Spraying asymmetry into functional membranes layer-by-layer

Ion and Molecular Sieving With Ultrathin Polydopamine Nanomembranes

In contrast to biological cell membranes, it is still a major challenge for synthetic membranes to efficiently separate ions and small molecules due to their similar sizes in the sub-nanometer range. Inspired by biological ion channels with their unique channel wall chemistry that facilitates ion sieving by ion-channel interactions, the first free-standing, ultrathin (10-17 nm) nanomembranes composed entirely of polydopamine (PDA) are reported here as ion and molecular sieves. These nanomembranes are obtained via an easily scalable electropolymerization strategy and provide nanochannels with various amine and phenolic hydroxyl groups that offer a favorable chemical environment for ion-channel electrostatic and hydrogen bond interactions. They exhibit remarkable selectivity for monovalent ions over multivalent ions and larger species with K+/Mg2+ of ≈4.2, K+/[Fe(CN)6]3- of ≈10.3, and K+/Rhodamine B of ≈273.0 in a pressure-driven process, as well as cyclic reversible pH-responsive gating properties. Infrared spectra reveal hydrogen bond formation between hydrated multivalent ions and PDA, which prevents the transport of multivalent ions and facilitates high selectivity. Chemically rich, free-standing, and pH-responsive PDA nanomembranes with specific interaction sites are proposed as customizable high-performance sieves for a wide range of challenging separation requirements.

3D Printing of Bioactive Gel-like Double Emulsion into a Biocompatible Hierarchical Macroporous Self-Lubricating Scaffold for 3D Cell Culture

The interconnected hierarchically porous structures are of key importance for potential applications as substrates for drug delivery, cell culture, and bioscaffolds, ensuring cell adhesion and sufficient diffusion of metabolites and nutrients. Here, encapsulation of a vitamin C-loaded gel-like double emulsion using a hydrophobic emulsifier and soy particles was performed to develop a bioactive bioink for 3D printing of highly porous scaffolds with enhanced cell biocompatibility. The produced double emulsions suggested a mechanical strength with the range of elastic moduli of soft tissues possessing a thixotropic feature and recoverable matrix. The outstanding flow behavior and viscoelasticity broaden the potential of gel-like double emulsion to engineer 3D scaffolds, in which 3D constructs showed a high level of porosity and excellent shape fidelity with antiwearing and self-lubricating properties. Investigation of cell viability and proliferation using fibroblasts (NIH-3T3) within vitamin C-loaded gel-like bioinks revealed that printed 3D scaffolds offered brilliant biocompatibility and cell adhesion. Compared to scaffolds without encapsulated vitamin C, 3D scaffolds containing vitamin C showed higher cell viability after 1 week of cell proliferation. This work represented a systematic investigation of hierarchical self-assembly in double emulsions and offered insights into mechanisms that control microstructure within supramolecular structures, which could be instructive for the design of advanced functional tissues.

Label-Free Chemiresistive Sensors Based on Self-Assembled Ti3C2Tx MXene Films for Monitoring of Microcystin-LR in Water Samples

Herein, we propose a label-free chemiresistive sensor for the highly sensitive and selective detection of microcystin (MC)-LR in water samples. The sensor uses a layer-by-layer (LBL) assembled conductive film consisting of Ti3C2Tx nanosheets as the sensing channel. It is further modified by using an aptamer for the specific recognition of MC-LR. The response signal is based on the change in resistance of the conductive channel upon binding of MC-LR with the aptamer. Our novel strategy is the first concept proposed for immobilizing the aptamer containing -SH on the channel surface through a Ti-S bond under weakly alkaline condition. The resulting sensor is highly sensitive and stable for the detection of MC-LR, with a detection limit of 0.18 ng L-1 and a wide linear range from 1 to 104 ng L-1. We used the sensor to continuously monitor MC-LR released by cultivated Microcystis aeruginosa, showing a strong relationship between MC-LR and cell density. Furthermore, the sensor was successfully used to measure MC-LR in freshwater lakes with moderate algal blooms, and the results agreed well with those obtained by liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. The present study provides a reliable method for highly sensitive and selective detection of MC-LR in environmental waters.

