Nip the bubble in the bud: a guide to avoid gas nucleation in microfluidics

Bioinspired Electrolyte-Gated Organic Synaptic Transistors: From Fundamental Requirements to Applications

Rapid development of artificial intelligence requires the implementation of hardware systems with bioinspired parallel information processing and presentation and energy efficiency. Electrolyte-gated organic transistors (EGOTs) offer significant advantages as neuromorphic devices due to their ultra-low operation voltages, minimal hardwired connectivity, and similar operation environment as electrophysiology. Meanwhile, ionic-electronic coupling and the relatively low elastic moduli of organic channel materials make EGOTs suitable for interfacing with biology. This review presents an overview of the device architectures based on organic electrochemical transistors and organic field-effect transistors. Furthermore, we review the requirements of low energy consumption and tunable synaptic plasticity of EGOTs in emulating biological synapses and how they are affected by the organic materials, electrolyte, architecture, and operation mechanism. In addition, we summarize the basic operation principle of biological sensory systems and the recent progress of EGOTs as a building block in artificial systems. Finally, the current challenges and future development of the organic neuromorphic devices are discussed.

TapeTech microfluidic connectors: adhesive tape-enabled solution for organ-on-a-chip system integration

A longstanding challenge in microfluidics has been the efficient delivery of fluids from macro-scale pumping systems into microfluidic devices, known as the "world-to-chip" problem. Thus far, the entire industry has accepted the use of imperfect, rigid tubing and connectors as the ecosystem within which to operate, which, while functional, are often cumbersome, labor-intensive, prone to errors, and ill-suited for high-throughput experimentation. In this paper, we introduce TapeTech microfluidics, a flexible and scalable solution designed to address the persistent "world-to-chip" problem in microfluidics, particularly in organ-on-a-chip (OoC) applications. TapeTech offers a streamlined alternative, utilizing adhesive tape and thin-film polymers to create adaptable, integrated multi-channel ribbon connectors that simplify fluidic integration with pumps and reservoirs. Key features of TapeTech include reduced pressure surges, easy priming, rapid setup, easy multiplexing, and broad compatibility with existing devices and components, which are essential for maintaining stable fluid dynamics and protecting sensitive cell cultures. Furthermore, TapeTech is designed to flex around the lids of Petri dishes, enhancing sterility and transportability by enabling easy transfer between incubators, biosafety cabinets (BSCs), and microscopes. The rapid design-to-prototype iteration enabled by TapeTech allows users to quickly develop connectors for a wide range of microfluidic devices. Importantly, we showcase the utility of TapeTech in OoC cultures requiring fluid flow. We also highlight other utilities, such as real-time microscopy and a well-plate medium exchanger. The accessibility of this technology should enable more laboratories to simplify design and setup of microfluidic experiments, and increase technology adoption.

Microfluidic Monodispersed Microbubble Generation for Production of Cavitation Nuclei

Microbubbles, acting as cavitation nuclei, undergo cycles of expansion, contraction, and collapse. This collapse generates shockwaves, alters local shear forces, and increases local temperature. Cavitation causes severe changes in pressure and temperature, resulting in surface erosion. Shockwaves strip material from surfaces, forming pits and cracks. Prolonged cavitation reduces the mechanical strength and fatigue life of materials, potentially leading to failure. Controlling bubble size and generating monodispersed bubbles is crucial for accurately modeling cavitation phenomena. In this work, we generate monodispersed microbubbles with controllable size using a novel and low-cost microfluidic method. We created an innovative T-junction structure that controls the two-phase flow for tiny, monodispersed bubble generation. Monodisperse microbubbles with diameters below one-fifth of the channel width (W = 100 µm) are produced due to the controlled pressure gradient. This microstructure, fabricated by a CNC milling technique, produces 20 μm bubbles without requiring high-resolution equipment and cleanroom environments. Bubble size is controlled with gas and liquid pressure ratio and microgeometry. This microbubble generation method provides a controllable and reproducible way for cavitation research.

Understanding, Mimicking, and Mitigating Radiolytic Damage to Polymers in Liquid Phase Transmission Electron Microscopy

Advances in liquid phase transmission electron microscopy (LP-TEM) have enabled the monitoring of polymer dynamics in solution at the nanoscale, but radiolytic damage during LP-TEM imaging limits its routine use in polymer science. This study focuses on understanding, mimicking, and mitigating radiolytic damage observed in functional polymers in LP-TEM. It is quantitatively demonstrated how polymer damage occurs across all conceivable (LP-)TEM environments, and the key characteristics and differences between polymer degradation in water vapor and liquid water are elucidated. Importantly, it is shown that the hydroxyl radical-rich environment in LP-TEM can be approximated by UV light irradiation in the presence of hydrogen peroxide, allowing the use of bulk techniques to probe damage at the polymer chain level. Finally, the protective effects of commonly used hydroxyl radical scavengers are compared, revealing that the effectiveness of graphene's protection is distance-dependent. The work provides detailed methodological guidance and establishes a baseline for polymer degradation in LP-TEM, paving the way for future research on nanoscale tracking of shape transitions and drug encapsulation of polymer assemblies in solution.

Integrated device for plasma separation and nucleic acid extraction from whole blood toward point-of-care detection of bloodborne pathogens

Sample preparation presents a major challenge in point-of-care (POC) diagnostic assays, including ones requiring whole blood as the starting specimen. This study presents an integrated sample preparation device - which we call PRECISE - that performs both plasma separation and nucleic acid extraction, enabling streamlined sample preparation from whole blood requiring only a commercially available blood collection tool and a syringe, and no other external equipment or electricity. Plasma separation is performed using a dual-membrane filter (which filters out blood components while limiting membrane clogging) integrated into the cartridge, and nucleic acid extraction is performed by users moving magnets (to mix the samples, and along a guided track). The plasma filtration demonstrated recovery on par with lab-based centrifugation, and the extraction module showed performance similar to benchtop-based magnetic bead extraction. A sample-to-result demonstration on 50 μL of whole blood spiked with virions of hepatitis C virus (HCV), operating the PRECISE cartridge in 16 minutes followed by benchtop PCR, showed a limit of detection (∼6770 IU mL-1) on the order of the minimal requirements of target product profile for POC HCV detection. Future work on the PRECISE cartridge, building on POC accessibility and fast sample preparation demonstrated in this work, may enable detection of bloodborne pathogens from whole-blood specimens collected at the POC.

