Rapid fabrication of precise high-throughput filters from membrane protein nanosheets

Artificial Channels Based on Bottlebrush Polymers: Enhanced Ion Transport Through Polymer Topology Control

Synthetic structures mimicking the transport function of natural ion channel proteins have a wide range of applications, including therapeutic treatments, separation membranes, sensing, and biotechnologies. However, the development of polymer-based artificial channels has been hampered due to the limitation on available models. In this study, we demonstrate the great potential of bottlebrush polymers as accessible and versatile molecular scaffolds for developing efficient artificial ion channels. Adopting the bottlebrush configuration enhanced ion transport activity of the channels compared to their linear analogs. Matching the structure of lipid bilayers, the bottlebrush channel with a hydrophilic-hydrophobic-hydrophilic triblock architecture exhibited the highest activity among the series. Functionalized with urea groups, these channels displayed high anion selectivity. Additionally, we illustrated that the transport properties could be fine-tuned by modifying the chemistry of ion binding sites. This work not only highlights the importance of polymer topology control in channel design, but also reveals the great potential for further developing bottlebrush channels with customized features and diverse functionalities.

Enhanced circularly polarized luminescence attained via self-assembly of heterochiral as opposed to homochiral dipeptides in water

Circularly polarized luminescence (CPL) is gaining interest across various disciplines, including materials science, pharmaceuticals, and sensing technologies. Organic molecules, due to their ease of synthesis and reduced toxicity, are a focus for achieving high dissymmetry values (g lum) in CPL. Here, we present a low molecular weight molecule (1), a dipeptide (Ala-Phe) covalently linked with tetraphenyl-ethylene (TPE), an Aggregation-Induced Emission luminophore (AIE-gen). Varying the stereochemistry of amino acid chiral centers, we synthesized homochiral 1-(l, l) & 1-(d, d) and heterochiral 1-(l, d) and 1-(d, l). In aqueous media, these molecules exhibit aggregation-induced chirality at the TPE chromophore. Heterochiral systems form sheet-like structures, displaying a bisignate induced circular dichroism signal and a good g lum value for CPL [7.5 (±0.04) × 10-3]. Conversely, homochiral systems adopt fibrillar morphology, exhibiting a monosignate induced circular dichroism signal with a lower dissymmetry value for CPL [1.3 (±0.05) × 10-3]. This study introduces the concept of chiroptical amplification, emphasizing enhanced CPL through heterochiral peptide-induced CPL compared to its homochiral counterpart, with an ON and OFF CPL signal at low and high temperature respectively.

Functionalized 2D membranes for separations at the 1-nm scale

The ongoing evolution of two-dimensional (2D) material-based membranes has prompted the realization of mass separations at the 1-nm scale due to their well-defined selective nano- and subnanochannels. Strategic membrane functionalization is further found to be key to augmenting channel accuracy and efficiency in distinguishing ions, gases and molecules within this range and is thus trending as a research focus in energy-, resource-, environment- and pharmaceutical-related applications. In this review, we present the fundamentals underpinning functionalized 2D membranes in various separations, elucidating the critical "method-interaction-property" relationship. Starting with an introduction to various functionalization strategies, we focus our discussion on functionalization-induced channel-species interactions and reveal how they shape the transport- and operation-related features of the membrane in different scenarios. We also highlight the limitations and challenges of current functionalized 2D membranes and outline the necessary breakthroughs needed to apply them as reliable and high-performance separation units across industries in the future.

Porous protein crystals: synthesis and applications

Large-pore protein crystals (LPCs) are an emerging class of biomaterials. The inherent diversity of proteins translates to a diversity of crystal lattice structures, many of which display large pores and solvent channels. These pores can, in turn, be functionalized via directed evolution and rational redesign based on the known crystal structures. LPCs possess extremely high solvent content, as well as extremely high surface area to volume ratios. Because of these characteristics, LPCs continue to be explored in diverse applications including catalysis, targeted therapeutic delivery, templating of nanostructures, structural biology. This Feature review article will describe several of the existing platforms in detail, with particular focus on LPC synthesis approaches and reported applications.

Intelligent Biomaterialomics: Molecular Design, Manufacturing, and Biomedical Applications

Materialomics integrates experiment, theory, and computation in a high-throughput manner, and has changed the paradigm for the research and development of new functional materials. Recently, with the rapid development of high-throughput characterization and machine-learning technologies, the establishment of biomaterialomics that tackles complex physiological behaviors has become accessible. Breakthroughs in the clinical translation of nanoparticle-based therapeutics and vaccines have been observed. Herein, recent advances in biomaterials, including polymers, lipid-like materials, and peptides/proteins, discovered through high-throughput screening or machine learning-assisted methods, are summarized. The molecular design of structure-diversified libraries; high-throughput characterization, screening, and preparation; and, their applications in drug delivery and clinical translation are discussed in detail. Furthermore, the prospects and main challenges in future biomaterialomics and high-throughput screening development are highlighted.

