Direct quantification of negatively charged functional groups on membrane surfaces

Unraveling the role of carboxylate groups and elastin particle size in medial calcification

While it is known that calcium phosphate (CaP) minerals deposit in elastin-rich medial layers of arteries during medial calcification, their nucleation and growth sites are still debated. Neutral carbonyl groups and carboxylate groups are possible candidates. Also, while it is known that elastin degradation leads to calcification, it is unclear whether this is due to formation of new carboxylate groups or elastin fragmentation. In this work, we disentangle effects of carboxylate groups and particle size on elastin calcification; in doing so, we shed light on CaP mineralization sites on elastin. We find carboxylate groups accelerate calcification only in early stages; they mainly function as Ca2+ ion chelation sites but not calcification sites. Their presence promotes formation (likely on Ca2+ ions adsorbed on nearby carbonyl groups) of CaP minerals with high calcium-to-phosphate ratio as intermediate phases. Larger elastin particles calcify slower but reach similar amounts of CaP minerals in late stages; they promote direct formation of hydroxyapatite and CaP minerals with low calcium-to-phosphate ratio as intermediate phases. This work provides new perspectives on how carboxylate groups and elastin particle size influence calcification; these parameters can be tuned to study the mechanism of medial calcification and design drugs to inhibit the process.

Black odorous water concentrating by forward osmosis: rejection performance of characteristic pollutants based on cation exchange

This study aimed to investigate pollutant concentration and nitrogen interception characteristics of a forward osmosis (FO) process for concentrating black odorous water. The membrane cell was operated in active layer facing feed solution (AL-FS) mode with aquaporin (AQP) as the membrane material and NaCl solution as the draw solution (DS). The organic pollutants (COD), TP, NH+4-N, NO-3-N, TN, Fe and Mn in black odorous water were concentrated non-intermittently for 24 h, and their interception characteristics were investigated. The results showed that the average interception rates of COD, TP, NO- 3-N, TN, Fe and Mn were 97.2%, 98.0%, 58.7%, 54.3%, 61.8% and 60.0%, respectively, while the average interception rate of NH+4-N was only 1.27%-3.47%. To explore the characteristics of nitrogen interception, a comparison was conducted between AQP membrane and thin film composite (TFC) membrane. Because the surface electronegativity of AQP membrane was stronger than that of TFC, the effect of cation exchange on ammonia nitrogen interception was more serious with AQP membrane. With NaCl solution as DS, the reverse osmosis flux of Na+ was (0.53 ± 0.02 mol·m-2·h-1), which was significantly higher than that of Cl- (0.29 ± 0.03 mol·m-2·h-1) (P < 0.05). The interception effect of AQP membrane on TN was related to the proportion of NH+4-N in TN. The pretreatment of black odorous water by aeration could transform part of NH+4-N into NO-3-N, and reduce the negative effect of cation exchange effect on nitrogen interception. The TN interception rate increased from 54.3% to 66.1%.

Digital Manufacturing of Functional Ready-to-Use Microfluidic Systems

Digital manufacturing (DM) holds great potential for microfluidics, but requirements for embedded conduits and high resolution beyond the capability of common manufacturing equipment, and microfluidic systems' dependence on peripheralshave limited its adoption. Capillaric circuits (CCs) are structurally encoded, self-contained microfluidic systems that operate and self-fill via precisely tailored hydrophilicity. CCs  are  heretofore hydrophilized in a plasma chamber, but which offers only transient hydrophilicity, lacks reproducibility, and limits CC design to open surface channels subsequently sealed with tape. Here, the additive DM of monolithic, fully functional, and intrinsically hydrophilic CCs is reported. CCs are 3D printed with commonly available light-engine-based 3D printers using poly(ethylene glycol)diacrylate-based ink co-polymerized with hydrophilic acrylic acid crosslinkers and optimized for hydrophilicity and printability. A new, robust capillary valve design and embedded conduits with circular cross-sections that prevent bubble trapping are presented, interwoven circuit architectures created, and CC use illustrated with an immunoassay. Finally, the external paper capillary pumps are eliminated by directly embedding the capillary pump in the chip as a porous gyroid structure, realizing fully functional, monolithic CCs. Thence, a digital file can be made into a CC by commonly available 3D printers in less than 30 min enabling low-cost, distributed DM of fully functional ready-to-use microfluidic systems.

NaHCO3 addition enhances water permeance and Ca/haloacetic acids selectivity of nanofiltration membranes for drinking water treatment

The existence of disinfection by-products such as haloacetic acids (HAAs) in drinking water severely threatens water safety and public health. Nanofiltration (NF) is a promising strategy to remove HAAs for clean water production. However, NF often possesses overhigh rejection of essential minerals such as calcium. Herein, we developed highly selective NF membranes with tailored surface charge and pore size for efficient rejection of HAAs and high passage of minerals. The NF membranes were fabricated through interfacial polymerization (IP) with NaHCO3 as an additive. The NaHCO3-tailored NF membranes exhibited high water permeance up to ∼24.0 L m - 2 h - 1 bar-1 (more than doubled compared with the control membrane) thanks to the formation of stripe-like features and enlarged pore size. Meanwhile, the tailored membranes showed enhanced negative charge, which benefitted their rejection of HAAs and passage of Ca and Mg. The higher rejection of HAAs (e.g., > 90%) with the lower rejection of minerals (e.g., < 30% for Ca) allowed the NF membranes to achieve higher minerals/HAAs selectivity, which was significantly higher than those of commercially available NF membranes. The simultaneously enhanced membrane performance and higher minerals/HAAs selectivity would greatly boost water production efficiency and water quality. Our findings provide a novel insight to tailor the minerals/micropollutants selectivity of NF membranes for highly selective separation in membrane-based water treatment.

