A Homochiral Porous Organic Cage-Polymer Membrane for Enantioselective Resolution.

Membrane-based enantioselective separation is a promising method for chiral resolution due to its low cost and high efficiency. However, scalable fabrication of chiral separation membranes displaying both high enantioselectivity and high flux of enantiomers is still a challenge. Here, the authors report the preparation of homochiral porous organic cage (Covalent cage 3 (CC3)-R)-based enantioselective thin-film-composite membranes using polyamide (PA) as the matrix, where fully organic and solvent-processable cage crystals have good compatibility with the polymer scaffold. The hierarchical CC3-R channels consist of chiral selective windows and inner cavities, leading to favorable chiral resolution and permeation of enantiomers; the CC3-R/PA composite membranes display an enantiomeric excess of 95.2% for R-(+)-limonene over S-(-)-limonene and a high flux of 99.9 mg h-1 m-2. This work sheds light on the use of homochiral porous organic cages for preparing enantioselective membranes and demonstrates a new route for the development of next-generation chiral separation membranes.

Accurate prediction of solvent flux in sub-1-nm slit-pore nanosheet membranes.

Nanosheet-based membranes have shown enormous potential for energy-efficient molecular transport and separation applications, but designing these membranes for specific separations remains a great challenge due to the lack of good understanding of fluid transport mechanisms in complex nanochannels. We synthesized reduced MXene/graphene hetero-channel membranes with sub-1-nm pores for experimental measurements and theoretical modeling of their structures and fluid transport rates. Our experiments showed that upon complete rejection of salt and organic dyes, these membranes with subnanometer channels exhibit remarkably high solvent fluxes, and their solvent transport behavior is very different from their homo-structured counterparts. We proposed a subcontinuum flow model that enables accurate prediction of solvent flux in sub-1-nm slit-pore membranes by building a direct relationship between the solvent molecule-channel wall interaction and flux from the confined physical properties of a liquid and the structural parameters of the membranes. This work provides a basis for the rational design of nanosheet-based membranes for advanced separation and emerging nanofluidics.

Dual-Channel-Ion Conductor Membrane for Low-Energy Lithium Extraction.

The development of energy-efficient and environmentally friendly lithium extraction techniques is essential to meet the growing global demand for lithium-ion batteries. In this work, a dual-channel ion conductor membrane was designed for a concentration-driven lithium-selective ion diffusion process. The membrane was based on a porous lithium-ion conductor, and its pores were modified with an anion-exchange polymer. Thus, the sintered lithium-ion conductors provided highly selective cation transport channels, and the functionalized nanopores with positive charges enabled the complementary permeation of anions to balance the transmembrane charges. As a result, the dual-channel membrane realized an ultrahigh Li+/Na+ selectivity of ∼1389 with a competitive Li+ flux of 21.6 mmol·m-2·h-1 in a diffusion process of the LiCl/NaCl binary solution, which was capable of further maintaining the high selectivity over 7 days of testing. Therefore, this work demonstrates the great potential of the dual-channel membrane design for high-performing lithium extraction from aqueous resources with low energy consumption and minimal environmental impact.

Effect of temperature on the conformation and functionality of poly(N-isopropylacrylamide) (PNIPAM)-grafted nanocellulose hydrogels.