Dehydrated Biomimetic Membranes with Skinlike Structure and Function

Novel vapor-permeable materials are sought after for applications in protective wear, energy generation, and water treatment. Current impermeable protective materials effectively block harmful agents but trap heat due to poor water vapor transfer. Here we present a new class of materials, vapor permeable dehydrated nanoporous biomimetic membranes (DBMs), based on channel proteins. This application for biomimetic membranes is unexpected as channel proteins and biomimetic membranes were assumed to be unstable under dry conditions. DBMs mimic human skin's structure to offer both high vapor transport and small molecule exclusion under dry conditions. DBMs feature highly organized pores resembling sweat pores in human skin, but at super high densities (>1012 pores/cm2). These DBMs achieved exceptional water vapor transport rates, surpassing commercial breathable fabrics by up to 6.2 times, despite containing >2 orders of magnitude smaller pores (1 nm vs >700 nm). These DBMs effectively excluded model biological agents and harmful chemicals both in liquid and vapor phases, again in contrast with the commercial breathable fabrics. Remarkably, while hydrated biomimetic membranes were highly permeable to liquid water, they exhibited higher water resistances after dehydration at values >38 times that of commercial breathable fabrics. Molecular dynamics simulations support our hypothesis that dehydration induced protein hydrophobicity increases which enhanced DBM performance. DBMs hold promise for various applications, including membrane distillation, dehumidification, and protective barriers for atmospheric water harvesting materials.

Bio-Inspired Functional Materials for Environmental Applications

With the global population expected to reach 9.7 billion by 2050, there is an urgent need for advanced materials that can address existing and developing environmental issues. Many current synthesis processes are environmentally unfriendly and often lack control over size, shape, and phase of resulting materials. Based on knowledge from biological synthesis and assembly processes, as well as their resulting functions (e.g., photosynthesis, self-healing, anti-fouling, etc.), researchers are now beginning to leverage these biological blueprints to advance bio-inspired pathways for functional materials for water treatment, air purification and sensing. The result has been the development of novel materials that demonstrate enhanced performance and address sustainability. Here, an overview of the progress and potential of bio-inspired methods toward functional materials for environmental applications is provided. The challenges and opportunities for this rapidly expanding field and aim to provide a valuable resource for researchers and engineers interested in developing sustainable and efficient processes and technologies is discussed.

An Artificial Liposome Compartment with Size Exclusion Molecular Transport

The cellular compartment plays an essential role in organizing the complex and diverse biochemical reactions within the cell. By mimicking the function of such cellular compartments, the challenge of constructing artificial compartments has been taken up to develop new biochemical tools for efficient material production and diagnostics. The important features required for the artificial compartment are that it isolates the interior from the external environment and is further functionalized to control the transport of target chemicals to regulate the interior concentration of both substrate and reaction products. In this study, an artificial compartment with size-selective molecular transport function was constructed by using a DNA origami-guided liposome prepared by modifying the method reported by Perrault et al. This completely isolates the liposome interior, including the DNA origami skeleton, from the external environment and allows the assembly of a defined number of molecules of interest inside and/or outside the compartment. By incorporating a bacterial membrane protein, OmpF, into the liposome, the resulting artificial compartment was shown to transport only the molecule of interest with a molecular weight below 600 Da from the external environment into the interior of the compartment.

Protein engineering of pores for separation, sensing, and sequencing

Proteins are critical to cellular function and survival. They are complex molecules with precise structures and chemistries, which allow them to serve diverse functions for maintaining overall cell homeostasis. Since the discovery of the first enzyme in 1833, a gamut of advanced experimental and computational tools has been developed and deployed for understanding protein structure and function. Recent studies have demonstrated the ability to redesign/alter natural proteins for applications in industrial processes of interest and to make customized, novel synthetic proteins in the laboratory through protein engineering. We comprehensively review the successes in engineering pore-forming proteins and correlate the amino acid-level biochemistry of different pore modification strategies to the intended applications limited to nucleotide/peptide sequencing, single-molecule sensing, and precise molecular separations.

