Novel thin-film nanofibrous composite membranes containing directional toxin transport nanochannels for efficient and safe hemodialysis application

UV-induced plasma welding and interface customization strategy of cellulose nanofiber/silver nanowire composite electrode for advanced flexible photoelectric applications

Significant advancements in flexible photoelectric devices have been achieved through extensive research on flexible transparent conductive electrodes (FTCEs) based on silver nanowires (AgNWs). However, two key challenges that need to be addressed are the high contact resistance of AgNWs and poor interface adhesion between AgNWs and the flexible substrate. In this study, we present a composite electrode comprising polydopamine-grafted cellulose nanofibers (PDA-TCNF) and AgNWs, fabricated through an interface customization strategy combined with UV-induced plasma welding. To enhance interfacial crosslinking, N, N-bis(acryloyl)cysteamine (BACA) was introduced as a surface adsorbate for AgNWs. The composite electrode exhibited rapid plasma welding of AgNWs under low-intensity UV irradiation. The optimized PDA-TCNF/AgNW-S/3 electrode demonstrated a sheet resistance of 7.26 Ω sq.-1 with a remarkable light transmittance of 85.7 %. The interface customization strategy facilitated enhanced diffusion of silver atoms at AgNW junctions during UV-induced heating, thereby strengthening their welding capability. These electrodes serve as high-performance FTCEs for electroluminescent devices and transparent electric heaters. Our work proposes a simple method to fabricate superior FTCEs by integrating nanocellulose with AgNWs, offering a promising environmentally friendly material for flexible optoelectronic applications.

Polyvinyl Alcohol-Based Membranes: A Review of Research Progress on Design and Predictive Modeling of Properties for Targeted Application

This review provides a comprehensive evaluation of the current state of polyvinyl alcohol (PVA)-based membranes, emphasizing their significance in membrane technology for various applications. The analysis encompasses both experimental and theoretical research articles, with a focus on recent decades, aiming to elucidate the potential and limitations of different fabrication approaches, structure-property relationships, and their applicability in the real world. The review begins by examining the advanced polymeric materials and strategies employed in the design and processing of membranes with tailored properties. Fundamental principles of membrane processes are introduced, with a focus on general modeling approaches for describing the fluid transport through membranes. A key aspect of discussion is the distinction between the membrane performance and process performance. Additionally, an in-depth analysis of PVA membranes in various applications is presented, particularly in environmental fields (e.g., fuel cell, water treatment, air purification, and food packaging) and biomedical domains (e.g., drug delivery systems, wound healing, tissue engineering and regenerative medicine, hemodialysis and artificial organs, and ophthalmic and periodontal treatment). Special attention is given to the relationship between membranes' characteristics, such as material composition, structure, and processing parameters, and their overall performance, in terms of permeability, selectivity, and stability. Despite their promising properties, enhanced through innovative fabrication methods that expand their applicability, challenges remain in optimizing long-term stability, improving fouling resistance, and increasing process scalability. Therefore, further research is needed to develop novel modifications and composite structures that overcome these limitations and enhance the practical implementation of PVA-based membranes. By offering a systematic overview, this review aims to advance the understanding of PVA membrane fabrication, properties, and functionality, providing valuable insights for continued development and optimization in membrane technology.

Biological testing unification for hemodialysis membranes evaluation: A step towards standardization

