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What is the purpose of eletrowetting on microfluidic chips?

What is the purpose of eletrowetting on microfluidic chips?



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I am doing a college BioMed project to make disease models and I have seen that Electrowetting-on-dielectric chips (EWOD) are widely used in the making of organs-on-a-chip, but I have yet to understand its advantages over continous-flow or droplet-based microfluidics.


Electrowetting Behavior and Digital Microfluidic Applications of Fluorescent, Polymer-Encapsulated Quantum Dot Nanofluids

Digital microfluidics is a liquid-handling technology capable of rapidly and autonomously controlling multiple discrete droplets across an array of electrodes and has seen continual growth in the fields of chemistry, biology, and optics. This technology is enabled by rapidly switching the wettability of a surface through the application of an electric field: a phenomenon known as electrowetting-on-dielectric. The results reported here elucidate the wetting behavior of fluorescent quantum dot nanofluids by varying the aqueous-solubilizing polymers, changing the size of the nanocrystals, and the addition of surfactants. Nanofluid droplets were demonstrated to have very large changes in contact angle (>100°) by employing alternating current voltage to aqueous droplets within a dodecane medium. The stability of quantum dot nanofluids is also evaluated within a digital microfluidics platform, and the optical properties are not perturbed even under high voltages (250 V). Multiple fluorescent droplets with varying emission can be simultaneously actuated and rapidly mixed (<10 s) to generate a new nanofluid with optical properties different from the parent solutions.

Keywords: colloids digital microfluidics electrowetting interfaces lab on a Chip optoelectronics quantum dots.


What is the purpose of eletrowetting on microfluidic chips? - Biology

Figure 1: (A) Cerenkov radiation (faint blue light) is produced when energetic particles travel through a medium faster than the speed of light in that medium. This image shows the reactor core of the Advanced Test Reactor (Source). (B) Cerenkov radiation is emitted as positrons decay within a microfluidic chip. (C) Photograph of a PDMS microfluidic chip. (D) Cerenkov image of the same chip when filled with radioactive solution.

The standard analytical tools of the radiochemistry lab, namely the dose calibrator, radio-HPLC, and radio-TLC, do not permit detailed study of what goes on inside microfluidic chips that handle radiolabeled compounds (e.g. synthesizer chips, assay chips, etc.).

Radio-TLC and radio-HPLC can only analyze the composition of radioactive species in liquids that can be removed from the chip. While this gives insights into the progress of radiochemical reactions, if radiolabeled substances are absorbed or adsorbed by the chip materials, they are not reflected in the chromatogram, and so it is necessary to be careful in the interpretation of the data. Furthermore, because the volume of microfluidic chips is so tiny, performing radio-TLC or radio-HPLC consumes a large portion of the liquid on the chip and often is an end-point measurement only.

Similarly, a dose calibrator measures only the total radioactivity in the whole chip at the time of measurement. In rare cases, if the chip can be disassembled during or after an experiment, the dose calibrator can also measure the radioactivity in different portions of the chip. Generally, however, it is not possible to track the amount of radioactivity in a specific part of a chip over time.

To solve these challenges, Dr. Arion Chatziioannou's group in the Crump Institute for Molecular Imaging at UCLA has developed a "radioactivity camera" based on the detection of Cerenkov radiation emitted by high-energy positrons travelling through nearby transparent materials such as solvent and the materials from which the microfluidic chip is made (see Figure 1) . Together we have been developing the system for in situ monitoring of processes involving radioisotopes (e.g., radiochemical synthesis) in microfluidic chips. This system is capable of near real-time imaging inside the chip at multiple time points, and can quantitate the amount of radioactivity in a selected region of interest (ROI) in the image for a variety of studies.


Abstract

When voltage is suddenly applied to vertical, parallel dielectric-coated electrodes dipped into a liquid with finite conductivity, the liquid responds by rising up to reach a new hydrostatic equilibrium height. On the microfluidic scale, the dominating mechanism impeding this electromechanically induced actuation appears to be a dynamic friction force that is directly proportional to the velocity of the contact line moving along the solid surface. This mechanism has its origin in the molecular dynamics of the liquid coming into contact with the solid surface. A simple reduced-order model for the rising column of liquid is used to quantify the magnitude of this frictional effect by providing estimates for the contact line friction coefficient. Above some critical threshold of voltage, the electromechanical force is clamped, presumably by the same mechanism responsible for contact angle saturation and previously reported static height-of-rise limits. The important distinction for the dynamic case is that the onset of the saturation effect is delayed in time until the column has risen more than about halfway to its static equilibrium height.