On the design and fabrication of nanoliter-volume hanging drop networks

Hanging drop cultures provide a favorable environment for the gentle, gel-free formation of highly uniform three-dimensional cell cultures often used in drug screening applications. Initial cell numbers can be limited, as with primary cells provided by minimally invasive biopsies. Therefore, it can be beneficial to divide cells into miniaturized arrays of hanging drops to supply a larger number of samples. Here, we present a framework for the miniaturization of hanging drop networks to nanoliter volumes. The principles of a single hanging drop are described and used to construct the fundamental equations for a microfluidic system composed of multiple connected drops. Constitutive equations for the hanging drop as a nonlinear capacitive element are derived for application in the electronic-hydraulic analogy, forming the basis for more complex, time-dependent numerical modeling of hanging drop networks. This is supplemented by traditional computational fluid dynamics simulation to provide further information about flow conditions within the wells. A fabrication protocol is presented and demonstrated for creating transparent, microscale arrays of pinned hanging drops. A custom interface, pressure-based fluidic system, and environmental chamber have been developed to support the device. Finally, fluid flow on the chip is demonstrated to align with expected behavior based on the principles derived for hanging drop networks. Challenges with the system and potential areas for improvement are discussed. This paper expands on the limited body of hanging drop network literature and provides a framework for designing, fabricating, and operating these systems at the microscale.

BioTrojans: viscoelastic microvalve-based attacks in flow-based microfluidic biochips and their countermeasures

Flow-based microfluidic biochips (FMBs) are widely used in biomedical research and diagnostics. However, their security against potential material-level cyber-physical attacks remains inadequately explored, posing a significant future challenge. One of the main components, polydimethylsiloxane (PDMS) microvalves, is pivotal to FMBs' functionality. However, their fabrication, which involves thermal curing, makes them susceptible to chemical tampering-induced material degradation attacks. Here, we demonstrate one such material-based attack termed "BioTrojans," which are chemically tampered and optically stealthy microvalves that can be ruptured through low-frequency actuations. To chemically tamper with the microvalves, we altered the associated PDMS curing ratio. Attack demonstrations showed that BioTrojan valves with 30:1 and 50:1 curing ratios ruptured quickly under 2 Hz frequency actuations, while authentic microvalves with a 10:1 ratio remained intact even after being actuated at the same frequency for 2 days (345,600 cycles). Dynamic mechanical analyzer (DMA) results and associated finite element analysis revealed that a BioTrojan valve stores three orders of magnitude more mechanical energy than the authentic one, making it highly susceptible to low-frequency-induced ruptures. To counter BioTrojan attacks, we propose a security-by-design approach using smooth peripheral fillets to reduce stress concentration by over 50% and a spectral authentication method using fluorescent microvalves capable of effectively detecting BioTrojans.

Laser-induced microbubble as an in vivo valve for optofluidic manipulation in living Mice's microvessels

Optofluidic regulation of blood microflow in vivo represents a significant method for investigating illnesses linked to abnormal changes in blood circulation. Currently, non-invasive strategies are limited to regulation within capillaries of approximately 10 μm in diameter because the adaption to blood pressure levels in the order of several hundred pascals poses a significant challenge in larger microvessels. In this study, using laser-induced microbubble formation within microvessels of the mouse auricle, we regulate blood microflow in small vessels with diameters in the tens of micrometers. By controlling the laser power, we can control the growth and stability of microbubbles in vivo. This controlled approach enables the achievement of prolonged ischemia and subsequent reperfusion of blood flow, and it can also regulate the microbubbles to function as micro-pumps for reverse blood pumping. Furthermore, by controlling the microbubble, narrow microflow channels can be formed between the microbubbles and microvessels for assessing the apparent viscosity of leukocytes, which is 76.9 ± 11.8 Pa·s in the in vivo blood environment. The proposed design of in vivo microbubble valves opens new avenues for constructing real-time blood regulation and exploring cellular mechanics within living organisms.

A Modular Microfluidic Organoid Platform Using LEGO-Like Bricks

The convergence of organoid and organ-on-a-chip (OoC) technologies is urgently needed to overcome limitations of current 3D in vitro models. However, integrating organoids in standard OoCs faces several technical challenges, as it is typically laborious, lacks flexibility, and often results in even more complex and less-efficient cell culture protocols. Therefore, specifically adapted and more flexible microfluidic platforms need to be developed to facilitate the incorporation of complex 3D in vitro models. Here, a modular, tubeless fluidic circuit board (FCB) coupled with reversibly sealed cell culture bricks for dynamic culture of embryonic stem cell-derived thyroid follicles is developed. The FCB is fabricated by milling channels in a polycarbonate (PC) plate followed by thermal bonding against another PC plate. LEGO-like fluidic interconnectors allow plug-and-play connection between a variety of cell culture bricks and the FCB. Lock-and-play clamps are integrated in the organoid brick to enable easy (un)loading of organoids. A multiplexed perfusion experiment is conducted with six FCBs, where thyroid organoids are transferred on-chip within minutes and cultured up to 10 d without losing their structure and functionality, thus validating this system as a flexible, easy-to-use platform, capable of synergistically combining organoids with advanced microfluidic platforms.

Air trap and removal on a pressure driven PDMS-based microfluidic device

With the development of microfluidic technology, microfluidic chips have played a positive role in applications such as cell culture, microfluidic PCR, and nanopore gene sequencing. However, the presence of bubbles interferes with fluid flow and has a significant impact on experimental results. There are many reasons for the generation of bubbles in microfluidic chips, such as pressure changes inside the chip, air vibration inside the chip, and the open chip guiding air into the chip when driving fluid. This study designed and prepared a microfluidic device based on polydimethylsiloxane. First, air was actively introduced into the microfluidic chip, and bubbles were captured through the microfluidic device to simulate the presence of bubbles inside the chip in biological experiments. To remove bubbles trapped in the microfluidic chip, distilled water, distilled water containing surfactants, and mineral oil were pumped into the microfluidic chip. We compared and discussed the bubble removal efficiency under different driving fluids, driving pressures, and open/closed channel configurations. This study helps to understand the mechanism of bubble formation and removal in microfluidic devices, optimize chip structure design and experimental reagent selection, prevent or eliminate bubbles, and reduce the impact of bubbles on experiments.

Simple dynamic cell culture system reduces recording noise in microelectrode array recordings

Microelectrode arrays (MEAs) have applications in drug discovery, toxicology, and basic research. They measure the electrophysiological response of tissue cultures to quantify changes upon exposure to biochemical stimuli. Unfortunately, manual addition of chemicals introduces significant noise in the recordings. Here, we report a simple-to-fabricate fluidic system that addresses this issue. We show that cell cultures can be successfully established in the fluidic compartment under continuous flow conditions and that the addition of chemicals introduces minimal noise in the recordings. This dynamic cell culture system represents an improvement over traditional tissue culture wells used in MEAs, facilitating electrophysiology measurements.

