Nanostructured Membranes Research Articles

Understanding the Nanoscale Structure of Inverted Hexagonal Phase Lyotropic Liquid Crystal Polymer Membranes.

Periodic, nanostructured porous polymer membranes made from the cross-linked inverted hexagonal phase of self-assembled lyotropic liquid crystals (LLCs) are a promising class of materials for selective separations. In this work, we investigate an experimentally characterized LLC polymer membrane using atomistic molecular modeling. In particular, we compare simulated X-ray diffraction (XRD) patterns with experimental XRD data to quantify and understand the differences between simulation and experiment. We find that the nanopores are likely composed of five columns of stacked LLC monomers which surround each hydrophilic core. Evidence suggests that these columns likely move independently of each other over longer time scales than accessible via atomistic simulation. We also find that wide-angle X-ray scattering structural features previously attributed to monomer tail tilt are likely instead due to ordered tail packing. Although this system has been reported as dry, we show that small amounts of water are necessary to reproduce all features from the experimental XRD pattern because of asymmetries introduced by hydrogen bonds between the monomer head groups and water molecules. Finally, we explore the composition and structure of the nanopores and reveal that there exists a composition gradient rather than an abrupt partition between the hydrophilic and hydrophobic regions. A caveat is that the time scales of the dynamics are extremely long for this system, resulting in simulated structures that appear too ordered, thus requiring careful examination of the metastable states observed in order to draw any conclusions. The clear picture of the nanoscopic structure of these membranes provided in this study will enable a better understanding of the mechanisms of small-molecule transport within these nanopores.

The Ionic Resistance of a Nanostructured Membrane Electrode Assembly under Nonequilibrium Conditions

The ionic resistance of the membrane electrode assembly (MEA) of O2/H2 fuel cells is studied in situ in a broad range of MEA compositions by using electrochemical impedance spectroscopy and polarization measurements. The MEAs are composed of platinum on carbon, carbon nanotubes, and Nafion, a proton- conducting polymer. We investigate atypical growth of the MEA resistance with the increasing Nafion content and spatial nonuniformity in the MEA ionic resistivity. A mechanism underlying this phenomenon is proposed.

The Role of Defects in Li+ Selective Nanostructured Membranes: Comment on “Tunable Nanoscale Interlayer of Graphene with Symmetrical Polyelectrolyte Multilayer Architecture for Lithium Extraction”

The authors declare no conflict of interest.

Nanostructured Active Media for Volatile Organic Compounds Abatement: the Synergy of Graphene Oxide and Semiconductor Coupling

Among the semiconductor-mediated photoprocesses, gas-phase photocatalytic decomposition of volatile organic compounds represents one of the most valid and feasible options for improving air quality. The present work is meant to show the preparation, characterization, and testing of photocatalytic systems for enhancing the performance of TiO2-based nanostructured membranes, namely, the coupling of semiconductors and addition of cocatalysts. In particular, the use of an additional semiconductor (Ag2CO3) and coupling of graphene oxide have been found to be promising for this purpose. All of the photocatalytic media have been tested in a specifically designed photoreactor with respect to the abatement of acetaldehyde and methanol in the gas phase; the obtained results showed complete degradation of 1600 ppm of acetaldehyde and 600 ppm of methanol in less than 15 and 40 min, respectively. The morphology of the nanostructured membranes and affinity of the catalytic system with the polymeric matrix have been fou...

Formation of Bottle-Shaped Pores with Petaloid Shoulder within Anodic Alumina

Porous anodic alumina (PAA) with distinct bottle-shaped pore channels was fabricated through annealing, reanodisation and chemical etching from phosphoric acid PAA. The effects of annealing at the elevated temperature up to 600°C on the subsequent treatments have been explored to obtain largest differential diameters of the two sections. It is shown that the structural change in the barrier layer induced by annealing at 500°C can be reversed by reanodisation, which is crucial for the fabrication process. Under proper conditions, the diameters of the two sections obtained are about 345 and 220 nm, respectively. Potential applications of such PAA include nano-structured material synthesis and through-hole membrane fabrication. Petaloid shoulder consisting of regular ridges and depressions was clearly revealed in the transition region, which can be attributed to the structural variation induced by a non-uniform electric field around the barrier layer within each cell. The redistribution of the space charge during annealing may enhance the variation of the electric field and hence preferred etching.