Supplementary files

A software-programmable microfluidic device for automated biology

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Anti-cancer drug screening and nano-drug preparation

Anti-cancer drug screening on microfluidic chip

According to the culture modes, the microfluidic models for drug screening are categorized as single cell line culture, multi-cell line culture to mimic TME and patient-derived tumor organoid. In addition to evaluating the efficacy, chemosensitivity and safety of a single drug, microfluidic chip can also provide patients with a reasonable drug combination regimen according to their own conditions. These functions allow the determination of specific types of drugs in advance for possible emergence of drug resistance.

Drug screening on microfluidic cancer models

Setting up a microphysiological system (Body-on-a-Chip) is one of the ways to screen drugs and determine the mode of administration. Inhalation therapy is an important treatment for lung diseases, in which drugs are inhaled directly to the desired sites with less drug accumulation at nontargeted sites [104]. A microfluidic platform with multi-organ and breathable lung chamber was reported for the screening and development of inhaled and intravenous drugs [105]. In this model, the lung compartment was linked with the liver and tumor compartment by channels. It is worth mentioning that researchers modified the traditional lung air-liquid interface (ALI) model and designed an “ALI bridge” to mimic lung breathing mechanisms (Figure 4a). Through the “ALI bridge”, the platform can confirm whether inhaled therapeutic drugs can be used for treating systemic disease. In addition, researchers used the improved hanging drop method to introduce several types of cells and create 3D structure of breast-cancer tumor [105]. Based on this platform, researchers can easily compare the cytotoxic effects of curcumin administered by intravenous injection and inhalation.

Utilizing patient derived tumor tissue for microfluidic-based chemo-sensitivity assay has become an important means for personalized therapy. Astolfi and colleagues described a method, named micro-dissected tissues (MDTs), in which patient derived tumor tissues were sectioned to submillimeter size [106]. MDTs were trapped by sedimentation in square-bottom wells, because trapping cells by sedimentation can shield MDTs from excessive shear stress and provide more stable environment for imaging and observation (Figure 4b). A high-grade serous ovarian cancer patient tissue sample was used to conducting drug screening on the chip. Compared with the clinical follow-up, it was found that the positive response measured by microfluidic chip in vitro was consistent with the clinical response of patient, indicating that the platform can identify potential responder [106].

In fact, the generation of quiescent microvascular networks always precedes the nascent tumors during tumorigenesis [107, 108], However, some studies showed that excessive tumor growth and insufficient vascular growth occurred when endothelial cells and tumor cells were seeded at the same time. By adjusting the seeding order of tumor and endothelial cells, Shirure et al. developed a patient-derived organoid microfluidic platform that can simultaneously test chemotherapeutics (such as paclitaxel) and anti-angiogenics (such as bevacizumab). After 7 days culture, the microvascular network was mature and patient-derived organoids were transplanted to the vicinity of the microvascular network, which reproduced the intravasation of tumor cells [109]. Moreover, through the microvascular networks, drug testing based on this platform better replicated the physiological delivery of drugs to tumor.

Drug screening in single-cell analysis

Anti-cancer drug screening by bionic microfluidic chip is often limited by the collective cell behaviors. Due to the hallmark of heterogeneity in tumor, various cell sub-populations exist in tumors, and some of them are the key factor for cancer metastasis, drug resistance and tumor relapse. Analysis focusing on each individual cell is increasingly important.

Considerable evidence suggests that microfluidic chip has become a state-of-the-art drug screening approach in the single-cell level. A variety of methods based on microfluidic devices have been developed for flexible use in the single-cell manipulation, such as: optical tweezers [110], droplets [111], magnetic beads [112], and deterministic lateral displacement (DLD) separation method [113]. Identifying tumor cells by electrical sensing modality (such as measuring cell impedance magnitude) [114, 115], Raman or fluorescence spectroscopy [116] and polymerase chain reaction (PCR) were developed.

