Microfluidic Design Research Articles

Analysis of barotactic and chemotactic guidance cues on directional decision-making of Dictyostelium discoideum cells in confined environments

Neutrophils and dendritic cells when migrating in confined environments have been shown to actuate a directional choice toward paths of least hydraulic resistance (barotaxis), in some cases overriding chemotactic responses. Here, we investigate whether this barotactic response is conserved in the more primitive model organism Dictyostelium discoideum using a microfluidic chip design. This design allowed us to monitor the behavior of single cells via live imaging when confronted with bifurcating microchannels, presenting different combinations of hydraulic and chemical stimuli. Under the conditions employed we find no evidence in support of a barotactic response; the cells base their directional choices on the chemotactic cues. When the cells are confronted by a microchannel bifurcation, they often split their leading edge and start moving into both channels, before a decision is made to move into one and retract from the other channel. Analysis of this decision-making process has shown that cells in steeper nonhydrolyzable adenosine- 3', 5'- cyclic monophosphorothioate, Sp- isomer (cAMPS) gradients move faster and split more readily. Furthermore, there exists a highly significant strong correlation between the velocity of the pseudopod moving up the cAMPS gradient to the total velocity of the pseudopods moving up and down the gradient over a large range of velocities. This suggests a role for a critical cortical tension gradient in the directional decision-making process.

Multiwalled Carbon Nanotubes in Microfluidic Chip for the Separation of X- and Y-Sperm Based on a Photolithography Technique

This study examined the performance of a microfluidic device for sperm separation assuming that X- and Y-sperm have different surface electrical charges. The proposed microfluidic chip was first tested with electrically charged particles, namely TiO2-coated polystyrene (PS) beads, to mimic spermatozoa. Negatively charged TiO2-coated PS beads were fabricated in a simple and efficient manner. These beads were characterised using X-ray diffraction, tungsten scanning electron microscopy with energy-dispersive X-ray spectroscopy mode, and X-ray absorption spectroscopy to determine the reason for the persistence of the negative surface charge. The fabricated TiO2-coated PS beads were partly coated in mixed forms of amorphous Ti4+, which caused a sustained negative charge on the surface after fabrication. The microfluidic device was simulated to obtain an optimal structure for fabrication. Negatively charged TiO2-coated PS beads were tested in designed microfluidic devices. Detailed structures for microfluidic device design with integrated microelectrodes were fabricated using a photolithographic technique, and the finished device was tested with PS beads. Based on PS-bead separation, a microfluidic device with a $150~\mu \text{m}$ microchannel and $100~\mu \text{m}$ distance between electrodes was the best performing prototype at 87.07% with a confidence level of 95%. Commercial positively and negatively charged PS beads were tested in the selected design for additional validation. Finally, sperm separation using the proposed device was conducted; the specially designed microfluidic device with multiwalled carbon nanotubes was fabricated, and the proposed device showed a X- and Y-sperm separation accuracy of 74.62%. [2020-0278]

A Microfluidic Platform Equipped With Magnetic Nano Films for Organizing Bio-Particle Arrays and Long-Term Studies

We introduce a microfluidic platform that combines hydrodynamic trapping and magnetic switching techniques for precise manipulating magnetic micro-particles and forming particle and cell arrays, in a massively parallel manner. In the first step, hydrodynamic forces transport and then trap the single particles and cells in a large array. Then, magnetic forces transfer them into adjacent low-shear compartments which are used as single cell culture micro-chambers. Furthermore, using this tool, we run single cell assays and perform drug screening as well as mRNA analysis experiments. The flawless magnetic transport in this work is obtained by growing a non-fouling layer on microchannel surfaces. The chip treatment became possible by a novel microfluidic chip design and a new simple self-aligned fabrication method, based on a silicon substrate, magnetic nano thin-films embedded in the microfluidic walls, and a glass lid. The resulting chip is an innovative tool suitable for long-term single cell phenotypic and genotypic studies, with applications in immunology and medicine.