Graphical abstract

Bubble Unidirectional Transportation on Multipath Aerophilic Surfaces by Adjusting the Surface Microstructure

Comprehending and controlling the behavior of bubbles on solid surfaces is of significant importance in various fields including catalysis and drag reduction, both industrially and scientifically. Herein, Inspired by the superaerophilic properties of the lotus leaf surface, a series of asymmetrically patterned aerophilic surfaces were prepared by utilizing a facile mask-spraying method for directional transport of underwater bubbles. The ability of bubbles to undergo self-driven transportation in an asymmetric pattern is attributed to the natural tendency of bubbles to move toward regions with lower surface energy. In this work, the microstructure of the aerophilic surface is demonstrated as a critical element that influences the self-driven transport of bubbles toward regions of lower surface energy. The microstructure characteristic affects the energy barrier of forming a continuous gas film on the final regions. We classify three distinct bubble behaviors on the aerophilic surface, which align with three different underwater gas film evolution states: Model I, Model II, and Model III. Furthermore, utilizing the energy difference between the energy barrier that forms a continuous gas film and the gas-gas merging, gas-liquid microreaction in a specific destination on the multiple paths can be easily realized by preinjecting a bubble in the final region. This work provides a new view of the microevolutionary process for the diffusion, transport, and merging behavior of bubbles upon contact with an aerophilic pattern surface.

Mesoporous hydrogel electrodes with flexible frameworks exhibiting enhanced mass transport for the oxygen evolution reaction

Mesoporous hydrogel electrodes with unique flexible mesopores surrounded by CoOOH nanosheets were prepared via the electrochemical deposition of hybrid cobalt hydroxide nanosheets, exhibiting high oxygen evolution reaction activity at a high current density owing to the enhanced mass transport of oxygen molecules.

Enhanced Performance of an Acoustofluidic Device by Integrating Temperature Control

Acoustofluidics is an emerging research field wherein either mixing or (bio)-particle separation is conducted. High-power acoustic streaming can produce more intense and rapid flow patterns, leading to faster and more efficient liquid mixing. However, without cooling, the temperature of the piezoelectric element that is used to supply acoustic power to the fluid could rise above 50% of the Curie point of the piezomaterial, thereby accelerating its aging degradation. In addition, the supply of excessive heat to a liquid may lead to irreproducible streaming effects and gas bubble formation. To control these phenomena, in this paper, we present a feedback temperature control system integrated into an acoustofluidic setup using bulk acoustic waves (BAWs) to elevate mass transfer and manipulation of particles. The system performance was tested by measuring mixing efficiency and determining the average velocity magnitude of acoustic streaming. The results show that the integrated temperature control system keeps the temperature at the set point even at high acoustic powers and improves the reproducibility of the acoustofluidic setup performance when the applied voltage is as high as 200 V.

Integration of multiple flexible electrodes for real-time detection of barrier formation with spatial resolution in a gut-on-chip system

In healthy individuals, the intestinal epithelium forms a tight barrier to prevent gut bacteria from reaching blood circulation. To study the effect of probiotics, dietary compounds and drugs on gut barrier formation and disruption, human gut epithelial and bacterial cells can be cocultured in an in vitro model called the human microbial crosstalk (HuMiX) gut-on-a-chip system. Here, we present the design, fabrication and integration of thin-film electrodes into the HuMiX platform to measure transepithelial electrical resistance (TEER) as a direct readout on barrier tightness in real-time. As various aspects of the HuMiX platform have already been set in their design, such as multiple compressible layers, uneven surfaces and nontransparent materials, a novel fabrication method was developed whereby thin-film metal electrodes were first deposited on flexible substrates and sequentially integrated with the HuMiX system via a transfer-tape approach. Moreover, to measure localized TEER along the cell culture chamber, we integrated multiple electrodes that were connected to an impedance analyzer via a multiplexer. We further developed a dynamic normalization method because the active measurement area depends on the measured TEER levels. The fabrication process and system setup can be applicable to other barrier-on-chip systems. As a proof-of-concept, we measured the barrier formation of a cancerous Caco-2 cell line in real-time, which was mapped at four spatially separated positions along the HuMiX culture area.

Microfluidic flow injection analysis system for the electrochemical detection of dopamine using diazonium-grafted copper nanoparticles on multi-walled carbon nanotube-modified surfaces

In this proof-of-concept study, a microfluidic flow injection analysis (FIA) system was developed using multi-walled carbon nanotube-modified screen-printed carbon electrodes (CNTSPEs) that were modified with copper nanoparticles (CuNPs) following the electrodeposition of the diazonium salt of 4-aminothiophenol to form 4-thiophenol-conjugated CuNPs (CuNPs-CNTSPE). Transmission electron microscopy (TEM), atomic force microscopy (AFM), and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) were used to characterize the size of CuNPs, morphology and elemental analysis of CuNPs-CNTSPE, respectively. Using electrochemical impedance spectroscopy (EIS), the charge-transfer resistance (Rct) of CuNPs-CNTSPE was found to be 20-fold lower than that of CNTSPE. The CuNPs-CNTSPE displayed an oxidation peak for dopamine at -0.08 V which is ∼80 mV lower than the one detected using CNTSPE. The modified electrode was used in microfluidic flow injection analysis and offline systems for sensitive detection of dopamine (DA). The pH, flow rate, loop volume, concentration, and type of surfactant were all optimized for on-chip detection. Under the optimal conditions, using phosphate electrolyte solution (pH 6) containing 0.05% (w/v) Tween 20® as the carrier at a flow rate of 0.6 mL min-1 and a loop volume of 50 μL, the calibration curve was linear from 1.5 to 500 nM with a limit of detection of 0.33 nM. This technique was used for the successful detection of DA in real samples with recovery ranging from 96.5% to 103.8%. The microfluidic FIA system described here has the potential to be used as an electrochemical point-of-care device for rapid DA detection with high sensitivity and reproducibility.

