Hybrid Microfluidic Research Articles

Compound Droplet Generation by a Hybrid Microfluidic Device.

Microfluidic technology based on a compound droplet plays an increasingly significant role in different disciplines, such as genetic detection, drug transportation, and cell culture. Low-cost, stable, and rapid methods to produce compound droplets are more and more in demand. In this paper, a hybrid 3D-printed microfluidic device was designed to realize efficient fabrication of multicore compound droplets, where a first oil phase (O1) is cut by a water phase (W) to form pure O1 droplets, and then the W phase containing O1 droplets is cut by a second oil phase (O2) to generate multicore compound droplets. A series of experiments were conducted to determine the influence of the flow rate and viscosity on the formation dynamics of compound droplets. It is found that the number of inner cores is mainly affected by the W and O2 phases, and a W phase with higher viscosity and a higher flow rate is more likely to produce compound droplets with more inner cores. This work provides new insights into the formation dynamics of compound droplets and can contribute to the optimization of emulsion production.

The Design and Investigation of Hybrid a Microfluidic Micromixer

Today, microfluidics has become a revolutionary interdisciplinary topic with considerable attention in a wide range of biotechnology applications. In this research work, a numerical investigation of a microfluidic micromixer is carried out using a hybrid actuation approach with different micropillar shapes and gaps. For this purpose, COMSOL Multiphysics v.5.2. is used with three different physics, such as thermoviscous acoustic physics to solve acoustic governing equations, laminar physics to solve fluid flow governing equations, and diluted transport species to solve mixing governing equations. The simulations were carried out at different Reynolds numbers such as 2, 4, 6, 8, 10, and 12 with an oscillation frequency of 15 kHz. The results were in the form of acoustic characteristics such as acoustic pressure, acoustic velocity, acoustic stream, mixing index, and fluid flow behaviour at various Reynolds numbers. The results revealed that the inclusion of micropillars improved the mixing performance and strength of the acoustic field, resulting in an improvement of the mixing performance compared to the case without micropillars. In addition, the mixing performance is also investigated at different Reynolds numbers, and a higher mixing index is investigated at lower Reynolds numbers. Moreover, it was also investigated that blade-shaped micropillars with 0.150 mm gaps deliver the best results compared to the other cases, and the maximum and minimum values of the mixing index are 0.97 and 0.72, respectively, at Reynolds number 2. The main reason behind this larger mixing index at low Reynolds numbers is due to the inclusion of micropillars that enhance the diffusion rate and contact area, leading to the homogenisation of the heterogeneous fluids in the microchamber. The obtained results can be extremely helpful for the design and modifications of a hybrid microfluidics micromixer.

Robust and Seamless Integration of Thiol‐Ene‐Epoxy Thermosets with Thermoplastics and Glass as Hybrid Microfluidic Devices Suitable for Drug Studies

AbstractFacile, durable and biocompatible integration of hybrid Lab‐on‐a‐Chip devices has remained an important challenge in microengineering. Here, the robust and seamless integration of off‐stoichiometry thiol‐ene‐epoxy (OSTE+) thermosets with a diverse range of thermoplastic and glass materials is demonstrated. While direct bonding offers sturdy proprieties for the majority of the material hybrids (up to 1.5 MPa), further surface priming enhances the bonding strength for those of lower surface energy (up to seven‐fold). Using microfluidic devices with a unique configuration of chambers and microchannels down to 100 µm, the impact of various bonding methods on their fluidic functionality is further shown. To investigate the utility of hybrid devices for pharmacological and toxicological studies, both pristine and primed devices are benchmarked against polydimethylsiloxane (PDMS) with regard to cell biocompatibility and drug absorption. While being on par with PDMS in terms of cell viability, pristine OSTE+ devices show an 11‐fold lower absorption of hydrophobic drug molecules. Although surface priming enhances the bonding strength, it compromises other criteria in device performance and biological applications. Combined, results demonstrate a novel integration approach for facile manufacturing of hybrid microfluidic devices using a material toolbox suitable for cell and pharmaceutical studies.