Phase Engineering and Synchrotron-Based Study on Two-Dimensional Energy Nanomaterials

In recent years, there has been significant interest in the development of two-dimensional (2D) nanomaterials with unique physicochemical properties for various energy applications. These properties are often derived from the phase structures established through a range of physical and chemical design strategies. A concrete analysis of the phase structures and real reaction mechanisms of 2D energy nanomaterials requires advanced characterization methods that offer valuable information as much as possible. Here, we present a comprehensive review on the phase engineering of typical 2D nanomaterials with the focus of synchrotron radiation characterizations. In particular, the intrinsic defects, atomic doping, intercalation, and heterogeneous interfaces on 2D nanomaterials are introduced, together with their applications in energy-related fields. Among them, synchrotron-based multiple spectroscopic techniques are emphasized to reveal their intrinsic phases and structures. More importantly, various in situ methods are employed to provide deep insights into their structural evolutions under working conditions or reaction processes of 2D energy nanomaterials. Finally, conclusions and research perspectives on the future outlook for the further development of 2D energy nanomaterials and synchrotron radiation light sources and integrated techniques are discussed.

Antioxidation Effect of Graphene Oxide on Silver Nanoparticles and Its Use in Antibacterial Applications

Silver nanoparticles (AgNPs) have drawn great attention due to their outstanding antibacterial effect in a wide range of applications, such as biomass packaging materials, wound dressings, flexible sensors, etc. However, the oxidation of AgNPs limits the antibacterial effect. Firstly, the effects of pretreatment methods on the antibacterial property of AgNPs were investigated by the shake flask method and agar diffusion plate method. Secondly, graphene oxide/silver nanoparticle (GO/AgNPs) nanocomposite prepared by an in-situ growth method was used as antibacterial filler for polyacrylate emulsion via a blending method. The antibacterial mechanism of GO/AgNPs was revealed by comparing the actual contents of oxygen with the theoretically calculated contents of oxygen. Finally, the polyacrylate/graphene oxide/silver nanoparticles (PA/GO/AgNPs) composite emulsion was applied onto a leather surface using a layer-by-layer spraying method to improve the leather's antibacterial properties. The results showed that ultraviolet irradiation could better maintain the antibacterial property of AgNPs, while GO could improve the dispersibility of AgNPs and prevent their oxidation. The leather finished with the PA/GO/AgNPs-2 wt% composite emulsion showed the highest bacteriostatic rate of 74%, demonstrating its great potential in the application of antibacterial leather products.

Recent development and application of membrane chromatography

Membrane chromatography is mainly used for the separation and purification of proteins and biological macromolecules in the downstream processing process, also applications in sewage disposal. Membrane chromatography is recognized as an effective alternative to column chromatography because it significantly improves chromatography from affinity, hydrophobicity, and ion exchange; the development status of membrane chromatography in membrane matrix and membrane equipment is thoroughly discussed, and the applications of protein capture and intermediate purification, virus, monoclonal antibody purification, water treatment, and others are summarized. This review will provide value for the exploration and potential application of membrane chromatography.

Conjugated microporous polymer membranes for light-gated ion transport

Inspired by the light-gated ion channels in cell membranes that play important roles in many biological activities, herein, we developed an artificial light-gated ion channel membrane out of conjugated microporous polymers. Through bottom-up design of the monomer molecular structure and by the electropolymerization method, the membrane pore size and thickness were precisely controlled on the molecular level. The obtained membrane exhibited uniform pore size and highly sensitive light-switchable response. The photoisomerization of the polymer chain resulted in a reversible "on and off" light control over the pore size and subsequently led to light-gated ion transport across the membrane for a series of ions including hydrogen, potassium, sodium, lithium, calcium, magnesium, and aluminum ions.