Tunable Ion Transport in Two-Dimensional Nanofluidic Channels

Layered two-dimensional (2D) materials with interlayer channels at the nanometer scale offer an ideal platform to control ion transport behaviors, including high-precision separation, ultrafast diffusion, and tunable permeation flux, which show great potential for energy conversion and storage, water treatment, catalysis, biosynthesis, and sensing. Recent advances in controlling the structure and functionality of 2D nanofluidic channels sustainably open doors for more revolutionary applications. In this Perspective, we first present a brief introduction to the fundamental mechanisms for ion transport in 2D nanofluidic channels and an overview of state-of-the-art assembly technologies of nanochannel membranes. We then point out new avenues for developing advanced nanofluidics, combining molecular-level cross-linking, and surface modification in nanoconfinement. Finally, we outline the potential applications of these 2D nanofluidic channel membranes and their technical challenges that need to be addressed to afford for practical applications.

Nuclear Magnetic Resonance Dipolar Cross-Relaxation Interaction between Nanoconfined Fluids and Matrix Solids

Many different methods have been developed to investigate fluid-solid interactions in nanoporous systems. These methods either only work in the liquid phase or provide an indirect measurement by probing the fluid-solid interaction based on a measured property change of the fluid or solid under different sample conditions. Here, we report a direct measurement technique using NMR dipolar cross-relaxation between the nanoconfined fluids and the matrix solids. The method was tested using a methyl-functionalized mesostructured silica saturated with methanol as a model sample. A formal theory was established to describe the enhanced dipolar cross-relaxation interaction between the nanoconfined fluids and the matrix solids. Both the experiment and theory showed that nanoconfinement of the fluids enhances the dipolar cross-relaxation interaction between the fluid and the matrix solids, which can be applied to investigate the fluid-solid interaction for various materials of a similar nanostructure.

Homogeneous hybrid droplet interface bilayers assembled from binary mixtures of DPhPC phospholipids and PB-b-PEO diblock copolymers

Hybrid membranes built from phospholipids and amphiphilic block copolymers seek to capitalize on the benefits of both constituents for constructing biomimetic interfaces with improved performance. However, hybrid membranes have not been formed or studied using the droplet interface bilayer (DIB) method, an approach that offers advantages for revealing nanoscale changes in membrane structure and mechanics and offers a path toward assembling higher-order tissues. We report on hybrid droplet interface bilayers (hDIBs) formed in hexadecane from binary mixtures of synthetic diphytanoyl phosphatidylcholine (DPhPC) lipids and low molecular weight 1,2 polybutadiene-b-polyethylene oxide (PBPEO) amphiphilic block copolymers and use electrophysiology measurements and imaging to assess the effects of PBPEO in the membrane. This work reveals that hDIBs containing up to 15 mol% PBPEO plus DPhPC are homogeneously mixtures of lipids and polymers, remain highly resistive to ion transport, and are stable-including under applied voltage. Moreover, they exhibit hydrophobic thicknesses similar to DPhPC-only bilayers, but also have significantly lower values of membrane tension. These characteristics coincide with reduced energy of adhesion between droplets and the formation of alamethicin ion channels at significantly lower threshold voltages, demonstrating that even moderate amounts of amphiphilic block copolymers in a lipid bilayer provide a route for tuning the physical properties of a biomimetic membrane.

Precise Assembly of Proteins and Carbohydrates for Next-Generation Biomaterials

The complexity and diversity of biomacromolecules make them a unique class of building blocks for generating precise assemblies. They are particularly available to a new generation of biomaterials integrated with living systems due to their intrinsic properties such as accurate recognition, self-organization, and adaptability. Therefore, many excellent approaches have been developed, leading to a variety of quite practical outcomes. Here, we review recent advances in the fabrication and application of artificially precise assemblies by employing proteins and carbohydrates as building blocks, followed by our perspectives on some of new challenges, goals, and opportunities for the future research directions in this field.

Self-Assembly of Functional Protein Nanosheets from Thermoresponsive Bolaamphiphiles

Nanosheets are two-dimensional materials, less than 100 nm thick, that can be used for separations, biosensing, and biocatalysis. Nanosheets can be made from inorganic and organic materials such as graphene, polymers, and proteins. Here, we report the self-assembly of nanosheets under aqueous conditions from functional proteins. The nanosheets are synthesized from two fusion proteins held together by high-affinity interactions of two leucine zippers to form bolaamphiphiles. The hydrophobic domain, Z_R-ELP-Z_R, contains the thermoresponsive elastin-like peptide (ELP) flanked by arginine-rich leucine zippers (Z_R), each of which binds the hydrophilic fusion protein, globule-Z_E, via the glutamate-rich leucine zipper (Z_E) fused to a functional, globular protein. Nanosheets form when the proteins are mixed at 4 °C in aqueous solutions and then heated to 25 °C as the container is rotated end-over-end causing expansion and contraction of the air-water interface. The nanosheets are robust with respect to the choice of globular protein and can incorporate small fluorescent proteins that are less than 30 kDa as well as large enzymes, such as 80 kDa malate synthase G. Upon incorporation into nanosheets, enzymes retain more than 70% of their original activity, demonstrating the potential of protein nanosheets to be used for biosensing or biocatalytic applications.