Local Microbubble Removal in Polydimethylsiloxane Microchannel by Balancing Negative and Atmospheric Pressures

Long-term experiments using organoids and tissues are crucial for drug development. Microfluidic devices have been regularly used in long-term experiments. However, microbubbles often form in these devices, and they may damage and starve cells. A method involving the application of negative pressure has been reported to remove microbubbles from microfluidic devices composed of polydimethylsiloxane; however, negative pressure affects the cells and tissues in microfluidic devices. In this study, a local microbubble removal method was developed using a microfluidic device with 0.5 mm thin polydimethylsiloxane sidewalls. The thin sidewalls counterbalanced the negative and atmospheric pressures, thereby localizing the negative pressure near the negatively pressurized chamber. Microbubbles were removed within 5 mm of the negatively pressurized chamber; however, those in an area 7 mm and more from the chamber were not removed. Using the local removal method, a long-term perfusion test was performed, and no contact was confirmed between the bubbles and the simulated tissue for 72 h.

Sub-5-Minute Ultrafast PCR using Digital Microfluidics

The development of a rapid and reliable polymerase chain reaction (PCR) method for point-of-care (POC) diagnosis is crucial for the timely identification of pathogens. Microfluidics, which involves the manipulation of small volumes of fluidic samples, has been shown to be an ideal approach for POC analysis. Among the various microfluidic platforms available, digital microfluidics (DMF) offers high degree of configurability in manipulating μL/nL-scale liquid and achieving automation. However, the successful implementation of ultrafast PCR on DMF platforms presents challenges due to inherent system instability. In this study, we developed a robust and ultrafast PCR in 3.7-5 min with a detection sensitivity comparable to conventional PCR. Specifically, the implementation of the pincer heating scheme homogenises the temperature within a drop. The utilization of a μm-scale porous hydrophobic membrane suppresses the formation of bubbles under high temperatures. The design of a groove around the high-temperature zone effectively mitigates the temperature interference. The integration of a soluble sensor into the droplets provides an accurate and instant in-drop temperature sensing. We envision that the fast, robust, sensitive, and automatic DMF system will empower the POC testing for infectious diseases.

Gas transport mechanisms through gas-permeable membranes in microfluidics: A perspective

Gas-permeable membranes (GPMs) and membrane-like micro-/nanostructures offer precise control over the transport of liquids, gases, and small molecules on microchips, which has led to the possibility of diverse applications, such as gas sensors, solution concentrators, and mixture separators. With the escalating demand for GPMs in microfluidics, this Perspective article aims to comprehensively categorize the transport mechanisms of gases through GPMs based on the penetrant type and the transport direction. We also provide a comprehensive review of recent advancements in GPM-integrated microfluidic devices, provide an overview of the fundamental mechanisms underlying gas transport through GPMs, and present future perspectives on the integration of GPMs in microfluidics. Furthermore, we address the current challenges associated with GPMs and GPM-integrated microfluidic devices, taking into consideration the intrinsic material properties and capabilities of GPMs. By tackling these challenges head-on, we believe that our perspectives can catalyze innovative advancements and help meet the evolving demands of microfluidic applications.

Size Ranges of Effective Nucleation Cavities on Gas-Evolving Surfaces

Bubble nucleation has a significant influence on mass transfer and energy conversion in electrochemical gas-evolving reactions. In this work, we establish a theoretical model for bubble nucleation from gas cavities on gas-evolving surfaces. Based on analyses of transient gas diffusion within the concentration boundary layer and supersaturation equation for stable bubble nuclei, we determined the size ranges of effective nucleation cavities on gas-evolving surfaces under different levels of supersaturation conditions. In addition, a criterion for the incipience of bubble nucleation on gas-evolving surfaces is proposed. We investigate the effects of the contact angle, cone angle, concentration boundary layer thickness, ambient pressure, and temperature on the size ranges of effective nucleation cavities, respectively. We demonstrate that a larger contact angle or a smaller cone angle can broaden the size range of effective cavities, thereby promoting bubble nucleation from cavities. We also show that increasing the concentration boundary layer thickness causes larger cavities to become effective nucleation sites, which significantly expands the size range of effective cavities. In contrast, increasing the ambient pressure enables smaller cavities to become effective nucleation sites, resulting in an expansion in the size range of effective cavities. Results of this work will contribute to the manipulation of bubble nucleation densities and the optimal design of gas-evolving electrodes in various electrochemical gas-evolving reactions.

Chemical Trends in Sample Preparation for Nucleic Acid Amplification Testing (NAAT): A Review

Nucleic acid amplification testing facilitates the detection of disease through specific genomic sequences and is attractive for point-of-need testing (PONT); in particular, the early detection of microorganisms can alert early response systems to protect the public and ecosystems from widespread outbreaks of biological threats, including infectious diseases. Prior to nucleic acid amplification and detection, extensive sample preparation techniques are required to free nucleic acids and extract them from the sample matrix. Sample preparation is critical to maximize the sensitivity and reliability of testing. As the enzymatic amplification reactions can be sensitive to inhibitors from the sample, as well as from chemicals used for lysis and extraction, avoiding inhibition is a significant challenge, particularly when minimising liquid handling steps is also desirable for the translation of the assay to a portable format for PONT. The reagents used in sample preparation for nucleic acid testing, covering lysis and NA extraction (binding, washing, and elution), are reviewed with a focus on their suitability for use in PONT.

Fluid flow to mimic organ function in 3D in vitro models

Many different strategies can be found in the literature to model organ physiology, tissue functionality, and disease in vitro; however, most of these models lack the physiological fluid dynamics present in vivo. Here, we highlight the importance of fluid flow for tissue homeostasis, specifically in vessels, other lumen structures, and interstitium, to point out the need of perfusion in current 3D in vitro models. Importantly, the advantages and limitations of the different current experimental fluid-flow setups are discussed. Finally, we shed light on current challenges and future focus of fluid flow models applied to the newest bioengineering state-of-the-art platforms, such as organoids and organ-on-a-chip, as the most sophisticated and physiological preclinical platforms.

Cancer-on-chip: a 3D model for the study of the tumor microenvironment

The approval of anticancer therapeutic strategies is still slowed down by the lack of models able to faithfully reproduce in vivo cancer physiology. On one hand, the conventional in vitro models fail to recapitulate the organ and tissue structures, the fluid flows, and the mechanical stimuli characterizing the human body compartments. On the other hand, in vivo animal models cannot reproduce the typical human tumor microenvironment, essential to study cancer behavior and progression. This study reviews the cancer-on-chips as one of the most promising tools to model and investigate the tumor microenvironment and metastasis. We also described how cancer-on-chip devices have been developed and implemented to study the most common primary cancers and their metastatic sites. Pros and cons of this technology are then discussed highlighting the future challenges to close the gap between the pre-clinical and clinical studies and accelerate the approval of new anticancer therapies in humans.

