Viability analysis and apoptosis induction of breast cancer cells in a microfluidic device: effect of cytostatic drugs

Unprecedented Approach of Fabrication and Analysis of a Bioactive PDMS/Hydroxyapatite/Graphene Nanocomposite Scaffold with a Vascular Channel to Combat Carcinogenesis

In the present investigation, natural bone-derived hydroxyapatite (HA, 2 wt %) and/or exfoliated graphene (Gr, 0.1 wt %)-embedded polydimethylsiloxane (PDMS) elastomeric films were prepared using a vascular method. The morphology, mechanical properties, crystallinity, and chemical structure of the composite films were evaluated. The in vitro biodegradation kinetics of the films indicates their adequate physiological stability. Most of the results favored PDMS/HA/Gr as a best composite scaffold having more than 703% elongation. A simulation study of the microfluidic vascular channel of the PDMS/HA/Gr scaffold suggests that the pressure drop at the outlet became greater (from 1.19 to 0.067 Pa) unlike velocity output (from 0.071 to 0.089 m/s), suggesting a turbulence-free laminar flow. Our bioactive scaffold material, PDMS/HA/Gr, showed highest cytotoxicity toward the lung cancer and breast cancer cells through Runx3 protein-mediated cytotoxic T lymphocyte (CTL) generation. Our data and predicted mechanism also suggested that the PDMS/HA/Gr-supported peripheral blood mononuclear cells (PBMCs) not only increased the generation of CTL but also upregulated the expression of RUNX3. Since the PDMS/HA/Gr scaffold-supported Runx3 induced CTL generation caused maximum cell cytotoxicity of breast cancer (MCF-7) and lung cancer (A549) cells, PDMS/HA/Gr can be treated as an excellent potential candidate for CTL-mediated cancer therapy.

Organ-on-a-chip platforms as novel advancements for studying heterogeneity, metastasis, and drug efficacy in breast cancer

Breast cancer has the highest cancer incidence rate in women worldwide. Therapies for breast cancer have shown high success rates, yet many cases of recurrence and drug resistance are still reported. Developing innovative strategies for studying breast cancer may improve therapeutic outcomes of the disease by providing better insight into the associated molecular mechanisms. A novel advancement in breast cancer research is the utilization of organ-on-a-chip (OOAC) technology to establish in vitro physiologically relevant breast cancer biomimetic models. This emerging technology combines microfluidics and tissue culturing methods to establish organ-specific micro fabricated culture models. Here, we shed light on the advantages of OOAC platforms over conventional in vivo and in vitro models in terms of mimicking tissue heterogeneity, disease progression, and facilitating pharmacological drug testing with a focus on models of the mammary gland in both normal and breast cancer states. By highlighting the various designs and applications of the breast-on-a-chip platforms, we show that the latter propose means to facilitate breast cancer-related studies and provide an efficient approach for therapeutic drug screening in vitro.

Breast tumor-on-chip models: From disease modeling to personalized drug screening

Breast cancer is one of the leading causes of mortality worldwide being the most common cancer among women. Despite the significant progress obtained during the past years in the understanding of breast cancer pathophysiology, women continue to die from it. Novel tools and technologies are needed to develop better diagnostic and therapeutic approaches, and to better understand the molecular and cellular players involved in the progression of this disease. Typical methods employed by the pharmaceutical industry and laboratories to investigate breast cancer etiology and evaluate the efficiency of new therapeutic compounds are still based on traditional tissue culture flasks and animal models, which have certain limitations. Recently, tumor-on-chip technology emerged as a new generation of in vitro disease model to investigate the physiopathology of tumors and predict the efficiency of drugs in a native-like microenvironment. These microfluidic systems reproduce the functional units and composition of human organs and tissues, and importantly, the rheological properties of the native scenario, enabling precise control over fluid flow or local gradients. Herein, we review the most recent works related to breast tumor-on-chip for disease modeling and drug screening applications. Finally, we critically discuss the future applications of this emerging technology in breast cancer therapeutics and drug development.

