Multi-layered, membrane-integrated microfluidics based on replica molding of a thiol-ene epoxy thermoset for organ-on-a-chip applications

YOLOv5 based object detection in reel package X-ray images of semiconductor component

The industrial manufacturing landscape is currently shifting toward the incorporation of technologies based on artificial intelligence (AI). This transition includes an evolution toward smart factory infrastructure, with a specific focus on AI-driven strategies in production and quality control. Specifically, AI-empowered computer vision has emerged as a potent tool that offers a departure from extant rule-based systems and provides enhanced operational efficiency at manufacturing sites. As the manufacturing sector embraces this new paradigm, the impetus to integrate AI-integrated manufacturing is evident. Within this framework, one salient application is AI deep learning-facilitated small-object detection, which is poised to have extensive implications for diverse industrial applications. This study describes an optimized iteration of the YOLOv5 model, which is known for its efficacious single-stage object-detection abilities underpinned by PyTorch. Our proposed "improved model" incorporates an additional layer to the model's canonical three-layer architecture, augmenting accuracy and computational expediency. Empirical evaluations using semiconductor X-ray imagery reveal the model's superior performance metrics. Given the intricate specifications of surface-mount technologies, which are characterized by a plethora of micro-scale components, our model makes a seminal contribution to real-time, in-line production assessments. Quantitative analyses show that our improved model attained a mean average precision of 0.622, surpassing YOLOv5's 0.349, and a marked accuracy enhancement of 0.865, which is a significant improvement on YOLOv5's 0.552. These findings bolster the model's robustness and potential applicability, particularly in discerning objects at reel granularities during real-time inferencing.

Performance and biocompatibility of OSTEMER 322 in cell-based microfluidic applications

The Off-Stoichiometry Thiol-ene and Epoxy (OSTE+) polymer technology has been increasingly utilised in the field of microfluidics and lab-on-a-chip applications. However, the impact of OSTEMER polymers, specifically the OSTEMER 322 formulation, on cell viability has remained limited. In this work, we thoroughly explored the biocompatibility of this commercial OSTEMER formulation, along with various surface modifications, through a broad range of cell types, from fibroblasts to epithelial cells. We employed cell viability and confluence assays to evaluate the performance of the material and its modified variants in cell culturing. The properties of the pristine and modified OSTEMER were also investigated using surface characterization methods including contact angle, zeta potential, and X-ray photoelectron spectroscopy. Mass spectrometry analysis confirmed the absence of leaching constituents from OSTEMER, indicating its safety for cell-based applications. Our findings demonstrated that cell viability on OSTEMER surfaces is sufficient for typical cell culture experiments, suggesting OSTEMER 322 is a suitable material for a variety of cell-based assays in microfluidic devices.

A microfluidic organ-on-a-chip: into the next decade of bone tissue engineering applied in dentistry

A comprehensive understanding of the complex physiological and pathological processes associated with alveolar bones, their responses to different therapeutics strategies, and cell interactions with biomaterial becomes necessary in precisely treating patients with severe progressive periodontitis, as a bone-related issue in dentistry. However, existing monolayer cell culture or pre-clinical models have been unable to mimic the complex physiological, pathological and regeneration processes in the bone microenvironment in response to different therapeutic strategies. In this point, 'organ-on-a-chip' (OOAC) technology, specifically 'alveolar-bone-on-a-chip', is expected to resolve the problems by better imitating infection site microenvironment and microphysiology within the oral tissues. The OOAC technology is assessed in this study toward better approaches in disease modeling and better therapeutics strategy for bone tissue engineering applied in dentistry.

Towards a microfluidic H295R steroidogenesis assay-biocompatibility study and steroid detection on a thiol-ene-based chip

The development of cell-based microfluidic assays offers exciting new opportunities in toxicity testing, allowing for integration of new functionalities, automation, and high throughput in comparison to traditional well-plate assays. As endocrine disruption caused by environmental chemicals and pharmaceuticals represents a growing global health burden, the purpose of the current study was to contribute towards the miniaturization of the H295R steroidogenesis assay, from the well-plate to the microfluidic format. Microfluidic chip fabrication with the established well-plate material polystyrene (PS) is expensive and complicated; PDMS and thiol-ene were therefore tested as potential chip materials for microfluidic H295R cell culture, and evaluated in terms of cell attachment, cell viability, and steroid synthesis in the absence and presence of collagen surface modification. Additionally, spike-recovery experiments were performed, to investigate potential steroid adsorption to chip materials. Cell aggregation with poor steroid recoveries was observed for PDMS, while cells formed monolayer cultures on the thiol-ene chip material, with cell viability and steroid synthesis comparable to cells grown on a PS surface. As thiol-ene overall displayed more favorable properties for H295R cell culture, a microfluidic chip design and corresponding cell seeding procedure were successfully developed, achieving repeatable and uniform cell distribution in microfluidic channels. Finally, H295R perfusion culture on thiol-ene chips was investigated at different flow rates (20, 10, and 2.5 µL/min), and 13 steroids were detected in eluting cell medium over 48 h at the lowest flow rate. The presented work and results pave the way for a time-resolved microfluidic H295R steroidogenesis assay.

Integration of Extracellular Matrices into Organ-on-Chip Systems

The extracellular matrix (ECM) is a complex, dynamic network present within all tissues and organs that not only acts as a mechanical support and anchorage point but can also direct fundamental cell behavior, function, and characteristics. Although the importance of the ECM is well established, the integration of well-controlled ECMs into Organ-on-Chip (OoC) platforms remains challenging and the methods to modulate and assess ECM properties on OoCs remain underdeveloped. In this review, current state-of-the-art design and assessment of in vitro ECM environments is discussed with a focus on their integration into OoCs. Among other things, synthetic and natural hydrogels, as well as polydimethylsiloxane (PDMS) used as substrates, coatings, or cell culture membranes are reviewed in terms of their ability to mimic the native ECM and their accessibility for characterization. The intricate interplay among materials, OoC architecture, and ECM characterization is critically discussed as it significantly complicates the design of ECM-related studies, comparability between works, and reproducibility that can be achieved across research laboratories. Improving the biomimetic nature of OoCs by integrating properly considered ECMs would contribute to their further adoption as replacements for animal models, and precisely tailored ECM properties would promote the use of OoCs in mechanobiology.

