Myofibroblasts impair myocardial impulse propagation by heterocellular connexin43 gap-junctional coupling through micropores

Aim: Composite population of myofibroblasts (MFs) within myocardial tissue is known to alter impulse propagation, leading to arrhythmias. However, it remains unclear whether and how MFs alter their propagation patterns when contacting cardiomyocytes (CMs) without complex structural insertions in the myocardium. We attempted to unveil the effects of the one-sided, heterocellular CM-MF connection on the impulse propagation of CM monolayers without the spatial insertion of MFs as an electrical or mechanical obstacle. Methods and results: We evaluated fluo8-based spatiotemporal patterns in impulse propagation of neonatal rat CM monolayers cultured on the microporous membrane having 8-μm diameter pores with co-culture of MFs or CMs on the reverse membrane side (CM-MF model or CM-CM model, respectively). During consecutive pacing at 1 or 2 Hz, the CM monolayers exhibited forward impulse propagation from the pacing site with a slower conduction velocity (θ) and a larger coefficient of directional θ variation in the CM-MF model than that in the CM-CM model in a frequency-dependent manner (2 Hz >1 Hz). The localized placement of an MF cluster on the reverse side resulted in an abrupt segmental depression of the impulse propagation of the upper CM layer, causing a spatiotemporally non-uniform pattern. Dye transfer of the calcein loaded in the upper CM layer to the lower MF layer was attenuated by the gap-junction inhibitor heptanol. Immunocytochemistry identified definitive connexin 43 (Cx43) between the CMs and MFs in the membrane pores. MF-selective Cx43 knockdown in the MF layer improved both the velocity and uniformity of propagation in the CM monolayer. Conclusion: Heterocellular Cx43 gap junction coupling of CMs with MFs alters the spatiotemporal patterns of myocardial impulse propagation, even in the absence of spatially interjacent and mechanosensitive modulations by MFs. Moreover, MFs can promote pro-arrhythmogenic impulse propagation when in face-to-face contact with the myocardium that arises in the healing infarct border zone.

Separation Mechanisms and Anti-Fouling Properties of a Microporous Polyvinylidene Fluoride-Polyacrylic Acid-Graphene Oxide (PVDF-PAA-GO) Composite Membrane with Salt and Protein Solutions

This research demonstrates the preparation of composite membranes containing graphene oxide (GO) and investigates the separation mechanisms of various salts and bovine serum albumin (BSA) solutions. A microporous polyvinylidene fluoride-polyacrylic acid-GO (PVDF-PAA-GO) separation layer was fabricated on non-woven support. The GO-incorporating composite resulted in enlarged pore size (0.16 μm) compared with the control membrane (0.12 μm). The zeta potential of the GO composite was reduced to -31 from -19 mV. The resulting membranes with and without GO were examined for water permeability and rejection efficiency with single salt and BSA solutions. Using the non-woven/PVDF-PAA composite, the permeance values were 88-190 kg/m²hMPa, and the salt rejection coefficients were 9-28% for Na₂SO₄, MgCl₂, MgSO₄, and NaCl solutions. These salt removals were based on the Donnan exclusion mechanism considering the ion radii and membrane pore size. Incorporating GO into the separation layer exhibited limited impacts on the filtration of salt solutions, but significantly reduced BSA membrane adhesion and increased permeance. The negatively charged protein reached almost complete removal (98.4%) from the highly negatively charged GO-containing membrane. The GO additive improved the anti-fouling property of the composite membrane and enhanced BSA separation from the salt solution.

A 3D Capillary-Driven Multi-Micropore Membrane-Based Trigger Valve for Multi-Step Biochemical Reaction

