Concentration Gradient Generator Research Articles

Development and customization of a concentration gradient microgenerator by extrusion 3D printing for drug testing in laboratory studies

A crucial step in creating reliable in vitro high-throughput screening technology platforms for the effect of pharmaceutical/chemical studies is the development of microfluidic systems. The power of concentration gradient generators in microfluidic systems could be harnessed to rapidly screen and investigate the mechanisms underlying the effects of pharmaceutical or chemical compounds on various disease models. A challenge of the current concentration gradient generator is the difficulty of fabricating them by common research laboratories. In order to overcome this challenge, additive manufacturing process as 3D printing can be utilized to produce customizable complex 3D structures using a layer-by-layer process. We developed a concentration gradient generator 3D printed on a tissue culture plate as a simplified strategy for in vitro pharmaceutical/chemical testing. The bottom layers used to print the concentration gradient microgenerators are regular culture plates used in common research laboratories. A Christmas tree-like network microfluidic channel was printed on the culture plate and generate a concentration gradient flow. The microfluidic network was printed on culture plates made from different cell culture plastic materials. The printed gradient generator was validated for drug testing function on cells. Our 3D printed concentration gradient microgenerators could provide a simplified strategy for common research laboratories to access microfluidic in vitro drug high-throughput screening technology.

Piezoresistive Effect with a Gauge Factor of 18 000 in a Semiconductor Heterojunction Modulated by Bonded Light-Emitting Diodes.

Giant piezoresistive effect enables the development of ultrasensitive sensing devices to address the increasing demands from hi-tech applications such as space exploration and self-driving cars. The discovery of the giant piezoresistive effect by optoelectronic coupling leads to a new strategy for enhancing the sensitivity of mechanical sensors, particularly with light from light-emitting diodes (LEDs). This paper reports on the piezoresistive effect in a 3C-SiC/Si heterostructure with a bonded LED that can reach a gauge factor (GF) as high as 18 000. This value represents an approximately 1000 times improvement compared to the configuration without a bonded LED. This GF is one of the highest GFs reported to date for the piezoresistive effect in semiconductors. The generation of carrier concentration gradient in the top thin 3C-SiC film under illumination from the LED coupling with the tuning current contributes to the modulation of the piezoresistive effect in a 3C-SiC/Si heterojunction. In addition, the feasibility of using different types of LEDs as the tools for modulating the piezoresistive effect is investigated by evaluating lateral photovoltage and photocurrent under LED's illumination. The generated lateral photovoltage and photocurrent are as high as 14 mV and 47.2 μA, respectively. Recent technologies for direct bonding of micro-LEDs on a Si-based device and the discovery reported here may have a significant impact on mechanical sensors.

Liver-lobule-mimicking patterning via dielectrophoresis and hydrogel photopolymerization

Patterning and cultivating heterogeneous cells on microfluidic chips is essential for engineering tissue regeneration. Current patterning technologies focus mainly on positioning cells at specific locations, but most do not mimic in-vivo cell patterns. Even few papers and reports care about maintaining cell patterns after the patterning process and several days of culture. Here, we report a liver-lobule-mimicking labchip consisting of three components: the concentration gradient generator, the dielectrophoretic cell-patterning, and four cell-culturing chambers providing culturing microenvironment. NIH/3T3 (fibroblast cell) and C3A cells (human hepatocyte) were patterned via dielectrophoresis to reconstruct the liver-lobule’s radial actinomorphic organization and pattern at each cell-culture chamber. Subsequently, GelMA at different concentrations was perfused to form GelMA culturing-microenvironment coverings with different concentrations of 5 %, 10 %, 15 % GelMA and 0 % GelMA for the control group. Cell viability was maintained 95 % at 5 % GelMA chamber after cultured for 72 h. For the 15 % GelMA chamber, cell viability was 78 % on 72-hrs culturing. Urea assays revealed that the co-cultured cells in 5 % GelMA maintained the high activity, which has the highest urea secretion, with the preserved biomimicking liver-lobule pattern compared with other culturing-microenvironments. By cultivating cells in our liver-lobule-mimicking labchip with cellular micropatterning and hydrogel covering, the liver-lobule-like cell pattern was not affected by the difference in cell growth rate and the streamline of the perfused culture medium. We also observed that the appropriate GelMA culturing-microenvironment not only preserves the biomimicking liver-lobule pattern but also enhances liver function related to urea production.