The Cultivation Modality and Barrier Maturity Modulate the Toxicity of Industrial Zinc Oxide and Titanium Dioxide Nanoparticles on Nasal, Buccal, Bronchial, and Alveolar Mucosa Cell-Derived Barrier Models

As common industrial by-products, airborne engineered nanomaterials are considered important environmental toxins to monitor due to their potential health risks to humans and animals. The main uptake routes of airborne nanoparticles are nasal and/or oral inhalation, which are known to enable the transfer of nanomaterials into the bloodstream resulting in the rapid distribution throughout the human body. Consequently, mucosal barriers present in the nose, buccal, and lung have been identified and intensively studied as the key tissue barrier to nanoparticle translocation. Despite decades of research, surprisingly little is known about the differences among various mucosa tissue types to tolerate nanoparticle exposures. One limitation in comparing nanotoxicological data sets can be linked to a lack of harmonization and standardization of cell-based assays, where (a) different cultivation conditions such as an air-liquid interface or submerged cultures, (b) varying barrier maturity, and (c) diverse media substitutes have been used. The current comparative nanotoxicological study, therefore, aims at analyzing the toxic effects of nanomaterials on four human mucosa barrier models including nasal (RPMI2650), buccal (TR146), alveolar (A549), and bronchial (Calu-3) mucosal cell lines to better understand the modulating effects of tissue maturity, cultivation conditions, and tissue type using standard transwell cultivations at liquid-liquid and air-liquid interfaces. Overall, cell size, confluency, tight junction localization, and cell viability as well as barrier formation using 50% and 100% confluency was monitored using trans-epithelial-electrical resistance (TEER) measurements and resazurin-based Presto Blue assays of immature (e.g., 5 days) and mature (e.g., 22 days) cultures in the presence and absence of corticosteroids such as hydrocortisone. Results of our study show that cellular viability in response to increasing nanoparticle exposure scenarios is highly compound and cell-type specific (TR146 6 ± 0.7% at 2 mM ZnO (ZnO) vs. ~90% at 2 mM TiO2 (TiO2) for 24 h; Calu3 93.9 ± 4.21% at 2 mM ZnO vs. ~100% at 2 mM TiO2). Nanoparticle-induced cytotoxic effects under air-liquid cultivation conditions declined in RPMI2650, A549, TR146, and Calu-3 cells (~0.7 to ~0.2-fold), with increasing 50 to 100% barrier maturity under the influence of ZnO (2 mM). Cell viability in early and late mucosa barriers where hardly influenced by TiO2 as well as most cell types did not fall below 77% viability when added to Individual ALI cultures. Fully maturated bronchial mucosal cell barrier models cultivated under ALI conditions showed less tolerance to acute ZnO nanoparticle exposures (~50% remaining viability at 2 mM ZnO for 24 h) than the similarly treated but more robust nasal (~74%), buccal (~73%), and alveolar (~82%) cell-based models.

Soft Hydroxyapatite Composites Based on Triazine-Trione Systems as Potential Biomedical Engineering Frameworks

Composites of triazine-trione (TATO) thiol-ene networks and hydroxyapatite (HA) have shown great potential as topological fixation materials for complex bone fractures due to their high flexural modulus, biocompatibility, and insusceptibility to forming soft-tissue adhesions. However, the rigid mechanical properties of these composites make them unsuitable for applications requiring softness. The scope of these materials could therefore be widened by the design of new TATO monomers that would lead to composites with a range of mechanical properties. In this work, four novel TATO-based monomers, decorated with either ester or amide linkages as well as alkene or alkyne end groups, have been proposed and synthesized via fluoride-promoted esterification (FPE) chemistry. The ester-modified monomers were then successfully formulated along with the thiol TATO monomer tris [2-(3-mercaptopropionyloxy)ethyl] isocyanurate (TEMPIC) and HA to give soft composites, following the established photo-initiated thiol-ene coupling (TEC) or thiol-yne coupling (TYC) chemistry methodologies. The most promising composite shows excellent softness, with a flexural modulus of 57 (2) MPa and ε_f at maximum σ_f of 11.8 (0.3)%, which are 117 and 10 times softer than the previously developed system containing the commercially available tri-allyl TATO monomer (TATATO). Meanwhile, the surgically convenient viscosity of the composite resins and their excellent cytotoxicity profile allow them to be used in the construction of soft objects in a variety of shapes through drop-casting suitable for biomedical applications.

Engineering approaches for cardiac organoid formation and their characterization

Cardiac organoids are 3-dimensional (3D) structures composed of tissue or niche-specific cells, obtained from diverse sources, encapsulated in either a naturally derived or synthetic, extracellular matrix scaffold, and include exogenous biochemical signals such as essential growth factors. The overarching goal of developing cardiac organoid models is to establish a functional integration of cardiomyocytes with physiologically relevant cells, tissues, and structures like capillary-like networks composed of endothelial cells. These organoids used to model human heart anatomy, physiology, and disease pathologies in vitro have the potential to solve many issues related to cardiovascular drug discovery and fundamental research. The advent of patient-specific human-induced pluripotent stem cell-derived cardiovascular cells provide a unique, single-source approach to study the complex process of cardiovascular disease progression through organoid formation and incorporation into relevant, controlled microenvironments such as microfluidic devices. Strategies that aim to accomplish such a feat include microfluidic technology-based approaches, microphysiological systems, microwells, microarray-based platforms, 3D bioprinted models, and electrospun fiber mat-based scaffolds. This article discusses the engineering or technology-driven practices for making cardiac organoid models in comparison with self-assembled or scaffold-free methods to generate organoids. We further discuss emerging strategies for characterization of the bio-assembled cardiac organoids including electrophysiology and machine-learning and conclude with prospective points of interest for engineering cardiac tissues in vitro.

Polymeric Microfluidic Devices Fabricated Using Epoxy Resin for Chemically Demanding and Day-Long Experiments

Polydimethylsiloxane (PDMS) is a widely used material in laboratories for fabricating microfluidic devices with a rapid and reproducible prototypingability, owing to its inherent properties (e.g., flexibility, air permeability, and transparency). However, the PDMS channel is easily deformed under pressures applied to generate flows because of its elasticity, which can affect the robustness of experiments. In addition, air permeability of PDMS causes the pervaporation of water, and its porous structure absorbs oil and even small hydrophobic molecules, rendering it inappropriate for chemically demanding or day-long experiments. In this study, we develop a rapid and reproducible fabrication method for polymer-based rigid microfluidic devices, using epoxy resin that can overcome the limitations of PDMS channels, which are structurally and chemically robust. We first optimize a high-resolution fabrication protocol to achieve convenient and repeatable prototyping of polymeric devices via epoxy casting using PDMS soft molds. In addition, we compare the velocity changes in PDMS microchannels by tracking fluorescent particles in various flows (~133 μL/min) to demonstrate the structural robustness of the polymeric device. Furthermore, by comparing the adsorption of fluorescent hydrophobic chemicals and the pervaporation through channel walls, we demonstrate the excellent chemical resistance of the polymeric device and its suitability for day-long experiments. The rigid polymeric device can facilitate lab-on-chip research and enable various applications, such as high-performance liquid chromatography, anaerobic bacterial culture, and polymerase chain reaction, which require chemically or physically demanding experiments.