Point-of-care testing (POCT) techniques based on microfluidic devices enabled rapid and accurate tests on-site, playing an increasingly important role in public health. As the critical component of capillary-driven microfluidic devices for POCT use, the capillary microfluidic valve could schedule multi-step biochemical operations, potentially being used for broader complex POCT tasks. However, owing to the reciprocal relationship between the capillary force and aperture in single-pore microchannels, it was challenging to achieve a high gating threshold and high operable liquid volume simultaneously with existing 2D capillary trigger valves. This paper proposed a 3D capillary-driven multi-microporous membrane-based trigger valve to address the issue. Taking advantage of the high gating threshold determined by micropores and the self-driven capillary channel, a 3D trigger valve composed of a microporous membrane for valving and a wedge-shaped capillary channel for flow pumping was implemented. Utilizing the capillary pinning effect of the multi-micropore membrane, the liquid above the membrane could be triggered by putting the drainage agent into the wedge-shaped capillary channel to wet the underside of the membrane, and it could also be cut off by taking away the agent. After theoretical analysis and performance characterizations, the 3D trigger valve performed a high gating threshold (above 1000 Pa) and high trigger efficiency with an operable liquid volume above 150 μL and a trigger-to-drain time below 6 s. Furthermore, the retention and trigger states of the valve could be switched for repeatable triggering for three cycles within 5 min. Finally, the microbead-based immunoreaction and live cell staining applications verified the valve's ability to perform multi-step operations. The above results showed that the proposed 3D trigger valve could be expected to play a part in wide-ranging POCT application scenarios.

Multilayered PVDF-HFP Porous Separator via Phase Separation and Selective Solvent Etching for High Voltage Lithium-Ion Batteries

The development of highly porous and thin separator is a great challenge for lithium-ion batteries (LIBs). However, the inevitable safety issues always caused by poor mechanical integrity and internal short circuits of the thin separator must be addressed before this type of separator can be applied to lithium-ion batteries. Here, we developed a novel multilayer poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) membrane with a highly porous and lamellar structure, through a combination of evaporation-induced phase separation and selective solvent etching methods. The developed membrane is capable of a greater amount of electrolyte uptake and excellent electrolyte retention resulting from its superior electrolyte wettability and highly porous structure, thereby offering better electrochemical performance compared to that of a commercial polyolefin separator (Celgard). Moreover, benefiting from the layered configuration, the tensile strength of the membrane can reach 13.5 MPa, which is close to the mechanical strength of the Celgard type along the transversal direction. The elaborate design of the multilayered structure allows the fabrication of a new class of thin separators with significant improvements in the mechanical and electrochemical performance. Given safer operation, the developed multilayer membrane may become a preferable separator required for high-power and high-energy storage devices.

Effect of Membrane Hydrophobicity and Thickness on Energy-Efficient Dissolved Oxygen Removal From Algal Culture

Removal of dissolved oxygen from algal photobioreactors is essential for high productivity in mass cultivation. Gas-permeating photobioreactor that uses hydrophobic membranes to permeate dissolved oxygen (pervaporation) from its body itself is an energy-efficient option for oxygen removal. This study comparably evaluated the characteristics of various commercial membranes and determined the criteria for the selection of suitable ones for the gas-permeating photobioreactors. It was found that oxygen permeability is limited not by that in the membrane but in the liquid boundary layer. Membrane thickness had a negative effect on membrane oxygen permeability, but the effect was as minor as less than 3% compared with the liquid boundary layer. Due to this characteristic, the lamination of non-woven fabric with the microporous film did not significantly decrease the overall oxygen transfer coefficient. The permeability in the liquid boundary layer had a significantly positive relationship with the hydrophobicity. The highest overall oxygen transfer coefficients in the water-to-air and water-to-water oxygen removal tests were 2.1 ± 0.03 × 10^–5 and 1.39 ± 0.09 × 10^–5 m s^–1, respectively. These values were considered effective in the dissolved oxygen removal from high-density algal culture to prevent oxygen inhibition. Furthermore, hydrophobicity was found to have a significant relationship also with water entry pressure, which needs to be high to avoid culture liquid leakage. Therefore, these results suggested that a microporous membrane with strong hydrophobicity laminated with non-woven fabric would be suitable characteristics for gas-permeating photobioreactor.

