Fluidic Experiments Research Articles

In Vitro-In Silico Modeling of Caffeine and Diclofenac Permeation in Static and Fluidic Systems with a 16HBE Lung Cell Barrier.

Static in vitro permeation experiments are commonly used to gain insights into the permeation properties of drug substances but exhibit limitations due to missing physiologic cell stimuli. Thus, fluidic systems integrating stimuli, such as physicochemical fluxes, have been developed. However, as fluidic in vitro studies display higher complexity compared to static systems, analysis of experimental readouts is challenging. Here, the integration of in silico tools holds the potential to evaluate fluidic experiments and to investigate specific simulation scenarios. This study aimed to develop in silico models that describe and predict the permeation and disposition of two model substances in a static and fluidic in vitro system. For this, in vitro permeation studies with a 16HBE cellular barrier under both static and fluidic conditions were performed over 72 h. In silico models were implemented and employed to describe and predict concentration–time profiles of caffeine and diclofenac in various experimental setups. For both substances, in silico modeling identified reduced apparent permeabilities in the fluidic compared to the static cellular setting. The developed in vitro–in silico modeling framework can be expanded further, integrating additional cell tissues in the fluidic system, and can be employed in future studies to model pharmacokinetic and pharmacodynamic drug behavior.

Validation of droplet-generation performance of a newly developed microfluidic device with a three-dimensional structure

We fabricated a microfluidic device with a three-dimensional (3D) structure and verified its droplet-generation performance for the stable production of droplets of around 10 μm in size. We compared the performance of the 3D device with that of conventional simple T-junction and cross-junction structures. The continuous phase sheared the dispersed phase into droplets from eight directions in the 3D device, compared with only one direction in the T-junction device and two in the cross-junction device. Droplets were produced efficiently over a wide range of fluid properties and flow conditions with the 3D device, unlike with the two conventional planar devices. Fluidic experiments were conducted using mineral oil with a surfactant as the continuous phase, deionized (DI) water as the dispersed phase, and DI water with glycerin to change the viscosity of the dispersed phase. The minimum droplet length was 47.2 μm in the T-junction device, 39.0 μm in the cross-junction device, and 22.4 μm in the 3D device when using a water and glycerin mixture with a viscosity of 9.0 mPa·s. Compared with the conventional devices, smaller droplets were produced using our 3D device, indicating that it has excellent droplet-generation performance.

Walking droplets through the lens of dynamical systems

Over the past decade the study of fluidic droplets bouncing and skipping (or “walking”) on a vibrating fluid bath has gone from an interesting experiment to a vibrant research field. The field exhibits challenging fluids problems, potential connections with quantum mechanics, and complex nonlinear dynamics. We detail advancements in the field of walking droplets through the lens of Dynamical Systems Theory, and outline questions that can be answered using dynamical systems analysis. The paper begins by discussing the history of the fluidic experiments and their resemblance to quantum experiments. With this physics backdrop, we paint a portrait of the complex nonlinear dynamics present in physical models of various walking droplet systems. Naturally, these investigations lead to even more questions, and some unsolved problems that are bound to benefit from rigorous Dynamical Systems Analysis are outlined.

Pore to pore validation of pore network modelling against micromodel experiment results

