Low Packing Density Research Articles

Shore hardness of bulk polyurethane affects the properties of nanofibrous materials differently

The present study shows the effect of the hardness of bulk polyurethane on the properties of nanofibrous materials produced in the solution blow spinning process. This study focuses on nanofibrous materials made from medical-grade polyurethanes with different hardness values on the Shore scale, from 75A to 75D. We aimed to determine the effect of the intrinsic properties of polyurethane used to produce nanofibers on the tensile properties of the resulting nanofibrous materials and in vitro platelet adhesiveness. This study used a solution blow spinning process to produce nanofibrous materials from polyurethane solutions. It evaluates their properties using scanning electron microscopy, followed by porosity determination, tensile testing, and platelet adhesion assays. Generally, the bulk polymer's Shore hardness affects nanofibrous products' porosity and tensile properties. In the tested Shore hardness range, the most visible differences in material properties were observed for the fibers produced from the hardest (75D) and softest (75A) polyurethanes. The nanofibrous material produced using 75D polyurethane exhibited the highest porosity, up to approximately 0.87, owing to the low packing density of the stiff nanofibers. It also remained the stiffest, with the highest Young’s modulus. On the other hand, the softest 75A polyurethane produced a less porous nanofibrous mat with the highest tensile strength among the tested polyurethanes. All tested nanofibrous materials retained their platelet adhesion resistance upon processing into nanofibers, with a mean platelet coverage below 1 % of the nanofibrous mat surface. The study results provide insights into the relationship between the hardness of bulk polyurethane and the properties of nanofibrous materials, which can be useful in various biomedical applications, particularly in producing tissue-engineered vascular grafts.

Cu3.21Bi4.79S9: Bimetal superionic strategy boosts ultrafast dynamics for Na-ion storage/extraction

Traditional metal sulfides used as anodes for sodium-ion batteries are hindered by sluggish kinetics, which limits their rate performance. Previous attempts to address this issue focused on nanostructured configurations with conductive frameworks. However, these nanomaterials often suffer from low packing density and the tendency for nanoparticles to agglomerate, posing significant challenges for practical applications. To overcome these limitations, this study presents a novel bimetal superionic anode material Cu3.21Bi4.79S9, which effectively resolves the conflict between sluggish kinetics and micrometer-scale particle size. By leveraging the vacancies created by free Cu and Bi atoms, this material forms rapid migration channels during sodium insertion and extraction, significantly reducing the migration barriers for sodium ions. The development of micrometer-scale Cu3.21Bi4.79S9 enables ultrafast charging-discharging capabilities, achieving a reversible capacity of 325.5 mAh g−1 after 4000 cycles at a high rate of 45 C (15 A g−1). This work marks a significant advancement in the field by offering a solution to the inherent trade-off between high capacity and rate performance in coarse-grained materials, reducing the need for reliance on nanostructured configurations for next-generation high-capacity anode materials.

Engineering Microgel Packing to Tailor the Physical and Biological Properties of Gelatin Methacryloyl Granular Hydrogel Scaffolds.

Granular hydrogel scaffolds (GHS) are fabricated via placing hydrogel microparticles (HMP) in close contact (packing), followed by physical and/or chemical interparticle bond formation. Gelatin methacryloyl (GelMA) GHS have recently emerged as a promising platform for biomedical applications; however, little is known about how the packing of building blocks, physically crosslinked soft GelMA HMP, affects the physical (pore microarchitecture and mechanical/rheological properties) and biological (in vitro and in vivo) attributes of GHS. Here, the GHS pore microarchitecture is engineered via the external (centrifugal) force-induced packing and deformation of GelMA HMP to regulate GHS mechanical and rheological properties, as well as biological responses in vitro and in vivo. Increasing the magnitude and duration of centrifugal force increases the HMP deformation/packing, decreases GHS void fraction and median pore diameter, and increases GHS compressive and storage moduli. MDA-MB-231 human triple negative breast adenocarcinoma cells spread and flatten on the GelMA HMP surface in loosely packed GHS, whereas they adopt an elongated morphology in highly packed GHS as a result of spatial confinement. Via culturing untreated or blebbistatin-treated cells in GHS, the effect of non-muscle myosin II-driven contractility on cell morphology is shown. In vivo subcutaneous implantation in mice confirms a significantly higher endothelial, fibroblast, and macrophage cell infiltration within the GHS with a lower packing density, which is in accordance with the in vitro cell migration outcome. These results indicate that the packing state of GelMA GHS may enable the engineering of cell response in vitro and tissue response in vivo. This research is a fundamental step forward in standardizing and engineering GelMA GHS microarchitecture for tissue engineering and regeneration.