Microfluidic Approaches for Affinity-Based Exosome Separation

As a subspecies of extracellular vesicles (EVs), exosomes have provided promising results in diagnostic and theranostic applications in recent years. The nanometer-sized exosomes can be extracted by liquid biopsy from almost all body fluids, making them especially suitable for mainly non-invasive point-of-care (POC) applications. To achieve this, exosomes must first be separated from the respective biofluid. Impurities with similar properties, heterogeneity of exosome characteristics, and time-related biofouling complicate the separation. This practical review presents the state-of-the-art methods available for the separation of exosomes. Furthermore, it is shown how new separation methods can be developed. A particular focus lies on the fabrication and design of microfluidic devices using highly selective affinity separation. Due to their compactness, quick analysis time and portable form factor, these microfluidic devices are particularly suitable to deliver fast and reliable results for POC applications. For these devices, new manufacturing methods (e.g., laminating, replica molding and 3D printing) that use low-cost materials and do not require clean rooms are presented. Additionally, special flow routes and patterns that increase contact surfaces, as well as residence time, and thus improve affinity purification are displayed. Finally, various analyses are shown that can be used to evaluate the separation results of a newly developed device. Overall, this review paper provides a toolbox for developing new microfluidic affinity devices for exosome separation.

Leveraging bioengineering to assess cellular functions and communication within human fetal membranes

The fetal membranes enclose the growing fetus and amniotic fluid. Preterm prelabor rupture of fetal membranes is a leading cause of preterm birth. Fetal membranes are composed of many different cell types, both structural and immune. These cells must coordinate functions for tensile strength and membrane integrity to contain the growing fetus and amniotic fluid. They must also balance immune responses to pathogens with maintaining maternal-fetal tolerance. Perturbation of this equilibrium can lead to preterm premature rupture of membranes without labor. In this review, we describe the formation of the fetal membranes to orient the reader, discuss some of the common forms of communication between the cell types of the fetal membranes, and delve into the methods used to tease apart this paracrine signaling within the membranes, including emerging technologies such as organ-on-chip models of membrane immunobiology.

A modular microfluidic platform to enable complex and customisable in vitro models for neuroscience

Disorders of the central nervous system (CNS) represent a global health challenge and an increased understanding of the CNS in both physiological and pathophysiological states is essential to tackle the problem. Modelling CNS conditions is difficult, as traditional in vitro models fail to recapitulate precise microenvironments and animal models of complex disease often have limited translational validity. Microfluidic and organ-on-chip technologies offer an opportunity to develop more physiologically relevant and complex in vitro models of the CNS. They can be developed to allow precise cellular patterning and enhanced experimental capabilities to study neuronal function and dysfunction. To improve ease-of-use of the technology and create new opportunities for novel in vitro studies, we introduce a modular platform consisting of multiple, individual microfluidic units that can be combined in several configurations to create bespoke culture environments. Here, we report proof-of-concept experiments creating complex in vitro models and performing functional analysis of neuronal activity across modular interfaces. This platform technology presents an opportunity to increase our understanding of CNS disease mechanisms and ultimately aid the development of novel therapies.

Applications of Polymers for Organ-on-Chip Technology in Urology

Organ-on-chips (OOCs) are microfluidic devices used for creating physiological organ biomimetic systems. OOC technology brings numerous advantages in the current landscape of preclinical models, capable of recapitulating the multicellular assemblage, tissue-tissue interaction, and replicating numerous human pathologies. Moreover, in cancer research, OOCs emulate the 3D hierarchical complexity of in vivo tumors and mimic the tumor microenvironment, being a practical cost-efficient solution for tumor-growth investigation and anticancer drug screening. OOCs are compact and easy-to-use microphysiological functional units that recapitulate the native function and the mechanical strain that the cells experience in the human bodies, allowing the development of a wide range of applications such as disease modeling or even the development of diagnostic devices. In this context, the current work aims to review the scientific literature in the field of microfluidic devices designed for urology applications in terms of OOC fabrication (principles of manufacture and materials used), development of kidney-on-chip models for drug-toxicity screening and kidney tumors modeling, bladder-on-chip models for urinary tract infections and bladder cancer modeling and prostate-on-chip models for prostate cancer modeling.

Microscopic Imaging Methods for Organ-on-a-Chip Platforms

Microscopic imaging is essential and the most popular method for in situ monitoring and evaluating the outcome of various organ-on-a-chip (OOC) platforms, including the number and morphology of mammalian cells, gene expression, protein secretions, etc. This review presents an overview of how various imaging methods can be used to image organ-on-a-chip platforms, including transillumination imaging (including brightfield, phase-contrast, and holographic optofluidic imaging), fluorescence imaging (including confocal fluorescence and light-sheet fluorescence imaging), and smartphone-based imaging (including microscope attachment-based, quantitative phase, and lens-free imaging). While various microscopic imaging methods have been demonstrated for conventional microfluidic devices, a relatively small number of microscopic imaging methods have been demonstrated for OOC platforms. Some methods have rarely been used to image OOCs. Specific requirements for imaging OOCs will be discussed in comparison to the conventional microfluidic devices and future directions will be introduced in this review.

Performance characterization of transparent and conductive grids one-step-printed on curved substrates using template-guided foaming

Next-generation electronic devices require electrically conductive, mechanically flexible, and optically transparent conducting electrodes (CEs) that can endure large deformations.

Design and Fabrication of Organ-on-Chips: Promises and Challenges

The advent of the miniaturization approach has influenced the research trends in almost all disciplines. Bioengineering is one of the fields benefiting from the new possibilities of microfabrication techniques, especially in cell and tissue culture, disease modeling, and drug discovery. The limitations of existing 2D cell culture techniques, the high time and cost requirements, and the considerable failure rates have led to the idea of 3D cell culture environments capable of providing physiologically relevant tissue functions in vitro. Organ-on-chips are microfluidic devices used in this context as a potential alternative to in vivo animal testing to reduce the cost and time required for drug evaluation. This emerging technology contributes significantly to the development of various research areas, including, but not limited to, tissue engineering and drug discovery. However, it also brings many challenges. Further development of the technology requires interdisciplinary studies as some problems are associated with the materials and their manufacturing techniques. Therefore, in this paper, organ-on-chip technologies are presented, focusing on the design and fabrication requirements. Then, state-of-the-art materials and microfabrication techniques are described in detail to show their advantages and also their limitations. A comparison and identification of gaps for current use and further studies are therefore the subject of the final discussion.