Insulated Interlaced Surface Electrodes for Bacterial Inactivation and Detachment

Effective and stable antibiofouling surfaces and interfaces have long been of research interest. In this study, we designed, fabricated, and evaluated a surface coated with insulated interlaced electrodes for bacterial fouling reduction. The electrodes were printed Ag filaments of 100 μm width and 400 μm spacing over an area of 2 × 2 cm². The insulating Ag electrode coating material was polydimethylsiloxane (PDMS) or thermoplastic polyurethane (TPU) with a thickness of 10 to 40 μm. To evaluate the antibiofouling potential, E. coli inactivation after 2 min contact with the electrified surface and P. fluorescens detachment after 15 and 40 h growth were examined. The extent of bacterial inactivation was related to the insulating material, coating thickness, and applied voltage (magnitude and AC vs DC). A high bacterial inactivation (>98%) was achieved after only 2 min of treatment at 50 V AC and 10 kHz using a 10 μm TPU coating. P. fluorescens detachment after 15 and 40 h incubation in the absence of applied potential was completed with simultaneous cross-flow rinsing and AC application. Higher AC voltages and longer cross-flow rinsing times resulted in greater bacterial detachment with bacterial coverage able to be reduced to <1% after only 2 min of rinsing at 50 V AC and 10 kHz. Theoretical electric field analysis indicated that at 10 V the field strength penetrating the aqueous solution is nonuniform (∼16,000-20,000 V m^-1 for the 20 μm TPU) and suggests that dielectrophoresis plays a key role in bacterial detachment. The bacterial inactivation and detachment trends observed in this study indicate that this technique has merit for future antibiofouling surface development.

Correlating the Role of Nanofillers with Active Layer Properties and Performance of Thin-Film Nanocomposite Membranes

Thin-film nanocomposite (TFN) membranes are emerging water-purification membranes that could provide enhanced water permeance with similar solute removal over traditional thin-film composite (TFC) membranes. However, the effects of nanofiller incorporation on active layer physico-chemical properties have not been comprehensively studied. Accordingly, we aimed to understand the correlation between nanofillers, active layer physico-chemical properties, and membrane performance by investigating whether observed performance differences between TFN and control TFC membranes correlated with observed differences in physico-chemical properties. The effects of nanofiller loading, surface area, and size on membrane performance, along with active layer physico-chemical properties, were characterized in TFN membranes incorporated with Linde Type A (LTA) zeolite and zeolitic imidazole framework-8 (ZIF-8). Results show that nanofiller incorporation up to ~0.15 wt% resulted in higher water permeance and unchanged salt rejection, above which salt rejection decreased 0.9-25.6% and 26.1-48.3% for LTA-TFN and ZIF-8-TFN membranes, respectively. Observed changes in active layer physico-chemical properties were generally unsubstantial and did not explain observed changes in TFN membrane performance. Therefore, increased water permeance in TFN membranes could be due to preferential water transport through porous structures of nanofillers or along polymer-nanofiller interfaces. These findings offer new insights into the development of high-performance TFN membranes for water/ion separations.

Pilot scale nanofiltration membrane fabrication containing ionic co-monomers and halloysite nanotubes for textile dye filtration

Wastewater from the textile industry contains high concentrations of pollutants, so the wastewater must be treated before it is discharged. In addition, the reuse of treated wastewater should be considered from an environmental point of view, as large volumes of wastewater are produced. Since textile wastewater mainly contains dyestuffs, it must be treated effectively using environmentally friendly technologies. Membrane processes are widely used in textile wastewater treatment as they have distinct advantages over conventional wastewater treatment methods. This study reports the pilot-scale manufacturing and characterization of three different NF membranes. Three different types of membranes were fabricated. The fabricated membranes were compared through characterization by surface properties, chemical structure and morphology. Membranes were tested for pure water flux. Then the synthetic wastewater (SWW) was tested for flux and rejection. Lastly, the textile wastewater was tested. The textile wastewater flux of pure piperazine (PIP), 60% S-DADPS and 0.04% halloysite nanotubes (HNTs) were 22.42, 79.58 and 40.06 L m^-2 h^-1. It has been proven that the 60% s-DADPS membrane provides up to four times improvement in wastewater flux and simultaneously. In addition, NF membranes produced using HNT and sDADPS on a pilot scale have brought innovation to the literature with the good results obtained.

Toward a universal framework for evaluating transport resistances and driving forces in membrane-based desalination processes

Desalination technologies using salt-rejecting membranes are a highly efficient tool to provide fresh water and augment existing water supplies. In recent years, numerous studies have worked to advance a variety of membrane processes with different membrane types and driving forces, but direct quantitative comparisons of these different technologies have led to confusing and contradictory conclusions in the literature. In this Review, we critically assess different membrane-based desalination technologies and provide a universal framework for comparing various driving forces and membrane types. To accomplish this, we first quantify the thermodynamic driving forces resulting from pressure, concentration, and temperature gradients. We then examine the resistances experienced by water molecules as they traverse liquid- and air-filled membranes. Last, we quantify water fluxes in each process for differing desalination scenarios. We conclude by synthesizing results from the literature and our quantitative analyses to compare desalination processes, identifying specific scenarios where each process has fundamental advantages.

