Multicompartmented microfluidic device for characterization of dose-dependent cadmium cytotoxicity in BALB/3T3 fibroblast cells

Bridging the academic-industrial gap: application of an oxygen and pH sensor-integrated lab-on-a-chip in nanotoxicology

Translation of advanced cell-based assays exhibiting a higher degree of automation, miniaturization, and integration of complementary sensing functions is mainly limited by the development of industrial-relevant prototypes that can be readily produced in larger volumes. Despite the increasing number of academic publications in recent years, the manufacturability of these microfluidic cell cultures systems is largely ignored, thus severely restricting their implementation in routine toxicological applications. We have developed a dual-sensor integrated microfluidic cell analysis platform using industrial specifications, materials, and fabrication methods to conduct risk assessment studies of engineered nanoparticles to overcome this academic-industrial gap. Non-invasive and time-resolved monitoring of cellular oxygen uptake and metabolic activity (pH) in the absence and presence of nanoparticle exposure is accomplished by integrating optical sensor spots into a cyclic olefin copolymer (COC)-based microfluidic platform. Results of our nanotoxicological study, including two physiological cell barriers that are essential in the protection from exogenous factors, the intestine (Caco-2) and the vasculature (HUVECs) showed that the assessment of the cells' total energy metabolism is ideally suited to rapidly detect cytotoxicities. Additional viability assay verification using state-of-the-art dye exclusion assays for nanotoxicology demonstrated the similarity and comparability of our results, thus highlighting the benefits of employing a compact and cost-efficient microfluidic dual-sensor platform as a pre-screening tool in nanomaterial risk assessment and as a rapid quality control measure in medium to high-throughput settings.

Influence of Silica Nanoparticle Density and Flow Conditions on Sedimentation, Cell Uptake, and Cytotoxicity

Careful evaluation of the toxicological response of engineered nanomaterials (ENMs) as a function of physicochemical properties can aid in the design of safe platforms for biomedical applications including drug delivery. Typically, in vitro ENM cytotoxicity assessments are performed under conventional static cell culture conditions. However, such conditions do not take into account the sedimentation rate of ENMs. Herein, we synthesized four types of similar size silica nanoparticles (SNPs) with modified surface roughness, charge, and density and characterized their cytotoxicity under static and dynamic conditions. Influence of particle density on sedimentation and diffusion velocities were studied by comparing solid dense silica nanoparticles of approximately 350 nm in diameter with hollow rattle shape particles of similar size. Surface roughness and charge had negligible impact on sedimentation and diffusion velocities. Lower cellular uptake and toxicity was observed by rattle particles and under dynamic conditions. Dosimetry of ENMs are primarily reported by particle concentration, assuming homogeneous distribution of nanoparticles in cell culture media. However, under static conditions, nanoparticles tend to sediment at a higher rate due to gravitational forces and hence increase effective doses of nanoparticles exposed to cells. By introducing shear flow to SNP suspensions, we reduced sedimentation and nonhomogeneous particle distribution. These results have implications for design of in vitro cytotoxicity assessment of ENMs and suggest that among other factors, sedimentation of nanoparticles in toxicity assessment should be carefully considered.

Dose dependent effects of cadmium on tumor angiogenesis

Angiogenesis is crucial for tumor growth and metastasis. Cadmium (Cd) exposure is associated with elevated cancer risk and mortality. Such association is, at least in part, attributable to Cd-induced tumor angiogenesis. Nevertheless, the reported effects of Cd on tumor angiogenesis appear to be either stimulatory or inhibitory, depending on the concentrations. Ultra-low concentrations of Cd (<0.5 μM) inhibit endothelial nitric oxide synthase activation, leading to reduced endothelial nitric oxide production and attenuated tumor angiogenesis. In contrast, low-lose Cd (1-10 μM) up-regulates vascular endothelial growth factor (VEGF)-mediated tumor angiogenesis by exerting sub-apoptotic levels of oxidative stress on both tumor cells and endothelial cells (ECs). The consequent activation of protein kinase B/Akt, nuclear factor-κB, and mitogen-activated protein kinase signaling cascades mediate the increased secretion of VEGF by tumor cells and the up-regulated VEGF receptor-2 expression in ECs. Furthermore, Cd in high concentrations (>10 μM) induces EC apoptosis via the activation of caspase-3, resulting in destruction of tumor vasculature. In this review, we summarize the current knowledge concerning the roles of Cd in tumor angiogenesis, with a focus on molecular mechanisms underlying the dose dependent effects of Cd on various EC phenotypes.