Enhancing fabrication of hybrid microfluidic devices through silane‐based bonding: A focus on polydimethylsiloxane‐cyclic olefin copolymer and PDMS‐lithium niobate

AbstractEffective manipulation and control of fluids in microfluidic channels requires robust bonding between the different components. Polydimethylsiloxane (PDMS) is widely employed in microchannel fabrication due to its affordability, biocompatibility, and straightforward fabrication process. However, PDMS's low surface energy poses challenges in bonding with many organic and inorganic substrates, hindering the development of hybrid microfluidic devices. In this study, a simple and versatile three step process is presented for bonding PDMS microchannels with organic (cyclic olefin copolymer (COC)) and inorganic substrates (lithium niobate (LiNbO3)) using plasma activation and a silane coupling agent. Initially, the PDMS surface undergoes oxygen/argon plasma activation, followed by functionalization with (3‐aminopropyl) triethoxysilane (APTES). Subsequently, the COC or LiNbO3 is plasma activated and brought into contact with PDMS under a load at a specific temperature. Characterization by Fourier transform infrared, scanning electron microscopy, atomic force microscopy, and contact angle measurements confirmed the successful treatment of the substrates. In addition, bonding strength of the fabricated hybrid devices was assessed through leakage and tensile tests. Under optimized conditions (100°C and 4% v/v APTES), PDMS‐COC hybrid microchannels achieved a flow rate of 600 mL/h without leakage and a tensile strength of 562 kPa. Conversely, the PDMS‐ LiNbO3 assembly demonstrated a flow rate of 216 mL/h before leakage, with a tensile strength of 334 kPa. This bonding method exhibits significant potential and versatility for various materials in microfluidic applications, ranging from biomedical research to enhanced oil recovery.

Inertial co-focusing of heterogeneous particles in hybrid microfluidic channels with constantly variable cross-sections.

Heterogeneous particles co-focusing to a single stream is a vital prerequisite for cell counting and enumeration, playing an essential role in flow cytometry and single-cell analysis. Microfluidics-based inertial focusing holds great research prospects due to its simplicity of devices, ease of operation, high throughput, and freedom from external fields. Combining microfluidic channels with two or more different geometries has become a powerful tool for high-efficiency particle focusing. Here, we explored hybrid microfluidic channels for heterogeneous particle co-focusing. Four different annular channels with obstacles distributed on the inner wall were constructed and simulated, obtaining constantly variable secondary flows. Then we used four different fluorescent particles with the size of 10 μm, 12 μm 15 μm, and 20 μm as well as their mixture to perform the inertial focusing experiments of multi-sized particles. Theoretical simulation and experimental results demonstrated a focusing efficiency of >99%. Finally, we further utilized human white blood cells to estimate the co-focusing performance of our hybrid microfluidic channel, resulting in a high focusing efficiency of >92% and a high throughput of ≈8000 cell s-1. The hybrid microfluidic channels, capable of high-precision heterogeneous particle co-focusing, could pave a broad avenue for microfluidic flow cytometry and single-cell analysis.

A novel microfluidics PMMA/paper hybrid bioimmunosensor for laser-induced fluorescence detection in the determination of alpha-fetoprotein from serum

Low loss and high capture efficiency of target samples are prerequisites for sensitive detection by fluorescence immunosensors. For quantitative and ultrasensitive detection of alpha-fetoprotein (AFP), we designed a novel microfluidics pump-free PMMA/paper hybrid immunosensor. Here, the 2D planar structure of the detection area of the plastic microfluidic chip is improved to a 3D spatial structure, which increases the number of capture antibodies immobilized and the cross-section area of the “intercept” target protein. PMMA channels efficiently transport target proteins. The paper-based, three-dimensional detection area not only increases the amount of immobilization of the captured antibody but also improves the contact probability between the captured antibody and the target protein. This greatly improves the efficiency of immune binding. A laser-induced fluorescence detector is applied to detect the target protein on the paper-based detecting unit. Under optimal conditions, the immunosensor ensures that the reaction time is 12 min and the residual liquid is only 6.1% of the original volume, achieving ultra-sensitive detection of AFP in the range of 0.01 ng/mL to 100 ng/mL with a limit of quantitation (LOQ) as low as 4.5 pg/mL. The recoveries for AFP ranged from 96.6% to 101.5%, which means the hybrid microfluidics chip is reliable and has great potential for early screening.