Evaluation of Membrane Fouling Control for Brackish Water Treatment Using a Modified Polyamide Composite Nanofiltration Membrane

In northwest China, the limited amount of water resources are classified mostly as brackish water. Nanofiltration is a widely applied desalination technology used for brackish water treatment; however, membrane fouling restricts its application. Herein, we modified the membrane with triethanolamine (TEOA) and optimized the operating conditions (transmembrane pressure, temperature, and crossflow velocity) to control the nanofiltration membrane fouling by brackish water. Based on the physiochemical characteristics and desalination performance of the prepared membranes, the membrane modified with 2% TEOA (MPCM2) was identified as the optimal membrane, and 0.5 MPa, 25 °C, and 7 cm/s were identified as the optimal operating conditions through a series of nanofiltration experiments. Moreover, the membrane cleaning procedure for fouled MPCM2 was further determined, and a two-step cleaning procedure using ethylene diamine tetraacetic acid disodium followed by HCl with a permeance recovery rate of 98.77% was identified as the optimal cleaning procedure. Furthermore, the characterizations of the fouled and cleaned MPCM2 showed that the optimized cleaning procedure could recover the properties of MPCM2 to near virgin. This study is of great significance for the long-term stable operation of nanofiltration processes in brackish water treatment to ensure the supply of healthy water in the water-deficient areas of northwest China.

The Influence of Forward Osmosis Module Configuration on Nutrients Removal and Microalgae Harvesting in Osmotic Photobioreactor

Microalgae have attracted great interest recently due to their potential for nutrients removal from wastewater, renewable biodiesel production and bioactive compounds extraction. However, one major challenge in microalgal bioremediation and the algal biofuel process is the high energy cost of separating microalgae from water. Our previous studies demonstrated that forward osmosis (FO) is a promising technology for microalgae harvesting and dewatering due to its low energy consumption and easy fouling control. In the present study, two FO module configurations (side-stream and submerged) were integrated with microalgae (C. vulgaris) photobioreactor (PBR) in order to evaluate the system performance, including nutrients removal, algae harvesting efficiency and membrane fouling. After 7 days of operation, both systems showed effective nutrients removal. A total of 92.9%, 100% and 98.7% of PO₄-P, NH₃-N and TN were removed in the PBR integrated with the submerged FO module, and 82%, 96% and 94.8% of PO₄-P, NH₃-N and TN were removed in the PBR integrated with the side-stream FO module. The better nutrients removal efficiency is attributed to the greater algae biomass in the submerged FO-PBR where in situ biomass dewatering was conducted. The side-stream FO module showed more severe permeate flux loss and biomass loss (less dewatering efficiency) due to algae deposition onto the membrane. This is likely caused by the higher initial water flux associated with the side-stream FO configuration, resulting in more foulants being transported to the membrane surface. However, the side-stream FO module showed better fouling mitigation by simple hydraulic flushing than the submerged FO module, which is not convenient for conducting cleaning without interrupting the PBR operation. Taken together, our results suggest that side-stream FO configuration may provide a viable way to integrate with PBR for a microalgae-based treatment. The present work provides novel insights into the efficient operation of a FO-PBR for more sustainable wastewater treatment and effective microalgae harvesting.

The Role of Surface Chemistry in the Osseointegration of PEEK Implants

Poly(etheretherketone) (PEEK) implants suffer from poor osseointegration because of chronic inflammation. In this study, we hypothesized that adding NH₂ and COOH groups to the surface of PEEK could modulate macrophage responses by altering protein adsorption and improve its osseointegration. NH₂ and COOH-functionalized PEEK surfaces induced pro- and anti-inflammatory macrophage responses, respectively, and differences in protein adsorption patterns on these surfaces were related to the varied inflammatory responses. The macrophage responses to NH₂ surfaces significantly reduced the osteogenic differentiation of mesenchymal stem cells (MSCs). MSCs cultured on NH₂ surfaces differentiated less than those on COOH surfaces even though NH₂ surfaces promoted the most mineralization in simulated body fluid solutions. After 14 days in rat tibia unicortical defects, the bone around NH₂ surfaces had thinner trabeculae and higher specific bone surface than the bone around unmodified implants; surprisingly, the NH₂ implants significantly increased bone-binding over the unmodified implants, while COOH implants only showed a trend for increasing bone-binding. Taken together, these results suggest that both mineral-binding and immune responses play a role in osseointegration, and PEEK implant integration may be improved with mixtures of these two functional groups to harness the ability to reduce inflammation and bind bone strongly.

Impacts of Surface Hydrophilicity of Carboxylated Polyethersulfone Supports on the Characteristics and Permselectivity of PA-TFC Nanofiltration Membranes

Our current study experimentally evaluates the impacts of surface hydrophilicity of supports on the properties of polyamide (PA) thin-film composite (TFC) nanofiltration (NF) membranes. A series of "carboxylated polyethersulfone" (CPES) copolymers with an increasing "molar ratio" (MR) of carboxyl units were used to prepare supports with diverse surface hydrophilicities by the classical nonsolvent-induced phase separation (NIPS) method. Then, the PA-TFC NF membranes were finely fabricated atop these supports by conventional interfacial polymerization (IP) reactions. The linkages between the surface hydrophilicity of the supports and the characteristics of the interfacially polymerized PA layers as well as the permselectivity of NF membranes were investigated systematically. The morphological details of the NF membranes indicate that the growth of PA layers can be adjusted through increasing the surface hydrophilicity of the supports. Moreover, the separation results reveal that the NF membrane fabricated on the relatively hydrophobic support exhibits lower permeability (7.04 L·m^-2·h^-1·bar^-1) and higher selectivity (89.94%) than those of the ones prepared on the hydrophilic supports (14.64~18.99 L·m^-2·h^-1·bar^-1 and 66.98~73.48%). A three-stage conceptual scenario is proposed to illustrate the formation mechanism of the PA layer in NF membranes, which is due to the variation of surface hydrophilicity of the supports. The overall findings specify how the surface hydrophilicity of the supports influences the formation of PA layers, which ultimately defines the separation performances of the corresponding NF membranes.