Overcoming the sensitivity vs. throughput tradeoff in Coulter counters: A novel side counter design

Microfabricated Coulter counters are attractive for point of care (POC) applications since they are label free and compact. However, these approaches inherently suffer from a trade off between sample throughput and sensitivity. The counter measures a change in impedance due to displaced fluid volume by passing cells, and thus the counter's signal increases with the fraction of the sensing volume displaced. Reducing the size of the sensing region requires reductions in volumetric throughput in the absence of increased hydraulic pressure and sensor bandwidth. The risk of mechanical clog formation, rendering the counter inoperable, increases markedly with reductions in the size of the constriction aperture. We present here a microfluidic coplanar Coulter counter device design that overcomes the problem of constriction clogging while capable of operating in microfluidic channels filled entirely with highly conductive sample. The device utilizes microfabricated planar electrodes projecting into one side of the microfluidic channel and is easily integrated with upstream electronic, hydrodynamic, or other focusing units to produce efficient counting which could allow for dramatically increased volumetric and sample throughput. The design lends itself to simple, cost effective POC applications.

In Situ Microfluidic Preparation and Solidification of Alginate Microgels

Biomimetic fabrication of alginate beads has promising applications in the field of synthetic bioarchitecture. Combining microfluidic technology with in situ gelation enables the creation of alginate microgels with precisely tunable size, as well as allowing control of the crosslinking process. Owing to the wide range of applications of alginate microgel beads, this study aimed to develop various microfluidic models for the generation of such beads by investigating the influence of several parameters on their morphologies and dispersity. Four types of glass microfluidic chips with flow focusing or co-flowing droplet generators were used to continuously form alginate droplets, with the possibility of either internal or external alginate gelation by a cross-linking agent supplied by a microfluidic channel. In all four models, alginate was used at a fixed concentration, Span 80 was used as a surfactant to improve the long-term stability of the beads, either mineral oil or oleic acid was used as a continuous phase, and either calcium carbonate (CaCO3) or calcium chloride (CaCl2) was used as a crosslinking agent. The generated beads exhibited various architectures, including individual monodisperse or polydisperse beads, small clusters, and multicompartment systems. The results of the study revealed the importance of microfluidic design and gelation strategy for the generation of stable polymeric architectures. The current study proposes a simple user’s guide to create alginate microgels in various architectures. The fabricated biomimetic models in the form of polymeric-based vesicles can be further exploited in several applications, including cell-like structures, tissue engineering, and cell and drug encapsulation. Additional investigations will be needed, however, to improve these models so that they more closely resemble the natural structures of cells and tissues.

A microfluidic computational fluid dynamics model for cellular interaction studies of sickle cell disease vaso-occlusions

Individuals with sickle cell disease are plagued with vaso-occlusions, chronic blockages within the vasculature. Several factors including stiffer sickle red blood cells and increased cell aggregation contribute to vaso-occlusion formation; however much remains to be understood. We present a computational fluid dynamics blood flow simulation within a microfluidic platform using the Carreau model and Murray's law. Vaso-occlusions form preferentially near bifurcations within 60 s in the sickle cell disease simulation. Velocity profiles and shear rates align with clinical and experimental reports. We assert that results from this study can be utilized to inform experimental investigations and microfluidic system design decisions.

Pathologic Shear and Elongation Rates Do Not Cause Cleavage of Von Willebrand Factor by ADAMTS13 in a Purified System.

Pathological flows in patients with severe aortic stenosis are associated with acquired von Willebrand syndrome. This syndrome is characterized by excessive cleavage of von Willebrand factor by its main protease, A Disintegrin and Metalloproteinase with a Thrombospondin Type 1 Motif, Member 13 (ADAMTS13) leading to decreased VWF function and mucocutaneous bleeding. Aortic valve replacement and correction of the flow behavior to physiological levels reverses the syndrome, supporting the association between pathological flow and acquired von Willebrand syndrome. We investigated the effects of shear and elongational rates on von Willebrand factor cleavage in the presence of ADAMTS13. We identified acquired von Willebrand syndrome in five patients with severe aortic stenosis. Doppler echography values from these patients were used to develop three computational fluid dynamic (CFD) aortic valve models (normal, mild and severe stenosis). Shear, elongational rates and exposure times identified in the CFD simulations were used as parameters for the design of microfluidic devices to test the effects of pathologic shear and elongational rates on the structure and function of von Willebrand factor. The shear rates (0-10,000s-1), elongational rates (0-1000 s-1) and exposure times (1-180 ms) tested in our microfluidic designs mimicked the flow features identified in patients with aortic stenosis. The shear and elongational rates tested in vitro did not lead to excessive cleavage or decreased function of von Willebrand factor in the presence of the protease. High shear and elongational rates in the presence of ADAMTS13 are not sufficient for excessive cleavage of von Willebrand Factor.