Current hemodialysis treatments can cause adverse effects, many of which are linked to the membranes used in the process. These issues are being addressed through new materials and technologies, making it urgent to establish minimum guidelines for evaluating such membranes. This review proposes standardizing the biological tests and variables to evaluate the performance of new membranes, aiming to replicate hemodialysis conditions closely. The tests were categorized into protein adsorption, protein transmission, platelet adhesion, platelet activation, blood coagulation times, hemolysis, complement activation, and cytotoxicity. For protein adsorption, static tests are recommended as an initial step to rule out membrane adhesion, followed by dynamic tests that must be conducted using a crossflow system (>250 mL/min flow) and a solution mimicking real conditions (BSA, lysozyme, trypsin, pepsin, creatinine, urea, albumin, fibrinogen, and γ-globulin). Protein transmission tests must employ dynamic conditions, using human blood or platelet-rich plasma for a minimum time of 3.5 h. Complement activation should be tested using human blood and ELISA assays to detect C3, C5 TCC, and SC5b-9. Blood coagulation times (APTT, TT, FT, TCT, and TAT) should be measured with platelet-poor and platelet-rich plasma. Hemolysis tests should transition from water bath to continuous mode for at least 3.5 h. Cytotoxicity tests should compare the MTT assay with other methods (Alamar Blue, Lactate Dehydrogenase Assay, Flow Cytometry, or Trypan Blue Exclusion Test) and use different cell types for comprehensive validation. By implementing these minimum biological tests, membrane evaluations would more accurately reflect the real-world applications, ensuring biocompatibility, effectiveness, and efficiency.

High-permeance nanocellulose/ZnO hybrid membranes with photo-induced anti-fouling performance for wastewater purification

A hybrid ultrafiltration membrane based on nanocellulose and zinc oxide nanoparticles (ZnO NPs) was prepared by simple layered filtration without any chemical modification. Microscopic morphology analysis showed that the loading ZnO NPs significantly increased the membrane roughness, and wettability test demonstrated that the membrane surface possessed underwater superoleophobicity. Due to the "puncture effect" of the embedded ZnO NPs, abundant nanochannels were formed in the nanocellulose membrane and the highest water permeance of 5439.7 L·m-2·h-1·bar-1 was achieved. The hybrid membranes exhibited high rejection of nanoparticles larger than 20 nm and macromolecules with molecular weights higher than 100 kDa. Furthermore, ZnO NPs significantly improved the wet tensile strength of membrane. The hybrid membranes achieved high separation efficiency of nano-sized emulsions via size exclusion and demulsification effect, as well as the efficient removal of organic dyes and antibiotics via filtration-adsorption. The combination of underwater superoleophobicity and photocatalytic self-cleaning performance effectively solved the problem of a sharp decrease in permeance caused by oil contamination. This type of nanocellulose/ZnO hybrid membrane, which integrates high permeance, high filtration accuracy, and photocatalytic anti-fouling performance in one design, offers an innovative approach to the preparation of nanocellulose membranes for the treatment of organic wastewater.

Chitosan particles embedded bacterial nanocellulose flat membrane for hemodialysis

The development of bio-based hemodialysis membranes continues to be a challenge. Bacterial nanocellulose (BNC) membranes show potential in hemodialysis but can hardly retain beneficial proteins. Here, chitosan particles/bacterial nanocellulose (CSP/BNC) membranes were designed to efficiently remove uremic toxins and retain beneficial proteins. First, CSPs were synthesized in situ within a BNC membrane by ionic gelation following negative pressure impregnation. Subsequently, these membranes were thoroughly characterized. Compared with the BNC membrane, the pore volume and pore size of the 3 % CSP/BNC membrane decreased by 42.2 % and 32.1 %, respectively. The increased 22.2 times of Young's modulus and 88.9 % of tensile strength in the 3 % CSP/BNC membrane confirmed enhanced mechanical property. The sieving coefficient of bovine serum albumin decreased to 0.05 ± 0.03 in the 3 % CSP/BNC membrane. Moreover, the CSP/BNC membrane exhibited good hemocompatibility and cytocompatibility. The simulated dialysis results showed that the 3 % CSP/BNC membrane exhibited high clearance of urea (16.37 %/cm2) and lysozyme (3.54 %/cm2), while efficiently retaining bovine serum albumin (98.04 %/cm2). This is the first demonstration of the construction of a BNC-based hemodialysis membrane with in situ CSP formation to effectively regulate the pore properties of the membrane, making the CSP/BNC membrane a promising candidate for hemodialysis applications.