In Situ Shape Control of Thermoplasmonic Gold Nanostars on Oxide Substrates for Hyperthermia-Mediated Cell Detachment

Gold nanostars (AuNSTs) are biocompatible, have large surface areas, and are characterized by high near-infrared extinction, making them ideal for integration with technologies targeting biological applications. We have developed a robust and simple microfluidic method for the direct growth of anisotropic AuNSTs on oxide substrates including indium tin oxide and glass. The synthesis was optimized to yield AuNSTs with high anisotropy, branching, uniformity, and density in batch and microfluidic systems for optimal light-to-heat conversion upon laser irradiation. Surface-enhanced Raman scattering spectra and mesoscale temperature measurements were combined with spatially correlated scanning electron microscopy to monitor nanostar and ligand stability and microbubble formation at different laser fluences. The capability of the platform for generating controlled localized heating was used to explore hyperthermia-assisted detachment of adherent glioblastoma cells (U87-GFP) grafted to the capillary walls. Both flow and laser fluence can be tuned to induce different biological responses, such as ablation, cell deformation, release of intracellular components, and the removal of intact cells. Ultimately, this platform has potential applications in biological and chemical sensing, hyperthermia-mediated drug delivery, and microfluidic soft-release of grafted cells with single-cell specificity.

Controlled pharmacokinetic anti-cancer drug concentration profiles lead to growth inhibition of colorectal cancer cells in a microfluidic device

We present a microfluidic device to expose cancer cells to a dynamic, in vivo-like concentration profile of a drug, and quantify efficacy on-chip. About 30% of cancer patients receive drug therapy. In conventional cell culture experiments drug efficacy is tested under static concentrations, e.g. 1 μM for 48 hours, whereas in vivo, drug concentration follows a pharmacokinetic profile with an initial peak and a decline over time. With the rise of microfluidic cell culture models, including organs-on-chips, there are opportunities to more realistically mimic in vivo-like concentrations. Our microfluidic device contains a cell culture chamber and a drug-dosing channel separated by a transparent membrane, to allow for shear stress-free drug exposure and label-free growth quantification. Dynamic drug concentration profiles in the cell culture chamber were controlled by continuously flowing controlled concentrations of drug in the dosing channel. The control over drug concentrations in the cell culture chambers was validated with fluorescence experiments and numerical simulations. Exposure of HCT116 colorectal cancer cells to static concentrations of the clinically used drug oxaliplatin resulted in a sensible dose-effect curve. Dynamic, in vivo-like drug exposure also led to statistically significant lower growth compared to untreated control. Continuous exposure to the average concentration of the in vivo-like exposure seems more effective than exposure to the peak concentration (Cmax) only. We expect that our microfluidic system will improve efficacy prediction of in vitro models, including organs-on-chips, and may lead to future clinical optimization of drug administration schedules.

Cytotoxic responses of carnosic acid and doxorubicin on breast cancer cells in butterfly-shaped microchips in comparison to 2D and 3D culture

Two dimensional (2D) cell culture systems lack the ability to mimic in vivo conditions resulting in limitations for preclinical cell-based drug and toxicity screening assays and modelling tumor biology. Alternatively, 3D cell culture systems mimic the specificity of native tissue with better physiological integrity. In this regard, microfluidic chips have gained wide applicability for in vitro 3D cancer cell studies. The aim of this research was to develop a 3D biomimetic model comprising culture of breast cancer cells in butterfly-shaped microchip to determine the cytotoxicity of carnosic acid and doxorubicin on both estrogen dependent (MCF-7) and independent (MDA-MB231) breast cancer cells along with healthy mammary epithelial cells (MCF-10A) in 2D, 3D Matrigel™ and butterfly-shaped microchip environment. According to the developed mimetic model, carnosic acid exhibited a higher cytotoxicity towards MDA-MB 231, while doxorubicin was more effective against MCF-7. Although the cell viabilities were higher in comparison to 2D and 3D cell culture systems, the responses of the investigated molecules were different in the microchips based on the molecular weight and structural complexity indicating the importance of biomimicry in a physiologically relevant matrix.

