Thermodynamic assessment of adsorptive fouling with the membranes modified via layer-by-layer self-assembly technique

Deciphering the Dynamic Assembling-Disassembling of Small Molecules on Solid/Liquid Interfaces within Microchannels by Pulsed Streaming Potential Measurement

Assembling small molecules at liquid/solid interfaces is relatively common and contributes to many unique properties of the interface. However, such an assembling process can be dynamic depending on the concentration of the molecule and the properties of the solid and liquid themselves, which poses serious challenges on the accurate evaluation of the assembling processes. Herein, we report a convenient way for in situ and real-time monitoring of assembling-disassembling of small-molecule surfactants on the surface of microchannels using pulsed streaming potential (SP) measurement based on the variation of surface charge. With this technique, five distinctive kinetic regimes, each responsible for a characteristic molecular behavior, can be differentiated during a typical assembling-disassembling cycle. Significant difference of the assembling-disassembling process was clearly reflected for surfactants with hydrophobic tails of only a two -CH2- difference (C16TAB/C18TAB and D10DAB/D12DAB). The relative SP (Er) value is positively correlated with the molecular weight at a concentration of 0.1 mM for the same kinds of surfactants. Moreover, the assembling kinetics of D10DAB exhibits an "overshoot effect" at high concentration, which means morphology adjustment. The consequences of such assembling/disassembling of these molecules for electrophoretic separation, protein immobilization, and photocatalysis in a microchannel were investigated through dynamic characterization, which proves its potential as a tool for dynamic solid/liquid interface characterization.

Quantification of interfacial interaction related with adhesive membrane fouling by genetic algorithm back propagation (GABP) neural network

Since adhesive membrane fouling is critically determined by the interfacial interaction between a foulant and a rough membrane surface, efficient quantification of the interfacial interaction is critically important for adhesive membrane fouling mitigation. As a current available method, the advanced extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory involves complicated rigorous thermodynamic equations and massive amounts of computation, restricting its application. To solve this problem, artificial intelligence (AI) visualization technology was used to analyze the existing literature, and the genetic algorithm back propagation (GABP) artificial neural network (ANN) was employed to simplify thermodynamic calculation. The results showed that GABP ANN with 5 neurons could obtain reliable prediction performance in seconds, versus several hours or even days time-consuming by the advanced XDLVO theory. Moreover, the regression coefficient (R) of GABP reached 0.9999, and the error between the prediction results and the simulation results was less than 0.01%, indicating feasibility of the GABP ANN technique for quantification of interfacial interaction related with adhesive membrane fouling. This work provided a novel strategy to efficiently optimize the thermodynamic prediction of adhesive membrane fouling, beneficial for better understanding and control of adhesive membrane fouling.

Layer-by-Layer Fabrication of PAH/PAMAM/Nano-CaCO3 Composite Films and Characterization for Enhanced Biocompatibility

Nanoparticle production and functionalization for various biomedical uses are still challenging. Polymer composites constituted of poly(amidoamine) (PAMAM), polyallylamine hydrochloride (PAH), and calcium carbonate (CaCO₃) nanoparticles have good biocompatibility with physiological tissue and fluids, making them excellent candidates for biomedical applications. This study investigated the characteristics of polymeric/nano-CaCO₃ composite films based on a PAH/PAMAM matrix, which were fabricated through layer-by-layer synthesis on quartz glass substrates. It was found that the as-prepared elastic moduli of the resultant (PAH/PAMAM)_n-CaCO₃ (where n represents the number of bilayers) composite films varied from 1.40 to 23.70 GPa for different degrees of cross-linking when 0.1 M nano-CaCO₃ particles were incorporated into the polymer matrix. The highly cross-linked (PAH/PAMAM)₁₅-CaCO₃ composite film had the highest recorded elastic modulus of 23.70 GPa, while it was observed that for all the composite films fabricated for the present study, the addition of the nano-CaCO₃ particles approximately doubled the elastic modulus regardless of the degree of polymerization. Live/Dead assays were used to determine whether the produced composite films were compatible with human lung fibroblast cells. The findings indicate that the (PAH/PAMAM)_7.5-CaCO₃ composite film had the most positive effect on cell growth and proliferation, with the (PAH/PAMAM)₁₅-CaCO₃ composite film demonstrating significant ion transport behavior with low impedance, which was considered good for in vivo rapid cell-to-cell communication. Therefore, the (PAH/PAMAM)_7.5-CaCO₃ and (PAH/PAMAM)₁₅-CaCO₃ composite films are potential tissue engineering biomaterials, but further studies are essential to generate more data to evaluate the suitability of these composites for this and other biomedical functions.