High-Throughput Cytotoxicity Testing System of Acetaminophen Using a Microfluidic Device (MFD) in HepG2 Cells

A lab-on-a-chip (LOC) is a microfluidic device (MFD) that integrates several lab functions into a single chip of only millimeters in size. LOC provides several advantages, such as low fluidic volumes consumption, faster analysis, compactness, and massive parallelization. These properties enable a microfluidic-based high-throughput drug screening (HTDS) system to acquire cell-based abundant cytotoxicity results depending on linear gradient concentration of drug with only few hundreds of microliters of the drug. Therefore, a microfluidic device was developed containing an array of eight separate microchambers for cultivating HepG2 cells to be exposed to eight different concentrations of acetaminophen (APAP) through a diffusive-mixing-based concentration gradient generator. Every chamber array with eight different concentrations (0, 5.7, 11.4, 17.1, 22.8, 28.5, 34.2, or 40 mM) APAP had four replicating cell culture chambers. Consequently, 32 experimental results were acquired with a single microfluidic device experiment. The microfluidic high-throughput cytotoxicity device (μHTCD) and 96-well culture system showed comparable cytotoxicity results with increasing APAP concentration of 0 to 40 mM. The HTDS system yields progressive concentration-dependent cytotoxicity results using minimal reagent and time. Data suggest that the HTDS system may be applicable as alternative method for cytotoxicity screening for new drugs in diverse cell types.

Microfluidic Chip for Site-Specific Neuropharmacological Treatment and Activity Probing of 3D Neuronal "Optonet" Cultures

The study introduces a "brain-on-a-chip" microfluidic platform that hosts brain-like 3D cultures ("optonets") whose activity and responses to flowing drugs are recorded optically. Optonets are viable, optically accessible 3D neural networks whose characteristics approximate cortical networks. The results demonstrate the ability to monitor complex 3D activity patterns during extended site-specific, reversible neuropharmacogical exposure, suggesting an interesting potential in drug screening.

Microfluidic shear stress-regulated surfactant secretion in alveolar epithelial type II cells in vitro

We investigated the role of flow-induced shear stress on the mechanisms regulating surfactant secretion in type II alveolar epithelial cells (ATII) using microfluidic models. Following flow stimulation spanning a range of wall shear stress (WSS) magnitudes, monolayers of ATII (MLE-12 and A549) cells were examined for surfactant secretion by evaluating essential steps of the process, including relative changes in the number of fusion events of lamellar bodies (LBs) with the plasma membrane (PM) and intracellular redistribution of LBs. F-actin cytoskeleton and calcium levels were analyzed in A549 cells subjected to WSS spanning 4-20 dyn/cm(2). Results reveal an enhancement in LB fusion events with the PM in MLE-12 cells upon flow stimulation, whereas A549 cells exhibit no foreseeable changes in the monitored number of fusion events for WSS levels ranging up to a threshold of ∼8 dyn/cm(2); above this threshold, we witness instead a decrease in LB fusion events in A549 cells. However, patterns of LB redistribution suggest that WSS can potentially serve as a stimulus for A549 cells to trigger the intracellular transport of LBs toward the cell periphery. This observation is accompanied by a fragmentation of F-actin, indicating that disorganization of the F-actin cytoskeleton might act as a limiting factor for LB fusion events. Moreover, we note a rise in cytosolic calcium ([Ca(2+)]c) levels following stimulation of A549 cells with WSS magnitudes ranging near or above the experimental threshold. Overall, WSS stimulation can influence key components of molecular machinery for regulated surfactant secretion in ATII cells in vitro.

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.

Determination of a threshold dose to reduce or eliminate CdTe-induced toxicity in L929 cells by controlling the exposure dose

With the widespread use of quantum dots (QDs), the likelihood of exposure to quantum dots has increased substantially. The application of quantum dots in numerous biomedical areas requires detailed studies on their toxicity. In this study, we aimed to determine the threshold dose which reduced or eliminated CdTe-induced toxicity in L929 cells by controlling the exposure dose. We established a cellular model of acute exposure to CdTe QDs. Cells were exposed to different concentrations of CdTe QDs (2.2 nm and 3.5 nm) followed by illustrative cytotoxicity analysis. The results showed that low concentrations of CdTe QDs (under 10 µg/mL) promoted cell viability, caused no obvious effect on the rate of cell apoptosis, intracellular calcium levels and changes in mitochondrial membrane potential, while high concentrations significantly inhibited cell viability. In addition, reactive oxygen species in the 10 µg/mL-treated group was significantly reduced compared with the control group. In summary, the cytotoxicity of CdTe QDs on L929 cell is dose-dependent, time-dependent and size-dependent. Low concentrations of CdTe QDs (below 10 µg/mL) may be nontoxic and safe in L929 cells, whereas high concentrations (above 10 µg/mL) may be toxic resulting in inhibition of proliferation and induction of apoptosis in L929 cells.

High-resolution dose-response screening using droplet-based microfluidics

A critical early step in drug discovery is the screening of a chemical library. Typically, promising compounds are identified in a primary screen and then more fully characterized in a dose-response analysis with 7-10 data points per compound. Here, we describe a robust microfluidic approach that increases the number of data points to approximately 10,000 per compound. The system exploits Taylor-Aris dispersion to create concentration gradients, which are then segmented into picoliter microreactors by droplet-based microfluidics. The large number of data points results in IC(50) values that are highly precise (± 2.40% at 95% confidence) and highly reproducible (CV = 2.45%, n = 16). In addition, the high resolution of the data reveals complex dose-response relationships unambiguously. We used this system to screen a chemical library of 704 compounds against protein tyrosine phosphatase 1B, a diabetes, obesity, and cancer target. We identified a number of novel inhibitors, the most potent being sodium cefsulodine, which has an IC(50) of 27 ± 0.83 μM.