Bridging the academic-industrial gap: application of an oxygen and pH sensor-integrated lab-on-a-chip in nanotoxicology

Translation of advanced cell-based assays exhibiting a higher degree of automation, miniaturization, and integration of complementary sensing functions is mainly limited by the development of industrial-relevant prototypes that can be readily produced in larger volumes. Despite the increasing number of academic publications in recent years, the manufacturability of these microfluidic cell cultures systems is largely ignored, thus severely restricting their implementation in routine toxicological applications. We have developed a dual-sensor integrated microfluidic cell analysis platform using industrial specifications, materials, and fabrication methods to conduct risk assessment studies of engineered nanoparticles to overcome this academic-industrial gap. Non-invasive and time-resolved monitoring of cellular oxygen uptake and metabolic activity (pH) in the absence and presence of nanoparticle exposure is accomplished by integrating optical sensor spots into a cyclic olefin copolymer (COC)-based microfluidic platform. Results of our nanotoxicological study, including two physiological cell barriers that are essential in the protection from exogenous factors, the intestine (Caco-2) and the vasculature (HUVECs) showed that the assessment of the cells' total energy metabolism is ideally suited to rapidly detect cytotoxicities. Additional viability assay verification using state-of-the-art dye exclusion assays for nanotoxicology demonstrated the similarity and comparability of our results, thus highlighting the benefits of employing a compact and cost-efficient microfluidic dual-sensor platform as a pre-screening tool in nanomaterial risk assessment and as a rapid quality control measure in medium to high-throughput settings.

Sorption of Neuropsychopharmaca in Microfluidic Materials for In Vitro Studies

Sorption (i.e., adsorption and absorption) of small-molecule compounds to polydimethylsiloxane (PDMS) is a widely acknowledged phenomenon. However, studies to date have largely been conducted under atypical conditions for microfluidic applications (lack of perfusion, lack of biological fluids, etc.), especially considering biological studies such as organs-on-chips where small-molecule sorption poses the largest concern. Here, we present an in-depth study of small-molecule sorption under relevant conditions for microphysiological systems, focusing on a standard geometry for biological barrier studies that find application in pharmacokinetics. We specifically assess the sorption of a broad compound panel including 15 neuropsychopharmaca at in vivo concentration levels. We consider devices constructed from PDMS as well as two material alternatives (off-stoichiometry thiol-ene-epoxy, or tape/polycarbonate laminates). Moreover, we study the much neglected impact of peristaltic pump tubing, an essential component of the recirculating systems required to achieve in vivo-like perfusion shear stresses. We find that the choice of the device material does not have a significant impact on the sorption behavior in our barrier-on-chip-type system. Our PDMS observations in particular suggest that excessive compound sorption observed in prior studies is not sufficiently described by compound hydrophobicity or other suggested predictors. Critically, we show that sorption by peristaltic tubing, including the commonly utilized PharMed BPT, dominates over device sorption even on an area-normalized basis, let alone at the typically much larger tubing surface areas. Our findings highlight the importance of validating compound dosages in organ-on-chip studies, as well as the need for considering tubing materials with equal or higher care than device materials.

CO2 laser fabrication of hydrogel-based open-channel microfluidic devices

This study proposed a rapid and low-cost fabrication method for open-channel hydrogel-based microfluidic devices using CO₂ laser ablation. The agarose hydrogel substrate was prepared with agarose gelation in DI water upon microwave heating, then a commercial CO₂ laser system was used for the direct laser ablation of microchannels on the surface of agarose hydrogel substrate, the hydrophilic nature of the microchannels fabricated on hydrogel substrate enables the self-driven of the liquid inside the microchannels with capillary force. The profiles of the laser ablated microchannels on agarose hydrogel substrate with various laser power and scan speed were studied in detail. Due to the loss of water when exposed to the atmosphere, significant deformation of the fabricated microchannels was observed, and the profile change was recorded for 48 h for comparison. An easy-to-access storage method of hydrogel-based microfluidic device in DI water was also proposed in this study. Unlike compact silicon or polymer-based microfluidic devices, the hydrogel is formed by cross-linked polymer chains filled with water, for a better understanding of the diffusion of small molecules into the bulk hydrogel material during fluid propagation inside the microchannel, the Nile red fluorescent was added into the liquid and the diffusion across the hydrogel-based microchannels with time was measured and discussed in this study. Several open-channel agarose hydrogel-based microfluidic devices were fabricated in this study for the demonstration of the proposed fabrication method. The CO₂ laser ablation approach for agarose hydrogel-based microfluidic devices has the advantages of rapid processing time, low-cost, highly biocompatible, and self-driven without pumps and could have wide application potentials in biological and medical fields.

Composite Elastomer-Enabled Rapid Photofabrication of Microfluidic Devices

Microfluidics, as an emerging technology, is highly dependent on the evolution of device materials and fabrication techniques. While replica molding of polydimethylsiloxane and hot embossing/injection molding of thermoplastics are most popular, they are either hard to scale up or inappropriate for laboratory-scale prototyping. Recently, photocurable resins, as a huge class of materials, have attracted extensive interest. However, very few of them can now be used in device fabrication due to the challenge in machining these materials. In response, we herein propose a novel concept of composite elastomers, which can covalently link with and consequently offer a flexible support to photocured thin films. This effect would allow most photocurable resins to be used in microfluidic device fabrication, greatly enriching the material choices for diverse applications. Moreover, the whole fabrication process becomes very simple and rapid, with an impressive throughput of at least hundreds of replicas per day. With these features, it is reasonably expected that the composite elastomer-enabled rapid photofabrication method will be very competent for laboratory prototyping, providing not only the ease of fabrication but also a possibility to select the materials specifically for ultimate applications and promising potential for volume production without the redevelopment process. These may offer a good opportunity to narrow the current gap between academic research and industrial practice.

Continuous Monitoring Reveals Protective Effects of N-Acetylcysteine Amide on an Isogenic Microphysiological Model of the Neurovascular Unit

Microphysiological systems mimic the in vivo cellular ensemble and microenvironment with the goal of providing more human-like models for biopharmaceutical research. In this study, the first such model of the blood-brain barrier (BBB-on-chip) featuring both isogenic human induced pluripotent stem cell (hiPSC)-derived cells and continuous barrier integrity monitoring with <2 min temporal resolution is reported. Its capabilities are showcased in the first microphysiological study of nitrosative stress and antioxidant prophylaxis. Relying on off-stoichiometry thiol-ene-epoxy (OSTE+) for fabrication greatly facilitates assembly and sensor integration compared to the prevalent polydimethylsiloxane devices. The integrated cell-substrate endothelial resistance monitoring allows for capturing the formation and breakdown of the BBB model, which consists of cocultured hiPSC-derived endothelial-like and astrocyte-like cells. Clear cellular disruption is observed when exposing the BBB-on-chip to the nitrosative stressor linsidomine, and the barrier permeability and barrier-protective effects of the antioxidant N-acetylcysteine amide are reported. Using metabolomic network analysis reveals further drug-induced changes consistent with prior literature regarding, e.g., cysteine and glutathione involvement. A model like this opens new possibilities for drug screening studies and personalized medicine, relying solely on isogenic human-derived cells and providing high-resolution temporal readouts that can help in pharmacodynamic studies.