Recent developments in layer-by-layer assembled systems application in water purification

Electrostatically-based layer-by-layer (LbL) assembly is a versatile surface functionalization technique allowing the construction of complex three-dimensional architectures on virtually any type of material using various combinations of nano-bricks. One of the most promising applications of LbL assembled systems is in water purification. The main two strategies developed in this purpose consist in either enhancing the barrier properties of separation membranes and in the construction of core-shell organic/inorganic sorbents. In this review, the recent achievements in this topic are discussed with respect to the use of LbL-based composites in desalination and removal of heavy metal ions or organic pollutants. Finally, some works dealing with economic aspects of using LbL assemblies for water purification are presented, thus highlighting forthcoming strategies to develop economically-viable materials for such applications.

Layer-by-layer assembly in nanochannels: assembly mechanism and applications

Layer-by-layer (LbL) assembly is a versatile technology to construct multifunctional nanomaterials using various supporting substrates, enabled by the large selection freedom of building materials and diversity of possible driving forces. The fine regulation over the film thickness and structure provides an elegant way to tune the physical/chemical properties by mild assembly conditions (e.g. pH, ion strength). In this review, we focus on LbL in nanochannels, which exhibit a different growth mechanism compared to "open", convex substrates. The assembly mechanism in nanochannels is discussed in detail, followed by the summary of applications of LbL assemblies liberated from nanochannel templates which can be used as nanoreactors, drug carriers and transporting channels across cell membranes. For fluidic applications, robust membrane substrates are required to keep in place nanotube arrays for membrane-based separation, purification, biosensing and energy harvesting, which are also discussed. The good compatibility of LbL with crossover technologies from other fields allows researchers to further extend this technology to a broader range of research fields, which is expected to result in an increased number of applications of LbL technology in the future.

Polymeric Membranes Incorporated With ZnO Nanoparticles for Membrane Fouling Mitigation: A Brief Review

Due to the flexibility of operation, high removal ability, and economic cost, separation membranes have proved to be one of the most significant technologies in various aspects including water treatment. However, membrane fouling is a predominant barrier which is severely limiting the whole membrane industry. To mitigate membrane fouling, researchers have carried out several modification strategies including the incorporation of hydrophilic inorganic components. Zinc oxide (ZnO) nanoparticles, known as a low-cost, environment-friendly, and hydrophilic inorganic material, have been used by worldwide researchers. As claimed by the scientific literatures, ZnO nanoparticles can not only endow the polymeric membranes with antifouling performance but also supply a photocatalytic self-cleaning ability. Therefore, polymer-ZnO composite membranes were considered to be an attractive hot topic in membrane technology. In the last decades, it has been significantly matured by a large mass of literature reports. The current review highlights the latest findings in polymeric membranes incorporated with ZnO nanoparticles for membrane fouling mitigation. The membrane fouling, ZnO nanoparticles, and modification technology were introduced in the first three sections. Particularly, the review makes a summary of the reports of polyvinylidene fluoride (PVDF)-ZnO composite membranes, polyethersulfone (PES)-ZnO composite membranes, and other composite membranes incorporated with ZnO nanoparticles. This review further points out several crucial topics for the future development of polymer-ZnO composite membranes.

