Advanced fabrication protocol of an elastic porous membrane for organ-on-a-chip applications

Engineering PDMS membranes with tunable biomimetic curvatures: from partial curing to vacuum-induced shaping

Flexible membranes created from porous carbon nanofibers (CNFs) hold great promise in the next generation wearable energy storage devices, but challenges still remain due to the poor mechanical properties of porous carbon nanofibers. Here, we report a facile strategy to fabricate elastic and hierarchical porous CNF membranes with NiFe2O4 nanocrystals embedded via multicomponent electrospinning and nano-doping methods. Benefiting from the scattering effect of NiFe2O4 nanocrystals and graphitized carbon layers for the condensed stress, the resultant CNF membranes exhibit an enhanced elasticity with a bending radius <12 μm, rapid recovery from the deformations, and a superior softness. Quantitative pore size distribution and fractal analysis reveal that the CNFs possessed tunable porous structures with a high surface area of 493 m(2) g(-1) and a pore volume of 0.31 cm(3) g(-1). Benefiting from the robust mechanical stability, hierarchical porous structures and good electrochemical properties, the NiFe2O4 doped CNF membranes demonstrate a high electrical capacitance of 343 F g(-1), and good reversibility with a cycling efficiency of 97.4% even after 10,000 cycles. The successful synthesis of elastic porous CNF membranes also provided a versatile platform for the design and development of functional CNF based materials for various applications.

Polymeric membranes are widely applied in biomedical applications, including in vitro organ models. In such models, they are mostly used as supports on which cells are cultured to create functional tissue units of the desired organ. To this end, the membrane properties, e.g., morphology and porosity, should match the tissue properties. Organ models of dynamic (barrier) tissues, e.g., lung, require flexible, elastic and porous membranes. Thus, membranes based on poly (dimethyl siloxane) (PDMS) are often applied, which are flexible and elastic. However, PDMS has low cell adhesive properties and displays small molecule ad- and absorption. Furthermore, the introduction of porosity in these membranes requires elaborate methods. In this work, we aim to develop porous membranes for organ models based on poly(trimethylene carbonate) (PTMC): a flexible polymer with good cell adhesive properties which has been used for tissue engineering scaffolds, but not in in vitro organ models. For developing these membranes, we applied evaporation-induced phase separation (EIPS), a new method in this field based on solvent evaporation initiating phase separation, followed by membrane photo-crosslinking. We optimised various processing variables for obtaining form-stable PTMC membranes with average pore sizes between 5 to 8 µm and water permeance in the microfiltration range (17,000–41,000 L/m2/h/bar). Importantly, the membranes are flexible and are suitable for implementation in in vitro organ models.

The ENR/PVC thin film has great potential as a membrane due to its ideal owing to unique characteristics such as freestanding, high-pressure resistance, and durability over time but low porosity. This research aims to investigate inside into chemical and morphological properties of developed composite epoxidized natural rubber with polyvinyl chloride-filled cellulose grafted polymethyl methacrylate (ENR/PVC/cellulose-g-PMMA) membrane. Solution blending of 60:40 wt. % ENR/PVC 10 % w/v of filler were mixed homogeneously for 24h stirring in THF solution. The membranes were cast onto a glass plate and the phase inversion technique was used to prepare ENR/PVC/Cell-g-PMMA membranes. The characterization of chemical properties was carried out by Fourier transform infrared spectroscopy (FTIR) to determine functional groups related to bond breaking and the formation of new bonds of the species during grafting copolymerization and membrane fabrication. Variable pressure scanning electron microscopy (VPSEM) was conducted to determine surface morphology and textural properties of fillers and membranes. Furthermore, it contributes to porosity and the formation of pores on the membrane. FTIR spectrum shows that absorption peaks around the range 1735-1725 cm-1 of the carbonyl ester -C=O functional group have been detected and proven successful of the grafting method between cellulose and PMMA. The rough surface of fibers, formation of open pores, and interspace structure between ENR/PVC matrix and filler affirmed the addition of cell-g-PMMA fillers caused by film-filler and filler-filler interfaces interaction as shown by the VPSEM micrograph. In summary, the chemical properties and morphological analysis give useful information on the effectiveness of potential ENR/PVC/Cell-g-PMMA membranes in developing standalone, highly pressure-resistant, porous, and elastic membranes.