Effect of Nutritional Protein Food on Metabolism and Physical Fitness of Wushu Athletes

In order to greatly improve the physical function of martial arts athletes, this topic studies the effect of high-protein food on the physical function of martial arts athletes. Forty-five athletes in martial arts events took 5 g of high-protein food every day, 6 times a week for 4weeks, and the left and right forearm, calcaneus bone mineral density, and venous blood was drawn to detect bone metabolism and biochemical indicators related to physical function. The experimental results showed that the bone mineral density of the right calcaneus of male martial arts athletes increased significantly after taking high-protein food, and the bone mineral density of left and right forearms and calcaneus of female martial arts athletes increased significantly. After taking high-protein food, the serum calcium and phosphorus of female athletes and the serum calcium of male athletes were significantly increased. Sex decreased, female athletes significantly decreased serum creatine kinase, and male athletes significantly increased IgM. It can be seen that taking high-protein food for 4 weeks has a certain improvement effect on the bone mineral density of female athletes’ forearm and calcaneus, but has little effect on the bone mineral density of male athletes’ forearm and calcaneus. It can be concluded that high-protein food has no adverse effect on athletes’ bone metabolism, blood biochemical indexes, and immune globulin, and can better maintain the physical function level of martial arts athletes.

Nanostructured block copolymer muscles

High-performance actuating materials are necessary for advances in robotics, prosthetics and smart clothing. Here we report a class of fibre actuators that combine solution-phase block copolymer self-assembly and strain-programmed crystallization. The actuators consist of highly aligned nanoscale structures with alternating crystalline and amorphous domains, resembling the ordered and striated pattern of mammalian skeletal muscle. The reported nanostructured block copolymer muscles excel in several aspects compared with current actuators, including efficiency (75.5%), actuation strain (80%) and mechanical properties (for example, strain-at-break of up to 900% and toughness of up to 121.2 MJ m^-3). The fibres exhibit on/off rotary actuation with a peak rotational speed of 450 r.p.m. Furthermore, the reported fibres demonstrate multi-trigger actuation (heat and hydration), offering switchable mechanical properties and various operating modes. The versatility and recyclability of the polymer fibres, combined with the facile fabrication method, opens new avenues for creating multifunctional and recyclable actuators using block copolymers.

Geometrically Induced Selectivity and Unidirectional Electroosmosis in Uncharged Nanopores

Selectivity toward positive and negative ions in nanopores is often associated with electroosmotic flow, the control of which is pivotal in several micro-nanofluidic technologies. Selectivity is traditionally understood to be a consequence of surface charges that alter the ion distribution in the pore lumen. Here we present a purely geometrical mechanism to induce ionic selectivity and electroosmotic flow in uncharged nanopores, and we tested it via molecular dynamics simulations. Our approach exploits the accumulation of charges, driven by an external electric field, in a coaxial cavity that decorates the membrane close to the pore entrance. The selectivity was shown to depend on the applied voltage and becomes completely inverted when reversing the voltage. The simultaneous inversion of ionic selectivity and electric field direction causes a unidirectional electroosmotic flow. We developed a quantitatively accurate theoretical model for designing pore geometry to achieve the desired electroosmotic velocity. Finally, we show that unidirectional electroosmosis also occurs in much more complex scenarios, such as a biological pore whose structure presents a coaxial cavity surrounding the pore constriction as well as a complex surface charge pattern. The capability to induce ion selectivity without altering the pore lumen shape or the surface charge may be useful for a more flexible design of selective membranes.