Four microfluidic chip for anti-cancer drug screening a. a three-chamber microfluidic chip consists with a breathable lung compartment, which can better mimic lung breathing mechanisms and easily compare the cytotoxic effects of drug administered by intravenous injection and inhalation b. MDT was trapped by sedimentation in square-bottom wells to avoid excessive shear stress and obtain more stable imaging observation c. Each island of this microfluidic device was formed by gel that pumping out of the main channel and single cells were loaded into each island and maintained high viability d. dielectrophoresis (DEP)/impedance analysis (IA) chip was consists in this microfluidic platform, which can realize high-throughput single cell capture. a. Copyright Wiley, 2020. Reproduced with permission from reference [105] b. Copyright The Royal Society of Chemistry, 2015. Reproduced with permission from reference [106] c. Copyright The Royal Society of Chemistry, 2016. Reproduced with permission from reference [117] d. Copyright American Chemical Society, 2019. Reproduced with permission from reference [115].

(Click on the image to enlarge.)

For example, a microfluidics 3D gel-island chip was reported to isolate single cell, categorize the cancer cell state and detect single cell drug susceptibility. 3D gel-island was a 3D ECM cell culture environment and each island were formed by gel that pumping out of the main channel. Single cells were loaded into each island and maintained high viability (Figure 4c) [117]. Utilizing this device, researchers monitored the drug resistant behavior of cells with single cell resolution after treating doxorubicin and cisplatin. After the administration, breast cancer stem-like cells and non-stem-like cells shows different drug resistant behavior, in which stem-like cells were more resistant than non-stem-like cells [117]. This result indicated that drug sensitivity was correlated with the change of status of cells and confirmed the great potential of using microfluidic single cell analysis platform for anti-cancer drug screening.

Drug testing methods often require high sensitivity in screening drugs in specific cell population and monitor cell status in limited patients` tumor tissue sample or blood [118]. Aside from the costly label reagents, the expensive optical equipment and complex microfabricated channel structures, a new microfluidic device using patient biopsies for drug screening has attracted attentions. The biggest characteristic of this platform is the label-free capture and analysis of targeted cells in real-time. Using the powerful dielectrophoresis (DEP) technique, high-throughput cell capture can be simply performed (Figure 4d). In addition, real-time and continuous cellular behavior analysis generated thousands of data point for each therapeutic-cell interaction [115].

The preparation of nano-drugs

Some chemotherapeutic and imaging agents with low molecular weight cannot be retained effectively in blood and tumor. NPs are an excellent tool to attack the targeted cancer cells while retain in healthy tissues. The enhanced permeability and retention (EPR) effect allows solid tumors selectively accumulate NPs [119]. Small size NPs can passively accumulate in tumors according to EPR effect and can also actively bound to target cells by surface target ligand modification [120]. Nanomaterial encapsulation of drugs can reduce toxicity and achieve drug tolerance, while encapsulated imaging agents or modify fluorescent probe are contributed to diagnostics and biological distribution [121].

Compared with the classical batch technology, the microfluidic process are particularly appealing in the synthesis of nanomaterials and the preparation of nano-drugs [122]. Micromixer integrated with microfluidic chip provides an efficient mixture in a small length scale the precise control of temperature and kinetics ensure the uniformity of nano-drugs. In addition, microfluidic device can also satisfy the in-situ monitoring of NPs formation. For example, adjusting the flow rate ratio and different lipid components can precisely controlled the NPs size and surface properties [123]. Microfluidic devices are now capable of preparing a variety of NPs, including lipid-based nanobiomaterials [124-126], polymeric nanoparticles [127-129], lipid-polymer hybrid nanoparticles [130, 131] and engineered exosomes [132, 133].

Since the flow state of the fluid on microfluidic device is different from that of the turbulence in large-scale channels, its laminar flow state and mass transfer is completely dependent on diffusion [134]. Therefore, the mixing step on chip often needs external mechanism, such as electrokinetic [135, 136], magnetic [137, 138] and the special design of channel geometry mentioned above [139], and often lacks the dynamic control of fluid interface. Under this premise, the combination of hydrodynamic focusing (HF) device and microfluidic chip can be a good choice for the synthesis of NPs. In simple terms, the HF process is a high flow rate sheath fluid compresses a low flow rate central fluid [140]. In practice, the precise control of relative flow rate of chemical components can regulate the concentration and solubility [129], thus the synthesis of NPs in microfluidic hydrodynamic flow focusing (HFF) device will produce a more uniform particle size distribution. Ran et al. developed an HFF platform for single-step preparation of multifunctional liposomes. In this platform, the plain liposomes, PEGylated liposomes and the folic acid modified liposomes that encapsulated fluorescence dye were synthesized and showed reliable stability in serum. The liposomes modified targeting ligand (folic acid) demonstrated stronger selectivity and internalization in 3D tumor spheroid model [141]. Conventional production of multifunctional liposomes often requires tedious post-processing, but this platform greatly reduced the difficulty of liposomal preparation and increased the uniformity of liposomes. More than that, a number of studies in recent years had proven that this technique has tremendous potential for high-throughput production of NPs [142, 143].