HYPOTHESIS: Poly(N-isopropylacrylamide) [PNIPAM]-grafted cellulose nanofibers (CNFs) are new thermo-responsive hydrogels which can be used for a wide range of applications. Currently, there is no clear understanding of the precise mechanism by which CNFs and PNIPAM interact together. Here, we hypothesize that the physical crosslinking of grafted PNIPAM on CNF inhibits the free movement of individual CNF, which increases the gel strength while sustaining its thermo-responsive properties. EXPERIMENTS: The thermo-responsive behaviour of PNIPAM-grafted CNFs (PNIPAM-g-CNFs), synthesized via silver-catalyzed decarboxylative radical polymerization, and PNIPAM-blended CNFs (PNIPAM-b-CNFs) was studied. Small angle neutron scattering (SANS) combined with Ultra-SANS (USANS) revealed the nano to microscale conformation changes of these polymer hybrids as a function of temperature. The effect of temperature on the optical and viscoelastic properties of hydrogels was also investigated. FINDINGS: Grafting PNIPAM from CNFs shifted the lower critical solution temperature (LCST) from 32 °C to 36 °C. Below LCST, the PNIPAM chains in PNIPAM-g-CNF sustain an open conformation and poor interaction with CNF, and exhibit water-like behaviour. At and above LCST, the PNIPAM chains change conformation to entangle and aggregate nearby CNFs. Large voids are formed in solution between the aggregated PNIPAM-CNF walls. In comparison, PNIPAM-b-CNF sustains liquid-like behaviour below LCST. At and above LCST, the blended PNIPAM phase separates from CNF to form large aggregates which do not affect CNF network and thus PNIPAM-b-CNF demonstrates low viscosity. Understanding of temperature-dependent conformation of PNIPAM-g-CNFs engineer thermo-responsive hydrogels for biomedical and functional applications.

Tailoring the humidity response of cellulose nanocrystal-based films by specific ion effects.

HYPOTHESIS: The optical properties and humidity response of iridescent films made of cellulose nanocrystal (CNC) and polyethylene glycol (PEG) can be tailored by the incorporation of electrolytes chosen based on specific ion effects (SIE). EXPERIMENTS: A series of inorganic salts comprising five different cations and five anions based on the Hofmeister series were mixed with CNC/PEG suspensions, followed by an air-dried process into iridescent solid films. These films were tested in changing relative humidity (RH) environments from 30% to 90% and their photonic properties and mass change monitored. The underlying structures and the mechanism of their formation were quantified in terms of interparticle distance derived from small angle X-ray scattering experiment and pitch size quantified by scanning electron microscope (SEM). FINDINGS: The specific color and color range of CNC/PEG based films are controlled by a specific anion effect achieved by selection of the salt while the specific cation effect is negligible. The salting-in type anions with the same valency result in a red-shift color when films are in the dried state. The salting-in type leads to a greater color changing range during RH changes than the salting-out type. The resultant mass gain/loss trend is consistent with the color change. In contrast, cations do not show any relationships between salting-in effect and the measured properties as observed for anions. The observed SIE can be used to engineer CNC/polymer-based humidity and bio-diagnostic colorimetric indicator devices.

Extrusion and 3D printing of novel lipid-polymer blends for oral drug applications.

Lipids are interesting biological materials that can offer a number of pharmaceutical benefits when used as carriers for drug delivery. However, 3D printing of lipids alone by fused deposition processing techniques is very difficult as they have very poor mechanical properties that cause their filaments to fail when they are loaded into a fused deposition 3D printer. If this problem could be overcome, then lipids could be 3D printed into bespoke tablets and assist progress towards such personalised medicines. This work aims to improve the mechanical properties of lipid filaments by developing novel lipid-EVA (ethylene vinyl acetate) blends suitable for 3D printing. Different types of lipids in varying proportions were melt blended with EVA and extruded using a micro compounder. The ultimate printability of the materials was tested by feeding the filaments into a material extrusion 3D printer. Flexural testing of the extruded blends demonstrates that a good balance between the strength and flexibility is required for a material to be printable and it was found that a filament has to have a modulus/strength ratio between 8 and 25 in order to be printable. SEM analysis of the fracture surface shows a network structure within the lipid matrix that could be playing a role in the improved properties of the best performing blends. DSC thermograms show a shift in thermal transitions, suggesting some level of miscibility of the components that could have contributed to a more robust structure. The TGA results show an onset of degradation of the blends greater than 200 °C, indicating that the materials can readily withstand the extrusion and printing temperatures. This study demonstrates the successful extrusion and 3D printing of novel EVA-lipid blends with lipid contents of up to 90%.

Detecting subtle yet fast skeletal muscle contractions with ultrasoft and durable graphene-based cellular materials.

