects of biofouling can be reduced and the performance of devices can be improved in in vivo and in vitro conditions.

Recreating a human trabecular meshwork outflow system on microfabricated porous structures

Glaucoma is the leading cause of irreversible blindness, resulting from an increase in intraocular pressure (IOP). IOP is the only modifiable risk factor of glaucoma and is controlled by the outflow of the aqueous humor through the human trabecular meshwork (HTM). Currently, the lack of a proper in vitro HTM model impedes advances in understanding outflow physiology and discovering effective IOP-lowering anti-glaucoma therapeutics. Therefore, we designed and constructed an in vitro HTM model using micropatterned, porous SU-8 scaffolds, which support cells to recapitulate functional HTM morphology and allow the study of outflow physiology. The pore size of SU-8 scaffolds, surface coating, cell seeding density, and culture duration were evaluated for HTM cell growth. The bioengineered HTM was characterized by F-actin staining and immunocytochemistry of HTM markers. A stand-alone perfusion chamber with an integrated pressure sensing system was further constructed and used for the investigation of the outflow facility of the bioengineered HTM treated with latrunculin B-an IOP lowering agent. Cells in the in vitro model exhibited HTM-like morphology, expression of α-smooth muscle actin, myocilin, and αß-crystallin, outflow characteristics and drug responsiveness. Altogether, we have developed an in vitro HTM model system for understanding HTM cell biology and screening of pharmacological or biological agents that affect trabecular outflow facility, expediting discovery of IOP-lowering, anti-glaucoma therapeutics.

Cell-based dose responses from open-well microchambers

Cell-based assays play a critical role in discovery of new drugs and facilitating research in cancer, immunology, and stem cells. Conventionally, they are performed in Petri dishes, tubes, or well plates, using milliliters of reagents and thousands of cells to obtain one data point. Here, we are introducing a new platform to realize cell-based assay capable of increased throughput and greater sensitivity with a limited number of cells. We integrated an array of open-well microchambers into a gradient generation system. Consequently, cell-based dose responses were examined with a single device. We measured IC50 values of three cytotoxic chemicals, Triton X-100, H2O2, and cadmium chloride, as model compounds. The present system is highly suitable for the discovery of new drugs and studying the effect of chemicals on cell viability or mortality with limited samples and cells.

The future of microfluidic assays in drug development

BACKGROUND

Microfluidic technology emerges as a convenient route to applying automated and reliable assays in a high-throughput manner with low cost.

OBJECTIVE

This review aims to answer questions related to the capabilities and potential applications of microfluidic assays that can benefit the drug development process and extends an outlook on its future trends.

METHODS

This article reviews recent publications in the field of microfluidics, with an emphasis on novel applications for drug development.

RESULTS/CONCLUSION

Microfluidics affords unique capabilities in sample preparation and separation, combinatorial synthesis and array formation, and incorporating nanotechnology for more functionalities. The pharmaceutical industry, facing challenges from limited productivity and accelerated competition, can thus greatly benefit from applying new microfluidic assays in various drug development stages, from target screening and lead optimization to absorption distribution metabolism elimination and toxicity studies in preclinical evaluations, diagnostics in clinical trials and drug formulation and manufacturing process optimization.