A PDMS-Agar Hybrid Microfluidic Device for the Investigation of Chemical-Mechanical Associative Learning Behavior of C. elegans.

Associative learning is a critical survival trait that promotes behavioral plasticity in response to changing environments. Chemosensation and mechanosensation are important sensory modalities that enable animals to gather information about their internal state and external environment. However, there is a limited amount of research on these two modalities. In this paper, a novel PDMS-agar hybrid microfluidic device is proposed for training and analyzing chemical-mechanical associative learning behavior in the nematode Caenorhabditis elegans. The microfluidic device consisted of a bottom agar gel layer and an upper PDMS layer. A chemical concentration gradient was generated on the agar gel layer, and the PDMS layer served to mimic mechanical stimuli. Based on this platform, C. elegans can perform chemical-mechanical associative learning behavior after training. Our findings indicated that the aversive component of training is the primary driver of the observed associative learning behavior. In addition, the results indicated that the neurotransmitter octopamine is involved in regulating this associative learning behavior via the SER-6 receptor. Thus, the microfluidic device provides a highly efficient platform for studying the associative learning behavior of C. elegans, and it may be applied in mutant screening and drug testing.

Continuous CTC separation through a DEP-based contraction-expansion inertial microfluidic channel.

The efficient isolation of viable and intact circulating tumor cells (CTCs) from blood is critical for the genetic analysis of cancer cells, prediction of cancer progression, development of drugs, and evaluation of therapeutic treatments. While conventional cell separation devices utilize the size difference between CTCs and other blood cells, they fail to separate CTCs from white blood cells (WBCs) due to significant size overlap. To overcome this issue, we present a novel approach that combines curved contraction-expansion (CE) channels with dielectrophoresis (DEP) and inertial microfluidics to isolate CTCs from WBCs regardless of size overlap. This label-free and continuous separation method utilizes dielectric properties and size variation of cells for the separation of CTCs from WBCs. The results demonstrate that the proposed hybrid microfluidic channel can effectively isolate A549 CTCs from WBCs regardless of their size with a throughput of 300 μL/min, achieving a high separation distance of 233.4 μm at an applied voltage of 50 Vp-p . The proposed method allows for the modification of cell migration characteristics by controlling the number of CE sections of the channel, applied voltage, applied frequency, and flow rate. With its unique features of a single-stage separation, simple design, and tunability, the proposed method provides a promising alternative to the existing label-free cell separation techniques and may have a wide range of applications in biomedicine.

A Multifunctional Hybrid Graphene and Microfluidic Platform to Interface Topological Neuron Networks

AbstractThe nervous system is as complex as difficult to probe. Innovative tools reducing the network complexity and being able to interrogate neurons are crucial to better understand its function and organization. In this study, solution‐gated graphene field effect transistors (GFETs) are combined with multi‐compartment microfluidic platform for multimodal and long‐lasting recording of neuron electrical activity. The fluidic microchannels, somatic and synaptic chambers enable to define the neuron network topology, while the graphene devices provide localized, highly sensitive, and optically transparent sensing sites. Immunofluorescence staining assesses for the healthy state and outgrowth of neurons within the microfluidic circuit, while calcium imaging demonstrates the maturation and spontaneous activity of the designed network. The efficient cell‐sensor alignment obtained by the microfluidic circuit enables to reach the highest reported signal‐to‐noise ratio for single‐units detection with GFETs, revealing additional information that can remain hidden from recordings when using conventional microelectrode arrays. Thus, the combination of graphene sensors and microfluidic circuits leverages the advantages of two state‐of‐the‐art technologies for highly efficient sensing of model neural networks. Being fully transparent and therefore compatible with optogenetic tools and high‐resolution microscopy, this novel platform can provide a versatile lab‐on‐chip for diagnosis and treatment of tomorrow.