Fluorescence Signal Enhancement by a Spray-Assisted Layer-by-Layer Technique on Aluminum Tape Devices for Biosensing Applications

Layer-by-layer (LbL) self-assembled polyelectrolyte multilayer (PEM) films are a simple yet elegant bottom-up technology to create films at the nano-microscale. This low-cost technology has been widely used as a universal functionalization technique on a broad spectrum of substrates. Biomolecules under investigation can be incubated onto films based on complementary charge interactions between the films and biomolecules. There is a great demand for developing an ultralow-cost biosensing device, which can optimally enhance the fluorescence signal of the adsorbed biomolecules from the traditional labeled sensing platforms. In this work, we have incorporated a blend of the conventional metal enhanced fluorescence technology and the PEM as a dielectric spacer and functionalized film, coated on an aluminum paper (tape)-based substrate. These device has been found to be capable of holding biomolecules in three-dimensional PEM space. The devices fabricated by the proposed spray LbL technique provide significant fluorescence signal enhancement by holding a relatively higher mass per volume of the adsorbed biomolecules, when compared to traditional spin- and dip-coating techniques. Interestingly, our proposed device has expressed a fluorescence enhancement factor, which is 9 times higher than PEM-functionalized glass-based devices. To demonstrate the practical utility of our devices, we also compared our devices to Whatman FAST slides. Our experimental fluorescence results are almost comparable to Whatman FAST slides. Such PEM devices fabricated on top of low-cost aluminum tape using a spray LbL technique give new insights into the future development of ultralow-cost, high-throughput, and disposable lab-on-chip diagnostic applications.

Biomaterials for Hemostasis

Uncontrolled bleeding is a major problem in trauma and emergency medicine. While materials for trauma applications would certainly find utility in traditional surgical settings, the unique environment of emergency medicine introduces additional design considerations, including the need for materials that are easily deployed in austere environments. Ideally, these materials would be available off the shelf, could be easily transported, and would be able to be stored at room temperature for some amount of time. Both natural and synthetic materials have been explored for the development of hemostatic materials. This review article provides an overview of classes of materials used for topical hemostats and newer developments in the area of injectable hemostats for use in emergency medicine. Expected final online publication date for the Annual Review of Biomedical Engineering, Volume 24 is June 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Layer-by-layer assembly methods and their biomedical applications

Various biomedical applications arising due to the development of different LbL assembly methods with unique process properties.

There is still plenty of room for layer-by-layer assembly for constructing nanoarchitectonics-based materials and devices

Nanoarchitectonics approaches can produce functional materials from tiny units through combination of various processes including atom/molecular manipulation, chemical conversion, self-assembly/self-organization, microfabrication, and bio-inspired procedures. Existing fabrication approaches can be regarded as fitting into the same concept. In particular, the so-called layer-by-layer (LbL) assembly method has huge potential for preparing applicable materials with a great variety of assembling mechanisms. LbL assembly is a multistep process where different components can be organized in planned sequences while simple alignment options provide access to superstructures, for example helical structures, and anisotropies which are important aspects of nanoarchitectonics. In this article, newly-featured examples are extracted from the literature on LbL assembly discussing trends for composite functional materials according to (i) principles and techniques, (ii) composite materials, and (iii) applications. We present our opinion on the present trends, and the prospects of LbL assembly. While this method has already reached a certain maturity, there is still plenty of room for expanding its usefulness for the fabrication of nanoarchitectonics-based materials and devices.

Photon Recycling in Semiconductor Thin Films and Devices

Photon recycling (PR) plays an important role in the study of semiconductor materials and impacts the properties of their optoelectronic applications. However, PR has not been investigated comprehensively and it has not been demonstrated experimentally in many different kinds of semiconductor materials and devices. In this review paper, first, the authors introduce the background of PR and describe how this phenomenon was originally identified in semiconductors. Then, the theory and modelling of PR is reviewed and some of the important parameters that are used to quantify PR are highlighted. Next, a variety of the methods used to achieve and characterize PR in materials and devices are discussed. Examples of how the performance parameters of different types of optoelectronic devices are affected by PR are described. Finally, a summary of the roles of PR in semiconductor materials and devices and an outlook on how PR can be used to solve existing problems and challenges in the field of optoelectronics are provided. From this review, it is apparent that PR can have a positive impact on optoelectronic device performance, and that further in-depth theoretical and experimental studies are needed to rigorously demonstrate the advantages and importance of PR.