Vertical Integration of Cell‐Laden Hydrogels with Bioinspired Photonic Crystal Membranes

AbstractThe native architecture of tissue segregates populations of cells through nanostructured membranes of biopolymers (e.g., basement membranes) which serve the dual purpose of providing scaffolding for cells and filtration through size‐exclusion. A multilayered approach to fabricate tissue scaffolds where populations of encapsulated cells are separated by porous silicon (PSi)‐based photonic crystal membranes with nano‐ and microstructure that mimics the basement membranes is reported here. The PSi films are fabricated to display discreet photonic bandgaps such that remote optical interrogation provides a specific resonance for each film. Through careful control of surface chemistry, nanostructured PSi films are engineered to serve as optical biosensors and biomolecule release reservoirs, where the optical signature can report on these distinct functions remotely using a simple light source. The promise of this approach is demonstrated as a “smart” tissue scaffolding by monitoring matrix metalloprotease (MMP) activity from encapsulated multilayered co‐cultures of mesenchymal stem cells and human microvascular endothelial cells, with concurrent attenuation of MMP activity through release of angiogenic‐modulating compounds. The integration of optically registered biosensing and drug‐release capabilities—within a multilayered hydrogel scaffold with multiple cell types—provides a new approach to tissue engineering where dynamic bioactivity can be monitored remotely in real‐time.

Anti-inflammatory and antioxidant nanostructured cellulose membranes loaded with phenolic-based ionic liquids for cutaneous application

The utilization of natural compounds, such as phenolic acids and biopolymers, in the healthcare domain is gaining increasing attention. In this study, bacterial nanocellulose (BC) membranes were loaded with ionic liquids (ILs) based on phenolic acids. These ionic compounds, with improved solubility and bioavailability, were prepared by combining the cholinium cation with anions derived from caffeic, ellagic and gallic acids. The obtained BC-ILs membranes were homogeneous, conformable and their swelling ability agreed with the solubility of each IL. These membranes revealed a controlled ILs dissolution rate in the wet state and high antioxidant activity. In vitro assays performed with Raw 264.7 macrophages and HaCaT keratinocytes revealed that these novel BC-ILs membranes are non-cytotoxic and present relevant anti-inflammatory properties. Diffusion studies with Hanson vertical diffusion cells showed a prolonged release profile of the ILs from the BC membranes. Thus, this work, successfully demonstrates the potential of BC-ILs membranes for skin treatment.

Improving the ionic conductivity in nanostructured membranes based on poly(vinyl alcohol) (PVA), chitosan (CS), phosphoric acid (H3PO4), and niobium oxide (Nb2O5)

Nanostructured membranes based on poly(vinyl alcohol) (PVA) and chitosan (CS) weight ratio of PVA:CS (80:20), mixed with 40% phosphoric acid (H3PO4) and finally doped with nanoporous niobium oxide (Nb2O5) at different concentrations, were prepared by solution casting method. The ionic transport, structural, and thermal properties were studied by different techniques. Thermal analysis shows the glass transition temperature between 8 and 18 °C with a melting point around 160 °C. Impedance spectroscopy shows a maximum conductivity value of 4.67 × 10−2 Scm−1 at 130 °C for the sample with 6% of Nb2O5, improving the ionic conductivity with respect to that of PVA:CS + 40% H3PO4 concentrations.

Novel Enhancer for Luminol-AuNP Electrochemiluminescence and Decoration on RNA Membranes for Effective Cytosensing.

Herein, a simple and nice method to synthesize RNA membrane nanostructures for a controlled capture and cytosensing by aptamer and luminol-AuNPs (luAu NPs) is presented. The RNA membrane made up of many RNA transcripts was prepared by a one-pot reaction, the rolling circle transcription (RCT) process using rNTP and RNA polymerase, so the efficient RNA membrane could be obtained successfully at a much lower cost than the system used for RNA molecule synthesis commercially. The modifications of the NH2 group could not degrade the stability of RNA membrane in the serum. The prepared RNA membrane nanostructures showed interesting capture efficiencies toward the Ramos cell due to the effect of aptamer-ligand interactions on the nanostructures. Additionally, based on the detection of the luAu NP electrochemiluminescence (ECL) system, a novel enhancing method was employed by 3-aminopropyl-triethoxysilane (APS) for luAu NP ECL, which has never been reported, to improve the sensitivity. The ECL intensity was proportional to the target cell amounts, and the dynamic range was 50-5000 cells. The detection limit of the target cell amounts reached level 50. The specificity test and recovery test showed that the method had a good selectivity, stability, and repeatability. Therefore, this method will provide a favorable analysis for biosensing.