On the Relation between the Viscoelastic Properties of Granular Hydrogels and Their Performance as Support Materials in Embedded Bioprinting.

Granular hydrogels, formed by jamming microgels suspension, are promising materials for three-dimensional bioprinting applications. Despite their extensive use as support materials for embedded bioprinting, the influence of the particle's physical properties on the macroscale viscoelasticity on one hand and on the printing performance on the other hand remains unclear. Herein, we investigate the linear and nonlinear rheology of κ-carrageenan granular hydrogel through small- and large-amplitude oscillatory shear measurements. We tuned the granular hydrogel's properties by changing the stiffness (soft, medium, stiff) and the packing density of the individual microgels. Characterizations in the linear viscoelasticity regime revealed that the storage modulus of granular hydrogels is not a simple function of microgel stiffness and depends on the microgel packing density. At larger strains, increasing the microgel stiffness reduced the energy dissipation of the granular beds and increased the solid-fluid transition point. To understand how the different rheological properties of granular support materials influence embedded bioprinting, we examined the printing fidelity and cellular filament shrinkage within the granular beds. We found that microgels with low packing density diminished the printing quality, while stiff microgels promoted filament roughness. In addition, we found that highly packed stiff microgels significantly reduced the postprinting contraction of cellular filaments. Overall, this work provides a comprehensive knowledge of the rheology of granular hydrogels that can be used to rationally design support beds for bioprinting applications with specific characteristics.

Scalable Self-Assembly of Composite Nanofibers into High-Energy-Density Li-Ion Battery Electrodes.

The application of nanosized active particles in Li-ion batteries has been the subject of intense investigation, yielding mixed results in terms of overall benefits. While nanoparticles have shown promise in improving rate performance and reducing issues related to cracking, they have also faced criticism due to side reactions, low packing density, and consequent subpar volumetric battery performance. Interesting processes such as self-assembly have been proposed to increase packing density, but these tend to be incompatible with scalable processes such as roll-to-roll coating, which are essential to manufacture electrodes at scale. Addressing these challenges, this research demonstrates the long-range self-assembly of carbon-decorated V2O5 nanofiber cathodes as a model system. These nanorods are closely packed into thick electrode films, exhibiting a high volumetric capacity of 205 mA h cm-3at 0.2 C. This surpasses the volumetric capacity of unaligned V2O5 nanofiber electrodes (82 mA h cm-3) under the same cycling conditions. We also demonstrate that these energy-dense electrodes retain an excellent capacity of up to 190.4 mA h cm-3(<2% loss) over 500 cycles without needing binders. Finally, we demonstrate that the proposed self-assembly process is compatible with roll-to-roll coating. This work contributes to the development of energy-dense coatings for next-generation battery electrodes with high volumetric energy density.

Proteome-Wide Assessment of Protein Structural Perturbations under High Pressure

One of the planet's more understudied ecosystems is the deep biosphere, where organisms can experience high hydrostatic pressures (30–110 MPa); yet, by current estimates, these subsurface and deep ocean zones host the majority of the Earth's microbial and animal life. The extent to which terrestrially relevant pressures up to 100 MPa deform most globular proteins—and which kinds—has not been established. Here, we report the invention of an experimental apparatus that enables structural proteomic methods to be carried out at high pressures for the first time. The method, called high-pressure limited proteolysis (Hi-P LiP), involves performing pulse proteolysis on whole cell extracts brought to high pressure. The resulting sites of proteolytic susceptibility induced by pressure are subsequently read out by sequencing the peptide fragments with tandem liquid chromatography–mass spectrometry. The method sensitively detects pressure-induced structural changes with residue resolution and on whole proteomes, providing a deep and broad view of the effect of pressure on protein structure. When applied to a piezosensitive thermophilic bacterium, , we find that approximately 40% of its soluble proteome is structurally perturbed at 100 MPa. Proteins with lower charge density are more resistant to pressure-induced deformation, as expected; however, contrary to expectations, proteins with lower packing density (i.e., more voids) are also more resistant to deformation. Furthermore, high pressure has previously been shown to preferentially alter conformations around active sites. Here, we show this is also observed in Hi-P LiP, suggesting that the method could provide a generic and unbiased modality to detect binding sites on a proteome scale. Hence, data sets of this kind could prove useful for training emerging artificial intelligence models to predict cryptic binding sites with greater accuracy. Published by the American Physical Society 2024