Chitosan-based smart hybrid materials: a physico-chemical perspective

Chitosan is one of the most studied cationic polysaccharides. Due to its unique characteristics of being water soluble, biocompatible, biodegradable, and non-toxic, this macromolecule is highly attractive for a broad range of applications. In addition, its complex behavior and the number of ways it interacts with different components in a system result in an astonishing variety of chitosan-based materials. Herein, we present recent advances in the field of chitosan-based materials from a physico-chemical perspective, with focus on aqueous mixtures with oppositely charged colloids, chitosan-based thin films, and nanocomposite systems. In this review, we focus our attention on the physico-chemical properties of chitosan-based materials, including solubility, mechanical resistance, barrier properties, and thermal behaviour, and provide a link to the chemical peculiarities of chitosan, such as its intrinsic low solubility, high rigidity, large charge separation, and strong tendency to form intra- and inter-molecular hydrogen bonds.

Interface chemistry of two-dimensional heterostructures - fundamentals to applications

Two-dimensional heterostructures (2D HSs) have emerged as a new class of materials where dissimilar 2D materials are combined to synergise their advantages and alleviate shortcomings. Such a combination of dissimilar components into 2D HSs offers fascinating properties and intriguing functionalities attributed to the newly formed heterointerface of constituent components. Understanding the nature of the surface and the complex heterointerface of HSs at the atomic level is crucial for realising the desired properties, designing innovative 2D HSs, and ultimately unlocking their full potential for practical applications. Therefore, this review provides the recent progress in the field of 2D HSs with a focus on the discussion of the fundamentals and the chemistry of heterointerfaces based on van der Waals (vdW) and covalent interactions. It also explains the challenges associated with the scalable synthesis and introduces possible methodologies to produce large quantities with good control over the heterointerface. Subsequently, it highlights the specialised characterisation techniques to reveal the heterointerface formation, chemistry and nature. Afterwards, we give an overview of the role of 2D HSs in various emerging applications, particularly in high-power batteries, bifunctional catalysts, electronics, and sensors. In the end, we present conclusions with the possible solutions to the associated challenges with the heterointerfaces and potential opportunities that can be adopted for innovative applications.

Multifunctional Textiles/Metal-Organic Frameworks Composites for Efficient Ultraviolet Radiation Blocking and Noise Reduction

Ultraviolet radiation (UVR) and noise are the ubiquitous environmental hazards with considerable detrimental effects on the physiological and psychological health of humans. Exploiting efficient protective materials that can be extensively used in daily life for simultaneous anti-UVR and noise mitigation will be of crucial importance, but it is still a significant challenge in materials design. Herein, we developed a series of protective textiles for efficient anti-UVR and noise reduction via MOFs nanocrystal-modified cotton textiles. The formation of MOFs@cotton textiles was confirmed by using electron microscopy, X-ray diffraction, infrared spectroscopy, and X-ray photoelectron spectroscopy. The fabricated MOFs@cotton textiles exhibited substantial improvement in the UVR blocking and acoustic absorption properties compared to blank cotton textiles. Therefore, this work provides a good strategy for designing and preparing multifunctional protective textiles.

Selective Ultrasonic Gravimetric Sensors Based on Capacitive Micromachined Ultrasound Transducer Structure-A Review

This review paper discusses the advances of the gravimetric detection devices based on capacitive micromachined ultrasound transducers structure. Principles of gravimetric operation and device modeling are reviewed through the presentation of an analytical, one-dimensional model and finite element modeling. Additionally, the most common fabrication techniques, including sacrificial release and wafer bonding, are discussed for advantages for gravimetric sensing. As functional materials are the most important part of the selective gravimetric sensing, the review of different functional material properties and coating and application methods is necessary. Particularly, absorption and desorption mechanisms of functional materials, like methylated polyethyleneimine, with examples of applications for gas sensing and using immune complexes for specific biomolecules detection are reviewed.