Pore network modelling (PNM) has been widely used to study the multiphase flow and transport in porous media. Although a number of recent papers discussed the PNM validation on core-scale parameters such as permeability, relative permeability and capillary pressure; quantitative predictive potential of PNM on pore by pore basis has rarely been studied. The aim of this paper is to present a direct comparison between PNM simulations and corresponding micro-model experiments at the same scale and the same geometry. A number of well-defined and constrained two-phase flow in porous medium experimental scenarios were utilized to validate the physics solving part in PNM (filling rules, capillary and viscous pressure). This work validates that a dynamic pore network flow solver can predict two-phase flow displacements for these experiments for drainage situations at both pore and plug scales. A glass-etched micro-model is used to quantify the accuracy of a dynamic PNM solver on pore and core levels. Two-phase drainage micro fluidic experiments at different flow conditions are performed on micro-models. PNM simulations are performed on the same pattern and flow conditions as used in micro-model experiments. The two-phase distribution extracted from experiment images is registered onto rsults of PNM simulations for direct pore to pore comparison. Pore-scale matching level is found at around 75 % for all three test cases. The matching level of core-scale parameters such as S w c and oil-phase permeability varies from case to case; the relative error to micro-model experiment measurements varies from 15 to 60 %. Possible reasons leading to discrepancies on core-scale parameters are discussed: missing considerations during validation of the combination of uncertainty in both simulator input parameters and experiments are seen as the principal factors.

An SOI CMOS-Based Multi-Sensor MEMS Chip for Fluidic Applications.

An SOI CMOS multi-sensor MEMS chip, which can simultaneously measure temperature, pressure and flow rate, has been reported. The multi-sensor chip has been designed keeping in view the requirements of researchers interested in experimental fluid dynamics. The chip contains ten thermodiodes (temperature sensors), a piezoresistive-type pressure sensor and nine hot film-based flow rate sensors fabricated within the oxide layer of the SOI wafers. The silicon dioxide layers with embedded sensors are relieved from the substrate as membranes with the help of a single DRIE step after chip fabrication from a commercial CMOS foundry. Very dense sensor packing per unit area of the chip has been enabled by using technologies/processes like SOI, CMOS and DRIE. Independent apparatuses were used for the characterization of each sensor. With a drive current of 10 µA–0.1 µA, the thermodiodes exhibited sensitivities of 1.41 mV/°C–1.79 mV/°C in the range 20–300 °C. The sensitivity of the pressure sensor was 0.0686 mV/(Vexcit kPa) with a non-linearity of 0.25% between 0 and 69 kPa above ambient pressure. Packaged in a micro-channel, the flow rate sensor has a linearized sensitivity of 17.3 mV/(L/min)−0.1 in the tested range of 0–4.7 L/min. The multi-sensor chip can be used for simultaneous measurement of fluid pressure, temperature and flow rate in fluidic experiments and aerospace/automotive/biomedical/process industries.

Simultaneous detection of multiple biological targets using optimized microfluidic microsphere-trap arrays

We propose an analytical framework to build a microfluidic microsphere-trap array device that enables simultaneous, efficient, and accurate screening of multiple biological targets in a single microfluidic channel. By optimizing the traps’ geometric parameters, the trap arrays in the channel of the device can immobilize microspheres of different sizes at different regions, obeying hydrodynamically engineered trapping mechanism. Different biomolecules can be captured by the ligands on the surfaces of microspheres of different sizes. They are thus detected according to the microspheres’ positions (position encoding), which simplifies screening and avoids target identification errors. To demonstrate the proposition, we build a device for simultaneous detection of two target types by trapping microspheres of two sizes. We evaluate the device performance using finite element fluidic dynamics simulations and microsphere-trapping experiments. These results validate that the device efficiently achieves position encoding of the two-sized microspheres with few fluidic errors, providing the promise to utilize our framework to build devices for simultaneous detection of more targets. We also envision utilizing the device to separate, sort, or enumerate cells, such as circulating tumor cells and blood cells, based on cell size and deformability. Therefore, the device is promising to become a cost-effective and point-of-care miniaturized disease diagnostic tool.