Integrating a Concentration Gradient Generator and a Single-Cell Trapper Array for High-Throughput Screening the Bioeffects of Nanomaterials.

We herein develop a concentration gradient generator (CGG) on a microfluidic chip for diluting different nanoparticles. Specifically designed compact disk (CD)-shaped microchannels in the CGG module could thoroughly mix the flowing solutions and generate a linear concentration gradient of nanoparticles without aggregation. We combine the CGG with a single-cell trapper array (SCA) on microfluidics to evaluate the concentration-dependent bioeffects of the nanoparticles. The precise control of the spatiotemporal generation of nanoparticle concentration on the CGG module and the single-cell-level monitoring of the cell behaviors on the SCA module by a high-content system in real time, render the CGG-SCA system a highly precise platform, which can exclude the average effect of cell population and reflect the response of individual cells to the gradient concentrations accurately. In addition, the CGG-SCA system provides an automated platform for high-throughput screening of nanomedicines with high precision and low sample consumption.

Integrating a Concentration Gradient Generator and a Single‐Cell Trapper Array for High‐Throughput Screening the Bioeffects of Nanomaterials

AbstractWe herein develop a concentration gradient generator (CGG) on a microfluidic chip for diluting different nanoparticles. Specifically designed compact disk (CD)‐shaped microchannels in the CGG module could thoroughly mix the flowing solutions and generate a linear concentration gradient of nanoparticles without aggregation. We combine the CGG with a single‐cell trapper array (SCA) on microfluidics to evaluate the concentration‐dependent bioeffects of the nanoparticles. The precise control of the spatiotemporal generation of nanoparticle concentration on the CGG module and the single‐cell‐level monitoring of the cell behaviors on the SCA module by a high‐content system in real time, render the CGG‐SCA system a highly precise platform, which can exclude the average effect of cell population and reflect the response of individual cells to the gradient concentrations accurately. In addition, the CGG‐SCA system provides an automated platform for high‐throughput screening of nanomedicines with high precision and low sample consumption.

An integrated microfluidic concentration gradient generator for mechanical stimulation and drug delivery

Mechanical stimuli, including fluid shear stress, osmotic pressure gradient, and extracellular matrix stiffness, significantly affect cellular interactions with drugs in biological structures. This paper introduces an integrated concentration gradient generator (CGG) capable of providing cell monolayers with these stimuli and demonstrates its design, fabrication, and quantification procedures. The proposed multi-layer chip consists of a CGG integrated with a membrane-based cell culture chamber (MCCC) and two bubble trappers for removal of micro-bubbles. The CGG provides cultured cells in the MCCC with four different concentrations of desirable inlet drug/chemical reagents. The MCCC is able to impose adjustable shear stresses, as well as osmotic pressure gradients on cell monolayers. The stiffness of the extracellular matrix (ECM) is also accommodating by utilizing a proper membrane in the MCCC. A numerical simulation based on the finite element method (FEM) is employed to design and optimize the integrated device, and then, the chip's performance is quantified using the experimental data. Finally, the biocompatibility of the proposed device is investigated by dynamic culturing of human lung cancer cells (A549 cell line) on the chip.

A novel concentration gradient microfluidic chip for high-throughput antibiotic susceptibility testing of bacteria.