Development and Optimization of an Airborne Formaldehyde Microfluidic Analytical Device Based on Passive Uptake through a Microporous Tube

This paper describes a compact microfluidic analytical device developed for the detection of low airborne formaldehyde concentrations. This microdevice was based on a three-step analysis, i.e., the passive gaseous formaldehyde uptake using a microporous membrane into an acetylacetone solution, the derivatization with acetylacetone to form 3,5-diacetyl-1,4-dihydrolutidine, and the quantification of the latter using fluorescence detection. For a rapid and easier implementation, a cylindrical geometry of the microporous element was considered to perform laboratory-controlled experiments with known formaldehyde concentrations and to establish the proof of concept. This work reports the evaluation of the uptake performance according to the microporous tube length, the liquid flow rate inside the tube, the gas flow rate outside the tube, and the gaseous formaldehyde concentration. A 10.0 cm microporous tube combined with a gas flow rate of 250 NmL/min (normal milliliters per minute) and a liquid flow rate of 17 µL/min were found to be the optimized conditions. In these experimental conditions, the fluorescence signal increased linearly with the gaseous formaldehyde concentration in the range 0-118 µg/m³, with the detection limit being estimated as 0.13 µg/m³ when considering a signal-to-noise ratio of 3.

Continuous in Situ Extraction toward Multiphase Complex Systems Based on Superwettable Membrane with Micro-/Nanostructures

Liquid-phase extraction is widely used in the chemical industry. Traditional extracting routes always involve multiple procedures, need a large floor space, and have long operating time. "Continuous in situ extraction" that can conduct a real-time integration of solutes extraction and solvents separation simultaneously would be of great significance. Superwettable materials offer us a good choice to separate different immiscible solvents; herein, we achieve continuous in situ extraction of multiphase complex systems by using a porous polytetrafluoroethylene membrane with nanostructure-induced superwettability. It realizes a rapid, selective, and efficient real-time removal of various extracting agents during a continuous process due to their wetting differences. Compared with traditional extraction, our route shows a distinct superiority on saving operating time, enhancing liquid recovery, and simplifying procedures, while still retaining high extracting performance. In addition, our membrane possesses excellent durability even after long-term work in harsh chemical environments or under strong mechanical impacts. Thus, we believe that it will provide a potential alternative for current industrial extractions.

Additive-manufactured microporous polymer membranes for biomedical in vitro applications

Microscale porous membranes are used in a wide range of technical and medical applications such as water treatment, dialysis and in vitro test systems. A promising approach to control membrane properties and overcome limitations of conventional fabrication techniques is given by additive manufacturing (AM). In this study, we designed and printed a microporous membrane via digital light processing and validated its use for biomedical in vitro applications based on the example of a cell culture insert. A multi-layer technique was developed, resulting in an eight-layer membrane with an average pore diameter of 25 µm. Image analyses proved the printing accuracy to be high with small deviations for an increasing number of layers. Permeability tests with brilliant blue FCF (E133, triarylmethane dye) and growth factors comparing the printed to track-etched membranes showed similar transfer dynamics and confirmed sufficient separation properties. Overall, the results showed that printing microporous polymer membranes is possible and highlight the potential of AM for biomedical in vitro applications such as cell culture inserts, scaffolds for tissue engineering or bioreactors.

Preparation of Microporous Polypropylene/Titanium Dioxide Composite Membranes with Enhanced Electrolyte Uptake Capability via Melt Extruding and Stretching

In this work, a blending strategy based on compounding the hydrophilic titanium dioxide (TiO₂) particles with the host polypropylene (PP) pellets, followed by the common membrane manufacture process of melt extruding/annealing/stretching, was used to improve the polarity and thus electrolyte uptake capability of the PP-based microporous membranes. The influence of the TiO₂ particles on the crystallinity and crystalline orientation of the PP matrix was studied using differential scanning calorimetry (DSC), X-ray diffraction (XRD), and infrared dichroic methods. The results showed that the TiO₂ incorporation has little influence on the oriented lamellar structure of the PP-based composite films. Investigations of the deformation behavior indicated that both the lamellar separation and interfacial debonding occurred when the PP/TiO₂ composite films were subjected to uniaxial tensile stress. The scanning electron microscopy (SEM) observations verified that two forms of micropores were generated in the stretched PP/TiO₂ composite membranes. Compared to the virgin PP membrane, the PP/TiO₂ composite membranes especially at high TiO₂ loadings showed significant improvements in terms of water vapor permeability, polarity, and electrolyte uptake capability. The electrolyte uptake of the PP/TiO₂ composite membrane with 40 wt % TiO₂ was 104%, which had almost doubled compared with that of the virgin PP membrane.