The Effect of Ozone Treatment on the Physicochemical Properties and Biocompatibility of Electrospun Poly(ε)caprolactone Scaffolds

Ozonation has been proved as a viable surface modification technique providing certain properties to the scaffolds that are essential in tissue engineering. However, the ozone (O3) treatment of PCL scaffolds in aqueous environments has not yet been presented. O3 treatment performed in aqueous environments is more effective compared with traditional, executed in ambient air treatment due to more abundant production of hydroxyl radicals (•OH) within the O3 reaction with water molecules. During interaction with •OH, the scaffold acquires functional groups which improve wettability properties and encapsulate growth factors. In this study, a poly(ε)caprolactone (PCL) scaffold was fabricated using solution electrospinning and was subsequently ozonated in a water reactor. The O3 treatment resulted in the expected occurrence of oxygen-containing functional groups, which improved scaffold wettability by almost 27% and enhanced cell proliferation for up to 14 days. The PCL scaffold was able to withhold 120 min of O3 treatment, maintaining fibrous morphology and mechanical properties.

Protein Adsorption on Surfaces Functionalized with COOH Groups Promotes Anti-inflammatory Macrophage Responses

Implants can induce a foreign body reaction that leads to chronic inflammation and fibrosis in the surrounding tissue. Macrophages help detect the foreign material, play a role in the inflammatory response, and may promote fibrosis instead of the desired tissue regeneration around implants. Implant surface properties impact macrophage responses by changing the nature of the adsorbed protein layer, but conflicting studies highlight the complexity of this relationship. In this study, the effect of surface chemistry on macrophage behavior was investigated with poly(styrene) surfaces containing common functional groups at similar surface densities. The protein layer was characterized to identify the proteins that adsorbed on the surfaces from the medium and the proteins secreted onto the surfaces by adherent macrophages. Of the surface chemistries studied, carboxylic acid (COOH) groups promoted anti-inflammatory responses from unstimulated macrophages and did not exacerbate inflammation upon stimulation. These surfaces also enhanced the adsorption of proteins involved in integrin signaling and promoted the secretion of proteins related to angiogenesis, integrin signaling, and cytokine signaling, which have been previously associated with improved biomaterial integration. Therefore, this study suggests that surface modification with COOH groups may help improve the integration of implants in the body by enhancing anti-inflammatory macrophage responses through altered protein adsorption.

Differentiating Solutes with Precise Nanofiltration for Next Generation Environmental Separations: A Review

Selective removal or enrichment of targeted solutes including micropollutants, valuable elements, and mineral scalants from complex aqueous matrices is both challenging and pivotal to the success of water purification and resource recovery from unconventional water resources. Membrane separation with precision at the subnanometer or even subangstrom scale is of paramount importance to address those challenges via enabling "fit-for-purpose" water and wastewater treatment. So far, researchers have attempted to develop novel membrane materials with precise and tailored selectivity by tuning membrane structure and chemistry. In this critical review, we first present the environmental challenges and opportunities that necessitate improved solute-solute selectivity in membrane separation. We then discuss the mechanisms and desired membrane properties required for better membrane selectivity. On the basis of the most recent progress reported in the literature, we examine the key principles of material design and fabrication, which create membranes with enhanced and more targeted selectivity. We highlight the important roles of surface engineering, nanotechnology, and molecular-level design in improving membrane selectivity. Finally, we discuss the challenges and prospects of highly selective NF membranes for practical environmental applications, identifying knowledge gaps that will guide future research to promote environmental sustainability through more precise and tunable membrane separation.

Recent Advances in the Rejection of Endocrine-Disrupting Compounds from Water Using Membrane and Membrane Bioreactor Technologies: A Review

Water is a critical resource necessary for life to be sustained, and its availability should be secured, appropriated, and easily obtainable. The continual detection of endocrine-disrupting chemicals (EDCs) (ng/L or µg/L) in water and wastewater has attracted critical concerns among the regulatory authorities and general public, due to its associated public health, ecological risks, and a threat to global water quality. Presently, there is a lack of stringent discharge standards regulating the emerging multiclass contaminants to obviate its possible undesirable impacts. The conventional treatment processes have reportedly ineffectual in eliminating the persistent EDCs pollutants, necessitating the researchers to develop alternative treatment methods. Occurrences of the EDCs and the attributed effects on humans and the environment are adequately reviewed. It indicated that comprehensive information on the recent advances in the rejection of EDCs via a novel membrane and membrane bioreactor (MBR) treatment techniques are still lacking. This paper critically studies and reports on recent advances in the membrane and MBR treatment methods for removing EDCs, fouling challenges, and its mitigation strategies. The removal mechanisms and the operating factors influencing the EDCs remediation were also examined. Membranes and MBR approaches have proven successful and viable to eliminate various EDCs contaminants.