Development of highly functional membranes through structural control of crystalline/amorphous phases

Molecular entanglements have been thought to restrict a desirable chain orientation during drawing. Therefore, a reduction in chain entanglements has been a focus for manufacturing high-performance fibers and membranes. In contrast, our melt-drawing technique utilizes molecular entanglements as a strain transmitter, achieving a nanoperiodic arrangement in which the crystalline and amorphous phases are interconnected. This periodic structure is similar to microphase separation in block copolymers, in which linked points are located at the boundaries between chemically different phases. The results show highly functional membranes can be successfully prepared from highly entangled homopolymer, as well as block copolymer, using solvent-free procedures. Molecular entanglements (left) divide the crystalline and amorphous phases and are similar to the linked points that cause microphase separation in block copolymer (right). Our melt-drawing technique results in periodic arrangement of these phases and replaces the conventional paradigm of “entanglement exclusion for high performance” with the novel “entanglement utilization for high functionality”. In this review, our recent developments for nanostructured membranes using block copolymers and homopolymers are compared and reviewed based on their structural similarities.

Preparation of cellulose acetate blended with chitosan nanostructured membrane via electrospinning for Cd2+ adsorption in artificial wastewater

This study focused on using chitosan (CS) as the functional polymer in the cellulose acetate (CA) matrix to provide reactive ion exchange sites for heavy metal ions. Pure CA and CA/CS blends (wt % 95:5, 90:10 and 85:15) were electrospun to determine the most qualified blend for the adsorption experiment. The morphologies of the electrospun nanostructured membranes were investigated using Scanning Electron Microscopy. The average fiber diameter was found to decrease with increasing CS concentration. CA and CS interaction was confirmed using Fourier Transform Infrared Spectroscopy. Upon characterization, the blend with 15% CS had the best properties for the adsorption process. The adsorption capacities of pure CA and CA/CS blend at different membrane loading and initial concentration showed a significant increase from 67.25 mg Cd2+/g pure CA membrane to 110.48 mg/g CS doped membrane. The experiment revealed that the adsorption kinetics of pure CA and CA/CS blend for Cd2+ were described by the pseudo-second order reaction model. The adsorption isotherm data for Cd2+on the surface of pure CA and CA/CS blend best fit the Freundlich isotherm and can be used to describe adsorption of Cd2+. This study produced an innovative nanostructured membrane for the removal of Cd2+ in wastewater.

3D polyelectrolyte scaffolds to mimic exocrine glands: a step towards a prostate-on-chip platform

Abstract We report our approach to creating a microfluidic chip (namely UroLOC) that mimics the acinar/tubular structure and the luminal microenvironment of exocrine glands. The chip utilises a nanostructured membrane that is designed to provide a 3-dimensional supporting scaffold for the growth of exocrine acinus epithelial cells. The nanostructured membrane was produced using layer-by-layer assembly of polyelectrolytes, and formed into 3-dimensional hemispherical cavities and “finger-like” structures in order to mimic the natural architecture of acini found in exocrine glands. We utilised normal (PNT2) and cancerous (PC3, LNCaP) prostate epithelial cells to demonstrate the proof-of-concept of using MALDI (Matrix Assisted Laser Desorption Ionisation) profiling of secretions collected after 48 hours of cell growth, with no concentration or purification steps and without any a priori on the knowledge of targeted proteins. This MALDI profiling analysis of the crude supernatants from 3 different cell lines (PNT2, PC3 and LNCaP) demonstrated the capacity of the MALDI profiling approach to discriminate between the different secretome signatures. The UroLOC concept and secretome profiling that we describe opens new opportunities in terms of liquid-biopsy based diagnosis, particularly for the early stages of carcinogenesis.