Hybrid Microfluidic Device for High Throughput Isolation of Cells Using Aptamer Functionalized Diatom Frustules

Circulating tumor cells (CTCs), secreted from primary and metastatic malignancies, hold a wealth of essential diagnostic and prognostic data for multiple cancers. Significantly, the information contained within these cells may hold the key to understanding cancer metastasis, both individually and fundamentally. Accordingly, developing ways to identify, isolate and interrogate CTCs plays an essential role in modern cancer research. Unfortunately, CTCs are typically present in the blood in vanishingly low titers and mixed with other blood components, making their isolation and analysis extremely challenging. Herein, we report the design, fabrication and optimization of a microfluidic device capable of automatically isolating CTCs from whole blood. This is achieved in two steps, via the passive viscoelastic separation of CTCs and white blood cells (WBCs) from red blood cells (RBCs), and subsequent active magnetophoretic separation of CTCs from WBCs. We detail the specific geometries required to balance the elastic and inertial forces required for successful passive separation of RBCs, and the use of computational fluid dynamics (CFD) to optimize active magnetophoretic separation. We subsequently describe the use of magnetic biosilica frustules, extracted from Chaetoceros sp. diatoms, to fluorescently tag CTCs and facilitate magnetic isolation. Finally, we use our microfluidic platform to separate HepG2-derived CTCs from whole blood, demonstrating exceptional CTC recovery (94.6%) and purity (89.7%)

Inertia-Acoustophoresis Hybrid Microfluidic Device for Rapid and Efficient Cell Separation.

In this paper, we proposed an integrated microfluidic device that could demonstrate the non-contact, label-free separation of particles and cells through the combination of inertial microfluidics and acoustophoresis. The proposed device integrated two microfluidic chips which were a PDMS channel chip on top of the silicon-based acoustofluidic chip. The PDMS chip worked by prefocusing the particles/cells through inducing the inertial force of the channel structure. The connected acoustofluidic chips separated particles based on their size through an acoustic radiation force. In the serpentine-shaped PDMS chip, particles formed two lines focusing in the channel, and a trifugal-shaped acoustofluidic chip displaced and separated particles, in which larger particles focused on the central channel and smaller ones moved to the side channels. The simultaneous fluidic works allowed high-efficiency particle separation. Using this novel acoustofluidic device with an inertial microchannel, the separation of particles and cells based on their size was presented and analyzed, and the efficiency of the device was shown. The device demonstrated excellent separation performance with a high recovery ratio (up to 96.3%), separation efficiency (up to 99%), and high volume rate (>100 µL/min). Our results showed that integrated devices could be a viable alternative to current cell separation based on their low cost, reduced sample consumption and high throughput capability.

A Hybrid Spiral Microfluidic Platform Coupled with Surface Acoustic Waves for Circulating Tumor Cell Sorting and Separation: A Numerical Study.

The separation of circulating tumor cells (CTCs) from blood samples is crucial for the early diagnosis of cancer. During recent years, hybrid microfluidics platforms, consisting of both passive and active components, have been an emerging means for the label-free enrichment of circulating tumor cells due to their advantages such as multi-target cell processing with high efficiency and high sensitivity. In this study, spiral microchannels with different dimensions were coupled with surface acoustic waves (SAWs). Numerical simulations were conducted at different Reynolds numbers to analyze the performance of hybrid devices in the sorting and separation of CTCs from red blood cells (RBCs) and white blood cells (WBCs). Overall, in the first stage, the two-loop spiral microchannel structure allowed for the utilization of inertial forces for passive separation. In the second stage, SAWs were introduced to the device. Thus, five nodal pressure lines corresponding to the lateral position of the five outlets were generated. According to their physical properties, the cells were trapped and lined up on the corresponding nodal lines. The results showed that three different cell types (CTCs, RBCs, and WBCs) were successfully focused and collected from the different outlets of the microchannels by implementing the proposed multi-stage hybrid system.

Analytical Study of the Electroosmotic Flow of Two Immiscible Power-Law Fluids in a Microchannel

The multilayer microchannel flow is a promising tool in microchannel-based systems such as hybrid microfluidics. To assist in the efficient design of two-liquid pumping system, a two-fluid electroosmotic flow of immiscible power-law fluids through a microtube is studied with consideration of zeta potential difference near the two-liquid interface. The modified Cauchy momentum equation in cylindrical coordinate governing the two-liquid velocity distributions is solved where both peripheral and inner liquids are represented by power-law model. The two-fluid velocity distribution under the combined interaction of power-law rheological effect and circular wall effect is evaluated at different viscosities and different electroosmotic characters of inner and peripheral power-law fluids. The velocity of inner flow is a function of the viscosities, electric properties and electroosmotic characters of two power-law fluids, while the peripheral flow is majorly influenced by the viscosity, electric property and electroosmotic characters of peripheral fluid. Irrespective of the configuration manner of power-law fluids, the shear thinning fluid is more sensitive to the change of other parameters.