Integrated and diffusion-based micro-injectors for open access cell assays

Currently, most microfluidic devices are fabricated with embedded micro-channels and other elements in a close form with outward connections. Although much functionality has been demonstrated and a large number of applications have been developed, they are not easy for routine operation in biology laboratories where most in vitro cell processing still relies on the use of culture dishes, glass slides, multi-well plates, tubes, pipettes, etc. We report here an open access device which consists of an array of isolated micro-channels plated on a large culture surface, each of them having tiny nozzles for localized drug delivery. In a diffusion dominant regime, steady gradients of molecule concentration could be obtained and varied by changing the flow rate inside the micro-channels. As assay examples, cell staining and drug-induced cell apoptosis were demonstrated, showing fast cell responses in close proximity of the nozzles.

A microfluidic-based neurotoxin concentration gradient for the generation of an in vitro model of Parkinson's disease

In this study, we developed a miniaturized microfluidic-based high-throughput cell toxicity assay to create an in vitro model of Parkinson's disease (PD). In particular, we generated concentration gradients of 6-hydroxydopamine (6-OHDA) to trigger a process of neuronal apoptosis in pheochromocytoma PC12 neuronal cell line. PC12 cells were cultured in a microfluidic channel, and a concentration gradient of 6-OHDA was generated in the channel by using a back and forth movement of the fluid flow. Cellular apoptosis was then analyzed along the channel. The results indicate that at low concentrations of 6-OHDA along the gradient (i.e., approximately less than 260 μM), the neuronal death in the channel was mainly induced by apoptosis, while at higher concentrations, 6-OHDA induced neuronal death mainly through necrosis. Thus, this concentration appears to be useful for creating an in vitro model of PD by inducing the highest level of apoptosis in PC12 cells. As microfluidic systems are advantageous in a range of properties such as throughput and lower use of reagents, they may provide a useful approach for generating in vitro models of disease for drug discovery applications.

Microfluidic gradient platforms for controlling cellular behavior

Concentration gradients play an important role in controlling biological and pathological processes, such as metastasis, embryogenesis, axon guidance, and wound healing. Microfluidic devices fabricated by photo- and soft lithography techniques can manipulate the fluidic flow and diffusion profile to create biomolecular gradients in a temporal and spatial manner. Furthermore, microfluidic devices enable the control of cell-extracellular microenvironment interactions, including cell-cell, cell-matrix, and cell-soluble factor interaction. In this paper, we review the development of microfluidic-based gradient devices and highlight their biological applications.

A new perspective on in vitro assessment method for evaluating quantum dot toxicity by using microfluidics technology

In this study, we demonstrate a new perspective on in vitro assessment method for evaluating quantum dot (QD) toxicity by using microfluidics technology. A new biomimetic approach, based on the flow exposure condition, was applied in order to characterize the cytotoxic potential of QD. In addition, the outcomes obtained from the flow exposure condition were compared to those of the static exposure condition. An in vitro cell array system was established that used an integrated multicompartmented microfluidic device to develop a sensitive flow exposure condition. QDs modified with cetyltrimethyl ammonium bromide∕trioctylphosphine oxide were used for the cytotoxicity assessment. The results suggested noticeable differences in the number of detached and deformed cells and the viability percentages between two different exposure conditions. The intracellular production of reactive oxygen species and release of cadmium were found to be the possible causes of QD-induced cytotoxicity, irrespective of the types of exposure condition. In contrast to the static exposure, the flow exposure apparently avoided the gravitational settling of particles and probably assisted in the homogeneous distribution of nanoparticles in the culture medium during exposure time. Moreover, the flow exposure condition resembled in vivo physiological conditions very closely, and thus, the flow exposure condition can offer potential advantages for nanotoxicity research.

Morphology-based assessment of Cd2+ cytotoxicity using microfluidic image cytometry (microFIC)

Microfluidic systems have significant implications in the field of in vitro cell-based assays since they may allow conventional cell-based assays to be conducted in an automated and high-throughput fashion. In this study, we combined a simple microfluidic cells-on-chip system with a morphology-based image cytometric analysis approach for the assessment of Cd(2+) induced apoptosis of Chang liver cell line. A simple and efficient in situ monitoring method for quantifying the progress of a cell death event was developed and is presented here. Reasonable agreement of the estimated EC(50) value from this study with those from the literature and a close correlation between the observed changes in cell morphology (i.e., circularity) and the amount of reactive oxygen species (ROS) generation confirmed the validity of this morphology-based microfluidic image cytometric (microFIC) assessment method. We propose this morphology-based microFIC approach as an easy and efficient way to assess cytotoxicity which can be adapted to high-throughput screening platforms for in vitro cytotoxicity assays as well as drug screening.