Pore Scale Models for Imbibition of CO2 Analogue Fluids in Etched Micro-model||junctions Using Micro-fluidic Experiments and Direct Flow Calculations

We investigate both drainage and spontaneous imbibition processes at the pore scale using a combination of micro- fluidic experiments and lattice-Boltzmann (LB) flow calculations. First, we have fabricated a range of specifically designed etched micro-models to investigate the role of pore shape and throat width on fluid displacement. These designs include junctions with both equal and unequal channel widths in order to achieve a range of capillary entry pressures. All models were etched into Poly(methyl methacrylate) (PMMA) and chemically treated to create a hydrophobic surface. The displacement process is captured via a high-speed video microscope under ambient conditions. The experimental results were then directly compared with LB simulations. For the drainage experiments, we observe that the fluid displacement in the junction follows the Young-Laplace Law. For the case of spontaneous imbibition, however, the models with unequal channel widths display different displacement behaviour. Our experimental observations are confirmed in detail by Lattice Boltzmann Method (LBM) simulations, lending credibility to our observations. Instead of following Young-Laplace filling rules, we observe that the throat in closest proximity fills up first. This has potentially important consequences for calculation of residual saturation of CO2 at the core scale, which is determined by spontaneous imbibition of brine following CO2 injection.

Stimulation and Inhibition of Bacterial Growth by Caffeine Dependent on Chloramphenicol and a Phenolic Uncoupler—A Ternary Toxicity Study Using Microfluid Segment Technique

A droplet-based microfluidic technique for the fast generation of three dimensional concentration spaces within nanoliter segments was introduced. The technique was applied for the evaluation of the effect of two selected antibiotic substances on the toxicity and activation of bacterial growth by caffeine. Therefore a three-dimensional concentration space was completely addressed by generating large sequences with about 1150 well separated microdroplets containing 216 different combinations of concentrations. To evaluate the toxicity of the ternary mixtures a time-resolved miniaturized optical double endpoint detection unit using a microflow-through fluorimeter and a two channel microflow-through photometer was used for the simultaneous analysis of changes on the endogenous cellular fluorescence signal and on the cell density of E. coli cultivated inside 500 nL microfluid segments. Both endpoints supplied similar results for the dose related cellular response. Strong non-linear combination effects, concentration dependent stimulation and the formation of activity summits on bolographic maps were determined. The results reflect a complex response of growing bacterial cultures in dependence on the combined effectors. A strong caffeine induced enhancement of bacterial growth was found at sublethal chloramphenicol and sublethal 2,4-dinitrophenol concentrations. The reliability of the method was proved by a high redundancy of fluidic experiments. The results indicate the importance of multi-parameter investigations for toxicological studies and prove the potential of the microsegmented flow technique for such requirements.

A buried vertical filter for micro and nanoparticle filtration

This paper presents a silicon micromachined filter concept suitable for separating micro- and nanoparticles. The filter is orientated vertically and buried beneath a silicon nitride surface layer. The vertically positioned structure accommodates highly uniform pores and allows for efficient use of die area while the buried aspect makes it possible for additional features to be integrated directly above the filter and its microchannels. The filter consists of a porous wall that is structurally defined inside the silicon substrate and is released, together with the microchannels, by isotropically etching the surrounding silicon. Fluidic experiments have confirmed the filtration functionality of fabricated devices using operating pressures up to 700kPa. The proposed concept also offers the possibility to have built-in cleansing of the cake layer formed on the porous wall, by reversing the fluid flow.

A Buried Vertical Filter for Micro and Nanoparticle Filtration

This paper presents a silicon micromachined filter for micro- and nanoparticles. The filter is vertical and completely buried beneath the surface. The buried aspect allows additional features to be integrated above the filter, while the vertical aspect allows the creation of highly uniform pores and efficient use of die area. The filter is composed out of a porous membrane released together with the microchannels by isotropically etching the surrounding silicon. Fluidic experiments have confirmed the filtration functionality of fabricated devices using operating pressures up to 400kPa. Moreover, by using a reversed fluid flow, cleansing of the cake layer build-up on the porous membrane is attained.