Advances in Enhancing Hemocompatibility of Hemodialysis Hollow-Fiber Membranes

Hemodialysis, the most common modality of renal replacement therapy, is critically required to remove uremic toxins from the blood of patients with end-stage kidney disease. However, the chronic inflammation, oxidative stress as well as thrombosis induced by the long-term contact of hemoincompatible hollow-fiber membranes (HFMs) contribute to the increase in cardiovascular diseases and mortality in this patient population. This review first retrospectively analyzes the current clinical and laboratory research progress in improving the hemocompatibility of HFMs. Details on different HFMs currently in clinical use and their design are described. Subsequently, we elaborate on the adverse interactions between blood and HFMs, involving protein adsorption, platelet adhesion and activation, and the activation of immune and coagulation systems, and the focus is on how to improve the hemocompatibility of HFMs in these aspects. Finally, challenges and future perspectives for improving the hemocompatibility of HFMs are also discussed to promote the development and clinical application of new hemocompatible HFMs.

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Recovery of Extracellular Polymeric Substances from Excess Sludge Using High-Flux Electrospun Nanofiber Membranes

The recycling of extracellular polymeric substances (EPSs) from excess sludge in wastewater treatment plants has received increasing attention in recent years. Although membrane separation has great potential for use in EPS concentration and recovery, conventional membranes tend to exhibit low water flux and high energy consumption. Herein, electrospun nanofiber membranes (ENMs) were fabricated using polyvinylidene fluoride (PVDF) and used for the recovery of EPSs extracted from the excess sludge using the cation exchange resin (CER) method. The fabricated ENM containing 14 wt.% PVDF showed excellent properties, with a high average water flux (376.8 L/(m2·h)) and an excellent EPS recovery rate (94.1%) in the dead-end filtration of a 1.0 g/L EPS solution at 20 kPa. The ENMs displayed excellent mechanical strength, antifouling properties, and high reusability after five recycles. The filtration pressure had a negligible effect on the average EPS recovery rate and water flux. The novel dead-end filtration with an EPS filter cake on the ENM surface was effective in removing heavy-metal ions, with the removal rates of Pb2+, Cu2+, and Cr6+ being 89.5%, 73.5%, and 74.6%, respectively. These results indicate the potential of nanofiber membranes for use in effective concentration and recycling of EPSs via membrane separation.

Manufacturing and Separation Characteristics of Hemodialysis Membranes to Improve Toxin Removal Rate

With the recently growing interest in health care, hemodialysis is being performed not only to treat patients with renal disease but also to improve blood circulation. At present, filters used for hemodialysis are manufactured only in certain countries, and all other countries must rely on imports. In this study, polyethersulfone (PES), which has excellent blood compatibility, was used as the main material to develop hemodialysis membranes for hemodialysis filters, and these hemodialysis membranes were prepared by adding a hydrophilic polymer, polyvinylpyrrolidone (PVP), and varying the type of nonsolvent during the manufacturing process to improve the toxin removal rate and biocompatibility. The addition of PVP was confirmed through attenuated total reflection Fourier transform infrared (ATR-FTIR), and the structure of the membranes depending on the nonsolvent was analyzed through scanning electron microscopy (SEM) and atomic force microscopy (AFM) images. The contact angle results indicated that the hydrophilicity of the membrane surface was improved as the concentration of PVP increased. The results of the toxin filtration efficiency experiment using urea, creatinine, and bovine serum albumin (BSA) confirmed removal rates of 58.8% and 56.87%, respectively, and a protein loss of less than 8%. Also, cell viability was over 90% at the PVP concentration of 2% or higher. A preliminary study was conducted on the improvement of toxin filtration efficiency and the development potential of these hemodialysis membranes with excellent biocompatibility.