The evaluation of inhalation toxicity, drug safety and efficacy assessment, as well as the investigation of complex disease pathomechanisms, are increasingly relying on in vitro lung models. This is due to the progressive shift towards human-based systems for more predictive and translational research. While several cellular models are currently available for the upper airways, modelling the distal alveolar region poses several constraints that make the standardization of reliable alveolar in vitro models relatively difficult. In this work, we present a new and reproducible alveolar in vitro model, that combines a human derived immortalized alveolar epithelial cell line (AXiAEC) and organ-on-chip technology mimicking the lung alveolar biophysical environment (AXlung-on-chip). The latter mimics key features of the in vivo alveolar milieu: breathing-like 3D cyclic stretch (10% linear strain, 0.2 Hz frequency) and an ultrathin, porous and elastic membrane. AXiAECs cultured on-chip were characterized for their alveolar epithelial cell markers by gene and protein expression. Cell barrier properties were examined by TER (Transbarrier Electrical Resistance) measurement and tight junction formation. To establish a physiological model for the distal lung, AXiAECs were cultured for long-term at air-liquid interface (ALI) on-chip. To this end, different stages of alveolar damage including inflammation (via exposure to bacterial lipopolysaccharide) and the response to a profibrotic mediator (via exposure to Transforming growth factor β1) were analyzed. In addition, the expression of relevant host cell factors involved in SARS-CoV-2 infection was investigated to evaluate its potential application for COVID-19 studies. This study shows that AXiAECs cultured on the AXlung-on-chip exhibit an enhanced in vivo-like alveolar character which is reflected into: 1) Alveolar type 1 (AT1) and 2 (AT2) cell specific phenotypes, 2) tight barrier formation (with TER above 1,000 Ω cm2) and 3) reproducible long-term preservation of alveolar characteristics in nearly physiological conditions (co-culture, breathing, ALI). To the best of our knowledge, this is the first time that a primary derived alveolar epithelial cell line on-chip representing both AT1 and AT2 characteristics is reported. This distal lung model thereby represents a valuable in vitro tool to study inhalation toxicity, test safety and efficacy of drug compounds and characterization of xenobiotics.

Many a child has enjoyed watching the gardens grow; many a physicist has puzzled over the transformation of self-organized, nonequilibrium patterns into permanent structures.

In vitro artery models constructed on a membrane-based microfluidic chip, called an artery-on-a-chip, have been spotlighted as a powerful platform for studying arterial physiology. However, due to the use of a flat and porous membrane that cannot mimic the in vivo internal elastic lamina (IEL), the physiological similarity in the phenotypes and the arrangements of the endothelial cells (ECs) and aortic smooth muscle cells (AoSMCs) has been limited in the previously developed artery-on-a-chips. Herein, we developed an innovative membrane mimicking the structures of IEL by utilizing electrospun aligned silk fibroin/polycaprolactone nanofiber membranes. An arterial IEL-mimicking (AIM) membrane was about 5 μm thick and composed of orthogonally aligned nanofibers with a diameter of around 400 nm, which were highly comparable to the IEL. Such structural similarity was found to induce the ECs and SMCs to be elongated and orthogonally aligned as in the in vivo artery. In particular, the SMCs cultured on the AIM membrane maintained a healthy state showing increased αSMA mRNA expression, which was easily lost on the conventional membrane. We constructed an AIM membrane-integrated artery-on-a-chip having an orthogonal arrangement of ECs and SMCs, which was desirable but difficult to be realized with the previous artery-on-a-chip.

Porous membranes used in co‐culture enable the in vitro partitioning of cellular microenvironments, while still permitting physical and biochemical crosstalk between cells. Thus, features of the co‐culture membrane are crucial for recapitulating the physiological functions of co‐cultured cells. This study presents elastic, porous, and ultrathin membranes (EPUMs), which enhance cell–cell interactions and control cell alignment with surface topology created by stretching the membranes. The EPUM is fabricated using poly(lactide‐co‐caprolactone) as the base material, and the porous feature is endowed by a vapor‐induced phase separation process induced by the presence of hygroscopic salt. Owing to its elastic property, the membrane can be stretched, and the deformed porous structures on the membrane surfaces act as nanostructured topographical cues, resulting in cell alignment. By co‐culturing human mesenchymal stem cells (hMSCs) and human umbilical vein endothelial cells (HUVECs) on the opposite sides of the membrane, rapid endothelialization occurs through the membranes, as compared to the commercial membranes. Furthermore, the stretched membranes induce the alignment of hMSCs and HUVECs and ultimately exhibit enhanced endothelial barrier function. The co‐culture membrane developed in this study may provide an effective tool for recapitulating endothelial basement membranes with a controllable endothelial barrier function.

Herein, we fabricated highly porous and stretchable electrospun nanofiber membranes using eco-friendly lignin and polycaprolactone polymers, which efficiently prevent mold colonization and invasion in pine sapwood. Membranes of different thicknesses were tested against four species of mold. Membrane thicknesses of above 38 μm were found to completely prevent mold invasion during the 2- and 4-week cultivation periods. The membranes were characterized using various qualitative and quantitative analytical methods, including tensile tests. The optimized fabrication conditions were established to protect wood from mold growth and to accommodate the periodic expansion and contraction of wood without degradation. The mechanically strong and elastic nanofiber membranes enable an assessment of the membrane’s suitability and feasibility as an alternative to the existing wallpapers or paints.

