Pillar array microtraps with negative dielectrophoresis

Real-time capture of single particles in controlled flow by a rapidly generated foci array with adjustable intensity and pattern

We propose a new, to the best of our knowledge, technique to capture single particles in real-time in a microfluidic system with controlled flow using micro-pillar traps fabricated by one-step. The micro pillars are fabricated in parallel by femtosecond multi-foci laser beams, which are generated by multiplexing gratings. As the generation process does not need integration loops, the pattern and the intensity distribution of the foci array can be controlled in real-time by changing the parameters of gratings. The real-time control of the foci array enables rapidly fabricating microtraps in the microchannel with adjustment of the pillar spaces and patterns according to the sizes and shapes of target particles. This technology provides an important step towards using platforms based on single-particle analysis, and it paves the way for the development of innovative microfluidic devices for single-cell analysis.

Predicting Hemiwicking Dynamics on Textured Substrates

The ability to predict liquid transport rates on textured surfaces is key to the design and optimization of devices and processes such as oil recovery, coatings, reaction-separation, high-throughput screening, and thermal management. In this work we develop a fully analytical model to predict the propagation coefficients for liquids hemiwicking through micropillar arrays. This is carried out by balancing the capillary driving force and a viscous resistive force and solving the Navier-Stokes equation for representative channels. The model is validated against a large data set of experimental hemiwicking coefficients harvested from the literature and measured in-house using high-speed imaging. The theoretical predictions show excellent agreement with the measured values and improved accuracy compared to previously proposed models. Furthermore, using lattice Boltzmann (LB) simulations, we demonstrate that the present model is applicable over a broad range of geometries. The scaling of velocity with texture geometry, implicit in our model, is compared against experimental data, where good agreement is observed for most practical systems. The analytical expression presented here offers a tool for developing design guidelines for surface chemistry and microstructure selection for liquid propagation on textured surfaces.

On-Chip Construction of Multilayered Hydrogel Microtubes for Engineered Vascular-Like Microstructures

Multilayered and multicellular structures are indispensable for constructing functional artificial tissues. Engineered vascular-like microstructures with multiple layers are promising structures to be functionalized as artificial blood vessels. In this paper, we present an efficient method to construct multilayer microtubes embedding different microstructures based on direct fabrication and assembly inside a microfluidic device. This four-layer microfluidic device has two separate inlets for fabricating various microstructures. We have achieved alternating-layered microtubes by controlling the fabrication, flow, and assembly time of each microstructure, and as well, double-layered microtubes have been built by a two-step assembly method. Modifications of both the inner and outer layers was successfully demonstrated, and the flow conditions during the on-chip assembly were evaluated and optimized. Each microtube was successfully constructed within several minutes, showing the potential applications of the presented method for building engineered vascular-like microstructures with high efficiency.

Dielectrophoretic concentrator enhancement based on dielectric poles for continuously flowing samples

We describe a novel continuous-flow cell concentrator microdevice based on dielectrophoresis, and its associated custom-made control unit. The performances of a classical interdigitated metal electrode-based dielectrophoresis microfluidic device and this enhanced version, that includes insulator-based pole structures, were compared using the same setup. Escherichia coli samples were concentrated at several continuous flows and the device's trapping efficiencies were evaluated by exhaustive cell counts. Our results show that pole structures enhance the retention up to 12.6%, obtaining significant differences for flow rates up to 20 μL/min, when compared to an equivalent classical interdigitated electrodes setup. In addition, we performed a subsequent proteomic analysis to evaluate the viability of the biological samples after the long exposure to the actuating electrical field. No Escherichia coli protein alteration in any of the two systems was observed.

Towards single-cell analysis for pharmacokinetics

Traditional ‘macroscopic’ pharmacokinetics (PK) investigates the fate of drugs or toxicants administered externally to living organisms, described by the extent and rate of absorption, distribution, metabolism and excretion. However, how a single cell affects a specific pharmaceutical after administration still remains a largely untouched area, primarily due to the technical restrictions imposed by minute amounts of chemicals involved. With the fast development of high-temporal and spatial-resolution detection techniques and single-cell handling techniques, it becomes possible to pursue single-cell PK. This review summarizes useful methodological and experimental techniques to investigate PK at the level of the single cell, including the microfluidics-based single-cell manipulation and the MS and electrochemical methods for single-cell analysis.