Microfluidic Biopsy Trapping Device for the Real-Time Monitoring of Tumor Microenvironment

The tumor microenvironment is composed of cellular and stromal components such as tumor cells, mesenchymal cells, immune cells, cancer associated fibroblasts and the supporting extracellular matrix. The tumor microenvironment provides crucial support for growth and progression of tumor cells and affects tumor response to therapeutic interventions. To better understand tumor biology and to develop effective cancer therapeutic agents it is important to develop preclinical platforms that can faithfully recapitulate the tumor microenvironment and the complex interaction between the tumor and its surrounding stromal elements. Drug studies performed in vitro with conventional two-dimensional cancer cell line models do not optimally represent clinical drug response as they lack true tumor heterogeneity and are often performed in static culture conditions lacking stromal tumor components that significantly influence the metabolic activity and proliferation of cells. Recent microfluidic approaches aim to overcome such obstacles with the use of cell lines derived in artificial three-dimensional supportive gels or micro-chambers. However, absence of a true tumor microenvironment and full interstitial flow, leads to less than optimal evaluation of tumor response to drug treatment. Here we report a continuous perfusion microfluidic device coupled with microscopy and image analysis for the assessment of drug effects on intact fresh tumor tissue. We have demonstrated that fine needle aspirate biopsies obtained from patient-derived xenograft models of adenocarcinoma of the lung can successfully be analyzed for their response to ex vivo drug treatment within this biopsy trapping microfluidic device, wherein a protein kinase C inhibitor, staurosporine, was used to assess tumor cell death as a proof of principle. This approach has the potential to study tumor tissue within its intact microenvironment to better understand tumor response to drug treatments and eventually to choose the most effective drug and drug combination for individual patients in a cost effective and timely manner.

Time-resolved, single-cell analysis of induced and programmed cell death via non-invasive propidium iodide and counterstain perfusion

Conventional propidium iodide (PI) staining requires the execution of multiple steps prior to analysis, potentially affecting assay results as well as cell vitality. In this study, this multistep analysis method has been transformed into a single-step, non-toxic, real-time method via live-cell imaging during perfusion with 0.1 μM PI inside a microfluidic cultivation device. Dynamic PI staining was an effective live/dead analytical tool and demonstrated consistent results for single-cell death initiated by direct or indirect triggers. Application of this method for the first time revealed the apparent antibiotic tolerance of wild-type Corynebacterium glutamicum cells, as indicated by the conversion of violet fluorogenic calcein acetoxymethyl ester (CvAM). Additional implementation of this method provided insight into the induced cell lysis of Escherichia coli cells expressing a lytic toxin-antitoxin module, providing evidence for non-lytic cell death and cell resistance to toxin production. Finally, our dynamic PI staining method distinguished necrotic-like and apoptotic-like cell death phenotypes in Saccharomyces cerevisiae among predisposed descendants of nutrient-deprived ancestor cells using PO-PRO-1 or green fluorogenic calcein acetoxymethyl ester (CgAM) as counterstains. The combination of single-cell cultivation, fluorescent time-lapse imaging, and PI perfusion facilitates spatiotemporally resolved observations that deliver new insights into the dynamics of cellular behaviour.

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.

The influence of preservation solution on the viability of grafts in hair transplantation surgery

Summary:

Hair transplantation techniques have changed in the last decades. Partial longitudinal follicular unit transplantation is a new hair transplantation technique, which differs from all other hair transplantation techniques by the size of the graft and therefore much more vulnerable grafts compared to the conventional hair transplantation grafts. In this study, we reveal the influence of the preservation solution on the viability of the grafts. We have extracted 15 hair transplantation grafts of 0.6 mm and 15 hair transplantation grafts of 0.7 mm from 3 different patients and investigated the influence of 2 commercially available preservation media, saline solution (Braun, Melsungen, Germany) and Ringer’s lactate (Braun), on the viability of grafts and compared these solutions with the preservation solution developed by Hair Science Institute with trypan blue. The grafts stored in the preservation solution developed by Hair Science Institute showed a significant better viability compared with the 2 commercially available preservation media saline solution and Ringer’s lactate. This study shows that a preservation solution could influence the viability of the grafts which could be essential for hair transplantations with small grafts such as in partial longitudinal follicular unit transplantation.