One-step synthesis of core shell cellulose-silica/n-octadecane microcapsules and their application in waterborne self-healing multiple protective fabric coatings

Exploiting water-based fabric coatings outfitted with multiple protections (e.g., waterproofness, ultraviolet (UV) resistance and thermal insulation) are urgently demanded. Nevertheless, achieving the multifunction and durability poses the major challenge. In the present study, novel multifunctional cellulose/silica hybrid microcapsules were developed by one-step emulsion-solvent diffusion; these microcapsules were well dispersed into waterborne silicone resins to form waterborne multiple protective fabric coatings. Since the encapsulated phase change materials were in the core of capsules, and the hydrophobic coupling reagent and UV absorber were grafted onto the silicas in the shell of capsules, these fabric coatings exhibited high superhydrophobicity, UV protection and thermal insulation. Moreover, because hydrophobic coupling reagent and UV absorber in the shell-cellulose of capsules exhibited easy mobility, the fabric coatings displayed self-repairability of superhydrophobicity and UV protection even after being damaged chemically or mechanically. The fabric coating presented in this study could have a range of applications, covering special protective fabric, high-altitude garments as well as self-cleaning materials.

Thickness controllable hypercrosslinked porous polymer nanofilm with high CO2 capture capacity

Thickness controllable porous polymer nanofilm with superior gas storage capacity has gradually emerged as promising adsorbents for capture of CO₂, due to extremely high surface area and micro-scale pore. In this work, we have developed a novel and facile strategy to fabricate thickness controllable two or three dimensional ordered porous nanofilm based on poly(styrene-butyl acrylate), in combination with covalently layer by layer (LBL) self-assemble process and hypercrosslinked post-treatment. Abundant microporous structures and a small number of mesoporous structures are formed in hypercorsslinked nanofilm and corresponding surface area derived from Brunauer-Emmett-Teller method (BET) were determined to be 605.7 m²/g. The capacity of CO₂ capture was also measured, which reach up to 53.6 wt% (12.2 mmol/g) at 273 K/1 bar, which is comparable to highest record. We have found that all the as prepared nanofilm with different thickness exhibited apparently enhanced micro- and meso-porosity after hypercrosslinking. Moreover, with the increase of thickness of nanofilm, the adsorption capacity decreases gradually, as well as the CO₂ adsorption capacity. An excellent recycling capacity for CO₂ capture have also found for this porous polymer nanofilm via repetitive adsorption-desorption assay. Our work confirmed that thickness controllable porous polymer nanofilm with superior CO₂ capture capacity can be fabricated by a very simple strategy which can meet the challenges of the current CO₂ capture and storage technology.

A thio-functionalized zinc phosphite with a large-channel framework and enhanced removal ability of mercury ion from aqueous solutions

New thio-functionalized zinc phosphite (NTOU-2S) exhibited the different structural properties and removal ability of Hg²⁺ cation from the sulfur-free NTOU-2.

Weakly charged droplets fundamentally change impact dynamics on flat surfaces

Electric charges are often found in naturally or artificially formed droplets, such as raindrops and those generated by Kelvin's water dropper. In contrast to the impact of neutral droplets on a flat solid surface upon which a thin convex lens shape layer of the gas film is typically formed, we show that the delicate gas thin film can be fundamentally altered for even weakly charged droplets. As the charge level is raised above a critical level of ∼1% of the Rayleigh limit for representative impact conditions, the Maxwell stress overcomes the gas pressure buildup to deform the droplet bottom surface. A conical liquid tip forms and pierces through the gas film, leading to a circular contact line moving outwards that does not trap any gas. The critical charge level only depends on the capillary number based on the gas viscosity. This finding applies to common liquids and molten alloy droplets, providing new insights into a range of applications such as mitigating pinhole defects in additive manufacturing.

Hyperthin Membranes for Gas Separations via Layer-by-Layer Assembly

Thin film formation via the Layer-by-Layer method is now a well-established and broadly used method in materials science. We have been keenly interested in exploiting this technique in the area of gas separations. Specifically, we have sought to create hyperthin (<100 nm) polyelectrolyte-based membranes that have practical potential for the separation of CO₂ from N₂ (flue gas) and H₂ from CO₂ (syngas). In this personal account, we summarize recent studies that have been aimed at measuring the influence of a variety of factors that can affect the permeability and permeation selectivity of hyperthin polyelectrolyte multilayers (PEMs).

The Future of Layer-by-Layer Assembly: A Tribute to ACS Nano Associate Editor Helmuth Möhwald

Layer-by-layer (LbL) assembly is a widely used tool for engineering materials and coatings. In this Perspective, dedicated to the memory of ACS Nano associate editor Prof. Dr. Helmuth Möhwald, we discuss the developments and applications that are to come in LbL assembly, focusing on coatings, bulk materials, membranes, nanocomposites, and delivery vehicles.