Antibiotic resistance has become a serious threat to food safety and public health globally. Therefore, the development of a sensitive, quick, and simple method for antibiotic susceptibility testing is an urgent and crucial need. A novel concentration gradient microfluidic chip was designed in this work to generate antibiotic concentration gradient, culture bacteria, and produce fluorescence emission. An in-house-assembled fluorescence detection platform was constructed, and experiments were conducted to verify the linearity of the generated concentration gradient, explore the appropriate incubation time and flow rate for the microfluidic chip, and study the effect of long-term acid-based food processing on antibiotic susceptibility testing. Experimental results show that the concentration gradient generated by the microfluidic chip exhibited good linearity, stability, and controllability. The appropriate flow rate and incubation time for the microfluidic chip were 2μL/min and 5 h, respectively. The use of this microfluidic chip for testing antibiotic resistance of Salmonella to ofloxacin and ampicillin generated results that were completely consistent with test results obtained using the gold-standard method. Furthermore, Salmonella showed greater sensitivity to antibiotics under strong acid conditions, confirming the potential influence of acid-based food processing on antibiotic susceptibility testing of real samples. The designed microfluidic chip provides a high-throughput, sensitive, and rapid antibiotic susceptibility testing method that combines the microfluidic chip and the fluorescence detection platform. The application of this method would facilitate determination of antibiotic-resistant bacterial strains for clinicians and researchers, and enable monitoring of changes in bacterial resistance during food processing.

Generation of flow and droplets with an ultra-long-range linear concentration gradient.

In the chemical and biological fields, the creation of concentration gradient microenvironments is an important approach for many applications, such as crystal growth and drug screening. Although many concentration gradient generators have been demonstrated, current generators can hardly produce ultra-long linear concentration gradients. In this paper, we propose a concentration-gradient flow/droplet generator which consists of a microfluidic flow switch, a cavity array for stage-by-stage concentration dilution, and an optional T-junction for droplet formation. The generator can realize an ultra-long continuously-varying concentration gradient along the flow direction. Generation of a 38 mm concentration gradient was demonstrated. The length can be further extended by enlarging the capacity of the cavities and increasing the number of the stages. The concentration gradient showed high linearity in the range of 10% to 90%. Moreover, cyclic generation of a concentration gradient flow and droplets with different concentrations was realized by the generator. In a demonstration of drug screening, the generator was employed to produce paclitaxel in different concentrations. A negative correlation between the 4T1 cell viability and the paclitaxel concentration was observed after the treatment. We envision that the concentration gradient generator will be a promising candidate for various drug screening applications.

Maternal Inositol Status and Neural Tube Defects: A Role for the Human Yolk Sac in Embryonic Inositol Delivery?

ABSTRACTSupplementation with myo-inositol during the periconceptional period of pregnancy may ameliorate the recurrence risk of having a fetus affected by a neural tube defect (NTD; e.g., spina bifida). This could be of particular importance in providing a means for preventing NTDs that are unresponsive to folic acid. This review highlights the characteristics of inositol and describes the role of myo-inositol in the prevention of NTDs in rodent studies and the evidence for its efficacy in reducing NTD risk in human pregnancy. The possible reduction in NTD risk by maternal myo-inositol implies functional and developmentally important maternal–embryonic inositol interrelationships and also suggests that embryonic uptake of myo-inositol is crucial for embryonic development. The establishment of active myo-inositol cellular uptake mechanisms in the embryonic stages of human pregnancy, when the neural tube is closing, is likely to be an important determinant of normal development. We draw attention to the generation of materno-fetal inositol concentration gradients and relationships, and outline a transport pathway by which myo-inositol may be delivered to the early developing human embryo. These considerations provide novel insights into the mechanisms that may underpin inositol's ability to confer embryonic developmental benefit.