Human bodily movements are primarily controlled by the contractions of skeletal muscles. Unlike joint or skeletal movements that are generally performed in the large displacement range, the contractions of the skeletal muscles that underpin these movements are subtle in intensity yet high in frequency. This subtlety of movement makes it a formidable challenge to develop wearable and durable soft materials to electrically monitor such motions with high fidelity for the purpose of, for example, muscle/neuromuscular disease diagnosis. Here we report that an intrinsically fragile ultralow-density graphene-based cellular monolith sandwiched between silicone rubbers can exhibit a highly effective stress and strain transfer mechanism at its interface with the rubber, with a remarkable improvement in stretchability (>100%). In particular, this hybrid also exhibits a highly sensitive, broadband-frequency electrical response (up to 180 Hz) for a wide range of strains. By correlating the mechanical signal of muscle movements obtained from this hybrid material with electromyography, we demonstrate that the strain sensor based on this hybrid material may provide a new, soft and wearable mechanomyography approach for real-time monitoring of complex neuromuscular-skeletal interactions in a broad range of healthcare and human-machine interface applications. This work also provides a new architecture-enabled functional soft material platform for wearable electronics.

Rapid Detection of Gram-Positive and -Negative Bacteria in Water Samples Using Mannan-Binding Lectin-Based Visual Biosensor.

Waterborne bacterial infection is a health threat worldwide, making accurate and timely bacteria detection crucial to prevent waterborne disease outbreaks. Inspired by the intrinsic capability of mannan-binding lectin (MBL) in recognizing the pathogen-associated molecular patterns (PAMPs), a visual biosensor is developed here for the on-site detection of both Gram-positive and -negative bacteria. The biosensor was synthesized by immobilization of the MBL protein onto the blue carboxyl-functionalized polystyrene microparticles (PSM), which is then used in a two-step assay to detect bacterial cells in water samples. The first step involved a 20 min incubation following the MBL-PSM and calcium chloride solution addition to the samples. The second step was to add ethanol to the resultant blue mixture and observe the color change with the naked eye after 15 min. The biosensor had a binary (all-or-none) response, which in the presence of bacterial cells kept its blue color, while in their absence the color changed from blue to colorless. Testing the water samples spiked with four Gram-negative bacteria including Acinetobacter baumannii, Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa and two Gram-positive bacteria of Enterococcus faecalis and Staphylococcus aureus showed that the biosensor could detect all tested bacteria with a concentration as low as 101.5 CFU/ml. The performance of biosensor using the water samples from a water treatment plant also confirmed its capability to detect the pathogens in real-life water samples without the need for instrumentation.

Thermoresponsive Poly(N-isopropylacrylamide) Grafted from Cellulose Nanofibers via Silver-Promoted Decarboxylative Radical Polymerization.

A family of thermoresponsive poly(N-isopropylacrylamide) [PNIPAM]-grafted cellulose nanofibers (CNFs) was synthesized via a novel silver-promoted decarboxylative polymerization approach. This method relies on the oxidative decarboxylation of carboxylic acid groups to initiate free radicals on the surface of CNFs. The polymerization reaction employs relatively mild reaction conditions and can be performed in a one-step, one-pot fashion. This rapid reaction forms a C─C bond between CNF and PNIPAM, along with the formation of free polymer in solution. The degree of functionalization (DF) and the amount of PNIPAM grafted can be controlled by the Ag concentration in the reaction. Similar to native bulk PNIPAM, PNIPAM-grafted CNFs (PNIPAM-g-CNFs) show remarkable thermoresponsive properties, albeit exhibiting a slight hysteresis between the heating and cooling stages. Grafting PNIPAM from CNFs changes its cloud point from about 32 to 36 °C, influenced by the hydrophilic nature of CNFs. Unlike physical blending, covalently tethering PNIPAM transforms the originally inert CNFs into thermosensitive biomaterials. The Ag concentration used does not significantly change the cloud point of PNIPAM-g-CNFs, while the cloud point slightly decreases with fiber concentration. Rheological studies demonstrated the sol-gel transition of PNIPAM-g-CNFs and revealed that the storage modulus (G') above cloud point increases with the amount of PNIPAM grafted. The novel chemistry developed paves the way for the polymerization of any vinyl monomer from the surface of CNFs and carbohydrates. This study validates a novel approach to graft PNIPAM from CNFs for the synthesis of new thermoresponsive and transparent hydrogels for a wide range of applications.