Layer-by-layer self-assembly of pillared two-dimensional multilayers

We report Layer-by-Layer (LbL) self-assembly of pillared two-dimensional (2D) multilayers, from water, onto a wide range of substrates. This LbL method uses a small molecule, tris(2-aminoethyl) amine (TAEA), and a colloidal dispersion of Ti₃C₂T_x MXene to LbL self-assemble (MXene/TAEA)_n multilayers, where n denotes the number of bilayers. Assembly with TAEA results in highly ordered (MXene/TAEA)_n multilayers where the TAEA expands the interlayer spacing of MXene flakes by only ~ 1 Å and reinforces the interconnection between them. The TAEA-pillared MXene multilayers show the highest electronic conductivity of 7.3 × 10⁴ S m^-1 compared with all reported MXene multilayers fabricated by LbL technique. The (MXene/TAEA)_n multilayers could be used as electrodes for flexible all-solid-state supercapacitors delivering a high volumetric capacitance of 583 F cm^-3 and high energy and power densities of 3.0 Wh L^-1 and 4400 W L^-1, respectively. This strategy enables large-scale fabrication of highly conductive pillared MXene multilayers, and potentially fabrication of other 2D heterostructures.

Electrospinning and Electrospun Nanofibers: Methods, Materials, and Applications

Electrospinning is a versatile and viable technique for generating ultrathin fibers. Remarkable progress has been made with regard to the development of electrospinning methods and engineering of electrospun nanofibers to suit or enable various applications. We aim to provide a comprehensive overview of electrospinning, including the principle, methods, materials, and applications. We begin with a brief introduction to the early history of electrospinning, followed by discussion of its principle and typical apparatus. We then discuss its renaissance over the past two decades as a powerful technology for the production of nanofibers with diversified compositions, structures, and properties. Afterward, we discuss the applications of electrospun nanofibers, including their use as "smart" mats, filtration membranes, catalytic supports, energy harvesting/conversion/storage components, and photonic and electronic devices, as well as biomedical scaffolds. We highlight the most relevant and recent advances related to the applications of electrospun nanofibers by focusing on the most representative examples. We also offer perspectives on the challenges, opportunities, and new directions for future development. At the end, we discuss approaches to the scale-up production of electrospun nanofibers and briefly discuss various types of commercial products based on electrospun nanofibers that have found widespread use in our everyday life.

UV/NIR-Light-Triggered Rapid and Reversible Color Switching for Rewritable Smart Fabrics

Remote, rapid, and ink-free printing/erasure on fabrics has great potential to revolutionize specialized clothing in numerous applications including fashion/aesthetic and security fields, but the construction of such smart fabrics has not been realized due to underlying obstacles in obtaining suitable photoreversible color-switching systems (PCSS). To address this problem, we have prepared TiO_{2- x} nanorods as photocatalytic and photothermal component. With redox dyes as reversible color indicators and hydroxyethyl cellulose (HEC) as polymer matrix, TiO_{2- x}/dye/HEC-based PCSS is coated on poly(dimethylsiloxane)-treated cotton fabric. Under 365 nm light irradiation, discoloration occurs in 180 s, resulting from the efficient photocatalytic reduction of the dye. On the contrary, when the colorless fabric is irradiated by 808 nm light, recoloration occurs in a very short time (∼100 s), far lower than the traditional heating mode (30-8 min at 90-150 °C). This rapid recoloration should be attributed to the localized high temperature (164.3-184.5 °C) induced by photothermal effect of TiO_{2- x}. Particularly, when TiO_{2- x}/dye/HEC-based PCSS is extended to coat commercial clothes (such as T-shirts), red/green/blue figures/letters can be rapidly and remotely printed by UV-light pen and then erased by near-infrared light, with high cycle stability. Therefore, such rewritable smart fabric represents an attractive alternative to regular clothes in meeting the increasing aesthetic or camouflage needs.