Mitigated membrane fouling and enhanced removal of extracellular antibiotic resistance genes from wastewater effluent via an integrated pre-coagulation and microfiltration process

Antibiotic resistance genes (ARGs) have been regarded as an emerging pollutant in municipal wastewater treatment plant (WWTP) effluents due to their potential risk to human health and ecological safety when reused for landscape and irrigation. Conventional wastewater treatment processes generally fail to effectively reduce ARGs, especially extracellular ARGs (eARGs), which are persistent in the environment and play an important role in horizontal gene transfer via transformation. Herein, an integrated process of pre-coagulation and microfiltration was developed for removal of ARGs, especially eARGs, from wastewater effluent. Results show that the integrated process could effectively reduce the absolute abundances of total ARGs (tARGs) (>2.9 logs) and eARGs (>5.2 logs) from the effluent. The excellent performance could be mainly attributed to the capture of antibiotic resistant bacteria (ARB) and eARGs by pre-coagulation and co-rejection during subsequent microfiltration. Moreover, the integrated process exhibited a good performance on removing common pollutants (e.g., dissolved organic carbon and phosphate) from the effluent to improve water quality. Besides, the integrated process also greatly reduced membrane fouling compared with microfiltration. These findings suggest that the integrated process of pre-coagulation and microfiltration is a promising advanced wastewater treatment technology for ARGs (especially eARGs) removal from WWTP effluents to ensure water reuse security.

Codeposition of Polydopamine and Zwitterionic Polymer on Membrane Surface with Enhanced Stability and Antibiofouling Property

Although abundant works have been developed in mussel-inspired antifouling coatings, most of them suffer from poor chemical stability, especially in a strongly alkaline environment. Herein, we report a robust one-step mussel-inspired method to construct a highly chemical stable and excellent antibiofouling membrane surface coating with a highly efficient codeposition of polydopamine (PDA) with zwitterionic polymer. In the study, PDA and polyethylenimine-quaternized derivative (PEI-S) are codeposited on the surface of poly(ether sulfone) (PES) ultrafiltration membrane in water at room temperature. In contrast to individual PDA coating, the obtained PDA/PEI-S coating exhibits excellent chemical stability even in a strongly alkaline environment owing to the cross-linking and unexpected cation-π interaction between the PEI-S and PDA. Thanks to the introduction of PEI-S, systematic protein adsorption tests and bacteria adhesion experiments demonstrated that the surfaces could prevent bovine serum fibrinogen and lysozyme adsorption and could reduce Gram-positive bacteria S. aureus and Gram-negative bacteria E. coli adhesion. Benefiting from the versatile functionality of PDA, the proposed strategy is not limited to PES membrane surface but also others such as poly(ethylene terephthalate) sheets and commercial polypropylene microfiltration membranes. Overall, this work enriches the exploration of a remarkable coating with enhanced stability and excellent antifouling property via a facile, robust, and material-independent approach to modifying the membrane surface.

Biomimetic Layer-by-Layer Self-Assembly of Nanofilms, Nanocoatings, and 3D Scaffolds for Tissue Engineering

Achieving surface design and control of biomaterial scaffolds with nanometer- or micrometer-scaled functional films is critical to mimic the unique features of native extracellular matrices, which has significant technological implications for tissue engineering including cell-seeded scaffolds, microbioreactors, cell assembly, tissue regeneration, etc. Compared with other techniques available for surface design, layer-by-layer (LbL) self-assembly technology has attracted extensive attention because of its integrated features of simplicity, versatility, and nanoscale control. Here we present a brief overview of current state-of-the-art research related to the LbL self-assembly technique and its assembled biomaterials as scaffolds for tissue engineering. An overview of the LbL self-assembly technique, with a focus on issues associated with distinct routes and driving forces of self-assembly, is described briefly. Then, we highlight the controllable fabrication, properties, and applications of LbL self-assembly biomaterials in the forms of multilayer nanofilms, scaffold nanocoatings, and three-dimensional scaffolds to systematically demonstrate advances in LbL self-assembly in the field of tissue engineering. LbL self-assembly not only provides advances for molecular deposition but also opens avenues for the design and development of innovative biomaterials for tissue engineering.