Optimization of polyvinylidene fluoride (PVDF) membrane fabrication for protein binding using statistical experimental design

Statistical experimental design was employed to optimize the preparation conditions of polyvinylidenefluoride (PVDF) membranes. Three variables considered were polymer concentration, dissolving temperature, and casting thickness, whereby the response variable was membrane-protein binding. The optimum preparation for the PVDF membrane was a polymer concentration of 16.55 wt%, a dissolving temperature of 27.5°C, and a casting thickness of 450 µm. The statistical model exhibits a deviation between the predicted and actual responses of less than 5%. Further characterization of the formed PVDF membrane showed that the morphology of the membrane was in line with the membrane-protein binding performance.

Reconstruction of hepatic stellate cell-incorporated liver capillary structures in small hepatocyte tri-culture using microporous membranes

In liver sinusoids, hepatic stellate cells (HSCs) locate the outer surface of microvessels to form a functional unit with endothelia and hepatocytes. To reconstruct functional liver tissue in vitro, formation of the HSC-incorporated sinusoidal structure is essential. We previously demonstrated capillary formation of endothelial cells (ECs) in tri-culture, where a polyethylene terephthalate (PET) microporous membrane was intercalated between the ECs and hepatic organoids composed of small hepatocytes (SHs), i.e. hepatic progenitor cells, and HSCs. However, the high thickness and low porosity of the membranes limited heterotypic cell-cell interactions, which are essential to form HSC-EC hybrid structures. Here, we focused on the effective use of the thin and highly porous poly( d, l-lactide-co-glycolide) (PLGA) microporous membranes in SH-HSC-EC tri-culture to reconstruct the HSC-incorporated liver capillary structures in vitro. First, the formation of EC capillary-like structures was induced on Matrigel-coated PLGA microporous membranes. Next, the membranes were stacked on hepatic organoids composed of small SHs and HSCs. When the pore size and porosity of the membranes were optimized, HSCs selectively migrated to the EC capillary-like structures. This process was mediated in part by platelet-derived growth factor (PDGF) signalling. In addition, the HSCs were located along the outer surface of the EC capillary-like structures with their long cytoplasmic processes. In the HSC-incorporated capillary tissues, SHs acquired high levels of differentiated functions, compared to those without ECs. This model will provide a basis for the construction of functional, thick, vascularized liver tissues in vitro.

Microporous membrane-based liver tissue engineering for the reconstruction of three-dimensional functional liver tissues in vitro

To meet the increasing demand for liver tissue engineering, various three-dimensional (3D) liver cell culture techniques have been developed. Nevertheless, conventional liver cell culture techniques involving the suspending cells in extracellular matrix (ECM) components and the seeding of cells into 3D biodegradable scaffolds have an intrinsic shortcoming, low cell-scaffold ratios. We have developed a microporous membrane-based liver cell culture technique. Cell behaviors and tissue organization can be controlled by membrane geometry, and cell-dense thick tissues can be reconstructed by layering cells cultured on biodegradable microporous membranes. Applications extend from liver parenchymal cell monoculture to multi-cell type cultures for the reconstruction of 3D functional liver tissue. This review focuses on the expanding role for microporous membranes in liver tissue engineering, primarily from our research.

Continuously infusing hyperpolarized 129Xe into flowing aqueous solutions using hydrophobic gas exchange membranes

Hyperpolarized (HP) (129)Xe yields high signal intensities in nuclear magnetic resonance (NMR) and, through its large chemical shift range of approximately 300 ppm, provides detailed information about the local chemical environment. To exploit these properties in aqueous solutions and living tissues requires the development of methods for efficiently dissolving HP (129)Xe over an extended time period. To this end, we have used commercially available gas exchange modules to continuously infuse concentrated HP (129)Xe into flowing liquids, including rat whole blood, for periods as long as one hour and have demonstrated the feasibility of dissolved-phase MR imaging with submillimeter resolution within minutes. These modules, which exchange gases using hydrophobic microporous polymer membranes, are compatible with a variety of liquids and are suitable for infusing HP (129)Xe into the bloodstream in vivo. Additionally, we have developed a detailed mathematical model of the infused HP (129)Xe signal dynamics that should be useful in designing improved infusion systems that yield even higher dissolved HP (129)Xe signal intensities.