Highly Conductive Paper/Textile Electrodes Using Ligand Exchange Reaction-Induced in Situ Metallic Fusion

Here, we report that metal nanoparticle (NP)-based paper/textile electrodes with bulk metallic conductivity can be prepared via organic linker-modulated ligand exchange reaction and in situ room-temperature metallic fusion without additional chemical or thermal treatments. For this study, amine-functionalized molecule linkers instead of bulky polymer linkers were layer-by-layer (LbL)-assembled with tetraoctylammonium bromide (TOABr)-stabilized Au NPs to form Au NP multilayered films. By conversion of the amine groups of the organic molecule linkers from -NH₃⁺ to the -NH₂ groups, as well as by a decrease in the size of the organic linkers, the LbL-assembled Au NPs became highly interconnected and fused during LbL deposition, resulting in Au NP multilayers with adjustable conductivity and transport behavior. These phenomena were also predicted by a density functional theory investigation for the model system. Particularly, LbL-assembled films composed of TOABr-Au NPs and diethylenetriamine ( M_w: ∼104) exhibited a remarkable electrical conductivity of 2.2 × 10⁵ S·cm^-1, which was higher than the electrical conductivity of the metal NP-based electrodes as well as the carbon material-based electrodes reported to date. Furthermore, based on our approach, a variety of insulating flexible papers and textiles were successfully converted into real metal-like paper and textile electrodes with high flexibility preserving their highly porous structure. This approach can provide a basis for further improving and controlling the electrical properties of flexible electrodes through the control of organic linkers.

Assessing the Binding Performance of Amyloid-Carbon Membranes toward Heavy Metal Ions

Amyloid-carbon hybrid membranes have exceptional performance in removing heavy metal ions from water because of the presence of multiple binding sites on the amyloid fibrils, but the binding process is still not fully understood. To understand the mechanisms of amyloid-metal ion binding, we perform adsorption isotherms on a model system given by β-lactoglobulin amyloid fibrils and four representative heavy metal ions: chromium (Cr), nickel (Ni), silver (Ag), and platinum (Pt). Furthermore, to get a comprehensive thermodynamic picture of the binding process between amino acid residues and heavy metals, we here use isothermal titration calorimetry on native β-lactoglobulin monomers and amyloid fibrils exposed to the two model metal ions, that is, silver and chromium. A conclusive thermodynamic insight on the binding process emerges by direct measurements of enthalpy and entropy changes, association binding constant, and average number of binding sites of the protein monomer and amyloid fibril. As a result of the strong amyloid binding affinity between amino acids and metal ions, when the protein is converted into amyloid fibrils and assembled into membranes, the resulting amyloid-activated carbon hybrids remove all the tested heavy metals with efficiencies beyond 99%. Importantly, the efficiency remains stable during several consecutive cycles, demonstrating a high adsorption capacity and a long lifetime and reusability of the membranes. The recovery of adsorbed precious metal ions converted into elemental metals is shown to be a general feature of these membranes, with platinum and silver successfully recovered from saturated hybrid membranes by a simple thermal reduction. The separation performance, evaluated on real electroplating industrial wastewater containing chromium and nickel, is found to exceed 99% at a permeability as high as 2.92 × 10^-16 m², that is, at least 4 orders of magnitude higher than typical nanofiltration membranes, conclusively validating the technology under stringent real conditions.

Spray Assembly of Metal-Phenolic Networks: Formation, Growth, and Applications

Hybrid conformal coatings, such as metal-phenolic networks (MPNs) that are constructed from the coordination-driven assembly of natural phenolic ligands, are of interest in areas including biomedicine, separations, and energy. To date, most MPN coatings have been prepared by immersing substrates in solutions containing the phenolic ligands and metal ions, which is a suitable method for coating small or flexible objects. In contrast, more industrially relevant methods for coating and patterning large substrates, such as spray assembly, have been explored to a lesser extent toward the fabrication of MPNs, particularly regarding the effect of process variables on MPN growth. Herein, a spray assembly method was used to fabricate MPN coatings with various phenolic building blocks and metal ions and their formation and patterning were explored for different applications. Different process parameters including solvent, pH, and metal-ligand pair allowed for control over the film properties such as thickness and roughness. On the basis of these investigations, a potential route for the formation of spray-assembled MPN films was proposed. Conditions favoring the formation of bis complexes could produce thicker coatings than those favoring the formation of mono or tris complexes. Finally, the spray-assembled MPNs were used to generate superhydrophilic membranes for oil-water separation and colorless films for UV shielding. The present study provides insights into the chemistry of MPN assembly and holds promise for advancing the fabrication of multifunctional hybrid materials.