Thyroid-on-a-Chip: An Organoid Platform for In Vitro Assessment of Endocrine Disruption

Thyroid is a glandular tissue in the human body in which the function can be severely affected by endocrine disrupting chemicals (EDCs). Current in vitro assays to test endocrine disruption by chemical compounds are largely based on 2D thyroid cell cultures, which often fail to precisely evaluate the safety of these compounds. New and more advanced 3D cell culture systems are urgently needed to better recapitulate the thyroid follicular architecture and functions and help to improve the predictive power of such assays. Herein, the development of a thyroid organoid-on-a-chip (OoC) device using polymeric membranous carriers is described. Mouse embryonic stem cell derived thyroid follicles are incorporated in a microfluidic chip for a 4 day experiment at a flow rate of 12 µL min-1 . A reversible seal provides a leak-tight sealing while enabling quick and easy loading/unloading of thyroid follicles. The OoC model shows a high degree of functionality, where organoids retain expression of key thyroid genes and a typical follicular structure. Finally, transcriptional changes following benzo[k]fluoranthene exposure in the OoC device demonstrate activation of the xenobiotic aryl hydrocarbon receptor pathway. Altogether, this OoC system is a physiologically relevant thyroid model, which will represent a valuable tool to test potential EDCs.

A Scalable, Modular Degasser for Passive In-Line Removal of Bubbles from Biomicrofluidic Devices

Bubbles are a common cause of microfluidic malfunction, as they can perturb the fluid flow within the micro-sized features of a device. Since gas bubbles form easily within warm cell culture reagents, degassing is often necessary for biomicrofluidic systems. However, fabrication of a microscale degasser that can be used modularly with pre-existing chips may be cumbersome or challenging, especially for labs not equipped for traditional microfabrication, and current commercial options can be expensive. Here, we address the need for an affordable, accessible bubble trap that can be used in-line for continuous perfusion of organs-on-chip and other microfluidic cultures. We converted a previously described, manually fabricated PDMS degasser to allow scaled up, reproducible manufacturing by commercial machining or fused deposition modeling (FDM) 3D printing. After optimization, the machined and 3D printed degassers were found to be stable for >2 weeks under constant perfusion, without leaks. With a ~140 µL chamber volume, trapping capacity was extrapolated to allow for ~5-20 weeks of degassing depending on the rate of bubble formation. The degassers were biocompatible for use with cell culture, and they successfully prevented bubbles from reaching a downstream microfluidic device. Both degasser materials showed little to no leaching. The machined degasser did not absorb reagents, while the FDM printed degasser absorbed a small amount, and both maintained fluidic integrity from 1 µL/min to >1 mL/min of pressure-driven flow. Thus, these degassers can be fabricated in bulk and allow for long-term, efficient bubble removal in a simple microfluidic perfusion set-up.

Towards spatially-organized organs-on-chip: Photopatterning cell-laden thiol-ene and methacryloyl hydrogels in a microfluidic device

Micropatterning techniques for 3D cell cultures enable the recreation of tissue-level structures, but the combination of patterned hydrogels with organs-on-chip to generate organized 3D cultures under microfluidic perfusion remains challenging. To address this technological gap, we developed a user-friendly in-situ micropatterning protocol that integrates photolithography of crosslinkable, cell-laden hydrogels with a simple microfluidic housing, and tested the impact of crosslinking chemistry on stability and spatial resolution. Working with gelatin functionalized with photo-crosslinkable moieties, we found that inclusion of cells at high densities (≥ 107/mL) did not impede thiol-norbornene gelation, but decreased the storage moduli of methacryloyl hydrogels. Hydrogel composition and light dose were selected to match the storage moduli of soft tissues. To generate the desired pattern on-chip, the cell-laden precursor solution was flowed into a microfluidic chamber and exposed to 405 nm light through a photomask. The on-chip 3D cultures were self-standing and the designs were interchangeable by simply swapping out the photomask. Thiol-ene hydrogels yielded highly accurate feature sizes from 100 - 900 μm in diameter, whereas methacryloyl hydrogels yielded slightly enlarged features. Furthermore, only thiol-ene hydrogels were mechanically stable under perfusion overnight. Repeated patterning readily generated multi-region cultures, either separately or adjacent, including non-linear boundaries that are challenging to obtain on-chip. As a proof-of-principle, primary human T cells were patterned on-chip with high regional specificity. Viability remained high (> 85%) after 12-hr culture with constant perfusion. We envision that this technology will enable researchers to pattern 3D co-cultures to mimic organ-like structures that were previously difficult to obtain.

Permeation-Enhanced Degassing Method Based on Xylem Embolism Repair and Gas Permeable Materials

Microfluidic devices have developed a wide range of applications in the fields of biomedicine, chemistry, and analytical science. But it is easy to form and accumulate bubbles in microfluidic devices. These bubbles could decrease the detection sensitivity, cause inaccurate analysis results, and even damage the functional region of the device. Inspired by the embolism repair mechanism of angiosperms and the permeability of gas permeable materials, this work proposes a bioinspired permeation-enhanced degassing method. Bionic redundant pits are used in this method to keep bubbles from spreading between microchannels and maintain the continuity of the flow. A hydrophobic gas permeable material is used to enhance the bubble capture capability and accelerate the degassing process. This method can eliminate bubbles automatically and continuously in real time without auxiliary equipment. Compared to the bubble removal only depending on solution in water, the degassing effect of the permeation-enhanced degassing method shows about 1.6 times improvement in the same conditions, and the capability of trapping bubbles is improved by 1.33 times. In this paper, this method was integrated into a concentration gradient generator and a cell culture device. The results show that the concentration gradient generator with degassing structures can dissolve bubbles in a rapid way and reach the stability of the concentration gradient within 5-15 min. The degassing method can run for a long time and improve the cell density and cell viability of HeLa cells up to 2.64 and 1.12 times, respectively. The method has a broad application prospect in microfluidic fields including biomedical fluid processing, virus detection, and microscale reactor operation.