MXene Composite Membranes with Enhanced Ion Transport and Regulated Ion Selectivity

Two-dimensional (2D) material-based membranes are promising candidates for various separation applications. However, the further enhancement of membrane ion conductance is difficult, and the regulation of membrane ion selectivity remains a challenge. Here, we demonstrate the facile fabrication of MXene composite membranes by incorporating spacing agents that contain SO₃H groups into the MXene interlayers. The synthesized membrane shows enhanced ion conductance and ion selectivity. Subsequently, the membranes are utilized for salinity gradient power (SGP) generation and lithium-ion (Li⁺) recovery. The membrane containing poly(sodium 4-styrenesulfonate) (PSS) as the spacing agent shows a much higher power density for SGP generation as compared to the pristine MXene membrane. Using artificial seawater and river water, the power density reaches 1.57 W/m² with a testing area of 0.24 mm². Also, the same membrane shows Li⁺/Na⁺ and Li⁺/K⁺ selectivities of 2.5 and 3.2, respectively. The incorporation of PSS increases both the size and charge density of the nanochannels inside the membrane, which is beneficial for ion conduction. In addition, the density functional theory (DFT) calculation shows that the binding energy between Li⁺ and the SO₃H group is lower than other alkali ion metals, and this might be one major reason why the membrane possesses high Li⁺ selectivity. This study demonstrates that incorporating spacing agents into the 2D material matrix is a viable strategy to enhance the performance of the 2D material-based membranes. The results from this study can inspire new membrane designs for emerging applications including energy harvesting and monovalent ion recovery.

The coming of age of water channels for separation membranes: from biological to biomimetic to synthetic

Water channels are one of the key pillars driving the development of next-generation desalination and water treatment membranes. Over the past two decades, the rise of nanotechnology has brought together an abundance of multifunctional nanochannels that are poised to reinvent separation membranes with performances exceeding those of state-of-the-art polymeric membranes within the water-energy nexus. Today, these water nanochannels can be broadly categorized into biological, biomimetic and synthetic, owing to their different natures, physicochemical properties and methods for membrane nanoarchitectonics. Furthermore, against the backdrop of different separation mechanisms, different types of nanochannel exhibit unique merits and limitations, which determine their usability and suitability for different membrane designs. Herein, this review outlines the progress of a comprehensive amount of nanochannels, which include aquaporins, pillar[5]arenes, I-quartets, different types of nanotubes and their porins, graphene-based materials, metal- and covalent-organic frameworks, porous organic cages, MoS₂, and MXenes, offering a comparative glimpse into where their potential lies. First, we map out the background by looking into the evolution of nanochannels over the years, before discussing their latest developments by focusing on the key physicochemical and intrinsic transport properties of these channels from the chemistry standpoint. Next, we put into perspective the fabrication methods that can nanoarchitecture water channels into high-performance nanochannel-enabled membranes, focusing especially on the distinct differences of each type of nanochannel and how they can be leveraged to unlock the as-promised high water transport potential in current mainstream membrane designs. Lastly, we critically evaluate recent findings to provide a holistic qualitative assessment of the nanochannels with respect to the attributes that are most strongly valued in membrane engineering, before discussing upcoming challenges to share our perspectives with researchers for pathing future directions in this coming of age of water channels.

Thermo-Osmotic Energy Conversion Enabled by Covalent-Organic-Framework Membranes with Record Output Power Density

A vast amount of energy can be extracted from the untapped low-grade heat from sources below 100 °C and the Gibbs free energy from salinity gradients. Therefore, a process for simultaneous and direct conversion of these energies into electricity using permselective membranes was developed in this study. These membranes screen charges of ion flux driven by the combined salinity and temperature gradients to achieve thermo-osmotic energy conversion. Increasing the charge density in the pore channels enhanced the permselectivity and ion conductance, leading to a larger osmotic voltage and current. A 14-fold increase in power density was achieved by adjusting the ionic site population of covalent organic framework (COF) membranes. The optimal COF membrane was operated under simulated estuary conditions at a temperature difference of 60 K, which yielded a power density of ≈231 W m^-2 , placing it among the best performing upscaled membranes. The developed system can pave the way to the utilization of the enormous supply of untapped osmotic power and low-grade heat energy, indicating the tremendous potential of using COF membranes for energy conversion applications.

Tailored design of nanofiltration membranes for water treatment based on synthesis-property-performance relationships

Tailored design of high-performance nanofiltration (NF) membranes is desirable because the requirements for membrane performance, particularly ion/salt rejection and selectivity, differ among the various applications of NF technology ranging from drinking water production to resource mining. However, this customization greatly relies on a comprehensive understanding of the influence of membrane fabrication methods and conditions on membrane properties and the relationships between the membrane structural and physicochemical properties and membrane performance. Since the inception of NF, much progress has been made in forming the foundation of tailored design of NF membranes and the underlying governing principles. This progress includes theories regarding NF mass transfer and solute rejection, further exploitation of the classical interfacial polymerization technique, and development of novel materials and membrane fabrication methods. In this critical review, we first summarize the progress made in controllable design of NF membrane properties in recent years from the perspective of optimizing interfacial polymerization techniques and adopting new manufacturing processes and materials. We then discuss the property-performance relationships based on solvent/solute mass transfer theories and mathematical models, and draw conclusions on membrane structural and physicochemical parameter regulation by modifying the fabrication process to improve membrane separation performance. Next, existing and potential applications of these NF membranes in water treatment processes are systematically discussed according to the different separation requirements. Finally, we point out the prospects and challenges of tailored design of NF membranes for water treatment applications. This review bridges the long-existing gaps between the pressing demand for suitable NF membranes from the industrial community and the surge of publications by the scientific community in recent years.