Modulating the chiral nanoarchitecture of cellulose nanocrystals through interaction with salts and polymer.

HYPOTHESIS: The conditions to allow self-assembly of cellulose nanocrystal (CNC) suspensions into chiral nematic structures are based on aspect ratio, surface charge density and a balance between repulsive and attractive forces between CNC particles. EXPERIMENTS: Three types of systems were characterized in suspensions and subsequently in their solid dried films: 1) neat water dialyzed CNC, 2) CNC combined with polyethylene glycol(PEG) (CNC/PEG), and 3) CNC with added salt (CNC/Salt). All suspensions were characterized by polarized optical microscope (POM) and small angle X-ray scattering (SAXS), while the resultant dried films were analyzed by reflectance spectrometer, scanning electron microscope (SEM) and SAXS. FINDINGS: The presence of chiral nematic (CN*) structures was not observed in dialyzed aqueous suspensions of CNC during water evaporation. By introducing salts or a non-adsorbing polymer, chirality was apparent in both suspensions and films. The interaxial angle between CNC rods increased when the suspensions of CNC/PEG and CNC/salt were dried to solid films. The angle was found to be dependent on both species of ions and ionic strength, while the inter-particle distance was only related to the salt concentration, as explained in terms of interaction energies. The CNC suspensions/film chirality can be modulated by controlling the colloidal forces.

A 3D-Printed Polymer-Lipid-Hybrid Tablet towards the Development of Bespoke SMEDDS Formulations.

3D printing is a rapidly growing area of interest within pharmaceutical science thanks to its versatility in creating different dose form geometries and drug doses to enable the personalisation of medicines. Research in this area has been dominated by polymer-based materials; however, for poorly water-soluble lipophilic drugs, lipid formulations present advantages in improving bioavailability. This study progresses the area of 3D-printed solid lipid formulations by providing a 3D-printed dissolvable polymer scaffold to compartmentalise solid lipid formulations within a single dosage form. This allows the versatility of different drugs in different lipid formulations, loaded into different compartments to generate wide versatility in drug release, and specific control over release geometry to tune release rates. Application to a range of drug molecules was demonstrated by incorporating the model lipophilic drugs; halofantrine, lumefantrine and clofazimine into the multicompartmental scaffolded tablets. Fenofibrate was used as the model drug in the single compartment scaffolded tablets for comparison with previous studies. The formulation-laden scaffolds were characterised using X-ray CT and dispersion of the formulation was studied using nephelometry, while release of a range of poorly water-soluble drugs into different gastrointestinal media was studied using HPLC. The studies show that dispersion and drug release are predictably dependent on the exposed surface area-to-volume ratio (SA:V) and independent of the drug. At the extremes of SA:V studied here, within 20 min of dissolution time, formulations with an SA:V of 0.8 had dispersed to between 90 and 110%, and completely released the drug, where as an SA:V of 0 yielded 0% dispersion and drug release. Therefore, this study presents opportunities to develop new dose forms with advantages in a polypharmacy context.

Modulating transparency and colour of cellulose nanocrystal composite films by varying polymer molecular weight.

HYPOTHESIS: Cellulose nanocrystals (CNC) can produce photonic composite films that selectively reflect light based on their periodic cholesteric structure. The hypothesis of this research is that by incorporating water-soluble polymer, photonic properties of CNC composite film can be designed by manipulating the polymer molecular weight. EXPERIMENTAL: Flexible free-standing composite films of five different poly (ethylene glycol) (PEG) molecular weights were prepared via air drying under a controlled environment, and characterised by reflectance UV-vis spectrometer, atomic force microscopy (AFM) and scanning electron microscopy (SEM). Films with each molecular weight were investigated over a concentration range. FINDINGS: The colour and transmission haze of the composite films was modified by varying both the PEG molecular weight and concentration. Depending on the molecular weight, the films were able to reflect light from the UV region (242 nm) across the visible spectrum to the near-infrared region (832 nm). Different trends in variation of the reflected light based on the molecular weight was found with increasing PEG concentration and was explained by weak depletion interactions occurring between CNC and PEG, which was reduced with increasing PEG molecular weight.