Endometrium On-a-Chip Reveals Insulin- and Glucose-induced Alterations in the Transcriptome and Proteomic Secretome

The molecular interactions between the maternal environment and the developing embryo are key for early pregnancy success and are influenced by factors such as maternal metabolic status. Our understanding of the mechanism(s) through which these individual nutritional stressors alter endometrial function and the in utero environment for early pregnancy success is, however, limited. Here we report, for the first time, the use of an endometrium-on-a-chip microfluidics approach to produce a multicellular endometrium in vitro. Isolated endometrial cells (epithelial and stromal) from the uteri of nonpregnant cows in the early luteal phase (Days 4-7) were seeded in the upper chamber of the device (epithelial cells; 4-6 × 104 cells/mL) and stromal cells seeded in the lower chamber (1.5-2 × 104 cells/mL). Exposure of cells to different concentrations of glucose (0.5, 5.0, or 50 mM) or insulin (Vehicle, 1 or 10 ng/mL) was performed at a flow rate of 1 µL/minute for 72 hours. Quantitative differences in the cellular transcriptome and the secreted proteome of in vitro-derived uterine luminal fluid were determined by RNA-sequencing and tandem mass tagging mass spectrometry, respectively. High glucose concentrations altered 21 and 191 protein-coding genes in epithelial and stromal cells, respectively (P < .05), with a dose-dependent quantitative change in the protein secretome (1 and 23 proteins). Altering insulin concentrations resulted in limited transcriptional changes including transcripts for insulin-like binding proteins that were cell specific but altered the quantitative secretion of 196 proteins. These findings highlight 1 potential mechanism by which changes to maternal glucose and insulin alter uterine function.

Membrane integration into PDMS-free microfluidic platforms for organ-on-chip and analytical chemistry applications

Membranes play a crucial role in many microfluidic systems, enabling versatile applications in highly diverse research fields. However, the tight and robust integration of membranes into microfluidic systems requires complex fabrication processes. Most integration approaches, so far, rely on polydimethylsiloxane (PDMS) as base material for the microfluidic chips. Several limitations of PDMS have resulted in the transition of many microfluidic approaches to PDMS-free systems using alternative materials such as thermoplastics. To integrate membranes in those PDMS-free systems, novel alternative approaches are required. This review provides an introduction into microfluidic systems applying membrane technology for analytical systems and organ-on-chip as well as a comprehensive overview of methods for the integration of membranes into PDMS-free systems. The overview and examples will provide a valuable resource and starting point for any researcher that is aiming at implementing membranes in microfluidic systems without using PDMS.

Facile Patterning of Thermoplastic Elastomers and Robust Bonding to Glass and Thermoplastics for Microfluidic Cell Culture and Organ-on-Chip

The emergence and spread of microfluidics over the last decades relied almost exclusively on the elastomer polydimethylsiloxane (PDMS). The main reason for the success of PDMS in the field of microfluidic research is its suitability for rapid prototyping and simple bonding methods. PDMS allows for precise microstructuring by replica molding and bonding to different substrates through various established strategies. However, large-scale production and commercialization efforts are hindered by the low scalability of PDMS-based chip fabrication and high material costs. Furthermore, fundamental limitations of PDMS, such as small molecule absorption and high water evaporation, have resulted in a shift toward PDMS-free systems. Thermoplastic elastomers (TPE) are a promising alternative, combining properties from both thermoplastic materials and elastomers. Here, we present a rapid and scalable fabrication method for microfluidic systems based on a polycarbonate (PC) and TPE hybrid material. Microstructured PC/TPE-hybrid modules are generated by hot embossing precise features into the TPE while simultaneously fusing the flexible TPE to a rigid thermoplastic layer through thermal fusion bonding. Compared to TPE alone, the resulting, more rigid composite material improves device handling while maintaining the key advantages of TPE. In a fast and simple process, the PC/TPE-hybrid can be bonded to several types of thermoplastics as well as glass substrates. The resulting bond strength withstands at least 7.5 bar of applied pressure, even after seven days of exposure to a high-temperature and humid environment, which makes the PC/TPE-hybrid suitable for most microfluidic applications. Furthermore, we demonstrate that the PC/TPE-hybrid features low absorption of small molecules while being biocompatible, making it a suitable material for microfluidic biotechnological applications.

Lung on a Chip Development from Off-Stoichiometry Thiol-Ene Polymer

Current in vitro models have significant limitations for new respiratory disease research and rapid drug repurposing. Lung on a chip (LOAC) technology offers a potential solution to these problems. However, these devices typically are fabricated from polydimethylsiloxane (PDMS), which has small hydrophobic molecule absorption, which hinders the application of this technology in drug repurposing for respiratory diseases. Off-stoichiometry thiol–ene (OSTE) is a promising alternative material class to PDMS. Therefore, this study aimed to test OSTE as an alternative material for LOAC prototype development and compare it to PDMS. We tested OSTE material for light transmission, small molecule absorption, inhibition of enzymatic reactions, membrane particle, and fluorescent dye absorption. Next, we microfabricated LOAC devices from PDMS and OSTE, functionalized with human umbilical vein endothelial cell (HUVEC) and A549 cell lines, and analyzed them with immunofluorescence. We demonstrated that compared to PDMS, OSTE has similar absorption of membrane particles and effect on enzymatic reactions, significantly lower small molecule absorption, and lower light transmission. Consequently, the immunofluorescence of OSTE LOAC was significantly impaired by OSTE optical properties. In conclusion, OSTE is a promising material for LOAC, but optical issues should be addressed in future LOAC prototypes to benefit from the material properties.

The material-enabled oxygen control in thiol-ene microfluidic channels and its feasibility for subcellular drug metabolism assays under hypoxia in vitro

Tissue oxygen levels are known to be critical to regulation of many cellular processes, including the hepatic metabolism of therapeutic drugs, but its impact is often ignored in in vitro assays. In this study, the material-induced oxygen scavenging property of off-stoichiometric thiol-enes (OSTE) was exploited to create physiologically relevant oxygen concentrations in microfluidic immobilized enzyme reactors (IMERs) incorporating human liver microsomes. This could facilitate rapid screening of, for instance, toxic drug metabolites possibly produced in hypoxic conditions typical for many liver injuries. The mechanism of OSTE-induced oxygen scavenging was examined in depth to enable precise adjustment of the on-chip oxygen concentration with the help of microfluidic flow. The oxygen scavenging rate of OSTE was shown to depend on the type and the amount of the thiol monomer used in the bulk composition, and the surface-to-volume ratio of the chip design, but not on the physical or mechanical properties of the bulk. Our data suggest that oxygen scavenging takes place at the polymer-liquid interface, likely via oxidative reactions of the excess thiol monomers released from the bulk with molecular oxygen. Based on the kinetic constants governing the oxygen scavenging rate in OSTE microchannels, a microfluidic device comprising monolithically integrated oxygen depletion and IMER units was designed and its performance validated with the help of oxygen-dependent metabolism of an antiretroviral drug, zidovudine, which yields a cytotoxic metabolite under hypoxic conditions.