Fine bubble diffusers are typically used for aerating activated sludge tanks in municipal wastewater treatment plants because medium or coarse bubble diffusers are not economical in medium depth tanks, which are prevalent in municipal applications. Two types of fine bubble diffusers are available on the market: — rigid porous diffusers; and — elastic/rubber membrane diffusers. The first rigid porous diffusers were made of sintered ceramics such as sintered alumina; many diffusers are still made of this material. Its biggest advantage lies in its chemical inertness. Rigid porous diffusers are manufactured in many shapes and types such as domes, cylinders, circular disks and plates (noncircular disk). Rubber membrane diffusers are made of a finely slotted rubber membrane mounted on a carrier, typically made of plastic. The most important difference between rigid porous diffusers and membrane diffusers is that membrane diffusers have built-in backflow prevention properties. This results from the elastic rubber membrane totally contracting when the air is cut off and thereby closing its pores. Keywords: wastewater; aeration; aeration efficiency; oxygen transfer; fine bubble diffusers; membrane diffusers; ceramic diffusers; membrane materials; diffuser fouling; diffuser scaling

From previous experimental investigations on a heaving sea cage, it has been observed that the hydrodynamic forces and motions of the sea cage are strongly affected by the deformation of the cage net. As a fundamental study, the hydrodynamic behaviours of elastic net sheets with a circular or a square shape are studied in the present work. The net sheet is regarded as a piece of elastic porous membrane. The deformation of the net sheet is expanded into a series of natural modes deduced from the free vibration of the membrane (dry mode). The boundary value problem of fluid motion is formulated on the basis of the linear wave theory. A Darcy-type law is applied to the porous boundary. The problem is solved either by the eigenfunction expansion (for the circular shape only) or by the hybrid method with the Rankine source as the Green’s function. To validate the theoretical work and the numerical calculation, experiments are carried out in a wave basin. The models used in the tests are square shaped with a metal frame. The net part of the models is made of elastic cords with pre-tension. Both diffraction tests and forced heaving tests are performed. In addition to the vertical force, the deformation of the net surface is recorded by video cameras and analysed with a video image analysis system.

The prospect of characterizing individual nanoparticles, molecules, or DNA base pairs has generated considerable interest in resistive pulse sensing. In addition to size and concentration analysis, this technique also has the capacity to measure the charge density of objects in situations where electrophoretic forces dominate their motion. Here we present a methodology to simultaneously extract, via appropriate theoretical models, the size and ζ-potential of objects from the resistive pulse signal they generate. The methodology was demonstrated using a size-tunable elastic pore sensor to measure a complex "bimodal" suspension composed of two particle sets with different size and charge. Elastically tuning the size of the pore sensor, by stretching the elastic pore membrane, enables a larger sample size range to be analyzed, improves measurement sensitivity, and fine-tunes the forces acting on objects. This methodology represents a new approach for investigating and understanding the fundamental behavior of nanoscale dispersions.