Intrapore energy barriers govern ion transport and selectivity of desalination membranes

State-of-the-art desalination membranes exhibit high water-salt selectivity, but their ability to discriminate between ions is limited. Elucidating the fundamental mechanisms underlying ion transport and selectivity in subnanometer pores is therefore imperative for the development of ion-selective membranes. Here, we compare the overall energy barrier for salt transport and energy barriers for individual ion transport, showing that cations and anions traverse the membrane pore in an independent manner. Supported by density functional theory simulations, we demonstrate that electrostatic interactions between permeating counterion and fixed charges on the membrane substantially hinder intrapore diffusion. Furthermore, using quartz crystal microbalance, we break down the contributions of partitioning at the pore mouth and intrapore diffusion to the overall energy barrier for salt transport. Overall, our results indicate that intrapore diffusion governs salt transport through subnanometer pores due to ion-pore wall interactions, providing the scientific base for the design of membranes with high ion-ion selectivity.

In Situ Ag-MOF Growth on Pre-Grafted Zwitterions Imparts Outstanding Antifouling Properties to Forward Osmosis Membranes

In this study, a polyamide forward osmosis membrane was functionalized with zwitterions followed by the in situ growth of metal-organic frameworks with silver as a metal core (Ag-MOFs) to improve its antibacterial and antifouling activity. First, 3-bromopropionic acid was grafted onto the membrane surface after its activation with N,N-diethylethylenediamine. Then, the in situ growth of Ag-MOFs was achieved by a simple membrane immersion sequentially in a silver nitrate solution and in a ligand solution (2-methylimidazole), exploiting the underlying zwitterions as binding sites for the metal. The successful membrane functionalization and the enhanced surface wettability were verified through an array of characterization techniques. When evaluated in forward osmosis tests, the modified membranes exhibited high performance and improved permeability compared to pristine membranes. Static antibacterial experiments, evaluated by confocal microscopy and colony-forming unit plate count, resulted in a 77% increase in the bacterial inhibition rate due to the activity of the Ag-MOFs. Microscopy micrographs of the Escherichia coli bacteria suggested the deterioration of the biological cells. The antifouling properties of the functionalized membranes translated into a significantly lower flux decline in forward osmosis filtrations. These modified surfaces displayed negligible depletion of silver ions over 30 days, confirming the stable immobilization of Ag-MOFs on their surface.

Ion partitioning and permeation in charged low-T* membranes

Understanding ion transport in membrane materials is key to engineering and development of desalination and water purification technologies as well as electro-membrane applications. To date, modeling of ion transport has mainly relied on mean-field approaches, originally intended for weak inter-ionic interactions, i.e., high reduced temperature T*. This condition is violated in many membranes, which could explain disagreement between predicted trends and experiments. The paper highlights observed discrepancies and develops a new approach based on the concept of ion association, more adequate in the low-T^⁎ limit. The new model addresses ion binding and mobility consistently within the same physical picture, applied to different types of single and mixed salts. The resulting relations show a significantly weaker connection between ion partitioning and permeability than the standard ones. Estimates using primitive model (PM) of ions in a homogeneous dielectric suggest that non-PM mechanisms, originating from the molecular structure of the ion-solvating environment, might enhance ion association in membranes. PM analysis also predicts that ion solvation and association must be rigidly related, yet non-PM effects may decouple these phenomena and allow a crossover to non-trivial regimes consistent with experiments and simulations. Despite the crude nature of the presented approach and some questions remaining open, it appears to explain most available experimental data and presents a step towards predictive modeling of ion-selective membrane separations in water-, environment- and energy-related applications.

A modular 3D printed lab-on-a-chip for early cancer detection

A functional polymeric 3D device is produced in a single step printing process using a stereolithography based 3D printer. The photocurable formulation is designed for introducing a controlled amount of carboxyl groups (-COOH), in order to perform a covalent immobilization of bioreceptors on the device. The effectiveness of the application is demonstrated by performing an immunoassay for the detection of protein biomarkers involved in angiogenesis, whose role is crucial in the onset of cancer and in the progressive metastatic behavior of tumors. The detection of angiogenesis biomarkers is necessary for an early diagnosis of the pathology, allowing the employment of a less invasive therapy for the patient. In particular, vascular endothelial growth factor and angiopoietin-2 biomarkers are detected with a limit of detection of 11 ng mL^-1 and 0.8 ng mL^-1, respectively. This study shows how 3D microfabrication techniques, material characterization, and device development could be combined to obtain an engineered polymeric chip with intrinsic tuned functionalities.

Dataset and detailed methodology for structure and performance characterization of modified polymeric membranes

The data contained in this publication refers to protocols adopted characterization of clay nanoparticles (CN) membranes with and without the use of polyethylene oxide (PEO) as pore former. The membrane casting solutions were produced by dissolving PS (18% w/w) in NMP with addition of CN (1–5% w/w CN/PS) and/or PEO (1–5% w/w PEO/PS) when applicable. Membranes with no CN or PEO were used as a control. Pure water permeability of cast membranes was determined using the cross-flow cell unit. Viscosity was measured for most casting solution compositions and contact angle was measured for all membranes. The control membrane was further compared in detail to the highest permeability membranes with only CN (1.5%), only PEO (5%), 1.5% CN and 5% PEO (combination of optimal individual permeabilities), and 4.5% CN and 5% PEO (optimal combined permeability) regarding thickness, porosity, rejection, fouling resistance, surface charge, and thermal/mechanical properties. The relevance of the data presented here is to show details about methods for characterizing membranes for future comparison of performance and eventual improvement of characterization methods.