On-chip investigation of cell-drug interactions

Investigation of cell-drug interaction is of great importance in drug discovery but continues to pose significant challenges to develop robust, fast and high-throughput methods for pharmacologically profiling of potential drugs. Recently, cell chips have emerged as a promising technology for drug discovery/delivery, and their miniaturization and flow-through operation significantly reduce sample consumption while dramatically improving the throughput, reliability, resolution and sensitivity. Herein we review various types of miniaturized cell chips used in investigation of cell-drug interactions. The design and fabrication of cell chips including material selection, surface modification, cell trapping/patterning, concentration gradient generation and mimicking of in vivo environment are presented. Recent advances of on-chip investigations of cell-drug interactions, in particular the high-throughput screening, cell sorting, cytotoxicity testing, drug resistance analysis and pharmacological profiling are examined and discussed. It is expected that this survey can provide thoughtful basics and important applications of on-chip investigations of cell-drug interactions, thus greatly promoting research and development interests in this area.

On-chip nanohole array based sensing: a review

The integration of nanohole array based plasmonic sensors into microfluidic systems has enabled the emergence of platforms with unique capabilities and a diversified palette of applications. Recent advances in fabrication techniques together with novel implementation schemes have influenced the progress of these optofluidic platforms. Here, we review the advances that nanohole array based sensors have experienced since they were first merged with microfluidics. We examine established and new fabrication methodologies that have enabled both the fabrication of nanohole arrays with improved optical attributes and a reduction in manufacturing costs. The achievements of several platforms developed to date and the significant benefits obtained from operating the nanoholes as nanochannels are also reviewed herein. Finally, we discuss future opportunities for on-chip nanohole array sensors by outlining potential applications and the use of the abilities of the nanostructures beyond the optical context.

Future Prospects in Breast Cancer Research - Cancer Stem Cells

Breast cancer is one of the leading causes of cancer deaths among women. Although significant advances in the prevention, diagnosis and management are made, still every year half a million women die of breast cancer. Personalised treatment has the potential to increase treatment efficacy, and hence decrease mortality rates. Moreover, understanding cancer biology and translating this knowledge to the clinic, will improve the breast cancer therapy regime tremendously. Recently, it has been proposed that cancer stem cells (CSC) play an important role in tumour biology. CSC have the ability for self-renewal and are pivotal in setting the heterogeneous character of a tumour. Additionally, CSC possess several characteristics that make them resistant and more aggressive to the conventional chemo- and radiotherapy. Nowadays, breast cancer therapy is focused on killing the differentiated tumour cells, leaving the CSC unharmed, potentially causing recurrence of the disease and metastasis. Specific targeting of the CSC will improve the disease-free survival of breast cancer patients. In this article, two methods are described, aiming at specifically attacking the differentiated tumour cells ('Apoptosis chip') and the cancer stem cell. For this, microfluidics is used.

Lab-on-a-chip pathogen sensors for food safety

There have been a number of cases of foodborne illness among humans that are caused by pathogens such as Escherichia coli O157:H7, Salmonella typhimurium, etc. The current practices to detect such pathogenic agents are cell culturing, immunoassays, or polymerase chain reactions (PCRs). These methods are essentially laboratory-based methods that are not at all real-time and thus unavailable for early-monitoring of such pathogens. They are also very difficult to implement in the field. Lab-on-a-chip biosensors, however, have a strong potential to be used in the field since they can be miniaturized and automated; they are also potentially fast and very sensitive. These lab-on-a-chip biosensors can detect pathogens in farms, packaging/processing facilities, delivery/distribution systems, and at the consumer level. There are still several issues to be resolved before applying these lab-on-a-chip sensors to field applications, including the pre-treatment of a sample, proper storage of reagents, full integration into a battery-powered system, and demonstration of very high sensitivity, which are addressed in this review article. Several different types of lab-on-a-chip biosensors, including immunoassay- and PCR-based, have been developed and tested for detecting foodborne pathogens. Their assay performance, including detection limit and assay time, are also summarized. Finally, the use of optical fibers or optical waveguide is discussed as a means to improve the portability and sensitivity of lab-on-a-chip pathogen sensors.