Molecular engineering of exosome is a new avenue for drug delivery. In fact, endogenous drug delivery system (DDS) often outperforms synthetic nanomaterials in terms of retention time and targeting. Red blood cell membrane, white blood cell membrane, cancer cell membrane (CCM) and other natural cell membranes have a better biocompatibility in vivo and are good raw materials for NPs synthesis [144-147]. It is worth mentioning that exosome membrane (EM) can also be used to prepare NPs after engineering. Conventional microfluidic devices have low efficiency in preparation of nanoparticle of natural membrane sources. Liu and colleagues applied microfluidic sonication to assemble tumor-derived EM-coated and CCM-coated poly (lactic-co-glycolic acid) (PLGA) NPs. EM- and CCM- coated NPs have the ability to enhance targeting efficacy because there are some specific surface antigens on their membrane. They can be modified to improve tumor targeting or reduce the clearance of NPs by mononuclear phagocyte system (MPS) [148]. This study showed that tumor-derived EM-coated NPs have better homotypic targeting. The underlying mechanism of this phenomenon might be that tumor cell-derived EM have both the endosomal and plasma membrane protein, which makes EM-coated NPs have the dual function of avoiding immune clearance and targeting homologous tumors [149]. Although there have been limited reports on the use of microfluidic device for exosome engineering, due to the unique properties of exosome membranes and the flexible functions of microfluidic devices, this research field will have a great prospect in the future.

Using microfluidic device for preclinical evaluation of NPs has also shown advantages. The special design of channel geometry (such as line and cross shape microstructure) and highly controlled fluidics provides a high fluid mixing and avoids pure laminar flow and NPs sedimentation, thus increasing the internalization of NPs by the cells[139]. Because of the enhanced permeability and retention (EFR) effect, NPs often accumulate in tumors. The technical Tumor-Vasculature-on-a-Chip (TVOC) was reported to assessing NPs extravasation through leaky vasculature and their accumulation in tumor tissues, which provided a powerful platform for the preclinical evaluation on NPs [150]. Chen and colleagues recently developed a microfluidic platform that composed of the breast-cancer multicellular tumor spheroids (MCT) with uniform size, the endothelial monolayer and ECM, which better recapitulated the pathophysiological barrier and the blood microvessels in breast cancer microenvironment [151]. More than that, real-time monitoring on the chip through microplate reader is more accurate than conventional fluorescence detection [152-154]. On the strength of these features, the researchers synthesized a carbon dots (CDs) drug delivery system as a model to monitored drug delivery capacity and assessed in-situ cytotoxicity on the chip [151]. The results showed that this microfluidic platform give the possibilities of integrating useful characteristics of high-throughput and high spatio-temporal resolution in nano-drug evaluation.


What is the purpose of eletrowetting on microfluidic chips? - Biology

Fabrication technology

We use a great variety of materials for the fabrication of microfluidic devices developed in house. We have adopted replica molding for the rapid prototyping of PDMS-based microfluidic components and devices. In addition, we have demonstrated a mass production amenable technology for fabrication and surface modification of plastic disposable microfluidic devices, namely direct lithography on the plastic substrate followed by deep polymer etching of materials such as Poly(dimethyl siloxane) PDMS, Poly(methyl methacrylate) PMMA, poly(ether ether ketone) PEEK, Polyimide PI, etc. To complement microfluidics fabrication, bonding processes have been developed based on plasma activation and functionalization of the substrates. We have developed a novel process for irreversible bonding of polymeric substrates including PDMS, PMMA, PS and SU8. More recently, a technology has been pioneered by our group for the fabrication of microfluidic devices on flexible and rigid printed circuit boards (PCB) allowing the mass fabrication of industrially produced microfluidic devices.