Layered Co-Immobilization of β-Glucosidase and Cellulase on Polymer Film by Visible-Light-Induced Graft Polymerization

Exploring a suitable immobilization strategy to improve catalytic efficiency and reusability of cellulase is of great importance to lowering the cost and promoting the industrialization of cellulose-derived bioethanol. In this work, a layered structure with a thin PEG hydrogel as the inner layer and sodium polyacrylate (PAANa) brush as the outer layer was fabricated on low density polyethylene (LDPE) film by visible-light-induced graft polymerization. Two enzymes, β-glucosidase (BG) and cellulase, were separately coimmobilized onto this hierarchical film. As supplementary to cellulase for improving catalytic efficiency, BG was in situ entrapped into the inner PEG hydrogel layer during the graft polymerization from the LDPE surface. After graft polymerization of sodium acrylate on the PEG hydrogel layer was reinitiated, cellulase was covalently attached on the outer PAANa brush layer. Owing to the mild reaction condition (visible-light irradiation and room temperature), the immobilized BG could retain a high activity after the graft polymerization. The immobilization did not alter the optimal pH and temperature of BG or the optimal temperature of cellulase. However, the optimal pH of cellulase shifts to 5.0 after immobilization. Compared with the original activity of single cellulase system and isolated BG/cellulase immobilization system, the dual-enzyme system exhibited 82% and 20% increase in catalytic activity, respectively. The dual-enzyme system could maintain 93% of carboxymethylcellulose sodium salt (CMC) activity after repeating 10 cycles of hydrolysis and 89% of filter paper activity after 6 cycles relative to original activity, exhibiting excellent reusability. This layer coimmobilization system of BG and cellulase on the polymer film displays tremendous potential for practical application in a biorefinery.

Characterization and Optimization of the Alkaline Hydrolysis of Polyacrylonitrile Membranes

There is currently an increasing interest in the development of polyacrylonitrile (PAN)-based membranes with new and enhanced properties which are of special importance in the processes of pervaporation, purification, and water treatment. Thus, the optimization of the functionalization of PAN membranes and its effect on their morphology, hydrophilicity, and mechanical properties plays an essential role in a wide range of applications. In this paper, the alkaline hydrolysis of asymmetric PAN membranes was investigated in order to get carboxyl-enriched surfaces that are of a great interest for more demanding subsequent modifications. The process was monitored using –C=NH intermediate bonds, which could be observed during the hydrolysis reaction by X-Ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FTIR) before the formation of carboxyl and amide groups. The amount of introduced carboxylic acid groups could be determined by thermogravimetric analysis (TGA) and by the interaction with toluidine blue O (TBO) dye. Hydrolysis was revealed as a simple way to modulate hydrophilicity (decreasing contact angle from 60 to 0° for reaction times from 0–3 h) and the mechanical properties of PAN membranes.

Mitigation of bidirectional solute flux in forward osmosis via membrane surface coating of zwitterion functionalized carbon nanotubes

Forward osmosis (FO) has emerged as a promising membrane technology to yield high-quality reusable water from various water sources. A key challenge to be solved is the bidirectional solute flux (BSF), including reverse solute flux (RSF) and forward solute flux (FSF). Herein, zwitterion functionalized carbon nanotubes (Z-CNTs) have been coated onto a commercial thin film composite (TFC) membrane, resulting in BSF mitigation via both electrostatic repulsion forces induced by zwitterionic functional groups and steric interactions with CNTs. At a coating density of 0.97 g m^-2, a significantly reduced specific RSF was observed for multiple draw solutes, including NaCl (55.5% reduction), NH₄H₂PO₄ (83.8%), (NH₄)₂HPO₄ (74.5%), NH₄Cl (70.8%), and NH₄HCO₃ (61.9%). When a synthetic wastewater was applied as the feed to investigate membrane rejection, FSF was notably reduced by using the coated membrane with fewer pollutants leaked to the draw solution, including NH₄⁺-N (46.3% reduction), NO₂^--N (37.0%), NO₃^--N (30.3%), K⁺ (56.1%), PO₄^3--P (100%), and Mg²⁺ (100%). When fed with real wastewater, a consistent water flux was achieved during semi-continuous operation with enhanced fouling resistance. This study is among the earliest efforts to address BSF control via membrane modification, and the results will encourage further exploration of effective strategies to reduce BSF.

Recent advances in thin film composites membranes for brackish groundwater treatment with critical focus on Saskatchewan water sources

Drinking water scarcity is an ever-increasing global concern. This issue appears as a greater threat to the countries with no access to sea water resources or rivers, since their potential water resources are only limited to ground waters only. There are serious concerns with the treatment of ground water resources, including landfill leachates, agricultural contaminations (pesticides, herbicides, and fertilizers), and rural contaminations. Membrane separation has been proved to be the governing technology in water and wastewater treatment plants, as these methods are responsible for more than half of the market share of the world's desalination capacity. This study intends to offer a holistic view of the groundwater contamination with specific focus on Saskatchewan province in Canada, and the recent efforts in the groundwater treatment using thin film composite membrane technology. This study begins with an introduction of the general aspects of ground water and membrane separation, polluting agents, and their sources. It is followed by a discussion of Saskatchewan's groundwater status and various issues. Furthermore, the recent research that became available since 2010 is reviewed in details and the results are summarized with respect to purification efficiency. Different affecting parameters in a groundwater-thin film composite system are synthesized and an in-depth overview is presented.