Optimal Control of Droplets on a Solid Surface Using Distributed Contact Angles.

Controlling the shape and position of moving and pinned droplets on a solid surface is an important feature often found in microfluidic applications. However, automating them, e.g., for high-throughput applications, rarely involves model-based optimal control strategies. In this work, we demonstrate the optimal control of both the shape and position of a droplet sliding on an inclined surface. This basic test case is a fundamental building block in plenty of microfluidic designs. The static contact angle between the solid surface, the surrounding gas, and the liquid droplet serves as the control variable. By using several control patches, e.g., like that performed in electrowetting, the contact angles are allowed to vary in space and time. In computer experiments, we are able to calculate mathematically optimal contact angle distributions using gradient-based optimization. The dynamics of the droplet are described by the Cahn-Hilliard-Navier-Stokes equations. We anticipate our demonstration to be the starting point for more sophisticated optimal design and control concepts.

Study of a microfluidic chip with converse fluid

The current microfluidic chip design generally forms a stagnation point in the exit flow area of the microfluidic chip. The presence of the stagnation area can cause problems such as choke of channel and sample purity degradation. For this problem, a microfluidic chip with converse fluid was designed. The converse sheath liquid can avoid the adverse effects caused by the presence of the stagnation point. It can prevent the cells from contacting the wall surface, and avoid the blocking problem of cell. At the same time, the introduction of the converse sheath liquid can also focus the sample flow in the sorting channel and the waste channel again, which is convenient for the detection of the sorted sample. The fluid flow state in this microfluidic chip was also simulated, and it verified the benefit of introducing converse sheath fluid, which has reference value for the design of microfluidic chip for cell analysis and sorting.

Voltage-gated ion channels mediate the electrotaxis of glioblastoma cells in a hybrid PMMA/PDMS microdevice.

Transformed astrocytes in the most aggressive form cause glioblastoma, the most common cancer in the central nervous system with high mortality. The physiological electric field by neuronal local field potentials and tissue polarity may guide the infiltration of glioblastoma cells through the electrotaxis process. However, microenvironments with multiplex gradients are difficult to create. In this work, we have developed a hybrid microfluidic platform to study glioblastoma electrotaxis in controlled microenvironments with high throughput quantitative analysis by machine learning-powered single cell tracking software. By equalizing the hydrostatic pressure difference between inlets and outlets of the microchannel, uniform single cells can be seeded reliably inside the microdevice. The electrotaxis of two glioblastoma models, T98G and U-251MG, requires an optimal laminin-containing extracellular matrix and exhibits opposite directional and electro-alignment tendencies. Calcium signaling is a key contributor in glioblastoma pathophysiology but its role in glioblastoma electrotaxis is still an open question. Anodal T98G electrotaxis and cathodal U-251MG electrotaxis require the presence of extracellular calcium cations. U-251MG electrotaxis is dependent on the P/Q-type voltage-gated calcium channel (VGCC) and T98G is dependent on the R-type VGCC. U-251MG electrotaxis and T98G electrotaxis are also mediated by A-type (rapidly inactivating) voltage-gated potassium channels and acid-sensing sodium channels. The involvement of multiple ion channels suggests that the glioblastoma electrotaxis is complex and patient-specific ion channel expression can be critical to develop personalized therapeutics to fight against cancer metastasis. The hybrid microfluidic design and machine learning-powered single cell analysis provide a simple and flexible platform for quantitative investigation of complicated biological systems.

Microfluidics chip design analysis and control

Micro-Electro-Mechanical Systems (MEMS) is an integrated electromechanical system where the feature size and operating range of the components are on a micro-scale. Unlike traditional mechanical processing, the production of the MEMS device uses semiconductor manufacturing, which includes surface microprocessing and bulk microprocessing, which can be compatible with an integrated circuit. These devices or systems have the ability to detect, control, activate, and create macro-scale effects. In this study, a 3-channel microfluidic channel design was realized by using the SolidWorks program, which is a 3D design program, to realize a microfluidic chip design. The preliminary physical tests and investigation of this microfluidics were made using the Comsol Multiphysics program and necessary time-dependent pressure tests. In this study, it is aimed to understand the pressure and speed values of the microfluidic chip according to the analysis. As a result of the analysis, it was found that the microfluidic chip has a maximum pressure of 6.1 Pa and a speed of 2.36×1014 mm/s.

Technical Model of Micro Electrical Discharge Machining (EDM) Milling Suitable for Bottom Grooved Micromixer Design Optimization.