In microfluidics, the control of wall surface properties is very crucial to the performance of the fabricated devices. For this reason, our group has paid special attention on the control of wetting properties of all materials implemented in microfluidics fabrication, as well as on the adsorption of biomolecules on such surfaces. Both plasma or wet chemistries have been used for the chemical modification of polymeric microfluidic surfaces, in order to enhance immobilization or prevent adsorption of biomolecules on surfaces, depending on the application. More specifically, selective protein adsorption has been demonstrated on various materials (SiO2, glass), significantly enhanced protein adsorption has been observed on plasma nanotextured polymeric surfaces and has been exploited for the sensitive detection of biomarkers (e.g. CRP-protein) and efficient bacteria capture on microfluidic surfaces. In addition, surface properties have been tuned to minimize biomolecule adsorption on microchannel walls in order to prevent inhibition of bioreactions. Finally, wettability of microfluidic walls has been also tuned to allow capillary pumping or provide hydrophobic valving in microfluidics.

Microfluidic devices

Funding: EU-FP5-Growth, GSRT-PENED, GSRT-Synergasia

Microtechnology allows the realization of miniaturized planar devices of micrometer-sized channels for performing small volume chemistry and biology, thus revolutionizing the life-sciences, medicine and diagnostics. Individual microfluidic components and devices, either as stand-alone or as parts of integrated lab-on-a-chip systems, have been designed, fabricated, and tested in our laboratories. Examples include digital microfluidics for electrowetting on dielectric-based transport of biomolecule-containing droplets in Si devices, PDMS-based microfluidic add-ons for sensors, microdevices for DNA amplification, micromixing, bacteria capturing, and DNA purification, on polymeric and printed circuit board (PCB) substrates. The group pioneered the implementation of flexible and rigid printed circuit board (PCB) approach that emerges as a very promising microfluidics manufacturing technology.

Electrowetting on dielectrics (EWOD) has gained considerable attention for its capacity of transporting smallest volumes of liquids especially in biochips and BioMEMS approaches. Optimized fluorocarbon films have been developed by our group as the hydrophobic top layer of droplet-based microfluidic devices , where droplet actuation and transport has been achieved via electrowetting on dielectric (EWOD). We have demonstrated droplet transport on an open microfluidic device with a series of sequentially activated microelectrodes.

Replica molding and rapid prototyping of PDMS-based components and devices has been adopted by our group for the fabrication of microfluidic modules and devices integrated with sensors, in collaboration with other groups. In particular, a gas chromatography microcolumn combined with a gas sensor has been shown to enhance the separation efficiency of the sensor. In addition, a multichannel microfluidic module has been integrated on a surface acoustic wave (SAW) sensor to allow for parallel biological multisample analysis (in collaboration with E. Gizeli, K. Mitsakakis , Univ. Crete & FORTH).

Chromatographic microcolumns on Si or PMMA substrates have been developed by our group to separate phosphopeptides , in collaboration with Biomedical Research Foundation , Academy of Athens. The microcolumns consisted of 32 parallel microchannels with common input and output and were fabricated by direct lithography and plasma etching on Silicon and polymeric substrates, and sealed with a lamination film. TiO2-ZrO2 or TiO2 films, used as stationary phase in the affinity column, were deposited with rf magnetron sputtering, or with liquid phase deposition.

Most molecular diagnostics rely on nucleic acid testing, with DNA amplification comprising an indispensable process with expanding applications in health, food safety and environmental monitoring. The most common DNA amplification method is the Polymerase Chain Reaction (PCR), which enables the detection of trace amounts of DNA within a biological sample. We have developed two generations of continuous flow microfluidic device for DNA amplification (μPCR), integrated with microresistors on commercially available substrates and processes compatible with the PCB industry. In the first generation of such devices, microchannels were formed on flexible polyimide (PI) substrates through the implementation of photopatternable layers by means of lithography. The small thermal mass of the chip, in combination with the low thermal diffusivity of PI substrate on which the heating elements reside, has yield an unprecedented low power consumption PCR chip with fast amplification rates (within few minutes compared to nearly 1 hour needed in conventional thermocyclers). In the second generation of continuous flow μPCR, commercially available, 4-layer printed circuit board (PCB) substrates have been employed, with in-house designed yet industrially manufactured embedded Cu micro-resistive heaters lying at very close distance from the microfluidic network. We demonstrated successful DNA amplification at total reaction times down to 2 min, with a power consumption of 2.7 W, rendering our μPCR device one of the fastest and lowest power-consuming devices , suitable for implementation in low-resource settings. Furthermore, we have demonstrated static well DNA amplification devices, implementing various amplification methods requiring either one single temperature ( isothermal , i.e. HDA) or up to three different temperatures ( thermocycled μPCR ). In particular, based on our microfluidics-on-PCB concept, we have developed microfluidic devices that enable isothermal nucleic acid (DNA) amplification methods, such as Rolling Circle Amplification (RCA @ 65◦C), Helicase Dependent Amplification (HDA @ 65◦C), Loop Mediated Amplification (LAMP @ 65◦C) and Recombinase Polymerase Amplification (RPA @ 40◦C) Chaon PCB substrates with embedded microresistors. In all such microdevices, the observed DNA amplification efficiencies were comparable with those on conventional thermocyclers.