Affordable, high-resolution bioprinting with embedded concentration gradients

Three-dimensional (3D) bioprinting has brought major innovations to the field in its ability to fabricate cell-laden constructs that closely resemble physiological tissue. Unfortunately, many bioprinters print only one material and at limited resolutions. Improving on the resolutions, functionality, and affordability necessitates attention to both printing techniques and printers. Here, we present our results towards building an affordable, partially open-source bioprinter, ModiPrint, that enables multiple cell-material combination printing with high resolution extrusions (100 ​μm) of alginate. We also introduce a new technique to improve extrusion resolution in complex geometries. The results show that we were able to maintain viability of human pluripotent stem cells (hiPSCs) after high resolution printing. Lastly, we were able to generate concentration gradients of small molecules or cytokines embedded within hydrogels by combining extrusion and drop-on-demand bioprinting. We expect ModiPrint and the novel techniques in our study will assist other bioprinting researchers.

Simulation and experimental investigation on the circular concentration gradient generator

This article introduced a specific design and an effective, low-cost production method of the concentration gradient generator. It can generate different concentration at eight outlets. Deep research on the position of inlet and the flow velocity of inlet were carried to study the effect on generating concentration gradient. The position of the entrance firstly was discussed. Then a variety of different concentration gradient profiles with different flow velocity were got. When the flow velocity of two inlets is 10−5m/s, the effect of concentration gradient curves is the best. The resulting concentration gradient changes when the flow velocity of the two inlets is out of step. In addition, the construction of the grid is also important in simulation. By comparing the concentration curves with different grid numbers, the grid number of concentration gradient generator is finally set to 5105969. The concentration gradient generators were fabricated using Polymethyl-methacrylate (PMMA) by CO2 laser machine and thermocompressor. Finally, the feasibility of simulation was clearly verified by a mixing experiment with blue ink and yellow ink. This simple microfluidic device can help the study of high-throughput concentration gradient applications such as cell biology of chemotaxis or hypotaxis.

3D microfluidic gradient generator for combination antimicrobial susceptibility testing

Microfluidic concentration gradient generators (µ-CGGs) have been utilized to identify optimal drug compositions through antimicrobial susceptibility testing (AST) for the treatment of antimicrobial-resistant (AMR) infections. Conventional µ-CGGs fabricated via photolithography-based micromachining processes, however, are fundamentally limited to two-dimensional fluidic routing, such that only two distinct antimicrobial drugs can be tested at once. This work addresses this limitation by employing Multijet-3D-printed microchannel networks capable of fluidic routing in three dimensions to generate symmetric multidrug concentration gradients. The three-fluid gradient generation characteristics of the fabricated 3D µ-CGG prototype were quantified through both theoretical simulations and experimental validations. Furthermore, the antimicrobial effects of three highly clinically relevant antibiotic drugs, tetracycline, ciprofloxacin, and amikacin, were evaluated via experimental single-antibiotic minimum inhibitory concentration (MIC) and pairwise and three-way antibiotic combination drug screening (CDS) studies against model antibiotic-resistant Escherichia coli bacteria. As such, this 3D µ-CGG platform has great potential to enable expedited combination AST screening for various biomedical and diagnostic applications.

Tradeoff Control of Multi-exposure Lithography for SU-8 Photochemical Reaction Channel Formation

A method involving multi-exposure with low-power is presented to fabricate an SU-8 mold based on a digital micromirror device (DMD) maskless lithography with an LED source at a wavelength of 405 nm. The SU-8 mold is used for the fabrication of a PDMS concentration gradient generator (CGG). During a one-time exposure, it is easy to over-expose at the top and under-expose at the bottom of a thick SU-8, which then forms a T-shaped structure. This is more obvious for high-absorption coefficients such as 365 nm. We found that by taking advantage of the partially absorbed and partially transmissive characteristics of the 405-nm wavelength, multi-exposure can form an effective photochemical reaction channel in SU-8 and can solve the problem mentioned above. However, excessive exposure will cause the linewidth to increase, therefore, it is necessary to find a tradeoff for the number of multi-exposure times. For a 55-µm thick SU-8, the tradeoff threshold is found to be 25. Three types of SU-8 CGG molds were fabricated at this threshold. The results indicate that the actual profile of the SU-8 mold shows good agreement with the design profile without any T-shaped structures.