In this paper, development of a technical model of micro Electrical Discharge Machining in milling configuration (EDM milling) is presented. The input to the model is a parametrically presented feature geometry and the output is a feature machining time. To model key factors influencing feature machining time, an experimental campaign by machining various microgrooves into corrosive resistant steel was executed. The following parameters were investigated: electrode dressing time, material removal rate, electrode wear, electrode wear control time and machining strategy. The technology data and knowledge base were constructed using data obtained experimentally. The model is applicable for groove-like features, commonly applied in bottom grooved micromixers (BGMs), with widths from 40 to 120 µm and depths up to 100 µm. The optimization of a BGM geometry is presented as a case study of the model usage. The mixing performances of various micromixer designs, compliant with micro EDM milling technology, were evaluated using computational fluid dynamics modelling. The results show that slanted groove micromixer is a favourable design to be implemented when micro EDM milling technology is applied. The presented technical model provides an efficient design optimization tool and, thus, aims to be used by a microfluidic design engineer.

A Rubik\u2019s microfluidic cube

A Rubik’s cube as a reconfigurable microfluidic system is presented in this work. Composed of physically interlocking microfluidic blocks, the microfluidic cube enables the on-site design and configuration of custom microfluidics by twisting the faces of the cube. The reconfiguration of the microfluidics could be done by solving an ordinary Rubik’s cube with the help of Rubik’s cube algorithms and computer programs. An O-ring-aided strategy is used to enable self-sealing and the automatic alignment of the microfluidic cube blocks. Owing to the interlocking mechanics of cube blocks, the proposed microfluidic cube exhibits good reconfigurability and robustness in versatile applications and proves to be a promising candidate for the rapid deployment of microfluidic systems in resource-limited settings.

Continuous Label-Free Electronic Discrimination of T Cells by Activation State.

The sensitivity and speed with which the immune system reacts to host disruption is unrivaled by any detection method for pathogenic biomarkers or infectious signatures. Engagement of cellular immunity in response to infections or cancer is contingent upon activation and subsequent cytotoxic activity by T cells. Thus, monitoring T cell activation can reliably serve as a metric for disease diagnosis as well as therapeutic prognosis. Rapid and direct quantification of T cell activation states, however, has been hindered by challenges associated with antigen target identification, labeling requirements, and assay duration. Here we present an electronic, label-free method for simultaneous separation and evaluation of T cell activation states. Our device utilizes a microfluidic design integrated with nanolayered electrode structures for dielectrophoresis (DEP)-driven discrimination of activated vs naïve T cells at single-cell resolution and demonstrates rapid (<2 min) separation of T cells at high single-pass efficiency as quantified by an on-chip Coulter counter module. Our device represents a microfluidic tool for electronic assessment of immune activation states and, hence, a portable diagnostic for quantitative evaluation of immunity and disease state. Further, its ability to achieve label-free enrichment of activated immune cells promises clinical utility in cell-based immunotherapies.

Label-Free, High-Throughput Assay of Human Dendritic Cells from Whole-Blood Samples with Microfluidic Inertial Separation Suitable for Resource-Limited Manufacturing.

Microfluidics technology has not impacted the delivery and accessibility of point-of-care health services, like diagnosing infectious disease, monitoring health or delivering interventions. Most microfluidics prototypes in academic research are not easy to scale-up with industrial-scale fabrication techniques and cannot be operated without complex manipulations of supporting equipment and additives, such as labels or reagents. We propose a label- and reagent-free inertial spiral microfluidic device to separate red blood, white blood and dendritic cells from blood fluid, for applications in health monitoring and immunotherapy. We demonstrate that using larger channel widths, in the range of 200 to 600 µm, allows separation of cells into multiple focused streams, according to different size ranges, and we utilize a novel technique to collect the closely separated focused cell streams, without constricting the channel. Our contribution is a method to adapt spiral inertial microfluidic designs to separate more than two cell types in the same device, which is robust against clogging, simple to operate and suitable for fabrication and deployment in resource-limited populations. When tested on actual human blood cells, 77% of dendritic cells were separated and 80% of cells remained viable after our assay.