Microfluidic Evaporation, Pervaporation, and Osmosis: From Passive Pumping to Solute Concentration

Evaporation, pervaporation, and forward osmosis are processes leading to a mass transfer of solvent across an interface: gas/liquid for evaporation and solid/liquid (membrane) for pervaporation and osmosis. This Review provides comprehensive insight into the use of these processes at the microfluidic scales for applications ranging from passive pumping to the screening of phase diagrams and micromaterials engineering. Indeed, for a fixed interface relative to the microfluidic chip, these processes passively induce flows driven only by gradients of chemical potential. As a consequence, these passive-transport phenomena lead to an accumulation of solutes that cannot cross the interface and thus concentrate solutions in the microfluidic chip up to high concentration regimes, possibly up to solidification. The purpose of this Review is to provide a unified description of these processes and associated microfluidic applications to highlight the differences and similarities between these three passive-transport phenomena.

Current status and future directions of self-assembled block copolymer membranes for molecular separations

One of the most efficient and promising separation alternatives to thermal methods such as distillation is the use of polymeric membranes that separate mixtures based on molecular size or chemical affinity. Self-assembled block copolymer membranes have gained considerable attention within the membrane field due to precise control over nanoscale structure, pore size, and chemical versatility. Despite the rapid progress and excitement, a significant hurdle in using block copolymer membranes for nanometer and sub-nanometer separations such as nanofiltration and reverse osmosis is the lower limit on domain size features. Strategies such as polymer post-functionalization, self-assembly of oligomers, liquid crystals, and random copolymers, or incorporation of artificial/natural channels within block copolymer materials are future directions with the potential to overcome current limitations with respect to separation size.

Protein Nanopore Membranes Prepared by a Simple Langmuir-Schaefer Approach

Filtration through membranes with nanopores is typically associated with high transmembrane pressures and high energy consumption. This problem can be addressed by reducing the respective membrane thickness. Here, a simple procedure is described to prepare ultrathin membranes based on protein nanopores, which exhibit excellent water permeance, two orders of magnitude superior to comparable, industrially applied membranes. Furthermore, incorporation of either closed or open protein nanopores allows tailoring the membrane's ion permeability. To form such membranes, the transmembrane protein ferric hydroxamate uptake protein component A (FhuA) or its open-pore variant are assembled at the air-water interface of a Langmuir trough, compressed to a dense film, crosslinked by glutaraldehyde, and transferred to various support materials. This approach allows to prepare monolayer or multilayer membranes with a very high density of protein nanopores. Freestanding membranes covering holes up to 5 μm in diameter are visualized by atomic force microscopy (AFM), helium ion microscopy, and transmission electron microscopy. AFM PeakForce quantitative nanomechanical property mapping (PeakForce QNM)  demonstrates remarkable mechanical stability and elastic properties of freestanding monolayer membranes with a thickness of only 5 nm. The new protein membrane can pave the way to energy-efficient nanofiltration.

Bottom-up synthesis of graphene films hosting atom-thick molecular-sieving apertures

Incorporation of a high density of molecular-sieving nanopores in the graphene lattice by the bottom-up synthesis is highly attractive for high-performance membranes. Herein, we achieve this by a controlled synthesis of nanocrystalline graphene where incomplete growth of a few nanometer-sized, misoriented grains generates molecular-sized pores in the lattice. The density of pores is comparable to that obtained by the state-of-the-art postsynthetic etching (10¹² cm^-2) and is up to two orders of magnitude higher than that of molecular-sieving intrinsic vacancy defects in single-layer graphene (SLG) prepared by chemical vapor deposition. The porous nanocrystalline graphene (PNG) films are synthesized by precipitation of C dissolved in the Ni matrix where the C concentration is regulated by controlled pyrolysis of precursors (polymers and/or sugar). The PNG film is made of few-layered graphene except near the grain edge where the grains taper down to a single layer and eventually terminate into vacancy defects at a node where three or more grains meet. This unique nanostructure is highly attractive for the membranes because the layered domains improve the mechanical robustness of the film while the atom-thick molecular-sized apertures allow the realization of large gas transport. The combination of gas permeance and gas pair selectivity is comparable to that from the nanoporous SLG membranes prepared by state-of-the-art postsynthetic lattice etching. Overall, the method reported here improves the scale-up potential of graphene membranes by cutting down the processing steps.