Adhesive tape-assisted etching of silk fibroin film with LiBr aqueous solution for microfluidic devices

The regenerated silk fibroin (RSF)-based microfluidic device has attracted tremendous interests in recent years due to its excellent biocompatibility, mild processing conditions, and all aqueous casting production. However, the need of a micro-fabricated mold in the manufacture process greatly hinder its practical applications. Herein, we introduce an adhesive tape-assisted etching method with LiBr solution as the etchant to prepare RSF microfluidic devices. An engraved adhesive tape is used as the mask to cover on the surface of a RSF film. Then, LiBr solution is dropped on the mask to etch RSF in concentration- and duration-dependent manners. During this process, the LiBr-treated RSF transits from insoluble β-sheet crystallites to soluble conformations. The as-prepared RSF microfluidic devices possess good chemical resistance and excellent tolerance to mechanical deformation. RSF microfluidic systems with different patterns were fabricated to demonstrate the universality of the approach. A concentration gradient generator and a blood vessel-like channel were manufactured for the preparation of solutions with gradient pHs and the growth of living cells, respectively. The proposed strategy has great potentials in the facile fabrication of low-cost RSF microfluidic devices for tissue engineering and biomedical analysis.

Multiplex measurement of diffusion in zinc battery electrolytes from microfluidics using Raman microspectroscopy

Rechargeable zinc batteries have emerged as an inexpensive and safe post-lithium-ion battery technology and have received increasing research interest. Developing suitable electrolytes and understanding their transport properties lie at the heart of successful zinc battery technologies as the battery behaviour is a strong function of ion transport in the electrolytes. To accelerate the research and development process, herein we demonstrate a low-cost and high-throughput approach to measure the diffusion in zinc electrolytes at different concentrations simultaneously. The new approach combines Raman microspectroscopy and a multiplexed microfluidic chip with integrated micromixers, concentration gradient generators and a Y-sensor array. Aqueous-based zinc sulphate electrolytes, widely used in zinc batteries, were used for a proof-of-concept. The measured diffusion coefficients for different electrolyte concentrations show good agreement with literature values. With four electrolyte samples in this study, the developed approach requires minimum 0.5 mL of the electrolyte solutions and 30 mins, which is over ten times faster than a typical diffusion measurement with the conventional electrochemical approach in restricted-diffusion cells. The microfluidic chip is readily scalable to further increase the throughput, and can be extended to for use of measuring different (i.e. organic and aqueous) and even mixtures of electrolytes (i.e. ethylene carbonate and dimethyl carbonate) as well as salts (Li+, Na+, Mg2+, etc.).

A Concentration Gradients Tunable Generator with Adjustable Position of the Acoustically Oscillating Bubbles.

It is essential to control concentration gradients at specific locations for many biochemical experiments. This paper proposes a tunable concentration gradient generator actuated by acoustically oscillating bubbles trapped in the bubble channels using a controllable position based on the gas permeability of polydimethylsiloxane (PDMS). The gradient generator consists of a glass substrate, a PDMS chip, and a piezoelectric transducer. When the trapped bubbles are activated by acoustic waves, the solution near the gas–liquid interface is mixed. The volume of the bubbles and the position of the gas–liquid interface are regulated through the permeability of the PDMS wall. The tunable concentration gradient can be realized by changing the numbers and positions of the bubbles that enable the mixing of fluids in the main channel, and the amplitude of the applied voltage. This new device is easy to fabricate, responsive, and biocompatible, and therefore has great application prospects. In particular, it is suitable for biological research with high requirements for temporal controllability.

Multichannel Synchronous Hydrodynamic Gating Coupling with Concentration Gradient Generator for High-Throughput Probing Dynamic Signaling of Single Cells.