Bio-inspired multicomponent carbon nanotube microfibers from microfluidics for supercapacitor

Fiber-shaped supercapacitors are considered to be one of the most promising power source candidates in flexible electronics for their light weight, high flexibility and wearability. Here, inspired by natural silkworms spinning and their hierarchical fiber structure, we present a multi-channel co-flow microfluidic strategy for one-step spinning of multicomponent carbon nanotubes (CNTs) microfiber supercapacitors. By injecting polyurethane (PU) and CNTs dispersed solutions into the microfluidic channels respectively, microfibers with single or double CNTs cores and PU shells could be continuously generated. These microfibers were also with highly tailorable structures, shapes and sizes of their encapsulated multicomponent CNTs cores through varying parameters such as microfluidic chip designs, flow rates and channel sizes. We have demonstrated that the resultant CNTs microfibers showed good flexibility, stability and cycle life performance for energy storage capacity through various electrochemical tests. Meanwhile, the practical application of CNTs microfibers in powering LED lights has also been successfully studied. Thus, we believe that these fiber-shaped CNT supercapacitors would reveal important utility in electronic applications which requiring flexible electronic systems.

Chemical Reactions-Based Microfluidic Transmitter and Receiver Design for Molecular Communication

The design of communication systems capable of processing and exchanging information through molecules and chemical processes is a rapidly growing interdisciplinary field, which holds the promise to revolutionize how we realize computing and communication devices. While molecular communication (MC) theory has had major developments in recent years, more practical aspects in designing components capable of MC functionalities remain less explored. This paper designs chemical reactions-based microfluidic devices to realize binary concentration shift keying (BCSK) modulation and demodulation functionalities. Considering existing MC literature on information transmission via molecular pulse modulation, we propose a microfluidic MC transmitter design, which is capable of generating continuously predefined pulse-shaped molecular concentrations upon rectangular triggering signals to achieve the modulation function. We further design a microfluidic MC receiver capable of demodulating a received signal to a rectangular output signal using a thresholding reaction and an amplifying reaction. Our chemical reactions-based microfluidic molecular communication system is reproducible and its parameters can be optimized. More importantly, it overcomes the slow-speed, unreliability, and non-scalability of biological processes in cells. To reveal design insights, we also derive the theoretical signal responses for our designed microfluidic transmitter and receiver, which further facilitate the transmitter design optimization. Our theoretical results are validated via simulations performed through the COMSOL Multiphysics finite element solver. We demonstrate the predefined nature of the generated pulse and the demodulated rectangular signal together with their dependence on design parameters.

Microfluidics for pharmaceutical nanoparticle fabrication: The truth and the myth.

Using micro-sized channels to manipulate fluids is the essence of microfluidics which has wide applications from analytical chemistry to material science and cell biology research. Recently, using microfluidic-based devices for pharmaceutical research, in particular for the fabrication of micro- and nano-particles, has emerged as a new area of interest. The particles that can be prepared by microfluidic devices can range from micron size droplet-based emulsions to nano-sized drug loaded polymeric particles. Microfluidic technology poses unique advantages in terms of the high precision of the mixing regimes and control of fluids involved in formulation preparation. As a result of this, monodispersity of the particles prepared by microfluidics is often recognised as being a particularly advantageous feature in comparison to those prepared by conventional large-scale mixing methods. However, there is a range of practical drawbacks and challenges of using microfluidics as a direct micron- and nano-particle manufacturing method. Technological advances are still required before this type of processing can be translated for application by the pharmaceutical industry. This review focuses specifically on the application of microfluidics for pharmaceutical solid nanoparticle preparation and discusses the theoretical foundation of using the nanoprecipitation principle to generate particles and how this is translated into microfluidic design and operation.

Printed Wearable Sensor Patch for Multi-Analytes Detection in the Sweat Range

Printed Wearable Sensor Patch for Multi-Analytes Detection in the Sweat Range

The Gap Sampler: A Versatile Microfluidic Autosampler for Electrospray Ionization Mass Spectrometry.

Microfluidic autosamplers for electrospray ionization mass spectrometry (ESI-MS) are of major importance when using ESI-MS as a high-throughput and low sample consumption analytical method. In this article, microfluidic ESI-MS autosampler designs are overviewed and a group-owned prototype is discussed. The socalled gap sampler is a pin-based sampler for miniaturized flow injection (FI) analysis. To date, it has been used in various applications. Following proof of concept applications with FI of small molecules, pin modifications were implemented for unspecific and specific extraction for the analysis of complex samples. Most recently, further optimization allowed the study of non-covalent protein-ligand interactions for bioaffinity screenings, which constitutes a major milestone in the development of this novel high-throughput autosampler.