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The multi-directional mechanical stimulation experienced by articular cartilage during motion is transferred to the chondrocytes through a thin layer of pericellular matrix around each cell; chondrocytes in turn respond by releasing matrix proteins and/or matrix-degrading enzymes. In the present study we investigated how different types of mechanical stimulation can affect a chondrocyte's phenotype and extracellular matrix (ECM) production. To this end, we employed a cartilage-on-chip system which allows exerting well-defined compressive and multi-directional mechanical stimulation on a 3D chondrocyte-laden agarose hydrogel using a thin deformable membrane and three individually addressed actuation chambers. First, the 3D chondrocyte culture in agarose responded to exposure to mechanical stimulation by an initial increase in IL-6 production and little-to-no change in IL-1β and TNF-α secretion after one day of on-chip culture. Exposure to mechanical stimulation enhanced COL2A1 (hyaline cartilage marker) and decreased COL1A1 (fibrotic cartilage) expression, this being more marked for the multi-directional stimulation. Remarkably, the production of glycosaminoglycans (GAGs), one of the main components of native cartilage ECM, was significantly increased after 15 days of on-chip culture and 14 days of mechanical stimulation. Specifically, a thin pericellular matrix shell (1–5 μm) surrounding the chondrocytes as well as an interstitial matrix, both reminiscent of the in vivo situation, were deposited. Matrix deposition was highest in chips exposed to multi-directional mechanical stimulation. Finally, exposure to mechanical cues enhanced the production of essential cartilage ECM markers, such as aggrecan, collagen II and collagen VI, a marker for the pericellular matrix. Altogether our results highlight the importance of mechanical cues, and using the right type of stimulation, to emulate in vitro, the chondrocyte microenvironment. [ABSTRACT FROM AUTHOR]

Variations in oxygen levels play key roles in numerous physiological and pathological processes, but are often not properly controlled in in vitro models, introducing a significant bias in experimental outcomes. Recent developments in microfluidic technology have introduced a paradigm shift by providing new opportunities to better mimic physiological and pathological conditions, which is achieved by both regulating and monitoring oxygen levels at the micrometre scale in miniaturized devices. In this review, we first introduce the nature and relevance of oxygen-dependent pathways in both physiological and pathological contexts. Subsequently, we discuss strategies to control oxygen in microfluidic devices, distinguishing between engineering approaches that operate at the device level during its fabrication and chemical approaches that involve the active perfusion of fluids oxygenated at a precise level or supplemented with oxygen-producing or oxygen-scavenging materials. In addition, we discuss readout approaches for monitoring oxygen levels at the cellular and tissue levels, focusing on electrochemical and optical detection schemes for high-resolution measurements directly on-chip. An overview of different applications in which microfluidic devices have been utilized to answer biological research questions is then provided. In the final section, we provide our vision for further technological refinements of oxygen-controlling devices and discuss how these devices can be employed to generate new fundamental insights regarding key scientific problems that call for emulating oxygen levels as encountered in vivo. We conclude by making the case that ultimately emulating physiological or pathological oxygen levels should become a standard feature in all in vitro cell, tissue, and organ models. [ABSTRACT FROM AUTHOR]

Lab on a Chip EDITORIAL Cite this: Lab Chip,2021, 21,987 DOI: 10.1039/d1lc90012a rsc.li/loc Musings on the future of scientific (physical but not socially distanced) conferences: testing the water with organizing the on-line MicroTAS2020 Séverine Le Gac * ab and Hang Lu * c As many people have experienced in the past year or so around the world, COVID19 has brought many changes in our lives. In hindsight - a wellorganized team and structure As for any other MicroTAS and other conferences, this online event was organized by the chairs, us, with the assistance of the professional conference organization Preferred Meeting Management, Inc. and several committees in charge of specific aspects. 2 Snapshots of some video contributions from members of the microfluidic community highlighting what the MicroTAS conference means to them, the importance of having a MicroTAS conference in this COVID-19 situation and the foreseen advantages of an online conference. [Extracted from the article]