Severe Traumatic Brain Injury Induces Early Changes in the Physical Properties and Protein Composition of Intracranial Extracellular Vesicles

Extracellular vesicles (EVs) are membranous nanostructures that can indicate undergoing processes in organs and thus help in diagnostics and prognostics. They are secreted by all cells, contained in body fluids, and able to transfer proteins, lipids and nucleic acids to distant cells. Intracranial EVs were shown to change their composition after severe traumatic brain injury (TBI) and therefore to have biomarker potential to evaluate brain events. Properties of intracranial EVs early after TBI, however, have not been characterized. Here, we assessed cerebrospinal fluid (CSF) up to seven days after isolated severe TBI for physical properties of EVs and their proteins associated with neuroregeneration. These findings were compared with healthy controls and correlated to patient outcome. The study included 17 patients with TBI and 18 healthy controls. EVs in TBI-CSF were visualized by electron microscopy and confirmed by immunoblotting for membrane associated Flotillin-1 and Flotillin-2. Using nanoparticle tracking analysis, we detected the highest range in EV concentration at day 1 after injury and significantly increased EV size at days 4-7. CSF concentrations of neuroregeneration associated proteins Flotillin-1, ADP-ribosylation Factor 6 (Arf6), and Ras-related protein Rab7a (Rab7a) were monitored by enzyme-linked immunosorbent assays. Flotillin-1 was detected solely in TBI-CSF in about one third of tested patients. Unfavorable outcomes included decreasing Arf6 concentrations and a delayed Rab7a concentration increase in CSF. CSF concentrations of Arf6 and Rab7a were negatively correlated. Our data suggest that the brain response within several days after severe TBI includes shedding of EVs associated with neuroplasticity. Extended studies with a larger number of participants and CSF collected at shorter intervals are necessary to further evaluate neuroregeneration biomarker potential of Rab7a, Arf6, and Flotillin-1.

Cells Adhering to 3D Vertical Nanostructures: Cell Membrane Reshaping without Stable Internalization.

The dynamic interface between the cellular membrane and 3D nanostructures determines biological processes and guides the design of novel biomedical devices. Despite the fact that recent advancements in the fabrication of artificial biointerfaces have yielded an enhanced understanding of this interface, there remain open questions on how the cellular membrane reacts and behaves in the presence of sharp objects on the nanoscale. Here we provide a multifaceted characterization of the cellular membrane's mechanical stability when closely interacting with high-aspect-ratio 3D vertical nanostructures, providing strong evidence that vertical nanostructures spontaneously penetrate the cellular membrane to form a steady intracellular coupling only in rare cases and under specific conditions. The cell membrane is able to conform tightly over the majority of structures with various shapes while maintaining its integrity.

In-Situ Measurement of Exhaled Formaldehyde and Acetone Kinetics As Early-Stage Non-Invasive Markers of Lung Disease Using Nanostructured Polymeric Membranes

Early stage discovery of lung cancer can significantly improve patient prognosis. Unfortunately, the impact of a well-known technique such as computed tomography screening on mortality rates is uncertain. It has been postulated that tumor growth may lead to peroxidation of cell membranes and is responsible for the observed emission of volatile organic compounds (VOC’s) such as acetone and formaldehyde. This observation has stimulated significant recent effort in the measurement of these compounds in exhaled breath. While promising approaches have been developed for analyzing average VOC concentrations in exhaled breath, an unrecognized drawback to current efforts is the presumption that gas partitioning between the blood and gas phases occurs so rapidly that the time averaged concentration of collected VOCs is representative of their saturation concentration in the lungs. In fact, when one considers the mass transport resistances encountered, VOC lung concentration is likely to be time-dependent and any sensing approach must have sufficient time resolution to capture the dynamic evolution of this concentration during a typical breath exhalation period of not more than 40 seconds in a high humidity environment. In this presentation, we describe development of an optical exhaled gas sensing approach utilizing a nanostructured polymeric membrane that meets these requirements and demonstrates the dynamic evolution of exhaled breath biomarker concentration. We show that the activity of a solid acid catalyst toward the heterogeneous condensation reactions of immobilized resorcinol reagent with gas-phase acetone and formaldehyde can be preserved even at 100% ambient relative humidity through the incorporation of organic acids such as vanillic or tiglic. The reaction produces a colored flavan and poly-condensation products that permits highly selective and sensitive correlation to acetone and formaldehyde concentrations in exhaled breath. Such behavior relies on the complex heterophase morphology of the membrane as will be described. Figure 1

Optimization of effective parameters in the synthesis of nanopore anodic aluminum oxide membrane and arsenic removal by prepared magnetic iron oxide nanoparicles in anodic aluminum oxide membrane via ultrasonic-hydrothermal method