Study of the Fabrication Technology of Hybrid Microfluidic Biochips for Label-Free Detection of Proteins.

A study of the peculiarities and a comparative analysis of the technologies used for the fabrication of elements of novel hybrid microfluidic biochips for express biomedical analysis have been carried out. The biochips were designed with an incorporated microfluidic system, which enabled an accumulation of the target compounds in a biological fluid to be achieved, thus increasing the biochip system’s sensitivity and even implementing a label-free design of the detection unit. The multilevel process of manufacturing a microfluidic system of a given topology for label-free fluorometric detection of protein structures is presented. The technological process included the chemical modification of the working surface of glass substrates by silanization using (3-aminopropyl) trimethoxysilane (APTMS), formation of the microchannels, for which SU-8 technologies and a last generation dry film photoresist were studied and compared. The solid-state phosphor layers were deposited using three methods: drop application; airbrushing; and mechanical spraying onto the adhesive surface. The processes of sealing the system, installing input ports, and packaging using micro-assembly technologies are described. The technological process has been optimized and the biochip was implemented and tested. The presented system can be used to design novel high-performance diagnostic tools that implement the function of express detection of protein markers of diseases and create low-power multimodal, highly intelligent portable analytical decision-making systems in medicine.

Technology for Formation of Hybrid Microfluidic Biosensor Systems for Label-Free Fluorimetric Express Detection of Protein Structures based on Molecular Recognition

The development and comparative study of technologies for manufacturing elements of hybrid biosensor systems intended for express biomedical analysis has been carried out. The technological process included the formation of the relief of microfluidic channels, chemical modification of their working surface, deposition of solid-state phosphor layers, sealing of the system, installation of inlet ports and packaging.

A microfluidic device for label-free separation sensitivity enhancement of circulating tumor cells of various and similar size

Due to the heterogeneity in the size of circulating tumor cells (CTCs), label-free, high-throughput, and efficient separation of CTCs for post-processing analysis is challenging. Recent advances in hybrid microfluidics have demonstrated enormous potential for the separation of complex samples. This paper presents a hybrid microfluidic platform for label-free cell separation that utilizes a cascade deterministic lateral displacement (DLD) array in conjunction with a traveling wave dielectrophoresis (twDEP) system. CTC clusters and red blood cells are separated from the blood sample in the cascade DLD unit. Other white blood cells (WBCs) and CTCs are classified according to their diameters, ranging from 10 to 15 µm, 15 to 20 µm, and 20 to 25 µm. Each category is connected via an outlet to a twDEP unit to separate CTCs from WBCs (even the same size cells). Our proposed structure outperforms conventional designs. Among them are the uniform pressure distribution at the DLD unit's outlets and the cell viability in the twDEP unit. The effect of flow rate and Reynolds number on the separation dynamics of a cascade DLD unit is investigated in this study, as is surveyed the effect of flow rate and variation in the applied voltage to the array of electrodes on the recovery rate of the twDEP units. According to numerical simulations, a recovery rate of nearly 93% for MDA-MB-231 cells spiked into the blood sample is achievable, which is a high recovery rate for systems that can separate cells of the same and different sizes.

Electrochemical Evaluation of Rhus Vernicifera Biocathodes for Oxygen Reduction Reaction in Neutral Media with Application in Air-Breathing Hybrid Microfluidic Fuel Cells

In this work, a Rhus vernicifera laccase electrodes (RvL-Vulcan/Toray and RvL-ABTS-Vulcan/Toray) were prepared by adsorption method and evaluated toward oxygen reduction reaction by cyclic voltammetry. The characterization was complemented by FTIR with ATR, these results indicates the presence of bands corresponding to the presence of enzymatic material for both electrodes and ABTS in the RvL-ABTS-Vulcan/Toray. The biocathodes were evaluated in an air-breathing microfluidic fuel cell reported previously by our group. For these experiments, a hybrid air-breathing microfluidic fuel cell configuration was constructed by an Au-Vulcan/Toray anode and 5 mM Glucose/0.3 M KOH as anolyte and the RvL-Vulcan/Toray and RvL-ABTS-Vulcan/Toray as biocathodes and PBS 7 as catholyte solution. The results showed that the RvL-ABTS-Vulcan/Toray 16 mWcm-2 performance was better than RvL 3.4 mWcm-2. This result it is attributed to the presence of ABTS in the material inmobilized.