An Optimization Framework for Silicon Photonic Evanescent-Field Biosensors Using Sub-Wavelength Gratings

Silicon photonic (SiP) evanescent-field biosensors aim to combine the information-rich readouts offered by lab-scale diagnostics, at a significantly lower cost, and with the portability and rapid time to result offered by paper-based assays. While SiP biosensors fabricated with conventional strip waveguides can offer good sensitivity for label-free detection in some applications, there is still opportunity for improvement. Efforts have been made to design higher-sensitivity SiP sensors with alternative waveguide geometries, including sub-wavelength gratings (SWGs). However, SWG-based devices are fragile and prone to damage, limiting their suitability for scalable and portable sensing. Here, we investigate SiP microring resonator sensors designed with SWG waveguides that contain a "fishbone" and highlight the improved robustness offered by this design. We present a framework for optimizing fishbone-style SWG waveguide geometries based on numerical simulations, then experimentally measure the performance of ring resonator sensors fabricated with the optimized waveguides, targeting operation in the O-band and C-band. For the O-band and C-band devices, we report bulk sensitivities up to 349 nm/RIU and 438 nm/RIU, respectively, and intrinsic limits of detection as low as 5.1 × 10-4 RIU and 7.1 × 10-4 RIU, respectively. This performance is comparable to the state of the art in SWG-based sensors, positioning fishbone SWG resonators as an attractive, more robust, alternative to conventional SWG designs.

Ultraviolet-Driven Janus Foams with Wetting Gradients: Unidirectional Penetration Control for Underwater Bubbles

Understanding the behavior of underwater bubbles and enabling their effective manipulation is important for bubble capture, collection, and transport. Here, to discuss the underwater permeation behavior of bubbles and critical influencing parameters in this process, the copper foams with tunable wettability were fabricated by utilizing the light-stimulated wettability response of TiO₂. The Janus copper foams had different wettability gradients from superhydrophobic/hydrophobic to superhydrophobic/hydrophilic after UV irradiation at different times, and the bubbles on the surfaces showed distinctly diverse penetration behaviors. In particular, the constructed superhydrophobic/hydrophilic surfaces showed more difficult to achieve bubble penetration than the fully superhydrophobic, superhydrophobic/hydrophobic surface. It was found that the wetting states of the foams exposed to different irradiation times underwater plays a crucial role in the bubble penetration behavior. In other words, the difficulty of bubble penetration depends on the difficulty of bubble transition from gas-liquid contact to gas-solid contact. This facile and low-cost fabrication approach for Janus foams provided a valuable approach to understand the penetration behaviors of underwater bubbles, which is significant for expanding potential applications in bubble capture, bubble transport, and control of unstable gas reactions in underwater conditions.

Review of Bubble Applications in Microrobotics: Propulsion, Manipulation, and Assembly

In recent years, microbubbles have been widely used in the field of microrobots due to their unique properties. Microbubbles can be easily produced and used as power sources or tools of microrobots, and the bubbles can even serve as microrobots themselves. As a power source, bubbles can propel microrobots to swim in liquid under low-Reynolds-number conditions. As a manipulation tool, microbubbles can act as the micromanipulators of microrobots, allowing them to operate upon particles, cells, and organisms. As a microrobot, microbubbles can operate and assemble complex microparts in two- or three-dimensional spaces. This review provides a comprehensive overview of bubble applications in microrobotics including propulsion, micromanipulation, and microassembly. First, we introduce the diverse bubble generation and control methods. Then, we review and discuss how bubbles can play a role in microrobotics via three functions: propulsion, manipulation, and assembly. Finally, by highlighting the advantages and current challenges of this progress, we discuss the prospects of microbubbles in microrobotics.

CFD Analysis and Life Cycle Assessment of Continuous Synthesis of Magnetite Nanoparticles Using 2D and 3D Micromixers

Magnetite nanoparticles (MNPs) have attracted basic and applied research due to their immense potential to enable applications in fields as varied as drug delivery and bioremediation. Conventional synthesis schemes led to wide particle size distributions and inhomogeneous morphologies and crystalline structures. This has been attributed to the inability to control nucleation and growth processes under the conventional conditions of bulk batch processes. Here, we attempted to address these issues by scaling down the synthesis process aided by microfluidic devices, as they provide highly controlled and stable mixing patterns. Accordingly, we proposed three micromixers with different channel configurations, namely, serpentine, triangular, and a 3D arrangement with abrupt changes in fluid direction. The micromixers were first studied in silico, aided by Comsol Multiphysics^® to investigate the obtained mixing patterns, and consequently, their potential for controlled growth and the nucleation processes required to form MNPs of uniform size and crystalline structure. The devices were then manufactured using a low-cost approach based on polymethyl methacrylate (PMMA) and laser cutting. Testing the micromixers in the synthesis of MNPs revealed homogeneous morphologies and particle size distributions, and the typical crystalline structure reported previously. A life cycle assessment (LCA) analysis for the devices was conducted in comparison with conventional batch co-precipitation synthesis to investigate the potential impacts on water and energy consumption. The obtained results revealed that such consumptions are higher than those of the conventional process. However, they can be reduced by conducting the synthesis with reused micromixers, as new PMMA is not needed for their assembly prior to operation. We are certain that the proposed approach represents an advantageous alternative to co-precipitation synthesis schemes, in terms of continuous production and more homogeneous physicochemical parameters of interest such as size, morphologies, and crystalline structure. Future work should be directed towards improving the sustainability indicators of the micromixers’ manufacturing process.

Air bubble removal: Wettability contrast enabled microfluidic interconnects

The presence of air bubbles boosts the shear resistance and causes pressure fluctuation within fluid-perfused microchannels, resulting in possible cell damage and even malfunction of microfluidic devices. Eliminating air bubbles is especially challenging in microscale where the adhesive surface tension force is often dominant over other forces. Here, we present an air bubble removal strategy from a novel surface engineering perspective. A microfluidic port-to-port interconnect was fabricated by modifying the peripheral of the microfluidic ports superhydrophobic, while maintaining the inner polymer microchannels hydrophilic. Such a sharp wettability contrast enabled a preferential fluidic entrance into the easy-wetting microchannels over the non-wetting boundaries of the microfluidic ports, while simultaneously filtering out any incoming air bubbles owing to the existence of port-to-port gaps. This bubble-eliminating capability was consistently demonstrated at varying flow rates and liquid analytes. Compared to equipment-intensive techniques and porous membrane-venting strategies, our wettability contrast-governed strategy provides a simple yet effective route for eliminating air bubbles and simultaneously sealing microfluidic interconnects.

Fundamentals, biomedical applications and future potential of micro-scale cavitation-a review

Thanks to the developments in the area of microfluidics, the cavitation-on-a-chip concept enabled researchers to control and closely monitor the cavitation phenomenon in micro-scale. In contrast to conventional scale, where cavitation bubbles are hard to be steered and manipulated, lab-on-a-chip devices provide suitable platforms to conduct smart experiments and design reliable devices to carefully harness the collapse energy of cavitation bubbles in different bio-related and industrial applications. However, bubble behavior deviates to some extent when confined to micro-scale geometries in comparison to macro-scale. Therefore, fundamentals of micro-scale cavitation deserve in-depth investigations. In this review, first we discussed the physics and fundamentals of cavitation induced by tension-based as well as energy deposition-based methods within microfluidic devices and discussed the similarities and differences in micro and macro-scale cavitation. We then covered and discussed recent developments in bio-related applications of micro-scale cavitation chips. Lastly, current challenges and future research directions towards the implementation of micro-scale cavitation phenomenon to emerging applications are presented.