Grafting Nature-Inspired and Bio-Based Phenolic Esters onto Cellulose Nanocrystals Gives Biomaterials with Photostable Anti-UV Properties.

Invited for this month's cover is the international collaborative work from the Bioresource Processing Research Institute of Australia (BioPRIA)-Monash University and URD Agro-Biotechnologies Industrielles (ABI)-AgroParisTech. The cover image shows how the grafting of Nature-inspired and bio-based phenolic esters on cellulose nanocrystals through click-chemistry provides materials with highly photostable UV-blocking properties. Cover art by David Mendoza. The Full Paper itself is available at 10.1002/cssc.202002017.

Grafting Nature-Inspired and Bio-Based Phenolic Esters onto Cellulose Nanocrystals Gives Biomaterials with Photostable Anti-UV Properties.

New nature-inspired and plant-derived p-hydroxycinnamate esters and p-hydroxycinnamate diesters provide excellent protection against UV radiation when incorporated into a matrix. Herein, an efficient and sustainable pathway is reported to graft these phenolic compounds onto cellulose nanocrystals (CNCs) via click-type copper-catalyzed azide/alkyne cycloaddition (CuAAC) reaction. The successful grafting of the phenolic esters on CNC surface was evidenced by a range of chemical analyses, and the degrees of substitution (DS) of the CNC were found to depend on the structure of the phenolic ester grafted. Moreover, aqueous suspensions of the phenolic ester-grafted CNCs not only strongly absorb in both the UVA and UVB regions, but they also exhibit average to very high photostability. Their wide spectrum UV-absorbing properties and their stability upon exposure to UV are highly influenced by the structure of the phenolic ester, particularly by the extra ester group in p-hydroxycinnamate diesters. These findings demonstrate that cellulose nanocrystals decorated with such plant-derived and nature-inspired phenolic esters are promising sustainable nanomaterials for anti-UV applications.

Selective Permeation of Water through Angstrom-Channel Graphene Membranes for Bioethanol Concentration.

Graphene-based laminate membranes have been theoretically predicted to selectively transport ethanol from ethanol-water solution while blocking water. Here, robust angstrom-channel graphene membranes (ACGMs) fabricated by intercalating carbon sheets derived from chitosan into thermally reduced graphene oxide (GO) sheets are reported. ACGMs with robust and continuous slit-shaped pores (an average pore size of 3.9 Å) are investigated for the dehydration of ethanol. Surprisingly, only water permeates through ACGMs in the presence of aqueous ethanol solution. For the water-ethanol mixture containing 90 wt% ethanol, water can selectively permeate through ACGMs with a water flux of 63.8 ± 3.2 kg m-2 h-1 at 20 °C and 389.1 ± 19.4 kg m-2 h-1 at 60 °C, which are over two orders of magnitude higher than those of conventional pervaporation membranes. This means that ACGMs can effectively operate at room temperature. Moreover, the ethanol can be fast concentrated to high purity (up to 99.9 wt%). Therefore, ACGMs are very promising for production of bioethanol with high efficiency, thus improving its process sustainability.

Controlling the transparency and rheology of nanocellulose gels with the extent of carboxylation.

TEMPO and periodate are combined in a one-shot reaction to oxidise cellulose and produce nanocellulose gels with a wide range of degree of substitution (DS). Highly-oxidised cellulose nanofibres with a high charge of -80 mV were produced. The strong electrical repulsion between TEMPO-periodate oxidised nanofibres (TPOF) results in the formation of well-separated nanofibres with a diameter of 2-4 nm, albeit depolymerised due to high oxidation. TPOF produces highly-transparent gels due to smaller aspect ratio and high surface charge. These properties induce a reduced viscosity and moduli of the gels by decreasing fibre entanglement. TPOF gels are more stable at basic pH and high ionic strength than TEMPO-oxidised gels due to their higher surface charge. Freeze-dried TPOF gels also exhibit remarkable water holding capacity due to enhanced immobilisation of water molecules. The excellent optical properties of the highly transparent gel for red blood cells analysis open new possibilities in diagnostics application.