Diffusion-Convection Hybrid Microfluidic Platform for Rapid Antibiotic Susceptibility Testing.

Conventional antibiotic susceptibility testing (AST) assays such as broth microdilution and Kirby-Bauer disk diffusion are time-consuming (e.g., 24-72 h) and labor-intensive. Here, we present a microfluidic platform to perform AST assays with a broad range of antibiotic concentrations and controls. A culture medium stream was serially enriched with antibiotics along the length of the platform via diffusion and flow-directing mass convection mechanisms, generating a concentration gradient captured in a series of microchamber duplicates. We observed an agreement between the simulated and experimental concentration gradients and applicability to a variety of different molecules by changing the loading time according to a simple linear equation. The AST assay in our platform is based on bacterial metabolism, indicated by resazurin fluorescence. The small reaction volume enabled a minimum inhibitory concentration (MIC) to be determined in 4-5 h. Proof-of-concept functionality testing, using human isolates and clinically important antibiotics from different classes, indicated a high rate of agreement (94%: MIC within ±1 two-fold dilution of the reference method) of on-chip MICs and conventional broth microdilution. Overall, our results showed that this microfluidic platform is capable of determining antibiotic susceptibility in a rapid and reliable manner.

A simple and low-cost approach for irreversible bonding of polymethylmethacrylate and polydimethylsiloxane at room temperature for high-pressure hybrid microfluidics

Microfluidic devices have been used progressively in biomedical research due to the advantages they offer, such as relatively low-cost, rapid and precise processing, and an ability to support highly automated analyses. Polydimethylsiloxane (PDMS) and polymethylmethacrylate (PMMA) are both biocompatible materials widely used in microfluidics due to their desirable characteristics. It is recognized that combining these two particular materials in a single microfluidic device would enable the development of an increasingly in-demand array of new applications, including those requiring high flow rates and elevated pressures. Whereas complicated and time-consuming efforts have been reported for bonding these two materials, the robust adhesion of PDMS and PMMA has not yet been accomplished, and remains a challenge. In this study, a new, simple, efficient, and low-cost method has been developed to mediate a strong bond between PMMA and PDMS layers at room temperature in less than 5 min using biocompatible adhesive tape and oxygen plasma treatment. The PDMS–PMMA bond was hydrolytically stable, and could tolerate a high influx of fluid without any leakage. This study addresses the limitations of existing approaches to bond these materials, and will enable the development of highly sought high-pressure and high-throughput biomedical applications.

Design and Operation of Hybrid Microfluidic Iontronic Probes for Regulated Drug Delivery

AbstractHighly controlled drug delivery devices play an increasingly important role in the development of new neuroengineering tools. Stringent—and sometimes contradicting—demands are placed on such devices, ranging from robustness in freestanding devices, to overall device miniaturization, while maintaining precise spatiotemporal control of delivery with high chemical specificity and high on/off ratio. Here, design principles of a hybrid microfluidic iontronic probe that uses flow for long‐range pressure‐driven transport in combination with an iontronic tip that provides electronically fine‐tuned pressure‐free delivery are explored. Employing a computational model, the effects of decoupling the drug reservoir by exchanging a large passive reservoir with a smaller microfluidic system are reported. The transition at the microfluidic‐iontronic interface is found to require an expanded ion exchange membrane inlet in combination with a constant fluidic flow, to allow a broad range of device operation, including low source concentrations and high delivery currents. Complementary to these findings, the free‐standing hybrid probe monitored in real time by an external sensor is demonstrated. From these computational and experimental results, key design principles for iontronic devices are outlined that seek to use the efficient transport enabled by microfluidics, and further, key observations of hybrid microfluidic iontronic probes are explained.