A bioinspired bubble removal method in microchannels based on angiosperm xylem embolism repair

It is difficult to remove and eliminate bubbles in microchannels in many devices used in various biomedical fields, such as those needed for microfluidic immunoassays, point-of-care testing, and cell biology evaluations. Accumulated bubbles are associated with a number of negative outcomes, including a decrease in device sensitivity, inaccuracy of analysis results, and even functional failure. Xylem conduits of angiosperm have the ability to remove bubbles in obstructed conduits. Inspired by such an embolism repair mechanism, this paper proposes a bioinspired bubble removal method, which exhibits a prominent ability to dissolve bubbles continuously within a large range of flow rates (2 µL/min-850 µL/min) while retaining the stability and continuity of the flow without auxiliary equipment. Such a method also shows significant bubble removal stability in dealing with Newtonian liquids and non-Newtonian fluids, especially with high viscosity (6.76 Pa s) and low velocity (152 nL/min). Such advantages associated with the proposed bioinspired method reveal promising application prospects in macro/microfluidic fields ranging from 3D printing, implantable devices, virus detection, and biomedical fluid processing to microscale reactor operation and beyond.

One-shot high-resolution melting curve analysis for KRAS point-mutation discrimination on a digital microfluidics platform

Single-nucleotide polymorphism (SNP) plays a critical role in personalized medicine, forensics, pharmacogenetics, and disease diagnostics. Among different existing SNP genotyping techniques, melting curve analysis (MCA) becomes increasingly popular due to its high accuracy and straightforward procedures in extracting the melting temperature (T_m). Yet, its study on existing digital microfluidic (DMF) platforms has intrinsic limitations due to the temperature inhomogeneity within a thickened droplet during the on-chip rapid heating process. Although the utilization of an on-chip thermostat can regulate and monitor the dynamic melting process in real time, the limited T_m accuracy resulting from the insufficient system response time to accommodate the fast-melting evolution still poses a great challenge for precise MCA with high throughput. This work proposes a one-shot MCA on a DMF platform. The tailoring of a functional substrate with hierarchical micro/nano structure enables high-resolution patterning of pL-scale droplets. Specifically, the hydrothermal and photocatalysis treatment allows the functional substrate to exhibit a superwettability contrast of >170°, facilitating passive isolation of the pL-scale DNA sample into highly-resolved pL droplets above the 200 μm superhydrophilic patterns. This high-resolution MCA technique can successfully discriminate KRAS gene targets with single-nucleotide mutations in 3 seconds. The high accuracy and consistency in the acquired T_m when compared with off-chip results demonstrate its opportunities for near-patient diagnostics, precision medicines, genetic counseling, and prevention strategies on DMF platforms.

Microfluidic acoustic sawtooth metasurfaces for patterning and separation using traveling surface acoustic waves

We demonstrate a sawtooth-based metasurface approach for flexibly orienting acoustic fields in a microfluidic device driven by surface acoustic waves (SAW), where sub-wavelength channel features can be used to arbitrarily steer acoustic fringes in a microchannel. Compared to other acoustofluidic methods, only a single travelling wave is used, the fluidic pressure field is decoupled from the fluid domain's shape, and steerable pressure fields are a function of a simply constructed polydimethylsiloxane (PDMS) metasurface shape. Our results are relevant to microfluidic applications including the patterning, concentration, focusing, and separation of microparticles and cells.

Development of a Heavy Metal Sensing Boat for Automatic Analysis in Natural Waters Utilizing Anodic Stripping Voltammetry

Determination of the levels of heavy metal ions would support assessment of sources and pathways of water pollution. However, traditional spatial assessment by manual sampling and off-site detection in the laboratory is expensive and time-consuming and requires trained personnel. Aiming to fill the gap between on-site automatic approaches and laboratory techniques, we developed an autonomous sensing boat for on-site heavy metal detection using square-wave anodic stripping voltammetry. A fluidic sensing system was developed to integrate into the boat as the critical sensing component and could detect ≤1 μg/L Pb, ≤6 μg/L Cu, and ≤71 μg/L Cd simultaneously in the laboratory. Once its integration was completed, the autonomous sensing boat was tested in the field, demonstrating its ability to distinguish the highest concentration of Pb in an effluent of a galena-enriched mine compared to those at other sites in the stream (Osor Stream, Girona, Spain).

A Fast Bubble Detection Method in Microtubes Based on Pulsed Ultrasound

In the process of biological microfluidic manipulation, the bubbles generated in the tube will seriously reduce the gauging accuracy. This paper introduces an improving method that can estimate the size of microbubbles in real time. Hence, the measurement data of the liquid volume can be modified according to this method. A microbubble detector based on the pulsed-ultrasound method was studied, including the device structure and the working principle. The assessment formula of the microbubbles in the tube was derived from the simulation results, which adopted the two-phase theory. The digital image processing method was applied to fulfill the microbubble calibration. This detection method was applied to measure the microbubbles in the tube and to modify the flow volume in a timely manner. The results of the experiments showed that this method is effective at improving the microflow gauging accuracy.

Electrochemical deposition of nickel from aqueous electrolytic baths prepared by dissolution of metallic powder

A new method of preparation of aqueous electrolyte baths for electrochemical deposition of nickel targets for medical accelerators is presented. It starts with fast dissolution of metallic Ni powder in a HNO3-free solvent. Such obtained raw solution does not require additional treatment aimed to removal nitrates, such as the acid evaporation and Ni salt precipitation-dissolution. It is used directly for preparation of the nickel plating baths after dilution with water, setting up pH value and after possible addition of H3BO3. The pH of the baths ranges from alkaline to acidic. Deposition of 95% of ca. 50 mg of Ni dissolved in the bath takes ca. 3.5 h for the alkaline electrolyte while for the acidic solution it requires ca. 7 h. The Ni deposits obtained from the acidic bath are physically and chemically more stable and possess smoother and crack-free surfaces as compared to the coatings deposited from the alkaline bath. A method of estimation of concentration of H2O2 in the electrolytic bath is also proposed.