In this study, a new anodized aluminum oxide (AAO) nanostructure membrane was synthesized by anodization process under a constant voltage, in oxalic acid solution that was improved with trace amounts of sulfuric acid at room temperature. The effect of various parameters on the morphology of the synthesized nanostructures such as voltage, electrolyte composition, anodization time and type of stripping solution were investigated. According to the results, corrosion of the walls, size regularity, diameter and number of the pores increased in the presence of sulfuric acid (0.018 mol.L−1). Nitrogen adsorption-desorption analysis confirmed significant porosity, array and uniformity of the pore size in the synthesized nanoporous membrane. A new modification method was used based on ultrasonic-hydrothermal method to modify the synthesized AAO with Fe3O4/SiO2 nanoparticles for metals and metalloids removal from aqueous solution. In this method, Fe3O4/SiO2 nanoparticles were placed very regularly and uniformly on the surface and inside the pores. This modification was confirmed by characterization techniques. The modified AAO@Fe3O4/SiO2 membrane showed excellent results for removing arsenic from aqueous media.

MoS2 nanosheet as a promising nanostructure membrane for gas separation

We investigated the capability of MoS2 membrane for separation of natural gas mixtures, including CH4/CO2, CH4/H2S and CH4/CO2/H2S mixtures. The permeation mechanisms of the gas molecules through the pore of MoS2 membrane were revealed by gas molecular structure analyzing, orientation of gas molecule in the simulation system and density map. The energy barrier for three types of gas molecules was calculated and showed that gas molecules with the low energy barrier could pass through the MoS2 pore. Hence, the present study introduces MoS2 membrane as a new nanostructure membrane for gas separation in the industries.

Separation of CH4/C2H6 Mixture Using Functionalized Nanoporous Silicon Carbide Nanosheet

A gas separation process by 2D structure membranes has recently been considered. Some nanostructure membranes such as graphene have already been used extensively, but silicon carbide nanosheet (SiCNS) capabilities for gas separation have not been studied yet. Due to properties and structure of this nanosheet, it can be used for gas separation with high permeability and selectivity. In this regard, the separation of alkane mixtures, such as methane/ethane mixtures, is important due to their many industrial applications. Accordingly, we studied the capability of a SiCNS membrane using molecular dynamics simulation technique for separation of the CH4/C2H6 mixture. To separate the gas mixture by a SiCNS membrane, some engineered pores were created on the surface of the membrane. At the same time, some of these pores were functionalized by appropriate chemical groups. The potential of the mean force of methane and ethane molecules was calculated in the path of the pores, and the calculations showed that gas mo...

Quantum tunneling of thermal protons through pristine graphene.

Engineering of atomically thin membranes for hydrogen isotope separation is an actual challenge which has a broad range of applications. Recent experiments [M. Lozada-Hidalgo et al., Science 351, 68 (2016)] unambiguously demonstrate an order-of-magnitude difference in permeabilities of graphene-based membranes to protons and deuterons at ambient conditions, making such materials promising for novel separation technologies. Here we demonstrate that the permeability mechanism in such systems changes from quantum tunneling for protons to quasi-classical transport for heavier isotopes. Quantum nuclear effects exhibit large temperature and mass dependence, modifying the Arrhenius activation energy and Arrhenius prefactor for protons by more than 0.5 eV and by seven orders of magnitude correspondingly. Our findings not only shed light on the separation process for hydrogen isotope ions passing through pristine graphene but also offer new insights for controlling ion transport mechanisms in nanostructured separation membranes by manipulating the shape of the barrier and transport process conditions.

Heat conduction tuning by hyperbranched nanophononic metamaterials

Phonon dispersion and thermal conduction properties of hyperbranched nanostructures with unique topological complexity are theoretically and numerically investigated in this research. We present analytical cantilever-in-mass models to analyze and control the inherent resonance hybridization in hyperbranched nanomembranes containing different configurations and cross sections. We show that these local resonances hosted by hyperbranched nanopillars can generate numerous flat bands in the phonon dispersion relation and dramatically lower the group velocities, consequently resulting in a significant reduction of the thermal conductivity. The applicability of the proposed analytical models in thermal conductivity tuning is demonstrated, and a superior performance in reducing the heat flux in nano-structured membranes is exhibited, which can potentially lead to improved thermoelectric energy conversion devices.