Protein purification is an increasingly important problem in the current era of bioengineering, medicine, and biological research. Modern biomanufacturing schemes attribute up to 80% of process costs to purification processes. Unfortunately, existing separation schemes rely on batch-process chromatography columns that are diffusion mass transport-limited and have already reached optimal maximum loading densities and throughputs for bioseparations. [1] Our present work improves a previously-demonstrated bioinspired separations concept that utilizes chemically functionalized, mesoporous, gold electrodes decorating the surface of anodized alumina membranes with well-controlled pore sizes. This separations platform is inspired by cellular transmembrane ATP-binding cassette (ABC) transporters that enable selective transport of nutrients across the cell membrane. In ABC transporters, a nutrient first binds selectively to the transporter and induces conformational changes in the transporter that effectively blocks the transporter active site and closes the transporter. Subsequently, the transporter hydrolyzes ATP to induce nutrient release, eluting the nutrient into the cellular cytoplasm. Finally, the transporter reforms into its original conformation and is ready to repeat the cycle. In our system, proteins are selectively separated across an alumina membrane in a similar two-step fashion that alternates between “open” pores and sterically “closed” pores. This system is enabled by three critical components: (1) the histidine tag-based affinity chromatography chemistry for selective binding and elution, (2) timed electrochemical pulses to trigger the two steps in the transport cycle, and (3) affinity chemistry-modified, gold nanoscale mesoporous electrodes on the alumina membrane with characteristic pore diameter on the same size scale as target protein size (typically 5-10nm). In the first step, the binding step, an electrochemical pulse triggers electrophoretic transport of proteins to the surface of the membrane. At the membrane surface, proteins bind to the affinity chemistry and induce steric blocking of the mesopores. Captured target proteins simultaneously create a steric hindrance effect, blocking transmembrane transport of non-specifically bound proteins during the binding cycle. In the second step, the elution step, imidazole is electrophoretically pumped from the permeate side of the membrane towards the membrane surface with bound protein. Imidazole induces elution of the protein and thus the imidazole concentration is carefully controlled to keep the top surface of the membrane pores blocked while facilitating protein release at the bottom edge of the electrode inside the membrane pores. This concept was successfully demonstrated and showed a separation factor for GFP:BSA of 16:1 (mass/mass). Additionally, the net transmembrane protein flux (320 ng cm-2 hr-1) yields a daily throughput for a 0.75 cm2 area membrane as comparable to 1 mL of chromatography resin. However, the prior work was not optimized and was performed in a batch operation. [2] This work further develops the concept into a scalable, continuous separation process optimized for increased throughput and improved separation factor. A laser-machined, thermally-fused thermoplastic acrylic flow cell enables continuous operation, pH control, and finer control of operational details. Process optimizations are realized by improvements in the membrane fabrication and preparation protocol, binding and release reaction kinetics modeling, and electrophoretic transport . The optimizations improved the separation factor >20 and increased flux from 320 ng cm-2 hr-1 to >1000 ng cm-2 hr-1. [1] S. S. Farid, Journal of Chromatography B, 848, 8–18 (2007). [2] Z. Chen, T. Chen, X. Sun, and B. J. Hinds, Advanced Functional Materials, 24, 4317–4323 (2014).

Aqueous zinc‐iodine batteries have garnered significant attention in substitution energy storage devices owing to their inherent environmental sustainability and exceptional theoretical capacity. Nevertheless, critical challenges such as the dissolution and shuttle effect of soluble polyiodides, coupled with inefficient reversible redox conversion, severely compromise long‐term cyclability and commercial viability. Herein, this work innovatively modified the conventional zeolitic–imidazolate framework (ZIF)‐derived carbons through precursor pre‐activation, integrating Ni/Zn bimetallic anchoring with nitrogen self‐doping to construct a concave polyhedron‐structure and defect‐rich NZ‐aNC carbon host. The abundant heteroatoms doping and tailored unsaturated coordination environment establish multiple strong chemisorption sites that synergistically suppress polyiodide migration while accelerating redox reaction kinetics. Moreover, the increased graphitic degree and enlarged micro‐/meso‐pore size can facilitate the electron transfer and iodine species immobilization efficiency. Therefore, the Zn//I 2 battery demonstrates a high specific capacity of 219 mAh g −1 at 5 A g −1 , ultralong cycling stability with 95% capacity retention over 20 000 cycles, and superior energy efficiency. This work not only establishes a simple and easy‐scalable precursor‐guided protocol for advanced iodine host fabrication but also elucidates mechanistic correlations between coordination defects and electrochemical dynamics in ZIF‐derived carbon systems.

Thin film composite (TFC) polyamide membranes are crucial for efficient reverse osmosis (RO) desalination, offering high selectivity and permeability. This study investigates the fabrication and optimization of TFC membranes on polysulfone supports, focusing on their structural, morphological, and performance properties for enhanced desalination efficiency using the phase inversion technique, a method that enables precise control over membrane structure. Key fabrication parameters including the concentrations of m-phenylene diamine (MPD) and trimesoyl chloride (TMC), and the immersion times for both monomers were systematically varied to investigate their impact on membrane hydrophilicity, morphology, and structure. Hydrophilicity was assessed via contact angle measurements, Scanning electron microscopy was used to characterize the morphology (SEM), and structural properties were analyzed by Fourier-transform infrared spectroscopy (FTIR). The RO membranes’ desalination performance was evaluated by measuring water flux and salt rejection in a cross-flow setup with saline water (10,000 ppm) under controlled processing conditions. Results indicated that variations in MPD and TMC concentrations, as well as immersion times, significantly influenced membrane hydrophilicity and pore structure, affecting water flux and salt rejection. The maximum salt rejection and water flux for the prepared thin film composite reverse osmosis membrane were 98.6% and 19.1 L/m2 h, respectively obtained at m-phenylenediamine concentration of 2 wt% and tri mesoyl chloride concentration of 0.1 wt/v reacted for 1 min. The study provides insights into optimizing TFC-RO membrane fabrication parameters to enhance desalination efficiency, highlighting the potential of these membranes for high-performance RO desalination applications.