Advection-Enhanced Kinetics in Microtiter Plates for Improved Surface Assay Quantitation and Multiplexing Capabilities

Surface assays such as ELISA are pervasive in clinics and research and predominantly standardized in microtiter plates (MTP). MTPs provide many advantages but are often detrimental to surface assay efficiency due to inherent mass transport limitations. Microscale flows can overcome these and largely improve assay kinetics. However, the disruptive nature of microfluidics with existing labware and protocols has narrowed its transformative potential. We present WellProbe, a novel microfluidic concept compatible with MTPs. With it, we show that immunoassays become more sensitive at low concentrations (up to 9× signal improvement in 12× less time), richer in information with 3-4 different kinetic conditions, and can be used to estimate kinetic parameters, minimize washing steps and non-specific binding, and identify compromised results. We further multiplex single-well assays combining WellProbe's kinetic regions with tailored microarrays. Finally, we demonstrate our system in a context of immunoglobulin subclass evaluation, increasingly regarded as clinically relevant.

Engineering mechanobiology through organoids-on-chip: A strategy to boost therapeutics

The mechanical environment of living cells is as critical as chemical signaling. Mechanical stimuli play a pivotal role in organogenesis and tissue homeostasis. Unbalances in mechanotransduction pathways often lead to diseases, such as cancer, cystic fibrosis, and neurodevelopmental disorders. Despite its inherent relevance, there is a lack of proper mechanoresponsive in vitro study systems. In this context, there is an urge to engineer innovative, robust, dynamic, and reliable organotypic technologies to better connect cellular processes to organ-level function and multi-tissue cross-talk. Mechanically active organoid-on-chip has the potential to surpass this challenge. These systems converge microfabrication, microfluidics, biophysics, and tissue engineering fields to emulate key features of living organisms, hence, reducing costs, time, and animal testing. In this review, we intended to present cutting-edge organ-on-chip platforms that integrate biomechanical stimuli as well as novel multicellular culture, such as organoids. We focused on its application in two main fields: precision medicine and drug development. Moreover, we also discussed the state of the art for the development of an engineered model to assess patient-derived tumor organoid metastatic potential. Finally, we highlighted the current drawbacks and emerging opportunities to match the industry needs. We envision the use of mechanoresponsive organotypic-on-chip microdevices as an indispensable tool for precision medicine, drug development, disease modeling, tissue engineering, and developmental biology.

SMILE Platform: An Innovative Microfluidic Approach for On-Chip Sample Manipulation and Analysis in Oral Cancer Diagnosis

Oral cancer belongs to the group of head and neck cancers, and, despite its large diffusion, it suffers from low consideration in terms of prevention and early diagnosis. The main objective of the SMILE platform is the development of a low-cost device for oral cancer early screening with features of high sensitivity, specificity, and ease of use, with the aim of reaching a large audience of possible users and realizing real prevention of the disease. To achieve this goal, we realized two microfluidic devices exploiting low-cost materials and processes. They can be used in combination or alone to obtain on-chip sample preparation and/or detection of circulating tumor cells, selected as biomarkers of oral cancer. The realized devices are completely transparent with plug-and-play features, obtained thanks to a highly customized architecture which enables users to easily use them, with potential for a common use among physicians or dentists with minimal training.

Embedded Microbubbles for Acoustic Manipulation of Single Cells and Microfluidic Applications

Acoustically excited microstructures have demonstrated significant potential for small-scale biomedical applications by overcoming major microfluidic limitations. Recently, the application of oscillating microbubbles has demonstrated their superiority over acoustically excited solid structures due to their enhanced acoustic streaming at low input power. However, their limited temporal stability hinders their direct applicability for industrial or clinical purposes. Here, we introduce the embedded microbubble, a novel acoustofluidic design based on the combination of solid structures (poly(dimethylsiloxane)) and microbubbles (air-filled cavity) to combine the benefits of both approaches while minimizing their drawbacks. We investigate the influence of various design parameters and geometrical features through numerical simulations and experimentally evaluate their manipulation capabilities. Finally, we demonstrate the capabilities of our design for microfluidic applications by investigating its mixing performance as well as through the controlled rotational manipulation of individual HeLa cells.

Lateral Degassing Method for Disposable Film-Chip Microfluidic Devices

It is critical to develop a fast and simple method to remove air bubbles inside microchannels for automated, reliable, and reproducible microfluidic devices. As an active degassing method, this study introduces a lateral degassing method that can be easily implemented in disposable film-chip microfluidic devices. This method uses a disposable film-chip microchannel superstrate and a reusable substrate, which can be assembled and disassembled simply by vacuum pressure. The disposable microchannel superstrate is readily fabricated by bonding a microstructured polydimethylsiloxane replica and a silicone-coated release polymeric thin film. The reusable substrate can be a plate that has no function or is equipped with the ability to actively manipulate and sense substances in the microchannel by an elaborately patterned energy field. The degassing rate of the lateral degassing method and the maximum available pressure in the microchannel equipped with lateral degassing were evaluated. The usefulness of this method was demonstrated using complex structured microfluidic devices, such as a meandering microchannel, a microvortex, a gradient micromixer, and a herringbone micromixer, which often suffer from bubble formation. In conclusion, as an easy-to-implement and easy-to-use technique, the lateral degassing method will be a key technique to address the bubble formation problem of microfluidic devices.

A Fast Alternative to Soft Lithography for the Fabrication of Organ-on-a-Chip Elastomeric-Based Devices and Microactuators

Organ-on-a-chip technology promises to revolutionize how pre-clinical human trials are conducted. Engineering an in vitro environment that mimics the functionality and architecture of human physiology is essential toward building better platforms for drug development and personalized medicine. However, the complex nature of these devices requires specialized, time consuming, and expensive fabrication methodologies. Alternatives that reduce design-to-prototype time are needed, in order to fulfill the potential of these devices. Here, a streamlined approach is proposed for the fabrication of organ-on-a-chip devices with incorporated microactuators, by using an adaptation of xurography. This method can generate multilayered, membrane-integrated biochips in a matter of hours, using low-cost benchtop equipment. These devices are capable of withstanding considerable pressure without delamination. Furthermore, this method is suitable for the integration of flexible membranes, required for organ-on-a-chip applications, such as mechanical actuation or the establishment of biological barrier function. The devices are compatible with cell culture applications and present no cytotoxic effects or observable alterations on cellular homeostasis. This fabrication method can rapidly generate organ-on-a-chip prototypes for a fraction of cost and time, in comparison to conventional soft lithography, constituting an interesting alternative to the current fabrication methods.