Controlling the Secondary Surface Morphology of Electrospun PVDF Nanofibers by Regulating the Solvent and Relative Humidity

This work presents a simple and reliable method for directly generating polyvinylidene fluoride (PVDF) nanofibers with secondary surface morphology (e.g., porous surfaces, rough surfaces, grooved surfaces, and interior porosity) by using single/binary solvent systems and relative humidity. We clarified the mechanisms responsible for the formation of these morphologies by systematically exploring the molecular interactions among the polymer, solvent(s), and water vapor. Our results proved that the formation of secondary surface morphology needed the presence of water vapor, a non-solvent of the polymer, at an appropriate level of relative humidity. The formation of secondary surface morphology was dependent on the speed of evaporation of the solvent(s) (ACE, DMF, and their mixtures), as well as the inter-diffusion and penetration of the non-solvent (water) and solvent(s). The results of N2 physical adsorption-desorption isotherms showed that the macro-porous fibers (> 300 nm) exhibited the highest specific surface area of 23.31 ± 4.30 m2/g and pore volume of 0.0695 ± 0.007 cm3/g, enabling the high oil absorption capacities of 50.58 ± 5.47 g/g, 37.74 ± 4.33 g/g, and 23.96 ± 2.68 g/g for silicone oil, motor oil, and olive oil, respectively. We believe this work may serve as guidelines for the formation of different structures of macro-porous, rough, and grooved nanofibers with interior porosity through electrospinning.

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.

Electroreductive Coupling Layer-by-Layer Assembly

Rapid and covalent layer-by-layer (LbL) assembly is of significance for practical applications because of superior chemical and mechanical stability. The electrochemical LbL assembly via an accelerating trigger can be automated and programmable in response to electrical signals to in situ fabricate covalently layered thin films with chemical and mechanical stability. In this paper, electroreductive coupling layer-by-layer assembly is introduced as both covalent and rapid methodology for preparing layered thin films. This assembly is triggered by C-C coupling of peripheral alkynyls, which have own absorption below 300 nm and can transform to optical and electrical inert double/single or triple/single alternative bonding formations significantly without optical or electric alternations of desirable photoelectric building blocks, superior to other linkers among covalent LbL assemblies. Not limited to fabrication of optical thin films, this assembly is readily available for oxygen sensitive substrates or materials and also a powerful addition to electrooxidative coupling LbL assembly for developing the economically dynamoelectric LbL machines without moving or changing experimental gears.

Hierarchically Porous Calcium Carbonate Scaffolds for Bone Tissue Engineering

Hierarchically porous CaCO₃ scaffolds comprised of micro- (diameter = 2.0 ± 0.3 μm) and nano-sized (diameter = 50.4 ± 14.4 nm) pores were fabricated on silicon substrates using a supercritical CO₂-based process. Differentiated human THP-1 monocytes exposed to the CaCO₃ scaffolds produced negligible levels of the inflammatory cytokine tumor necrosis factor-alpha (TNF-α), confirming the lack of immunogenicity of the scaffolds. Extracellular matrix (ECM) proteins, vitronectin and fibronectin, displayed enhanced adsorption to the scaffolds compared to the silicon controls. ECM protein-coated CaCO₃ scaffolds promoted adhesion, growth, and proliferation of osteoblast MC3T3 cells. MC3T3 cells grown on the CaCO₃ scaffolds produced substantially higher levels of transforming growth factor-beta and vascular endothelial growth factor A, which regulate osteoblast differentiation, and exhibited markedly increased alkaline phosphatase activity, a marker of early osteoblast differentiation, compared to controls. Moreover, the CaCO₃ scaffolds stimulated matrix mineralization (calcium deposition), an end point of advanced osteoblast differentiation and an important biomarker for bone tissue formation. Taken together, these results demonstrate the significant potential of the hierarchically porous CaCO₃ scaffolds for bone tissue engineering applications.