3D printed dual macro-, microscale porous network as a tissue engineering scaffold with drug delivering function

Tissue engineering macroporous scaffolds are important for regeneration of large volume defects resulting from diseases such as breast or bone cancers. Another important part of the treatment of these conditions is adjuvant drug therapy to prevent disease recurrence or surgical site infection. In this study, we developed a new type of macroporous scaffolds that have drug loading and release functionality to use in these scenarios. 3D printing allows for building macroporous scaffolds with deterministically designed complex architectures for tissue engineering yet they often have low surface areas thus limiting their drug loading capability. In this proof-of-concept study, we aimed to introduce microscale porosity into macroporous scaffolds to allow for efficient yet simple soak-loading of various clinical drugs and control their release. Manufacturing of scaffolds having both macroporosity and microscale porosity remains a difficult task. Here, we combined porogen leaching and 3D printing to achieve this goal. Porogen microparticles were mixed with medical grade polycaprolactone and extruded into scaffolds having macropores of 0.7 mm in size. After leaching, intra-strut microscale pores were realized with pore size of 20-70 μm and a total microscale porosity of nearly 40%. Doxorubicin (DOX), paclitaxel (PTX) and cefazolin (CEF) were chosen as model drugs of different charges and solubilities to soak-load the scaffolds and achieved loading efficiency of over 80%. The microscale porosity was found to significantly reduce the burst release allowing the microporous scaffolds to release drugs up to 200, 500 and 150 h for DOX, PTX and CEF, respectively. Finally, cell assays were used and confirmed the bioactivities and dose response of the drug-loaded scaffolds. Together, the findings from this proof-of-concept study demonstrate a new type of scaffolds with dual micro-, macro-porosity for tissue engineering applications with intrinsic capability for efficient loading and sustained release of drugs to prevent post-surgery complications.

Calcium-Carboxyl Intrabridging during Interfacial Polymerization: A Novel Strategy to Improve Antifouling Performance of Thin Film Composite Membranes

This study reports a novel intrabridging strategy to improve the antifouling performance of a thin-film composite (TFC) membrane. We demonstrate that the addition of Ca²⁺ during the interfacial polymerization reaction led to the formation of stable Ca²⁺-carboxyl complexes within the polyamide rejection layer. This intrabridging of carboxyl groups by Ca²⁺ effectively sequestrated them, reducing their availability for binding divalent metal ions in the aqueous solution and for forming foulant-metal-membrane interbridges. Membrane fouling and cleaning experiments confirmed improved flux stability and fouling reversibility for the Ca²⁺ modified membranes. The greatly enhanced antifouling performance of these membranes, together with their better surface hydrophilicity and greater water permeability, makes the intrabridging approach highly attractive in overcoming the classical permeability-selectivity-antifouling trade-off. Our findings pave a new direction for synthesizing high-performance TFC membranes.

A novel positively charged composite nanofiltration membrane based on polyethyleneimine with a tunable active layer structure developed via interfacial polymerization

A novel positively charged composite nanofiltration (NF) membrane with tunable active layer structure was successfully developed via interfacial polymerization on a polysulfone (PSF) ultrafiltration (UF) membrane surface, using polyethyleneimine (PEI) as the monomer of the aqueous phase, and a mixture of isophthaloyl dichloride (IPC) and tri-mesoyl chloride (TMC) as the monomer of the organic phase. Interestingly, a synergetic effect of the mass ratio of IPC and TMC was observed on the pore size and the structure of the active layer of the resultant polyamide (PA)/polysulfone (PSF) composite NF membrane. The rejection (R) to the inorganic electrolytes increased with the mass ratio of IPC to TMC, while the permeate flux (F) escalated up to a 1 : 1 mixing ratio of IPC to TMC and dropped at higher mixing ratios. The rejection to different inorganic electrolytes decreased in the order of ZnCl₂, MgCl₂, CaCl₂, CuCl₂, MgSO₄, NaCl, and Na₂SO₄. At ambient temperature and 0.4 MPa, the optimized membrane demonstrated R and F to 1 g L⁻¹ MgCl₂ aqueous solution as 98.1% and 27.6 L m⁻² h⁻¹, respectively. Its rejection to various dyes reduced significantly in the order of cationic red X-GTL (100%), rhodamine B (94.2%), cationic gold yellow X-GL (93.5%), and brilliant blue KN-R (43.9%), in agreement with the decrease in the molecular weight (M_w) and the overall charges of the dye.

The tunable active layer structure was developed via interfacial polymerization, using polyethyleneimine as the monomer of the aqueous phase, and a mixture of isophthaloyl dichloride and tri-mesoyl chloride as the monomer of the organic phase.