Three-Dimensional Chemical Profile Manipulation Using Two-Dimensional Autonomous Microfluidic Control

The ability to specify or control spatiotemporal chemical environments is critical for controlling diverse processes from chemical synthesis to cellular responses. When established by microfluidics methods, this chemical control has largely been limited to two dimensions and by the need for using complex approaches. The ability to create three-dimensional (3D) chemical patterns is becoming more critical as microfluidics is beginning to have novel applications at larger millifluidic scales, including model organism behavior, embryonic development, and optofluidics. Here, we present a simple approach to create 3D chemical patterns that can be controlled in space and time via two-dimensional (2D), single-layer fluidic modules. Not only can we employ autonomous flow in a 2D fluidic configuration to produce a 3D pattern, but with very simple changes in the 2D configuration, the chemical pattern can be "focused and defocused" within the 3D cross section. We also show that these chemical patterns can be predicted by computational fluid dynamics simulations with high experimental correlation. These simulations allow analyses of the characteristics of interface behaviors with respect to three basic yet critical parameters that need to be thoroughly considered in scaling-up from microfluidic to millifluidic research: Reynolds number (Re), inlet geometry, and channel height. The findings not only indicate proof of concept for 3D pattern creation but also reveal that a number of fluidic experiments may have inherent limitations resulting from unrecognized 3D profiles that depend on these parameter choices. These results will be useful for research areas including embryonic development, cellular stimulation, and chemical fabrication approaches.

A multichamber fluidic device for 3D cultures under interstitial flow with live imaging: Development, characterization, and applications

Interstitial flow is an important biophysical cue that can affect capillary morphogenesis, tumor cell migration, and fibroblast remodeling of the extracellular matrix, among others. Current models that incorporate interstitial flow and that are suitable for live imaging lack the ability to perform multiple simultaneous experiments, for example, to compare effects of growth factors, extracellular matrix composition, etc. We present a nine-chamber radial flow device that allows simultaneous 3D fluidic experiments for relatively long-term culture with live imaging capabilities. Flow velocity profiles were characterized by fluorescence recovery after photobleaching (FRAP) for flow uniformity and estimating the hydraulic conductivity. We demonstrate lymphatic and blood capillary morphogenesis in fibrin gels over 10 days, comparing flow with static conditions as well as the effects of an engineered variant of VEGF that binds fibrin via Factor XIII. We also demonstrate the culture of contractile fibroblasts and co-cultures with tumor cells for modeling the tumor microenvironment. Therefore, this device is useful for studies of capillary morphogenesis, cell migration, contractile cells like fibroblasts, and multicellular cultures, all under interstitial flow.

An integrated flow-cell for full sample stream control

In this study, we present a novel three-dimensional hydrodynamic sheath flow chip that allows full control of a sample stream. The chip offers the possibility to steer each of the four side sheath flows individually. The design of the flow-cell exhibits high flexibility in creating different sample stream profiles (width and height) and allows navigation of the sample stream to every desired position inside the microchannel (vertical and horizontal). This can be used to bring the sample stream to a sensing area for analysis, or to an area of actuation (e.g. for cell sorting). In addition, we studied the creation of very small sample stream diameters. In microchannels (typically 25 × 40 μm²), we created sample stream diameters that were five to ten times smaller than the channel dimensions, and the smallest measured sample stream width was 1.5 μm. Typical flow rates are 0.5 μl/min for the sample flow and around 100 μl/min for the cumulated sheath flows. The planar microfabricated chip, consisting of a silicon–glass sandwich with an intermediate SU-8 layer, is much smaller (6 × 9 mm²) than the previously presented sheath flow devices, which makes it also cost-effective. We present the chip design, fluidic simulation results and experiments, where the size, shape and position of the sample stream have been established by laser scanning confocal microscopy and dye intensity analysis.