Tumor-derived extracellular vesicles (tdEVs) are promising blood biomarkers for cancer disease management. However, blood is a highly complex fluid that contains multiple objects in the same size range as tdEVs (30 nm–1 μm), which obscures an unimpeded analysis of tdEVs. Here, we report a multi-modal analysis platform for the specific capture of tdEVs on antibody-functionalized stainless steel substrates, followed by their analysis using SEM, Raman spectroscopy and AFM, at the single EV level in terms of size and size distribution, and chemical fingerprint. After covalent attachment of anti-EpCAM (epithelial cell adhesion molecule) antibodies on stainless steel substrates, EV samples derived from a prostate cancer cell line (LnCAP) were flushed into a microfluidic device assembled with this stainless steel substrate for capture. To track the captured objects between the different analytical instruments and subsequent correlative analysis, navigation markers were fabricated onto the substrate from a cyanoacrylate glue. Specific capture of tdEVs on the antibody-functionalized surface was demonstrated using SEM, AFM and Raman imaging, with excellent correlation between the data acquired by the individual techniques. The particle distribution was visualized with SEM. Furthermore, a characteristic lipid–protein band at 2850–2950 cm−1 was observed with Raman spectroscopy, and with AFM the size distribution and surface density of the captured EVs was assessed. Finally, correlation of SEM and Raman images enabled discrimination of tdEVs from cyanoacrylate glue particles, highlighting the capability of this multi-modal analysis platform for distinguishing tdEVs from contamination. The trans-instrumental compatibility of the stainless steel substrate and the possibility to spatially correlate the images of the different modalities with the help of the navigation markers open new avenues to a wide spectrum of combinations of different analytical and imaging techniques for the study of more complex EV samples. [ABSTRACT FROM AUTHOR]

We report a wafer-scale fabrication process for the production of glass-FEP-glass microdevices using UV-curable adhesive (NOA81) as gluing material, which is applied using a novel “spin & roll” approach. Devices are characterized for the uniformity of the gluing layer, presence of glue in the microchannels, and alignment precision. Experiments on lipid bilayers with electrophysiological recordings using a model pore-forming polypeptide are demonstrated. [ABSTRACT FROM AUTHOR]

We present a microtiter plate-sized standalone chip holder for precise control of physiological conditions inside closed microfluidic cell culture systems, made from gas-impermeable materials. Specifically, we demonstrate the suitability of the holder to support cell growth in a glass chip, to allow time-lapse imaging of live cells and the creation of a hypoxic environment, all relevant for applications in regenerative medicine research. [ABSTRACT FROM AUTHOR]

We present a novel electrode configuration consisting of coplanar side electrode pairs integrated at the half height of the microchannels for the creation of a homogeneous electric field distribution as well as for synchronous optical and electrical measurements. For the integration of such electrodes in fused silica microsystems, a dedicated microfabrication method was utilized, whereby an intermediate bonding layer was applied to lower the temperature for fusion bonding to avoid thereby metal degradation and subsequently to preserve the electrode structures. Finally, we demonstrate the applicability of our devices with integrated electrodes for single cell electrical lysis and simultaneous fluorescence and impedance measurements for both cell counting and characterization. [ABSTRACT FROM AUTHOR]

The aim of regenerative medicine is to restore or establish normal function of damaged tissues or organs. Tremendous efforts are placed into development of novel regenerative strategies, involving (stem) cells, soluble factors, biomaterials or combinations thereof, as a result of the growing need caused by continuous population aging. To satisfy this need, fast and reliable assessment of (biological) performance is sought, not only to select the potentially interesting candidates, but also to rule out poor ones at an early stage of development. Microfluidics may provide a new avenue to accelerate research and development in the field of regenerative medicine as it has proven its maturity for the realization of high-throughput screening platforms. In addition, microfluidic systems offer other advantages such as the possibility to create in vivo-like microenvironments. Besides the complexity of organs or tissues that need to be regenerated, regenerative medicine brings additional challenges of complex regeneration processes and strategies. The question therefore arises whether so much complexity can be integrated into microfluidic systems without compromising reliability and throughput of assays. With this review, we aim to investigate whether microfluidics can become widely applied in regenerative medicine research and/or strategies. [ABSTRACT FROM AUTHOR]

We present here a novel microchamber sealing valve that is self-actuated by a pressure change during the temperature change in the thermal activation of reactions. Actuation of our valve requires only the use of the same heating device as employed for the reactions. A thermoplastic UV-curable polymer is used as a device material; the polymer allows realization of the temperature-driven valve actuation as well as the fabrication of multi-layered devices. The self-actuated valve achieves effective sealing of the microchamber for the polymerase chain reaction (PCR) even at 90 °C, which is essential for developing highly parallel PCR array devices without the need for complicated peripherals to control the valve operation.

In the fields of MicroElectroMechanical Systems (MEMS) and Lab On a Chip (LOC), a device is often fabricated using diverse substrates which are processed separately and finally assembled together using a bonding process to yield the final device. Here we describe and demonstrate a novel straightforward, rapid and low-temperature bonding technique for the assembly of complete microfluidic devices, at the chip level, by employing an intermediate layer of gluing material. This technique is applicable to a great variety of materials (e.g., glass, SU-8, parylene, UV-curable adhesive) as demonstrated here when using NOA 81 as gluing material. Bonding is firstly characterized in terms of homogeneity and thickness of the gluing layer. Following this, we verified the resistance of the adhesive layer to various organic solvents, acids, bases and conventional buffers. Finally, the assembled devices are successfully utilized for fluidic experiments.