Nano architectured cues as sustainable membranes for ultrafiltration in blood hemodialysis

Membranes with zeolites are encouraging for performing blood dialysis because zeolites can eliminate uremic toxins through molecular sieving. Although the addition of various pore-gen and adsorbent in the membrane can certainly impact the membrane production along with creatinine adsorption, however, it is not directed which pore-gen along with zeolite leads to better performance. The research was aimed at reducing the adsorption of protein-bound and uremic toxins by using mordenite zeolite as an adsorbent while polyethylene glycol and cellulose acetate as a pore generating agent. Membranes were cast by a phase-inversion technique which is cheap and easy to handle as compared to the electro-spinning technique. Through this strategy, the ability to adsorb creatinine and solute rejection percentage were measured and compared against the pristine PSU, when only PEG was used as a pore-modifier and when PEG along with CA was used as a pore-modifier along with a different concentration of zeolite. The experiments revealed that PEG membranes can give a better solute rejection percentage (93%) but with a low creatinine adsorption capacity that is 7654 μg/g and low bio-compatibility (PRT 392 s, HR 0.46%). However, PEG/CA membranes give maximum creatinine adsorption that is 9643 μg/g and also better bio-compatibility (PRT 490 s, HR 0.37%) but with a low BSA rejection (72%) as compared to the pristine PSU and PEG membranes. The present study finds that the concentration of mordenite zeolite affects the membrane performance because its entrapment and large pore size of the membrane decreases solute rejection but increases creatinine uptake level along with the better bio-compatibility.

Surface Modification of Reduced Graphene Oxide Beads: Integrating Efficient Endotoxin Adsorption and Improved Blood Compatibility

As a pathogenic toxin, endotoxins are the culprit for endotoxemia and can be generally removed from the blood by hemoperfusion. Reduced graphene oxide (rGO) is a promising endotoxin sorbent for hemoperfusion owing to its excellent adsorption capacity, but it has the side effect of nonspecific adsorption and low blood compatibility. Polymyxin B (PMB) acts as an organic affinity ligand that can specifically bind endotoxins. As a natural anticoagulant, heparin (Hep) can reduce the risk of coagulation and improve the blood compatibility of materials. Herein, an rGO bead adsorbent was prepared by coupling with PMB and Hep and used for endotoxin adsorption; in this, polydopamine (pDA) served as an active coating for immobilization of PMB and further coupling with Hep. The physicochemical characteristics indicated that PMB and Hep were successfully immobilized on rGO beads with a hierarchical pore structure. PMB endowed rGO beads with higher adsorption capacity (143.84 ± 3.28 EU/mg) and good adsorption selectivity for endotoxins. Hep significantly improved the blood compatibility of rGO beads. These modified rGO beads also achieved good adsorption capacity and adsorption selectivity for endotoxins in plasma, serum, or blood. Therefore, rGO/pDA/PMB/Hep beads are potential adsorbents for endotoxins in hemoperfusion.

Cellulose acetate-polyvinyl alcohol blend hemodialysis membranes integrated with dialysis performance and high biocompatibility

Hemodialysis considered as therapy of end-stage renal disease (ESRD) for the separation of protein and uremic toxins based on their molecular weights using semi-permeable membranes. Cellulose Acetate (CA) hemodialysis membrane has been widely used in the biomedical field particularly for hemodialysis applications. The main issue of CA membrane is less selectivity and hemocompatibility. In this study, to enhance the filtration capability and biocompatibility of CA hemodialysis membrane modified by using Polyvinyl Alcohol (PVA) and Polyethylene Glycol (PEG) as additives. CA-PVA flat sheet membranes were cast by phase inversion method, and separation was done by dead-end filtration cell. The synthesized membranes were described in terms of chemical structure using Fourier Transform Infrared Spectroscopy (FTIR) and morphology by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), pure water flux, solute permeation, and protein retention. Biocompatibility of the membranes was tested by the platelet adherence, hemolysis ratio, thrombus formation, and plasma recalcification time. SEM images exposed that the CA-PVA membrane has a uniform porous structure. 42.484 L/m² h is the maximum pure water flux obtained. The CA-PVA rejected up to 95% of bovine serum albumin (BSA). A similar membrane separated 93% of urea and 89% of creatinine. Platelet adhesion and hemolysis ratio of casted membranes were less than the pure CA membrane. Increased clotting time and less thrombus formation on the membrane's surface showed that the fabricated membrane is biocompatible. CA-PVA hemodialysis membranes are more efficient than conventional reported hemodialysis membranes. It revealed that CA-PVA is high performing biocompatible hemodialysis membrane.