Self-standing, conducting and capacitive biomimetic hybrid nanomembranes for selective molecular ion separation

Hybrid free-standing biomimetic materials are developed by integrating the VDAC36 β-barrel protein into robust and flexible three-layered polymer nanomembranes. The first and third layers are prepared by spin-coating a mixture of poly(lactic acid) (PLA) and poly(vinyl alcohol) (PVA). PVA nanofeatures are transformed into controlled nanoperforations by solvent-etching. The two nanoperforated PLA layers are separated by an electroactive layer, which is successfully electropolymerized by introducing a conducting sacrificial substrate under the first PLA nanosheet. Finally, the nanomaterial is consolidated by immobilizing the VDAC36 protein, active as an ion channel, into the nanoperforations of the upper layer. The integration of the protein causes a significant reduction of the material resistance, which decreases from 21.9 to 3.9 kΩ cm2. Electrochemical impedance spectroscopy studies using inorganic ions and molecular metabolites (i.e.l-lysine and ATP) not only reveal that the hybrid films behave as electrochemical supercapacitors but also indicate the most appropriate conditions to obtain selective responses against molecular ions as a function of their charge. The combination of polymers and proteins is promising for the development of new devices for engineering, biotechnological and biomedical applications.

Porous block copolymer separation membranes for 21st century sanitation and hygiene

Removing hazardous particulate and macromolecular contaminants as well as viruses with sizes from a few nm up to the 100 nm-range from water and air is crucial for ensuring sufficient sanitation and hygiene for a growing world population. To this end, high-performance separation membranes are needed that combine high permeance, high selectivity and sufficient mechanical stability under operating conditions. However, design features of separation membranes enhancing permeance reduce selectivity and vice versa. Membrane configurations combining high permeance and high selectivity suffer in turn from a lack of mechanical robustness. These problems may be tackled by using block copolymers (BCPs) as a material platform for the design of separation membranes. BCPs are macromolecules that consist of two or more chemically distinct block segments, which undergo microphase separation yielding a wealth of ordered nanoscopic domain structures. Various methods allow the transformation of these nanoscopic domain structures into customized nanopore systems with pore sizes in the sub-100 nm range and with narrow pore size distributions. This tutorial review summarizes design strategies for nanoporous state-of-the-art BCP separation membranes, their preparation, their device integration and their use for water purification.

De novo design of transmembrane β barrels

Transmembrane β-barrel proteins (TMBs) are of great interest for single-molecule analytical technologies because they can spontaneously fold and insert into membranes and form stable pores, but the range of pore properties that can be achieved by repurposing natural TMBs is limited. We leverage the power of de novo computational design coupled with a "hypothesis, design, and test" approach to determine TMB design principles, notably, the importance of negative design to slow β-sheet assembly. We design new eight-stranded TMBs, with no homology to known TMBs, that insert and fold reversibly into synthetic lipid membranes and have nuclear magnetic resonance and x-ray crystal structures very similar to the computational models. These advances should enable the custom design of pores for a wide range of applications.

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.

Pathways and Challenges for Biomimetic Desalination Membranes with Sub-Nanometer Channels

Transmembrane protein channels, including ion channels and aquaporins that are responsible for fast and selective transport of water, have inspired membrane scientists to exploit and mimic their performance in membrane technologies. These biomimetic membranes comprise discrete nanochannels aligned within amphiphilic matrices on a robust support. While biological components have been used directly, extensive work has also been conducted to produce stable synthetic mimics of protein channels and lipid bilayers. However, the experimental performance of biomimetic membranes remains far below that of biological membranes. In this review, we critically assess the status and potential of biomimetic desalination membranes. We first review channel chemistries and their transport behavior, identifying key characteristics to optimize water permeability and salt rejection. We compare various channel types within an industrial context, considering transport performance, processability, and stability. Through a re-examination of previous vesicular stopped-flow studies, we demonstrate that incorrect permeability equations result in an overestimation of the water permeability of nanochannels. We find in particular that the most optimized aquaporin-bearing bilayer had a pure water permeability of 2.1 L m^-2 h^-1 bar^-1, which is comparable to that of current state-of-the-art polymeric desalination membranes. Through a quantitative assessment of biomimetic membrane formats, we analytically show that formats incorporating intact vesicles offer minimal benefit, whereas planar biomimetic selective layers could allow for dramatically improved salt rejections. We then show that the persistence of nanoscale defects explains observed subpar performance. We conclude with a discussion on optimal strategies for minimizing these defects, which could enable breakthrough performance.