A real-time dynamic imaging system for centrifugal microflow platforms

Based on the operational concept of quasi-static state and optoelectronic measurement technology, this research develops a real-time dynamic imaging system for centrifugal microfluidic platforms. Unlike the conventional centrifugal inspection system, which can only be used for examination of the final steady stage in microflow analysis, the developed system with a multi-speed controller and object tracking design is fabricated with low cost to recognize dynamic microflow patterns for different kinds of compact disc-type centrifugal microstructures. The characteristics of rotational control efficiency and image acquisition quality are obtained from fluidic microvalve experiments that are achieved in measuring microflow dynamic responses and in visualizing transient microflow patterns. A man–machine interface was connected with a computer to perform the control and alignment adjustments to catch exact image data for following analysis. The rotation stability of the system has been evaluated, and the rotation speed up to 4500 rpm with vertical vibration less than ±0.2 mm is achieved measured at radial distance of 5 cm. The image acquisition is transferred via USB 2.0 at a speed of up to 30 images per second to the display and memory module.

Fabrication of Flexible Neural Probes With Built-In Microfluidic Channels by Thermal Bonding of Parylene

This paper describes the fabrication technology and characterization of Parylene neural probes containing fluidic channels for delivery of small amounts of drugs into biological tissue as well as neural recording. We present a first attempt to realize such neural probes by micromolding and thermal bonding of Parylene. Compared to the common fabrication method, where a sacrificial photoresist layer is sandwiched between two Parylene layers, the major advantages of this process are, that the time consuming photoresist dissolution is omitted, and that the adhesion between the Parylene layers could be improved. The electrodes were characterized by impedance measurements, in which an impedance sufficiently low for neural recording was observed. Fluidic injection experiments with the microchannel have shown that nanoliter volumes can be injected

Fully Integrated Miniature Device for Automated Gene Expression DNA Microarray Processing

A DNA microarray with 12,000 features was integrated with a microfluidic cartridge to automate the fluidic handling steps required to carry out a gene expression study of the human leukemia cell line (K562). The fully integrated microfluidic device consists of microfluidic pumps/mixers, fluid channels, reagent chambers, and a DNA microarray silicon chip. Microarray hybridization and subsequent fluidic handling and reactions (including a number of washing and labeling steps) were performed in this fully automated and miniature device before fluorescent image scanning of the microarray chip. Electrochemical micropumps were integrated into the cartridge to provide pumping of liquid solutions. The device was completely self-contained: no external pressure sources, fluid storage, mechanical pumps, mixers, or valves were necessary for fluid manipulation, thus eliminating possible sample contamination and simplifying device operation. Fluidic experiments were performed to study the on-chip washing efficiency and uniformity. A single-color transcriptional analysis of K562 cells with a series of calibration controls (spiked-in controls) to characterize this new platform with regard to sensitivity, specificity, and dynamic range was performed. The device detected sample RNAs with a concentration as low as 0.375 pM. Experiment also showed that the performance of the integrated microfluidic device is comparable with the conventional hybridization chambers with manual operations, indicating that the on-chip fluidic handling (washing and reaction) is highly efficient and can be automated with no loss of performance. The device provides a cost-effective solution to eliminate labor-intensive and time-consuming fluidic handling steps in genomic analysis.

Single-use, thermally actuated paraffin valves for microfluidic applications

A new thermally actuated valving concept using paraffin as single-use valving material was developed. The paraffin undergoes a phase transition in response to changes in temperature. A variety of single-use paraffin-based microvalves, including “close–open,” “open–close–open,” “T,” and toggle designs, were demonstrated. Fluidic experiments showed that these microvalves had zero leakage and a maximum hold-up pressure of 40 psi in a “closed” position. A DNA polymerase chain reaction microdevice containing paraffin-based microvalves to enclose the sample solution in the reaction chamber during the thermal cycling was demonstrated. The paraffin-based microvalving technique has advantages over many existing active microvalve approaches, including a simple design, ease of fabrication, low cost, and ease of integration into complex microfluidic systems. Moreover, this technique is particularly attractive for single-use and disposable microfluidic devices.

Hybridization enhancement using cavitation microstreaming.