Electrolyte gating in graphene-based supercapacitors and its use for probing nanoconfined charging dynamics.

Graphene-based nanoporous materials have been extensively explored as high-capacity ion electrosorption electrodes for supercapacitors. However, little attention has been paid to exploiting the interactions between electrons that reside in the graphene lattice and the ions adsorbed between the individual graphene sheets. Here we report that the electronic conductance of a multilayered reduced graphene oxide membrane, when used as a supercapacitor electrode, can be modulated by the ionic charging state of the membrane, which gives rise to a collective electrolyte gating effect. This gating effect provides an in-operando approach for probing the charging dynamics of supercapacitors electrically. Using this approach, we observed a pore-size-dependent ionic hysteresis or memory effect in reduced graphene oxide membranes when the interlayer distance is comparable to the ion diameter. Our results may stimulate the design of novel devices based on the ion-electron interactions under nanoconfinement.

Development of a Paper-Based Microfluidic System for a Continuous High-Flow-Rate Fluid Manipulation.

The current study describes the development of a disposable paper-based microfluidic system, which unlike its predecessors that are only capable of processing a small amount of fluid, can continuously process the fluid at a high flow rate of up to 1.5 mL/min. The fabrication procedure was clean-room-free and robust, involving the use of a CO2 laser to engrave the microchannels on a paper substrate, followed by alkenyl ketene dimer treatment to hydrophobize the paper and lamination. The microchannel down to a minimum depth of ∼80 µm with an average roughness of ∼8 µm was engraved on the substrate. As a proof of concept, the applicability of this system to enrich the microparticles based on the inertial focusing mechanism was tested. This new generation of paper-based microfluidic system can be potentially used for the diagnostic applications where the analyte is low in quantity and processing a large volume of fluid sample is required.

Vertically Aligned Gold Nanowires as Stretchable and Wearable Epidermal Ion-Selective Electrode for Noninvasive Multiplexed Sweat Analysis.

The noninvasive continuous analysis of human sweat is of great significance for improved healthcare diagnostics and treatment in the future, for which a wearable potentiometry-based ion-selective electrode (ISE) has attracted increasing attention, particularly involving ion detection. Note that traditional solid-state ISE electrodes are rigid ion-to-electron transducers that are not conformal to soft human skin and cannot function under stretched states. Here, we demonstrated that vertically aligned mushroom-like gold nanowires (v-AuNW) could serve as stretchable and wearable ion-to-electron transducers for multiplexed, in situ potentiometric analysis of pH, Na+, and K+ in sweat. By modifying v-AuNW electrodes with polyaniline, Na ionophore X, and a valinomycin-based selective membrane, we could specifically detect pH, Na+, and K+, respectively, with high selectivity, reproducibility, and stability. Importantly, the electrochemical performance could be maintained even under 30% strain and during stretch-release cycles without the need of extrinsic structural design. Furthermore, our stretchable v-AuNW ISEs could be seamlessly integrated with a flexible printed circuit board, enabling wireless on-body detection of pH, Na+, and K+ with fast response and negligible cross-talk, indicating considerable promise for noninvasive wearable sweat analysis.

Polycrystalline Advanced Microporous Framework Membranes for Efficient Separation of Small Molecules and Ions.

Advanced porous framework membranes with excellent selectivity and high permeability of small molecules and ions are highly desirable for many important industrial separation applications. There has been significant progress in the fabrication of polycrystalline microporous framework membranes (PMFMs) in recent years, such as metal-organic framework and covalent organic framework membranes. These membranes possess small pore sizes, which are comparable to the kinetic diameter of small molecules and ions on the angstrom scale, very low thickness, down to tens to hundreds of nanometers, highly oriented crystalline structures, hybrid membrane structures, and specific functional groups for enhancing membrane selectivity and permeability. Recent advances in the fabrication methods of advanced PMFMs are summarized. Following this, four emerging separation applications of these advanced microporous framework membranes, including gas separation, water desalination, ion separation, and chiral separation, are highlighted and discussed in detail. Finally, a summary and some perspectives of future developments and challenges in this exciting research field are presented.