Cell signaling greatly affected by complicated and temporally dynamic extracellular microenvironments controls most of the physiological functions in vivo. To reconstruct or simulate such microenvironments in vitro represents a fundamental approach for revealing the underlying mechanisms of those sophisticated processes. Recent advances in microfluidics have added a new dimension to cell signaling analysis, for example, concentration gradient generators (amplitude aspect) or hydrodynamic gating strategy (frequency aspect), but it is still challengeable to capture single-cell dynamic signaling in response to a mimicked extracellular microenvironment with varied stimuli waveforms of different amplitude and frequency in a high-throughput manner. In this article, we proposed a novel microfluidic strategy coupling multichannel synchronous hydrodynamic gating with microfluidic concentration gradient generators (μMHG-CGG) to probe dynamic signaling of single cells with high throughput. The μMHG-CGG allows rapid delivery of dynamic chemical signals in both high frequency (as high as 670 mHz) and multiple amplitude domains at the same time and simultaneously high-throughput probing cell dynamics at single-cell resolution in real time. By applying the proposed system, the mechanisms for encoding/decoding systems (termed "frequency coding" or "amplitude coding") via GPCRs-mediated signaling pathways responding to histamine (HA) and adenosine triphosphate (ATP) in single HeLa cells were investigated. The optimal drug concentrations of single cells responses to HA and ATP individually or in combination were also successfully discussed, allowing us to obtain both single-cell heterogeneity and statistics from the cell population.

Non-Newtonian effects on the slip and mobility of a self-propelling active particle

Abstract

A microfluidic concentration gradient generator for simultaneous delivery of two reagents on a millimeter-sized sample

Microfluidic concentration gradient generators (μCGGs) are indispensable parts of many emerging lab-on-a-chip platforms for biological studies and drug delivery applications. Most of the μCGGs reported in the literature can only generate the desired concentration gradients in a micron-sized sample (e.g., cells). As such, there is an unmet need to design a μCGG that can generate continuous concentration gradients of multi reagents (e.g., drugs) in a millimeter-sized sample (e.g., tissue). Herein, we report the proof-of-concept of this class of μCGG by combining a modified tree-like CGG with a micromixer. By conducting both experimental investigation and numerical analysis, we show that the proposed device can generate a continuous concentration gradient of two reagents and deliver all the possible combinations of their concentrations to a millimeter-sized sample. The proposed device can be used in a broad range of applications, especially ex-vivo drug chemosensitivity testing in personalized medicine.

Inverse design of microfluidic concentration gradient generator using deep learning and physics-based component model

This paper presents a new paradigm of deep neural network (DNN) for the inverse design of microfluidic concentration gradient generators (µCGGs) with complex network topology. In this method, a concentration gradient (CG) and design parameters yielding the CG are, respectively, used as inputs and outputs of DNN, and the relationship between them is mapped. Several new elements are also proposed, including utilization of fast-running physics-based component model in the closed form to generate a large amount of data for DNN learning which otherwise is not available through computationally demanding computational fluid dynamics (CFD) simulation; and a divide-and-conquer strategy and DNN formulation combining classification and regression to mitigate many-to-one design complications for enhanced accuracy. Several DNN structures are investigated and developed, including single fully connected neural network (FCNN), convolutional neural network, and a new cascade FCNN for a divide-and-conquer implementation. Case studies are performed on a triple-Y µCGG to evaluate design performance of the proposed method in a six-dimensional space that only includes sample concentrations at inlet reservoirs as design parameters, and in a nine-dimensional design space, to which inlet flow pressures are also added. It is verified in high-fidelity CFD simulation that widely used CGs can be produced using DNN-predicted design parameters accurately with average error < 4% and < 8.5% relative to the prescribed CGs, respectively, in the six- and nine-dimensional design space. The learned design rules are packaged into the DNN model that allows to generate accurate µCGGs designs instantaneously (~ 3 ms) and eliminates requirements of simulation and optimization knowledge, facilitating distribution of the design capabilities to microfluidic end users.