Conventional DNA microarray hybridization relies on diffusion of target to surface-bound probes, and thus is a rate-limited process. In this paper, a micromixing technique based on cavitation microstreaming principle that was developed to accelerate hybridization process is explained. Fluidic experiments showed that air bubbles resting on a solid surface and set into vibration by a sound field generated steady circulatory flows, resulting in global convection flows and, thus, rapid mixing. The time to fully mix dyed solutions in a 50-microL chamber using cavitation microstreaming was significantly reduced from hours (a pure diffusion-based mixing) to 6 s. Cavitation microstreaming was implemented to enhance DNA hybridization in both fluorescence-detection-based and electrochemical-detection-based DNA microarray chips. The former showed that cavitation microstreaming results in up to 5-fold hybridization signal enhancement with significantly improved signal uniformity, as compared to the results obtained in conventional diffusion-based biochips for a given time (2 h). Hybridization kinetics study in the electrochemical detection-based chips showed that acoustic microstreaming results in up to 5-fold kinetics acceleration. Acoustic microstreaming has many advantages over most existing techniques used for hybridization enhancement, including a simple apparatus, ease of implementation, low power consumption (approximately 2 mW), and low cost.

Bubble-induced acoustic micromixing.

A mixing technique based on the principle of bubble-induced acoustic microstreaming was developed. The mixer consists of a piezoelectric disk that is attached to a reaction chamber, which is designed in such a way that a set of air bubbles with desirable size is trapped in the solution. Fluidic experiments showed that air bubbles resting on a solid surface and set into vibration by the sound field generated steady circulatory flows, resulting in global convection flows and thus rapid mixing. The time to fully mix a 22 microL chamber is significantly reduced from hours (for a pure diffusion-based mixing) to tens of seconds. Numerical simulations showed that the induced flowfield and thus degree of mixing strongly depend on bubble positions. Optimal simulated mixing results were obtained for staggered bubble distribution that minimizes the number of internal flow stagnation regions. Immunomagnetic cell capture experiments showed that acoustic microstreaming provided efficient mixing of bacterial cell (Esherichia coli K12) matrix suspended in blood with magnetic capture beads, resulting in highly effective immunomagnetic cell capture. Bacterial viability assay experiments showed that acoustic microstreaming has a relatively low shear strain field since the blood cells and bacteria remained intact after mixing. Acoustic microstreaming has many advantages over most existing chamber micromixing techniques, including simple apparatus, ease of implementation, low power consumption (2 mW), and low cost.

Lab-on-a-chip sample preparation using laminar fluid diffusion interfaces--computational fluid dynamics model results and fluidic verification experiments.

Microfluidic structures for the generation of laminar fluid diffusion interfaces (LFDIs) for sample preparation and analysis are discussed. Experimental data and the results of fluid modeling are shown. LFDIs are generated when two or more streams flow in parallel in a single microfluidic structure without any mixing of the fluids other than by diffusion of particles across the diffusion interface. It has been shown that such structures can be used for diffusion-based separation and detection applications. The method has been applied to DNA desalting, the extraction of small proteins from whole blood samples, and the detection of various constituents in whole blood, among other examples. In this paper the design and manufacture of self-contained microfluidic cartridges for the extraction of small molecules from a mixture of small and large molecules by diffusion is demonstrated. The cards are operated without any external instrumentation, and use hydrostatic pressure as the driving force. The performance of the cartridges is illustrated by separating fluorescein from a mixture of fluorescein and dextran of molecular weight 2 x 10(6). In a single pass, 98.6% of dextran was retained in the product whereas 43.1% of fluorescein was removed. The method is adjustable for different separation requirements, and computational fluid dynamics (CFD) models are shown that demonstrate the tuning of various microfluidic parameters to optimize separation performance. Other applications of LFDIs for establishment of stable concentration gradients, and the exposure of chemical constituents or biological particles to these concentration gradients are shown qualitatively. Microfluidic chips have been designed for high-throughput screening applications that enable the uniform and controlled exposure of cells to lysing agents, thus enabling the differentiation of cells by their sensitivity to specific agents in an on-chip cytometer coupled directly to the lysing structure.