Mixing is imperative in microfluidics for the efficient performance of reactions in lab-on-chip systems. Passive micromixers (no external energy required) of various geometries have been designed, fabricated and demonstrated by our group. Examples include a micromixer with a zig-zag microchannel to perform simultaneously mixing of a restriction enzyme with DNA and digestion of DNA. When heated at 37 C, the micromixer achieved both complete mixing of the reagents and DNA digestion with restriction enzymes within 2.5 min. A novel, highly enhanced split and merge (SAM) passive micromixer has been also developed, with labyrinth-like microchannels to efficiently mix biomolecular solutions. Enzymatic digestion within 30 s was demonstrated.

Sample preparation is indispensable functionality of most lab-on-chip devices for rapid pathogen detection at the point of need. We designed, fabricated, and demonstrated a novel sample preparation module comprising bacteria cell capture and thermal lysis on chip with potential applications in food sample pathogen analysis. Plasma nanotexturing of the polymeric substrate allowed enhancement of the surface area of the chip and the antibody binding capacity. The module exhibited 100% efficiency in Salmonella enterica serovar Typhimurium bacteria capture for cell suspensions below 10 5 cells/ml, and efficiency larger than 50% for 10 7 cells/ml. Moreover, thermal lysis achieved on chip from as low as 10 captured cells was demonstrated and was shown to compare well with off-chip lysis. Excellent selectivity (over 1:300) was obtained in a sample containing, in addition to S. Typhimurium, E-coli bacteria.

For molecular diagnostics applied in food industry, medicine, forensics and water industry, DNA purification is a procedure of high significance. A polymeric microfluidic chip capable of purifying DNA through solid phase extraction was designed, fabricated and evaluated in our group. Here again, plasma nanotextured surfaces were implemented to create high surface area as well as high density of carboxyl groups (eCOOH) able to bind DNA on the microchannel surface. The chip design incorporates a mixer so that sample and buffer can be efficiently mixed on chip under continuous flow. The chip was able to isolate DNA with high recovery efficiency (96± 11%) in an extremely large dynamic range of pre-purified Salmonella DNA as well as from Salmonella cell lysates that correspond to a range of 5 to 1.9 10 8 cells.

Lab-on-a-chip (LoC)

Funding: GSRT (Corallia), FP7, H2020, SNF

Since the introduction of the micro total analysis system (μTAS) concept in 1990 and thanks to the extensive research efforts from the increasingly growing lab-on-a-chip (LoC) community since then, the global excitement for this revolutionary technology has been exponentially increasing, owing to its appealing advantages over conventional laboratory tests: rapid response time, miniaturized sample volumes, reduced cost, automation and portability. Leveraging our novel microfluidic devices, we are designing and developing more integrated lab-on-a-chip devices accommodating sample preparation (e.g., bacteria capture, thermal lysis, DNA purification, DNA amplification) and detection (mainly through collaborations S. Chatzandroulis, E. Gizeli) addressing pathogen screening or quantification for application in food safety, healthcare, and environmental monitoring. Examples include a LoC for foodborne pathogen detection and a Lab-on-Printed Circuit Board (LoPCB) accompanied by a point-of-care platform for molecular diagnosis of urinary tract infections, both at unprecedented short time-to-result.

Building on the successful fabrication of microfluidics with photopatternable polyimide, we have developed a Lab-On-a-Chip platform on Printed Circuit Board substrates, seamlessly integrating a μPCR module and Si-based biosensors (placed in a hybridization chamber on the PCB), to allow DNA amplification and detection on the same chip. Currently, a lab-on- a-chip where bacterial DNA is amplified rapidly and efficiently, combined with detection of amplified DNA on sensitive graphene-oxide biosensors is being developed. This LoPCB is accompanied by a prototype, automated, portable diagnostic platform (Point-of-Care), for temperature and flow control and sensor read-out. This platform is currently tested for urinary tract infections, but it can be easily extended to other bacterial or viral infections.