Apoptosis induced by sonodynamic treatment by protoporphyrin IX on MDA-MB-231 cells

Sonodynamic therapy (SDT) is a promising modality for cancer treatment, involving the synergistic interaction of ultrasound and some chemical compounds termed as sono-sensitizers. It has been found that SDT can lead to apoptotic cell death because of the induction of direct sonochemical and subsequent redox reactions. However, the detailed mechanisms are not clear. This study was to identify the cytotoxic effects of ultrasound-activated protoporphyrin IX (PpIX) on MDA-MB-231 cells. The fluorescence microscope was used to detect the sub-cellular localization of PpIX. Several distinct sonochemical effects were found after SDT treatment, including the decrease of cell viability, generation of intracellular ROS, the loss of mitochondrial membrane potential. The activation of some special apoptosis-associated proteins [Caspase-9, Caspase-3 and polypeptide poly (ADP-robose) polymerase] was evaluated by western blotting. The results show that PpIX mediated SDT (PpIX-SDT) treatment could obviously inhibit the proliferation of MDA-MB-231 cells, and which was significantly reduced by the pan-Caspase inhibitor z-VAD-fmk and the reactive oxygen species (ROS) scavenger N-acetylcysteine (NAC). Further, SDT induced a conspicuous loss of mitochondrial membrane potential (MMP) and a mass of ROS accumulation in MDA-MB-231 cells at 1h post-treatment and the SDT-treated cells showed obvious Caspase-3 and Caspase-9 activation, and PARP cleavage at 6h after treatment. And, the general apoptosis marker-Caspase-3 activation-was also greatly relieved by NAC. These findings primarily indicate a Caspase-depended apoptosis could be induced by PpIX-SDT in MDA-MB-231 cells, and the intracellular ROS was involved during the apoptotic process.

TWIST represses estrogen receptor-alpha expression by recruiting the NuRD protein complex in breast cancer cells

Loss of estrogen receptor α (ERα) expression and gain of TWIST (TWIST1) expression in breast tumors correlate with increased disease recurrence and metastasis and poor disease-free survival. However, the molecular and functional regulatory relationship between TWIST and ERα are unclear. In this study, we found TWIST was associated with a chromatin region in intron 7 of the human ESR1 gene coding for ERα. This association of TWIST efficiently recruited the nucleosome remodeling and deacetylase (NuRD) repressor complex to this region, which subsequently decreased histone H3K9 acetylation, increased histone H3K9 methylation and repressed ESR1 expression in breast cancer cells. In agreement with these molecular events, TWIST expression was inversely correlated with ERα expression in both breast cancer cell lines and human breast ductal carcinomas. Forced expression of TWIST in TWIST-negative and ERα-positive breast cancer cells such as T47D and MCF-7 cells reduced ERα expression, while knockdown of TWIST in TWIST-positive and ERα-negative breast cancer cells such as MDA-MB-435 and 4T1 cells increased ERα expression. Furthermore, inhibition of histone deacetylase (HDAC) activity including the one in NuRD complex significantly increased ERα expression in MDA-MB-435 and 4T1 cells. HDAC inhibition together with TWIST knockdown did not further increase ERα expression in 4T1 and MDA-MB-435 cells. These results demonstrate that TWIST/NuRD represses ERα expression in breast cancer cells. Therefore, TWIST may serve as a potential molecular target for converting ERα-negative breast cancers to ERα-positive breast cancers, allowing these cancers to restore their sensitivity to endocrine therapy with selective ERα antagonists such as tamoxifen and raloxifene.

Flexible planar microfluidic chip employing a light emitting diode and a PIN-photodiode for portable flow cytometers

Detection of fluorescence particles is a key method of flow cytometry. We evaluate the performance of a design for a microfluidic fluorescence particle detection device. Due to the planar design with low layer thicknesses, we avoid optical components such as lenses or dichroic mirrors and substitute them with a shadow mask and colored film filters. A commercially available LED is used as the light source and a PIN-photodiode as detector. This design approach reduces component cost and power consumption and enables supplying the device with power from a standard USB port. From evaluation of this design, we obtain a maximum particle detection frequency of up to 600 particles per second at a sensitivity of better than 4.7 × 10(5) MESF (molecules of equivalent soluble fluorochrome) measured with particles for FITC sensitivity calibration. Lowering the flow rate increases the instrument sensitivity by an order of magnitude enabling the detection of particles with 4.5 × 10(4) MESF.