Direct Single-Step Printing of Conductive Grids on Curved Surfaces Using Template-Guided Foaming

Advanced transparent conductors have been studied intensively in the aspects of materials, structures, and printing methods. The material and structural advancements have been successfully accomplished with various conductive nanomaterials and spring-like structures for better electrical conductivity and high mechanical flexibility of the transparent conductors. However, the capability to print submicrometer conductive patterns directly and conformally on curved surfaces with low processing cost and high throughput remains a technological challenge to achieve, primarily because of the original two-dimensional (2D) nature of conventional lithography processes. In our study, we exploit a liquid-mediated patterning approach in the development of flexible templates, enabling printing of curvilinear silver grids in a single-step and strain-free manner at a submicrometer resolution within several minutes with minimum loss of noble metals. The template can guide arrays of receding liquid-air interfaces on curved substrates during liquid evaporation, thereby generating ordered 2D foam structures that can confine and assemble silver nanoparticles in grid patterns. The printed silver grids exhibit suitable optical, electrical, and Joule-heating performances, enabling their application in transparent heaters. Our technique has the potential to extend the existing 2D micro/nanofluidic liquid-mediated patterning approach to three-dimensional (3D) control of liquid-air interfaces for low-cost all-liquid-processed functional 3D optoelectronics in the future.

Microfluidic channel integrated with a lattice lightsheet microscopic system for continuous cell imaging

In this study, a continuous cell-imaging system with subcellular resolution was developed by integrating a microfluidic platform with lattice lightsheet microscopy (LLSM). To reduce aberrations of the lightsheet propagating into the device, a microfluidic channel sealed with a water refractive index-matched thin film was fabricated. When the lightsheet emerged from the water-immersed objectives and penetrated through the water refractive-matched thin film into the microfluidic channel at an incident angle, less light scattering and fewer aberrations were found. Suspended cells flowed across the lattice lightsheet, and an imaging system with the image plane perpendicular to the lightsheet was used to sequentially acquire cell images. By applying a thinner lattice lightsheet, higher-resolution, higher-contrast images were obtained. Furthermore, three-dimensional cell images could be achieved by reconstructing sequential two-dimensional cell images.

Facile Nanoimprinting of Robust High-Aspect-Ratio Nanostructures for Human Cell Biomechanics

High-aspect-ratio and hierarchically nanostructured surfaces are common in nature. Synthetic variants are of interest for their specific chemical, mechanic, electric, photonic, or biologic properties but are cumbersome in fabrication or suffer from structural collapse. Here, we replicated and directly biofunctionalized robust, large-area, and high-aspect-ratio nanostructures by nanoimprint lithography of an off-stoichiometric thiol-ene-epoxy polymer. We structured-in a single-step process-dense arrays of pillars with a diameter as low as 100 nm and an aspect ratio of 7.2; holes with a diameter of 70 nm and an aspect ratio of >20; and complex hierarchically layered structures, all with minimal collapse and defectivity. We show that the nanopillar arrays alter mechanosensing of human hepatic cells and provide precise spatial control of cell attachment. We speculate that our results can enable the widespread use of high-aspect-ratio nanotopograhy applications in mechanics, optics, and biomedicine.

Microfluidics and organ-on-a-chip technologies: A systematic review of the methods used to mimic bone marrow

Bone marrow (BM) is an organ responsible for crucial processes in living organs, e. g., hematopoiesis. In recent years, Organ-on-a-Chip (OoC) devices have been used to satisfy the need for in vitro systems that better mimic the phenomena occurring in the BM microenvironment. Given the growing interest in these systems and the diversity of developed devices, an integrative systematic literature review is required. We have performed this review, following the PRISMA method aiming to identify the main characteristics and assess the effectiveness of the devices that were developed to represent the BM. A search was performed in the Scopus, PubMed, Web of Science and Science Direct databases using the keywords (("bone marrow" OR "hematopoietic stem cells" OR "haematopoietic stem cells") AND ("organ in a" OR "lab on a chip" OR "microfluidic" OR "microfluidic*" OR ("bioreactor" AND "microfluidic*"))). Original research articles published between 2009 and 2020 were included in the review, giving a total of 21 papers. The analysis of these papers showed that their main purpose was to study BM cells biology, mimic BM niches, model pathological BM, and run drug assays. Regarding the fabrication protocols, we have observed that polydimethylsiloxane (PDMS) material and soft lithography method were the most commonly used. To reproduce the microenvironment of BM, most devices used the type I collagen and alginate. Peristaltic and syringe pumps were mostly used for device perfusion. Regarding the advantages compared to conventional methods, there were identified three groups of OoC devices: perfused 3D BM; co-cultured 3D BM; and perfused co-cultured 3D BM. Cellular behavior and mimicking their processes and responses were the mostly commonly studied parameters. The results have demonstrated the effectiveness of OoC devices for research purposes compared to conventional cell cultures. Furthermore, the devices have a wide range of applicability and the potential to be explored.

Beyond Polydimethylsiloxane: Alternative Materials for Fabrication of Organ-on-a-Chip Devices and Microphysiological Systems

Polydimethylsiloxane (PDMS) is the predominant material used for organ-on-a-chip devices and microphysiological systems (MPSs) due to its ease-of-use, elasticity, optical transparency, and inexpensive microfabrication. However, the absorption of small hydrophobic molecules by PDMS and the limited capacity for high-throughput manufacturing of PDMS-laden devices severely limit the application of these systems in personalized medicine, drug discovery, in vitro pharmacokinetic/pharmacodynamic (PK/PD) modeling, and the investigation of cellular responses to drugs. Consequently, the relatively young field of organ-on-a-chip devices and MPSs is gradually beginning to make the transition to alternative, nonabsorptive materials for these crucial applications. This review examines some of the first steps that have been made in the development of organ-on-a-chip devices and MPSs composed of such alternative materials, including elastomers, hydrogels, thermoplastic polymers, and inorganic materials. It also provides an outlook on where PDMS-alternative devices are trending and the obstacles that must be overcome in the development of versatile devices based on alternative materials to PDMS.