A novel anticoagulant affinity membrane for enhanced hemocompatibility and bilirubin removal

Affinity membrane is widely employed to promote specific adsorption of toxins and reduce the blood purification therapeutic time. However, it suffers from insufficient toxin binding and low hemocompatibility. Herein, a novel anticoagulant affinity membrane (AAM) was developed to clear bilirubin from human blood in a pore-flow-through way. Firstly, a nylon net membrane with a regularly arranged pore as the matrix was coated with poly(pyrrole-3-carboxylic acid) via chemical vapor deposition (CVD) method. Then, poly(L-arginine) (PLA) as a highly specific ligand of bilirubin, was immobilized onto the surface of the composited membrane after the modification of heparin. Owing to the 3-dimensional molecular architecture of PLA, up to 86.1 % of bilirubin was efficiently cleared. Besides, the AAM exhibited effective anticoagulant activity in the measurement of clotting time, with suppressed thrombus formation, low hemolysis ratio, minimized platelet and leukocyte adhesion, and excellent biosafety. Therefore, the AAM has enormous potential in blood purification therapy for enhancing hemocompatibility and bilirubin removal.

Hierarchical Surface Architecture of Hemodialysis Membranes for Eliminating Homocysteine Based on the Multifunctional Role of Pyridoxal 5'-phosphate

Patients with end-stage renal disease are prone to developing a complication of hyperhomocysteinemia, manifesting as an elevation of the homocysteine (Hcy) concentration in human plasma. However, Hcy as a protein-bound toxin is barely removed by conventional hemodialysis membranes. Here, we report a novel hemodialysis membrane by preparing a bioactive coating of pyridoxal 5'-phosphate (PLP) and adding biocompatible hyperbranched polyglycerol (HPG) brushes to achieve Hcy removal. The dip-applied PLP coating, a coenzyme with a role in Hcy metabolism, dramatically promoted a decrease in the Hcy concentration in human plasma. Moreover, the aldehyde group of PLP had an intrinsic chemical reactivity toward the terminal amino group to immobilize the HPG brushes on the hemodialysis membrane surface. The hierarchical PLP-HPG layer-functionalized membranes had a high efficacy for eliminating Hcy, with a concentration from the initial stage of 150 μmol/L reduced to a nearly normal level of 20 μmol/L in simulated dialysis. By analyzing the impact of HPG brushes with various chain lengths, we found that HPG brushes with a medium length enabled the PLP coating with the bioactive function of Hcy conversion to additionally protect Hcy-attacked target cells by providing excellent hydrophilicity and a dense enough chain volume overlap of the hyperbranched architecture. Simultaneously, the densely packed HPG brushes generated a maximal steric and hydration barrier that significantly improved biofouling resistance against blood proteins. The optimally functionalized membranes showed a clearance of 83.1% urea and 49.6% lysozyme and a rejection of 96.0% bovine serum albumin. The diversely functionalized PLP-HPG layers demonstrate a potential route for a more integrated hemodialysis membrane that can cope with the urgent issue of hyperhomocysteinemia in clinical hemodialysis therapy.