Development of high flux nanofiltration membranes through single bilayer polyethyleneimine/alginate deposition

The aim of this study is to prepare high flux, stable, antifouling nanofiltration membranes through single bilayer polyelectrolyte deposition. To this end, a tight ultrafiltration support membrane was prepared from a polysulfone/sulfonated polyethersulfone blend. Deposition of a polyethyleneimine and alginate pair on this support has reduced the molecular weight cut off from 6 kDa to below 1 kDa. The pure water permeability and polyethylene glycol 1000 rejection of the coated membrane were found to be 15.5 ± 0.3 L/m²·h·bar and 90 ± 0.6%, respectively, by setting the deposition pH for each layer to 8 and the ionic strengths to 0.5 M and 0 M. This membrane has exhibited significantly higher permeability than commercial membranes with the same molecular weight cut off, retaining 98% of the initial flux during 15 h filtration of bovine serum albumine. In addition, the membrane has been able to completely remove anionic dyes from aqueous solution by showing 99.9% retentions to Reactive red 141, Brilliant blue G and Congo red with a 2 bar transmembrane pressure. High flux and membrane stability in acidic and salty environments have been achieved when deposition conditions favor high adsorption levels for the first layer and strong ionic cross-linking between the carboxyl group on the alginate and the amine groups on the polyethyleneimine.

Achieving low concentrations of chromium in drinking water by nanofiltration: membrane performance and selection

This study evaluates nanofiltration as a feasible process to reach low concentrations of chromium in drinking water and provides means for the selection of the most suitable membrane based on the specific treatment needs. Chromium removal is concerning since new stringent limits (10 μg/L) for hexavalent Cr concentration in potable water were recently adopted in various countries. Three commercial nanofiltration membranes were tested against this threshold value: two membranes made of semi-aromatic polyamide and the third having a sulfonated polyethersulfone asymmetric film as the selective layer. The rejection observed as a function of chemical composition in the feed solution suggests that electrostatic effect is an important mechanism of chromium(VI) removal for the membranes with higher surface charge and lower film density. The performance of such membranes is strongly affected by the presence of salts, especially divalent cations, which reduce both Cr(VI) rejection and the permeate flux. The removal of Cr(VI) by denser membranes is dominated by solution-diffusion and is not influenced by feed ionic strength. The exposure of membranes to high chromium concentrations and to hypochlorite, typically employed as an oxidizing agent in water treatment plants, was also investigated. An analysis of the operational membrane life is thus discussed, based on the loss in performance due to active film degradation. All three membranes showed adequate rejection of chromium from tap and well water of diverse chemical composition, suggesting that nanofiltration is an effective process to remove chromium for the production of safe drinking water. However, membranes with different properties should be adopted depending on specific feed water composition and on the productivity required from the system. A final analysis is presented to help with the choice of the most suitable nanofiltration membrane based on initial and target Cr(VI) concentration in feed and product water, respectively.

High Performance Nanofiltration Membrane for Effective Removal of Perfluoroalkyl Substances at High Water Recovery

We demonstrate the fabrication of a loose, negatively charged nanofiltration (NF) membrane with tailored selectivity for the removal of perfluoroalkyl substances with reduced scaling potential. A selective polyamide layer was fabricated on top of a poly(ether sulfone) support via interfacial polymerization of trimesoyl chloride and a mixture of piperazine and bipiperidine. Incorporating high molecular weight bipiperidine during the interfacial polymerization enables the formation of a loose, nanoporous selective layer structure. The fabricated NF membrane possessed a negative surface charge and had a pore diameter of ∼1.2 nm, much larger than a widely used commercial NF membrane (i.e., NF270 with pore diameter of ∼0.8 nm). We evaluated the performance of the fabricated NF membrane for the rejection of different salts (i.e., NaCl, CaCl₂, and Na₂SO₄) and perfluorooctanoic acid (PFOA). The fabricated NF membrane exhibited a high retention of PFOA (∼90%) while allowing high passage of scale-forming cations (i.e., calcium). We further performed gypsum scaling experiments to demonstrate lower scaling potential of the fabricated loose porous NF membrane compared to NF membranes having a dense selective layer under solution conditions simulating high water recovery. Our results demonstrate that properly designed NF membranes are a critical component of a high recovery NF system, which provide an efficient and sustainable solution for remediation of groundwater contaminated with perfluoroalkyl substances.

Carbodiimide-mediated immobilization of acidic biomolecules on reversed-charge zwitterionic sensor chip surfaces

The carbodiimide-mediated amine coupling of protein ligands to sensor chips coated with anionic polycarboxylate hydrogels, such as carboxymethyl dextran, is the predominant covalent immobilization procedure utilized in optical biosensors, namely surface plasmon resonance (SPR) biosensors. Usually, electrostatic interactions at a slightly acidic pH and low ionic strength are employed to efficiently accumulate neutral and basic ligands on the chip surface, which are then covalently coupled by surface-bound active N-hydroxysuccinimide (NHS) esters. Unfortunately, this approach is not suitable for acidic proteins or other ligands with low isoelectric points (IEPs), such as nucleic acids, because the charge density of the polycarboxylates is greatly reduced at acidic pH or because electrostatic attraction cannot be achieved. To overcome these drawbacks, we have established a charge-reversal approach that allows the preconcentration of acidic proteins above their IEPs. A precisely controlled amount of tertiary amines is applied to reverse the previous anionic surface charge while maintaining carbodiimide compatibility with future protein immobilization. The mechanism of this reversed-charge immobilization approach was demonstrated employing protein A as a model protein and using attenuated total reflectance Fourier transform infrared spectroscopy, dynamic contact angle measurements, colorimetric quantification, and SPR analysis to characterize surface derivatization. Furthermore, even though it had previously proven impossible to preconcentrate DNA electrostatically and to covalently couple it to polyanionic chip surfaces, we demonstrated that our approach allowed DNA to be preconcentrated and immobilized in good yields. Graphical abstract Principle of the covalent immobilization of acidic ligands on reversed-charge zwitterionic sensor chip surfaces.