Apoptosis goes on a chip: advances in the microfluidic analysis of programmed cell death

Recent years have brought enormous progress in cell-based lab-on-a-chip technologies, allowing dynamic studies of cell death with an unprecedented accuracy. As interest in the microfabricated technologies for cell-based bioassays is rapidly gaining momentum, we highlight the most promising technologies that provide a new outlook for the rapid assessment of programmed and accidental cell death and are applicable in drug discovery, high-content drug screening, and personalized clinical diagnostics.

An integrated microfluidic cell array for apoptosis and proliferation analysis induction of breast cancer cells

In vitro sensitivity testing of tumor cells could rationalize and improve the choice of chemotherapy and hormone therapy. In this report, a microfluidic device made from poly(dimethylsiloxane) and glass was developed for an assay of drug induced cytotoxicity. We evaluated the apoptotic and proliferation-inhibitory effects of anticancer drugs mitomycin C (MMC) and tamoxifen (TAM) using MCF-7 breast cancer cells. MMC and TAM both induced apoptosis and inhibited proliferation of MCF-7 cells in a concentration-dependent manner. MMC caused the expression of antiapoptotic protein Bcl-2 a dose-dependent reduction in MCF-7 cells. The expression of Bcl-2 did not change significantly in MCF-7 cells treated by TAM. The results in the microfluidic device were correlated well with the data obtained from the parallel experiments carried out in the conventional culture plates. The developed microfluidic device could be a potential useful tool for high content screening and high throughput screening research.

Retinal vascular changes after glial disruption in rats

Glial dysfunction is found in a number of retinal vascular diseases but its link with blood-retinal barrier (BRB) breakdown remains poorly understood. The present study tested the hypothesis that glial dysfunction is a major contributor to the BRB breakdown that is a hallmark of retinal vascular diseases. We investigated the specificity of the purportedly selective glial toxin, DL-alpha-aminoadipic acid (DL-alpha-AAA) on different types of ocular cells in vitro and then tested the effect of glial disruption on retinal vasculature after intraocular injection of DL-alpha-AAA or siRNA targeting glutamine synthetase (GS) in rats. DL-alpha-AAA was toxic to astrocytes and Müller cells but not to other types of BRB-related cells in vitro. Subretinal injection of DL-alpha-AAA disrupted retinal glial cells, induced vascular telangiectasis and increased vascular permeability from 4 days to over 2 months post-injection. Vascular changes induced by DL-alpha-AAA were observed predominantly in regions of glial disruption, as reflected by reduced expression of GS and increased expression of glial fibrillary acidic protein and vimentin. Confocal microscopy showed changes in all three layers of the retinal vasculature, which co-localised with areas of Müller cell disruption. Double labeling immunohistochemistry revealed that retinal glial disruption after DL-alpha-AAA injection was accompanied by increased expression of vascular endothelial growth factor and reduced expression of the tight junction protein claudin-5. Intravitreal injection of GS siRNA induced similar changes in Müller cells and BRB breakdown. Our data are consistent with the hypothesis that glial dysfunction is a primary contributor to the BRB breakdown in retinal vascular diseases.

Microfluidic cell culture systems for drug research

In pharmaceutical research, an adequate cell-based assay scheme to efficiently screen and to validate potential drug candidates in the initial stage of drug discovery is crucial. In order to better predict the clinical response to drug compounds, a cell culture model that is faithful to in vivo behavior is required. With the recent advances in microfluidic technology, the utilization of a microfluidic-based cell culture has several advantages, making it a promising alternative to the conventional cell culture methods. This review starts with a comprehensive discussion on the general process for drug discovery and development, the role of cell culture in drug research, and the characteristics of the cell culture formats commonly used in current microfluidic-based, cell-culture practices. Due to the significant differences in several physical phenomena between microscale and macroscale devices, microfluidic technology provides unique functionality, which is not previously possible by using traditional techniques. In a subsequent section, the niches for using microfluidic-based cell culture systems for drug research are discussed. Moreover, some critical issues such as cell immobilization, medium pumping or gradient generation in microfluidic-based, cell-culture systems are also reviewed. Finally, some practical applications of microfluidic-based, cell-culture systems in drug research particularly those pertaining to drug toxicity testing and those with a high-throughput capability are highlighted.