100th Anniversary of Macromolecular Science Viewpoint: Integrated Membrane Systems

Membranes fabricated from self-assembled materials are one recent example of how polymer science has been leveraged to advance membrane technology. Due to their well-defined nanostructures, the performance of membranes made from these materials is pushing the boundaries of size-selective filtration. Still, there remains a need for higher performance and more selective membranes. The advent of functional membrane platforms that rely on mechanisms beyond steric hindrance (e.g., charge-selective membranes and membrane sorbents) is one approach to realize improved solute-solute selectivity and further advance membrane technology. To date, the lab-scale demonstration of these platforms has often relied on fabrication schemes that require extended processing times. However, in order to translate lab-scale demonstrations to larger-scale implementation, it is critical that the rate of the functionalization scheme is reconciled with membrane manufacturing rates. In this viewpoint, it is postulated that substrates lined by reactive moieties that are amenable to postfabrication modification would enable the production of membranes with controlled nanostructures while providing access to a diverse array of pore wall chemistries. A comparison of reaction and manufacturing rates suggests that mechanisms that exhibit second-order reaction rate constants of at least 1 M^-1 s^-1 are needed for roll-to-roll processing. Furthermore, for mechanisms that exhibit rate constants greater than 300 M^-1 s^-1, it may be possible to integrate multiple functional domains over the membrane surface such that useful properties emerge. These multifunctional systems can expand the capabilities of membranes when the patterned chemistries interact at the heterojunctions between domains (e.g., Janus and charge-patterned mosaic membranes) or if they exhibit cooperative responses to external operating conditions (e.g., membrane pumps).

Water-ion permselectivity of narrow-diameter carbon nanotubes

Carbon nanotube (CNT) pores, which mimic the structure of the aquaporin channels, support extremely high water transport rates that make them strong candidates for building artificial water channels and high-performance membranes. Here, we measure water and ion permeation through 0.8-nm-diameter CNT porins (CNTPs)-short CNT segments embedded in lipid membranes-under optimized experimental conditions. Measured activation energy of water transport through the CNTPs agrees with the barrier values typical for single-file water transport. Well-tempered metadynamics simulations of water transport in CNTPs also report similar activation energy values and provide molecular-scale details of the mechanism for water entry into these channels. CNTPs strongly reject chloride ions and show water-salt permselectivity values comparable to those of commercial desalination membranes.

Nanoconfined Fluids: What Can We Expect from Them?

Nanoconfined fluids (NCFs), which are confined in nanospaces, exhibit distinctive nanoscale effects, including surface effects, small-size effects, quantum effects, and others. The continuous medium hypothesis in fluid mechanics is not valid in this context because of the comparable characteristic length of spaces and molecular mean free path, and accordingly, the classical continuum theories developed for the bulk fluids usually cannot describe the mass and energy transport of NCFs. In this Perspective, we summarize the nanoscale effects on the thermodynamics, mass transport, flow dynamics, heat transfer, phase change, and energy transport of NCFs and highlight the related representative works. The applications of NCFs in the fields of membrane separation, oil and gas production, energy harvesting and storage, and biological engineering are especially indicated. Currently, the theoretical description framework of NCFs is still missing, and it is expected that this framework can be established by adopting the classical continuum theories with the consideration of nanoscale effects.

Recent Advances in Hybrid Biomimetic Polymer-Based Films: from Assembly to Applications

Biological membranes, in addition to being a cell boundary, can host a variety of proteins that are involved in different biological functions, including selective nutrient transport, signal transduction, inter- and intra-cellular communication, and cell-cell recognition. Due to their extreme complexity, there has been an increasing interest in developing model membrane systems of controlled properties based on combinations of polymers and different biomacromolecules, i.e., polymer-based hybrid films. In this review, we have highlighted recent advances in the development and applications of hybrid biomimetic planar systems based on different polymeric species. We have focused in particular on hybrid films based on (i) polyelectrolytes, (ii) polymer brushes, as well as (iii) tethers and cushions formed from synthetic polymers, and (iv) block copolymers and their combinations with biomacromolecules, such as lipids, proteins, enzymes, biopolymers, and chosen nanoparticles. In this respect, multiple approaches to the synthesis, characterization, and processing of such hybrid films have been presented. The review has further exemplified their bioengineering, biomedical, and environmental applications, in dependence on the composition and properties of the respective hybrids. We believed that this comprehensive review would be of interest to both the specialists in the field of biomimicry as well as persons entering the field.