OSTE+ for in situ SAXS analysis with droplet microfluidic devices

In recent years, microfluidic-based sample preparation techniques have emerged as a powerful tool for measurements at large scale X-ray facilities. Most often the microfluidic device was a form of hybrid system, i.e. an assembly of different materials, because a simple, versatile and inexpensive microfabrication method, on the one hand, and X-ray compatibility, on the other hand, cannot generally be achieved by the same material. The arrival of a new polymer family based on off-stoichiometric thiol-ene-epoxy (OSTE+) has recently redistributed the cards. In this context, we studied the relevance and the compatibility of OSTE+ for small-angle X-ray scattering (SAXS) studies. The material was characterized regarding its X-ray properties (transmission coefficient, attenuation coefficient, scattering pattern and polymer aging under X-ray light) and their comparison with those of the usual polymers used in microfluidics and/or for synchrotron radiation experiments. We show that OSTE+ has a better SAXS signal than polyimide, the polymer of reference in the SAXS community. Then a detailed protocol to manufacture a suitably thin full OSTE+ chip (total thickness <500 μm) is described and the potency of full OSTE+ devices for in situ SAXS studies is highlighted in two case-studies: the characterization of gold nanoparticles and the precipitation of cerium oxalate particles, both in moving droplets. Additionally, a method to analyze the scattering signals from droplet and carrier phase in a segmented flow is proposed.

Microphysiological systems for the modeling of wound healing and evaluation of pro-healing therapies

Wound healing is a multivariate process involving the coordinated response of numerous proteins and cell types. Accordingly, biomedical research has seen an increased adoption of the use of in vitro wound healing assays with complexity beyond that offered by traditional well-plate constructs. These microphysiological systems (MPS) seek to recapitulate one or more physiological features of the in vivo microenvironment, while retaining the analytical capacity of more reductionist assays. Design efforts to achieve relevant wound healing physiology include the use of dynamic perfusion over static culture, the incorporation of multiple cell types, the arrangement of cells in three dimensions, the addition of biomechanically and biochemically relevant hydrogels, and combinations thereof. This review provides a brief overview of the wound healing process and in vivo assays, and we critically review the current state of MPS and supporting technologies for modelling and studying wound healing. We distinguish between MPS that seek to inform a particular phase of wound healing, and constructs that have the potential to inform multiple phases of wound healing. This distinction is a product of whether analysis of a particular process is prioritized, or a particular physiology is prioritized, during design. Material selection is emphasized throughout, and relevant fabrication techniques discussed.

Advanced Fabrication Techniques of Microengineered Physiological Systems

The field of organs-on-chips (OOCs) has experienced tremendous growth over the last decade. However, the current main limiting factor for further growth lies in the fabrication techniques utilized to reproducibly create multiscale and multifunctional devices. Conventional methods of photolithography and etching remain less useful to complex geometric conditions with high precision needed to manufacture the devices, while laser-induced methods have become an alternative for higher precision engineering yet remain costly. Meanwhile, soft lithography has become the foundation upon which OOCs are fabricated and newer methods including 3D printing and injection molding show great promise to innovate the way OOCs are fabricated. This review is focused on the advantages and disadvantages associated with the commonly used fabrication techniques applied to these microengineered physiological systems (MPS) and the obstacles that remain in the way of further innovation in the field.

Thiol-Ene Based Polymers as Versatile Materials for Microfluidic Devices for Life Sciences Applications

While there is a steady growth in the number of microfluidics applications, the search for an optimal material that delivers the diverse characteristics needed for the numerous tasks is still nowhere close to being settled. Often overlooked and still underrepresented, the thiol-ene family of polymer materials has an enormous potential for applications in organs-on-a-chip, droplet productions, microanalytics, and point of care testing. In this review, the main characteristics of the thiol-ene materials are given, and advantages and drawbacks with respect to their potential in microfluidic chip fabrication are critically assessed. Select applications, which exploit the versatility of the thiol-ene polymers, are presented and discussed. It is concluded that, in particular, the rapid prototyping possibility combined with the material's resulting mechanical strength, solvent resistance, and biocompatibility, as well as the inherently easy surface functionalization, are strong factors to make thiol-ene polymers strong contenders for promising future materials for many biological, clinical, and technical lab-on-a-chip applications.

A compression transmission device for the evaluation of bonding strength of biocompatible microfluidic and biochip materials and systems

Bonding of a variety of inorganic and organic polymers as multi-layered structures is one of the main challenges for biochip production even to date, since the chemical nature of these materials often does not allow easy and straight forward bonding and proper sealing. After selection of an appropriate method to bond the chosen materials to form a complex biochip, function and stability of bonding either requires qualitative burst tests or expensive mechanical multi-test stations, that often do not have the right adaptors to clamp biochip slides without destruction. Therefore, we have developed a simple and inexpensive bonding test based on 3D printed transmission elements that translate compressive forces via manual compression, hand press or hydraulic press compression into shear and tensile force. Mechanical stress simulations showed that design of the bonding geometry and size must be considered for bonding tests since the stress distribution thus bonding strength heavily varies with size but also with geometry. We demonstrate the broad applicability of our 3D printed bonding test system by testing the most frequent bonding strategies in combination with the respective most frequently used biochip material in a force-to-failure study. All evaluated materials are biocompatible and used in cell-based biochip devices. This study is evaluating state-of-the-art bonding approaches used for sealing of microfluidic biochips including adhesive bonding, plasma bonding, solvent bonding as well as bonding mediated by amino-silane monolayers or even functional thiol-ene epoxy biochip materials that obviate intermediate adhesive layers.

Magnetic micropump embedded in contact lens for on-demand drug delivery

In this paper, we report a thin magnetic micropump embedded in contact lens, which is capable of on-demand one-directional drug delivery. The proposed micropump can be actuated by the external magnetic field whenever needed without the need of battery. A micro check valve was integrated with the micropump for one-directional drug delivery from the micropump to the post-lens tear film. With actuation of the external magnetic field, the micro check valve is opened, and on-demand drug release can be realized. On the contrary, without an external magnetic field, the micro check valve is closed, and the undesired drug diffusion can be prevented. Through the control of the strength and the frequency of the magnetic field pulse, on-demand drug release and controlled dose can be realized.

Current Strategies and Future Perspectives of Skin-on-a-Chip Platforms: Innovations, Technical Challenges and Commercial Outlook

The skin is the largest and most exposed organ in the human body. Not only it is involved in numerous biological processes essential for life but also it represents a significant endpoint for the application of pharmaceuticals. The area of in vitro skin tissue engineering has been progressing extensively in recent years. Advanced in vitro human skin models strongly impact the discovery of new drugs thanks to the enhanced screening efficiency and reliability. Nowadays, animal models are largely employed at the preclinical stage of new pharmaceutical compounds development for both risk assessment evaluation and pharmacokinetic studies. On the other hand, animal models often insufficiently foresee the human reaction due to the variations in skin immunity and physiology. Skin-on-chips devices offer innovative and state-of-the-art platforms essential to overcome these limitations. In the present review, we focus on the contribution of skin-on-chip platforms in fundamental research and applied medical research. In addition, we also highlighted the technical and practical difficulties that must be overcome to enhance skin-on-chip platforms, e.g. embedding electrical measurements, for improved modeling of human diseases as well as of new drug discovery and development.