Mini-Review: Mixed Ionic-Electronic Charge Carrier Localization and Transport in Hybrid Organic-Inorganic Nanomaterials

In this mini-review, a comprehensive discussion on the state of the art of hybrid organic–inorganic mixed ionic–electronic conductors (hOI-MIECs) is given, focusing on conducting polymer nanocomposites comprising inorganic nanoparticles ranging from ceramic-in-polymer to polymer-in-ceramic concentration regimes. First, a brief discussion on fundamental aspects of mixed ionic–electronic transport phenomena considering the charge carrier transport at bulk regions together with the effect of the organic–inorganic interphase of hybrid nanocomposites is presented. We also make a recount of updated instrumentation techniques to characterize structure, microstructure, chemical composition, and mixed ionic–electronic transport with special focus on those relevant for hOI-MIECs. Raman imaging and impedance spectroscopy instrumentation techniques are particularly discussed as relatively simple and versatile tools to study the charge carrier localization and transport at different regions of hOI-MIECs including both bulk and interphase regions to shed some light on the mixed ionic–electronic transport mechanism. In addition, we will also refer to different device assembly configurations and in situ/operando measurements experiments to analyze mixed ionic–electronic conduction phenomena for different specific applications. Finally, we will also review the broad range of promising applications of hOI-MIECs, mainly in the field of energy storage and conversion, but also in the emerging field of electronics and bioelectronics.

Under-oil self-driven and directional transport of water on a femtosecond laser-processed superhydrophilic geometry-gradient structure

Self-driven and continuous directional transport of water droplets in an oil environment has great potential applications in microfluidics, oil-water separation, etc. Nevertheless, most current studies exploit water behaviors occurring in air, and the directional regulation of water in a viscous oil medium remains a challenge. In this work, a superhydrophilic geometry-gradient stainless steel platform with nanoparticle-covered nanoripple structures is proposed using femtosecond laser direct writing technology. The as-prepared platform spontaneously and directionally transported water droplets in the oil environment from the minor side to the large side of the trapezoidal platform surface, but not in the opposite direction. The transport velocity of water droplets as a function of trapezoid angle and tilt angle of the as-prepared platform was investigated in detail. In addition, a pumpless under-oil water transport platform was successfully prepared on other substrates including Ti and Ni sheets, polyimide film, and C cloth, and exhibited transport capabilities when the platform was flexed and combined into various shapes. This work offers insight into the simple fabrication of a flexible and substrate-independent pumpless under-oil directional transport device for water.

Carbon Nanotube/Conducting Polymer Hybrid Nanofibers as Novel Organic Bioelectronic Interfaces for Efficient Removal of Protein-Bound Uremic Toxins

Protein-bound uremic toxins (PBUTs) can cause noxious effects in patients suffering from renal failure as a result of inhibiting the transport of proteins and inducing their structural modification. They are difficult to remove through standard hemodialysis (HD) treatment. Herein, we report an organic bioelectronic HD device system for the effective removal of PBUTs through electrically triggered dissociation of protein-toxin complexes. To prepare this system, we employed electrospinning to fabricate electrically conductive quaternary composite nanofiber mats-comprising multiwalled carbon nanotubes (MWCNTs), poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS), poly(ethylene oxide) (PEO), and (3-glycidyloxypropyl)trimethoxysilane (GOPS)-on conventional polyethersulfone (PES) dialysis membranes. These composite nanofiber platforms exhibited (i) long-term water resistance (due to cross-linking among PSS, PEO, and GOPS), (ii) high adhesion strength on the PES membrane (due to GOPS functioning as an adhesion promoter), (iii) enhanced electrical properties [due to the MWCNTs and PEDOT:PSS promoting effective electrical stimulation (ES) operation in devices containing bioelectronic interfaces (BEI)], and (iv) good anticoagulant ability and negligible hemolysis of red blood cells. We employed this organic BEI electronic system as a novel single-membrane HD device to study the removal efficiency of four kinds of uremic toxins [p-cresol (PC), indoxyl sulfate, and hippuric acid as PBUTs; creatinine as a non-PBUT] as well as the effects of ES on lowering the protein binding ratio. Our organic BEI devices provided a high rate of removal of PC with low protein loss after 4 h of a simulated dialysis process. It also functioned with low complement activation, low contact activation levels, and lower amounts of platelet adsorption, suggesting great suitability for use in developing next-generation bioelectronic medicines for HD.