Diseases initiated by food-borne pathogens represent an increasing threat for the public health and safety worldwide, therefore, rapid and reliable pathogen detection is of utmost importance. However, the duration of common food analysis practices is typically 2–5 days. Lab-on-chip devices can reduce labor and analysis time to a few hours, proving its beneficial use and rendering the response of food industry as well as public safety agents faster. The aim of our work was the fabrication and evaluation of an integrated Lab-on-Chip platform for sample preparation, accommodating bacteria capture, lysis, DNA purification (where necessary), and DNA amplification, addressing pathogen screening in milk samples. Three generations of LoC devices were developed for rapid detection of bacteria in dairy products, in collaboration with FORTH-Univ. Crete, Pasteur Institute, Jobst Technologies GmbH, SENSeOR SA and Univ. Pardubice the most advanced device integrated in a single chamber the steps of bacteria capture, lysis and isothermal amplification (LAMP), while detection was achieved on an acoustic (SAW) device, providing a sensitive, highly integrated and user-friendly platform for sample-to-result analysis within 4.5 h.

  • Molecular testing with Colorimetric detection at the Point-of-need for Food and Environmental safety

Food- and water-borne infections are commonly caused by bacteria. Very recently Legionella has been identified by the World Health Organization as the highest health burden of all waterborne pathogens in the European Union. However, the low frequency sampling and the long duration of legionella cultures (up to 10 days) do not allow for prevention of legionella outbreaks. Thus, the development of more efficient water diagnostics for pathogens and faster analyses methods is recognized worldwide. Our group, leveraging the expertise acquired in the molecular testing of food-borne bacteria and in collaboration with Nanoplasmas PC , is realizing a lab-on-a-chip based on colorimetric detection (visual inspection) for ultra-rapid and easy L. pneumophila detection at the point of need.

Organ-on-a-chip

Funding: State Scholarships Foundation (IKY)

Conventional biomedical research models are confined to static cell culture models and animal testing, both of them representing suboptimal preclinical models. Organs-on-chips (OOCs) are novel 3D microfluidic cell culture devices lined with living cells that allow for faithful mimicry of the physiology and function of a vital human organ unit. Currently, we are developing a purely in vitro and scaffold-free bone marrow-on-a-chip, intended for both the generation and sustainment of the hematopoietic niche, to serve as a study platform for the chronic autoimmune disease of systemic lupus erythematosus (SLE, in collaboration with BRFAA, Prof. D. Boumbas).


PurpleDrop

PurpleDrop is a digital microfluidic device (DMF) for lab automation. DMFs use electricity to move tiny droplets of water—or any aqueous solution—on a grid of electrodes. You can move droplets around, mix them up, and split them apart. Combine that with heaters, sensors, or anything else that you can put on the chip, and you’ve got a general purpose lab-on-a-chip!

We want to develop a DMF device that’s cheap, reliable, and capable enough be the foundation of computer systems with molecular components. The Puddle software stack complements the PurpleDrop hardware, making it easy to automate complex protocols in synthetic biology or any other domain. For example, Puddle includes a computer vision system that detects and automatically corrects droplet movement errors.


Material Classification

Microfluidics has properties that make it attractive as practical and feasible tools in biotechnology areas. The knowledge of several possibilities of materials is an important aspect for developing new microfluidic designs with proper applications. The characteristics and properties of the materials used are quite relevant aspects for the desired microfluidic platforms. Commercial microfluidic devices are primarily etched and/or molded from mechanically sturdy and chemically durable materials, such as glass, polydimethylsiloxane (PDMS), and thermoplastics. Glass- and polymer-based microfluidics in biochemical analyses and related applications has made the spectacular success. Not far behind this, the investigation of microfluidic systems in other classes of materials has been rapidly growing.

Common Materials in Microfluidics

Early miniaturized total analysis systems (μTAS) devices were fabricated from silicon and glass using clean-room techniques that were translated to microfluidic device fabrication. This was largely a choice of convenience and necessity (early microfluidics focused largely on electrophoretic phenomena where glass is a preferred material), but not a long-term solution for cell biology research. Silicon is opaque to visible and ultraviolet light, making this material incompatible with popular microscopy methods. Glass and silicon are both brittle materials, they have non-trivial bonding protocols for closing microchannels, and in general they require expensive, inaccessible fabrication methods. These materials were well suited for some applications (for example, electrophoresis), but were ultimately limited in their growth potential. Cheaper, more accessible materials and fabrication methods were needed to fuel the growth of microfluidic technology development and adoption.