Flat and microstructured polymeric membranes in organs-on-chips

In recent years, organs-on-chips (OOCs) have been developed to meet the desire for more realistic in vitro cell culture models. These systems introduce microfluidics, mechanical stretch and other physiological stimuli to in vitro models, thereby significantly enhancing their descriptive power. In most OOCs, porous polymeric membranes are used as substrates for cell culture. The polymeric material, morphology and shape of these membranes are often suboptimal, despite their importance for achieving ideal cell functionality such as cell-cell interaction and differentiation. The currently used membranes are flat and thus do not account for the shape and surface morphology of a tissue. Moreover, the polymers used for fabrication of these membranes often lack relevant characteristics, such as mechanical properties matching the tissue to be developed and/or cytocompatibility. Recently, innovative techniques have been reported for fabrication of porous membranes with suitable porosity, shape and surface morphology matching the requirements of OOCs. In this paper, we review the state of the art for developing these membranes and discuss their application in OOCs.

Microfluidic nutrient gradient-based three-dimensional chondrocyte culture-on-a-chip as an in vitro equine arthritis model

In this work, we describe a microfluidic three-dimensional (3D) chondrocyte culture mimicking in vivo articular chondrocyte morphology, cell distribution, metabolism, and gene expression. This has been accomplished by establishing a physiologic nutrient diffusion gradient across the simulated matrix, while geometric design constraints of the microchambers drive native-like cellular behavior. Primary equine chondrocytes remained viable for the extended culture time of 3 weeks and maintained the low metabolic activity and high Sox9, aggrecan, and Col2 expression typical of articular chondrocytes. Our microfluidic 3D chondrocyte microtissues were further exposed to inflammatory cytokines to establish an animal-free, in vitro osteoarthritis model. Results of our study indicate that our microtissue model emulates the basic characteristics of native cartilage and responds to biochemical injury, thus providing a new foundation for exploration of osteoarthritis pathophysiology in both human and veterinary patients.

Characterization of four functional biocompatible pressure-sensitive adhesives for rapid prototyping of cell-based lab-on-a-chip and organ-on-a-chip systems

In the advent of affordable photo- and soft-lithography using polydimethylsiloxane (PDMS), low cost multi-step microfabrication methods have become available to a broad scientific community today. Although these methods are frequently applied for microfluidic prototype production in academic and industrial settings, fast design iterations and rapid prototyping within a few minutes with a high degree of flexibility are nearly impossible. To reduce microfluidic concept-to-chip time and costs, a number of alternative rapid prototyping techniques have recently been introduced including CNC micromachining, 3D printing and plotting out of numeric CAD designs as well as micro-structuring of thin PDMS sheets and pressure sensitive adhesives. Although micro-structuring of pressure sensitive adhesives promises high design flexibility, rapid fabrication and simple biochip assembly, most adhesives are toxic for living biological systems. Since an appropriate bio-interface and proper biology-material interaction is key for any cell chip and organ-on-a-chip system, only a limited number of medical-grade materials are available for microfluidic prototyping. In this study, we have characterized four functional biomedical-grade pressure sensitive adhesives for rapid prototyping (e.g. less than 1 hour) applications including structuring precision, physical and optical properties as well as biocompatibilities. While similar biocompatibility was found for all four adhesives, significant differences in cutting behavior, bonding strength to glass and polymers as well as gas permeability was observed. Practical applications included stability testing of multilayered, membrane-integrated organ-on-a-chip devices under standard cell culture conditions (e.g. 2-3 weeks at 37 °C and 100% humidity) and a shear-impact up to 5 dynes/cm². Additionally, time- and shear-dependent uptake of non-toxic fluorescently labelled nanoparticles on human endothelial cells are demonstrated using micro-structured adhesive-bonded devices. Our results show that (a) both simple and complex microdevices can be designed, fabricated and tested in less than 1 hour, (b) these microdevices are stable for weeks even under physiological shear force conditions and (c) can be used to maintain cell monolayers as well as 3D cell culture systems.

Oxygen Management at the Microscale: A Functional Biochip Material with Long-Lasting and Tunable Oxygen Scavenging Properties for Cell Culture Applications

Oxygen plays a pivotal role in cellular homeostasis, and its partial pressure determines cellular function and fate. Consequently, the ability to control oxygen tension is a critical parameter for recreating physiologically relevant in vitro culture conditions for mammalian cells and microorganisms. Despite its importance, most microdevices and organ-on-a-chip systems to date overlook oxygen gradient parameters because controlling oxygen often requires bulky and expensive external instrumental setups. To overcome this limitation, we have adapted an off-stoichiometric thiol-ene-epoxy polymer to efficiently remove dissolved oxygen to below 1 hPa and also integrated this modified polymer into a functional biochip material. The relevance of using an oxygen scavenging material in microfluidics is that it makes it feasible to readily control oxygen depletion rates inside the biochip by simply changing the surface-to-volume aspect ratio of the microfluidic channel network as well as by changing the temperature and curing times during the fabrication process.

E-Beam Nanostructuring and Direct Click Biofunctionalization of Thiol-Ene Resist

Electron beam lithography (EBL) is of major importance for ultraminiaturized biohybrid system fabrication, as it allows combining biomolecular patterning and mechanical structure definition on the nanoscale. Existing methods are limited by multistep biomolecule immobilization procedures, harsh processing conditions that are harmful to sensitive biomolecules, or the structural properties of the resulting protein monolayers or hydrogel-based resists. This work introduces a thiol-ene EBL resist with chemically reactive thiol groups on its native surface that allow the direct and selective "click" immobilization of biomolecules under benign processing conditions. We constructed EBL structured features of size down to 20 nm, and direct functionalized the nanostructures with a sandwich of biotin and streptavidin. The facile combination of polymer nanostructuring with biomolecule immobilization enables mechanically robust biohybrid components of interest for nanoscale biomedical, electronic, photonic, and robotic applications.

Tomorrow today: organ-on-a-chip advances towards clinically relevant pharmaceutical and medical in vitro models

Organ-on-a-chip technology offers the potential to recapitulate human physiology by keeping human cells in a precisely controlled and artificial tissue-like microenvironment. The current and potential advantages of organs-on-chips over conventional cell cultures systems and animal models have captured the attention of scientists, clinicians and policymakers as well as advocacy groups in the past few years. Recent advances in tissue engineering and stem cell research are also aiding the development of clinically relevant chip-based organ and diseases models with organ level physiology for drug screening, biomedical research and personalized medicine. Here, the latest advances in organ-on-a-chip technology are reviewed and future clinical applications discussed.