Microscale liquid dynamics and the effect on macroscale propagation in pillar arrays

Liquid dynamics in micropillar arrays have received significant fundamental interest and have offered opportunities for the development of advanced microfluidic, thermal management, and energy-harvesting devices. However, a comprehensive understanding of complex liquid behavior and the effect on macroscopic propagation rates in micropillar arrays is needed. In this work, we investigated the microscopic sweeping behavior of the liquid front along the spreading direction in micropillar arrays where the sweeping distance scales with the one-fifth power of time. We explain the scaling with a simplified model that captures the capillary pressure gradient at the liquid front. Furthermore, we show that such microscopic dynamics is the mechanism that decreases the macroscopic propagation rate. This effect is a result of the reduction in the interfacial energy difference used to generate the capillary pressure, which is explained with an energy-based model and corroborated with experiments. The results indicate the importance of accounting for the microscopic dynamics of the liquid on microstructured surfaces, particularly in sparse geometries.

Design of a compact microfludic device for controllable cell distribution

A compact microfluidic device with 96 microchambers allocated within four circular units was designed and examined for cell distribution. In each unit, cells were distributed to the surrounding chambers radially from the center. The circular arrangement of the chambers makes the design simple and compact. A controllable and quantitative cell distribution is achievable in this device. This design is significant to the microfluidic applications where controllable distribution of cells in multipule microchambers is demanded.

Prediction and optimization of liquid propagation in micropillar arrays

Prediction and optimization of liquid propagation rates in micropillar arrays are important for various lab-on-a-chip, biomedical, and thermal management applications. In this work, a semianalytical model based on the balance between capillary pressure and viscous resistance was developed to predict liquid propagation rates in micropillar arrays with height-to-period ratios greater than 1 and diameter-to-period ratios less than 0.57. These geometries represent the most useful regimes for practical applications requiring large propagation rates. The capillary pressure was obtained using an energy approach where the meniscus shape was predicted using Surface Evolver simulations and experimentally verified by interference microscopy. The combined viscous resistance of the pillars and the substrate was determined using Brinkman's equation with a numerically obtained permeability and corroborated with finite element simulations. The model shows excellent agreement with one-dimensional propagation experiments of deionized water in silicon micropillar arrays, highlighting the importance of accurately capturing the details of the meniscus shape and the viscous losses. Furthermore, an effective propagation coefficient was obtained through dimensionless analysis that is functionally dependent only on the micropillar geometry. The work offers design guidelines to obtain optimal liquid propagation rates on micropillar surfaces.

A unified scaling model for flow through a lattice of microfabricated posts

A scaling model is presented for low Reynolds number viscous flow within an array of microfabricated posts. Such posts are widely used in several lab-on-a-chip applications such as heat pipes, antibody arrays and biomolecule separation columns. Finite element simulations are used to develop a predictive model for pressure driven viscous flow through posts. The results indicate that the flow rate per unit width scales as approximately h1.17g1.33/d0.5 where h is the post height, d post diameter and g is the spacing between the posts. These results compare favorably to theoretical limits. The scaling is extended to capillary pressure driven viscous flows. This unified model is the first report of a scaling that incorporates both viscous and capillary forces in the microfabricated post geometry. The model is consistent with Washburn dynamics and was experimentally validated to within 8% using wetting on microfabricated silicon posts.

Dielectrophoretic-field flow fractionation analysis of dielectric, density, and deformability characteristics of cells and particles

Dielectrophoretic field-flow fractionation (DEP-FFF) has been used to discriminate between particles and cells based on their dielectric and density properties. However, hydrodynamic lift forces (HDLF) at flow rates needed for rapid separations were not accounted for in the previous theoretical treatment of the approach. Furthermore, no method was developed to isolate particle or cell physical characteristics directly from DEP-FFF elution data. An extended theory of DEP-FFF is presented that accounts for HDLF. With the use of DS19 erythroleukemia cells as model particles with frequency-dependent dielectric properties, it is shown that the revised theory accounts for DEP-FFF elution behavior over a wide range of conditions and is consistent with sedimentation-FFF when the DEP force is zero. Conducting four elution runs under specified conditions, the theory allows for the derivation of the cell density distribution and provides good estimates of the distributions of the dielectric properties of the cells and their deformability characteristics that affect HDLF. The approach allows for rapid profiling of the biophysical properties of cells, the identification and characterization of subpopulations, and the design of optimal DEP-FFF separation conditions. The extended DEP-FFF theory is widely applicable, and the parameter measurement methods may be adapted easily to other types of particles.