PDMS is an optically transparent, gas- and vapor-permeable elastomer. PDMS was first used in 1998 for the fabrication of more complex microfluidic devices and helped soft lithography become the most widely adopted method for fabricating microfluidic devices. Adoption of the material can be attributed to several key factors, including (1) the relatively cheap and easy set-up for fabricating small numbers of devices using PDMS in a university setting (2) the ability to tune the hydrophobic surface properties to become more hydrophilic (3) the ability to reversibly and (in some cases) irreversibly bond PDMS to glass, plastic, PDMS itself, and other materials and (4) the elasticity of PDMS, which allows for easy removal from delicate silicone molds for feature replication. However, perhaps most importantly, the elasticity of PMDS allows for valving and actuation, which has led to a plethora of microfluidic designs and publications.

Despite all the beneficial properties of PDMS that enabled its rapid adoption amongst university engineers, there are several limitations to implementing the material in biomedical research. For example, PDMS has been shown to absorb small molecules, which can affect critical cell signaling dynamics. Thus, polystyrene may be preferred over PDMS for many cell biology applications, particularly because biologists have a long history of using polystyrene for cell culture. Furthermore, the use of polystyrene mitigates or eliminates many material property issues associated with PDMS, including the bulk absorption of small molecules and evaporation through the device, and polystyrene makes handling and packaging easier for use in collaborations.

In addition to thermoplastic materials, there has been substantial progress in using destructible, cheap materials such as paper, wax, and cloth for point-of-care applications in low-resource settings. These materials have the benefit of being cheap and easily incinerated, making them ideal choices for settings where safe disposal of biological samples is challenging. Currently, there is increasing activity in developing microfluidic paper-based analytical devices (μPADs). These μPAD devices are expansions on tried-and-tested lateral-flow assays (for example, pregnancy strip test) and operate by passively wicking biological samples through patterned hydrophilic regions using capillary forces.

Fig.1 Materials other than PMDS are being used for microfluidic device design. (Sackmann, 2014)

A microfluidic biomaterial is a biomaterial (most commonly, a hydrogel such as alginate or type I collagen) that contains a microscale channel that can sustain fluid flow. The material should be compatible with the culture of cells within the bulk of the material. Microfluidic biomaterials possess many advantages for potential biological applications. First, and most importantly, these materials are inherently able to sustain fluid flow. As a result, immediate perfusion is possible, which is desirable when the biomaterial contains embedded cells to which nutrients are to be delivered and from which metabolites are to be removed. Second, the transport of substances and/or cells to and from the biomaterial can be tailored with the geometry of the microfluidic network. Third, because the sizes and locations of microfluidic channels are chosen by design, the microfluidic geometry within the biomaterial is well-controlled and reproducible. Fourth, microfluidic biomaterials contain micrometer-scale channel widths that are particularly well-suited for replicating the geometry of microvessels and other tubular structures that are desired in engineered tissues.

Fig.2 Strategies for forming microfluidic biomaterials and representative implementations. (Tien, 2021)

Services at Creative Biolabs

Different materials have different applications in microfluidic development and every material has its unique purpose. What is important is to choose appropriate materials corresponding to your final purpose in microfluidic development. Creative Biolabs has been focusing on microfluidics over years and is experienced in this field. We have established a comprehensive one-stop microfluidic solution platform and provide a variety of microfluidic-based services including but not limited to:

  • Microfluidic Chip Development for Nucleic Acids Solution
  • Microfluidic Chip Development for Protein Solution
  • Microfluidic Chip Development for Small Molecule Solution
  • Microfluidic Chip Development for Cell Solution
  • Microfluidic Chip Development for Organ-On-A-Chip
  • Microfluidic Services for Immunoassay
  • Microfluidic Services for Therapy
  • Emulsions Synthesis
  • Gas Bubbles Synthesis
  • Particles Synthesis
  • Encapsulation Services

If you are interested in any one of our services or you have any questions about microfluidics, please don’t hesitate to contact us for more information.


Watch the video: Fabrication of Microfluidic Devices (August 2022).