A prototypic microfluidic platform generating stepwise concentration gradients for real-time study of cell apoptosis

This work describes the development of a prototypic microfluidic platform for the generation of stepwise concentration gradients of drugs. A sensitive apoptotic analysis method is integrated into this microfluidic system for studying apoptosis of HeLa cells under the influence of anticancer drug, etoposide, with various concentrations in parallel; it measures the yellow fluorescent proteincyan fluorescent protein fluorescence resonance energy transfer (FRET) signal that responds to the activation of caspase-3, an indicator of cell apoptosis. Sets of microfluidic valves on the chip generate stepwise concentration gradient of etoposide in various cell-culture microchambers. The FRET signals from multiple chambers are simultaneously monitored under a fluorescent microscope for long-time observation and the on-chip results are compared with those from 96-well plate study and the methylthiazolyldiphenyl-tetrazolium bromide (MTT) assay. The microfluidic platform shows several advantages including high-throughput capacity, low drug consumption, and high sensitivity.

A micro surface tension alveolus (MISTA) in a glass microchip

We have designed a non-membrane micro surface tension alveolus (MISTA) in a glass microchip for direct gas exchange and micro gradient control. Hemoglobin (Hb) in the liquid phase indicates the rapid gas gradient changes of O2 and CO2 shifted by the difference in pressure between the liquid and the gas.

Single cells as experimentation units in lab-on-a-chip devices

'Lab-on-a-chip' technology (LOC) has now reached a mature state and is employed commonly in research in the life sciences. LOC devices make novel experimentation possible while providing a sophisticated environment for cellular investigation. As a next step, we introduce here the concept of a 'lab-in-a-cell': the use of a single cell as a minimal and highly confined experimental unit, or experimentation in the simple, but still unequalled, platform provided by nature itself. LOC provides the appropriate format and set of tools for LIC experimentation, and we discuss here three types of LIC investigation: the elucidation of signaling pathways; the creation of novel production units; and the use of microfluidics for assisted reproduction techniques.

Microfluidics as a functional tool for cell mechanics

Living cells are a fascinating demonstration of nature's most intricate and well-coordinated micromechanical objects. They crawl, spread, contract, and relax-thus performing a multitude of complex mechanical functions. Alternatively, they also respond to physical and chemical cues that lead to remodeling of the cytoskeleton. To understand this intricate coupling between mechanical properties, mechanical function and force-induced biochemical signaling requires tools that are capable of both controlling and manipulating the cell microenvironment and measuring the resulting mechanical response. In this review, the power of microfluidics as a functional tool for research in cell mechanics is highlighted. In particular, current literature is discussed to show that microfluidics powered by soft lithographic techniques offers the following capabilities that are of significance for understanding the mechanical behavior of cells: (i) Microfluidics enables the creation of in vitro models of physiological environments in which cell mechanics can be probed. (ii) Microfluidics is an excellent means to deliver physical cues that affect cell mechanics, such as cell shape, fluid flow, substrate topography, and stiffness. (iii) Microfluidics can also expose cells to chemical cues, such as growth factors and drugs, which alter their mechanical behavior. Moreover, these chemical cues can be delivered either at the whole cell or subcellular level. (iv) Microfluidic devices offer the possibility of measuring the intrinsic mechanical properties of cells in a high throughput fashion. (v) Finally, microfluidic methods provide exquisite control over drop size, generation, and manipulation. As a result, droplets are being increasingly used to control the physicochemical environment of cells and as biomimetic analogs of living cells. These powerful attributes of microfluidics should further stimulate novel means of investigating the link between physicochemical cues and the biomechanical response of cells. Insights from such studies will have implications in areas such as drug delivery, medicine, tissue engineering, and biomedical diagnostics.