Sandwich-structured bimodal fiber/bead-on-string fiber composite membrane for comfortable PM0.3 filter

Particulate matter (PM) pollution causes critical harm to human health and global environment. However, the protective respirators attain high-performance filtration of the most permeable PM0.3 by tight stacking of fibers and seriously compromising their wearing comfort. Herein, a fluffy sandwich-structured membrane (SSM) composed of bimodal fibrous layers and bead-on-string fibrous layer is designed to endow the air filter with both high-performance filtration and superior thermal-wet comfort. Based on the electrospinning technique, the bimodal fibers made of nano-/submicron-fibers (about 46 nm and 155 nm) are formed by inducing the jet splitting while the bead-on-string fibers consisting of submicron-fibers (≈ 120 nm) and micro-beads (≈ 3.37 μm) are prepared through manipulating the Rayleigh instability of jets. Due to the structural design of small pores and low packing density, the SSM exhibits excellent PM0.3 removal of 99.8%, low filtration resistance of 65 Pa, and high quality factor of 0.097 Pa-1. It also shows long-term filtration stability and durability under high humidity conditions. Moreover, the SSM simultaneously possesses superior thermal-wet comfort of heat dissipation, air permeability of 164 mm·s-1, and water vapor transmission of 7.6 kg·m-2·d-1. This work may offer a novel insight for exploiting high-performance and comfortable personal protective materials.

Pressure‐Induced Dense and Robust Ge Architecture for Superior Volumetric Lithium Storage

AbstractThe germanium (Ge) anode attains wide attention in lithium‐ion batteries because of its high theoretical volumetric capacity (8646 mAh cm−3). However, the huge volume expansion (≈230%) results in its poor electrochemical performances. The strategies reported in the literature to solve the issue often cause a low packing density, lowering the volumetric capacity. Here, a pressure‐induced route is proposed to fabricate a Ge architecture, in which nano‐sized Ge (≈15 nm) is encapsulated by robust TiO2 and highly conductive carbon, which offer the advantages of a low stress–strain characteristic, low volume expansion in thickness change, high electrical conductivity (463.2 S m−1), high Li‐ion diffusion coefficient (9.55 × 10−9–8.51 × 10−12 cm2 s−1), and high tapping density (1.79 g cm−3). As a result, the dense architecture obtains outstanding volumetric capacities of 3559.8 mAh cm−3 at 0.1 A g−1 and 2628.2 mAh cm−3 at 20 A g−1, along with excellent cycling life over 5000 cycles at 10 A g−1. Remarkably, the full cell achieves a high volumetric energy density of 1760.1 Wh L−1, along with impressive fast‐charging performances and long cycling life. This work provides a new synthesis strategy and deep insight into the design of high‐volumetric capacity alloy‐based lithium‐ion‐battery anodes.

Transparent and antibacterial air filters based on nanofiber/nets membrane

Air pollution is a serious human health issue worldwide, especially the pollution of particulate matter (PM) and the spread of airborne bacteria. However, most existing filters are opaque, have limited filtration efficiency and no antimicrobial properties. We report an electrospinning/netting technology to prepare high-performance and transparent air filters with antibacterial properties. By regulating the ejection and phase separation of charged droplets, nanofiber/nets (NFN) membrane is created. The resulting NFN filter has integrated properties of low packing density (0.32 g cm−3), high porosity (85 %), desirable pore size (280 nm), robust tensile strength (12.8 MPa) and high PM0.3 removal efficiency (99.996 %). Furthermore, the NFN filter also exhibits ideal transparency (90 %) and excellent bactericidal rate (99.99 %). This work should be a positive attempt to develop efficient, transparent and antibacterial filtration materials.

Spreading Behavior of Non-Spherical Particles with Reconstructed Shapes Using Discrete Element Method in Additive Manufacturing.

The spreading behavior of particles has a significant impact on the processing quality of additive manufacturing. Compared with spherical metal material, polymer particles are usually non-spherical in shape. However, the effects of particle shape and underlying mechanisms remain unclear. Here, the spreading process of particles with reconstructed shapes (non-spherical particles decomposed into several spherical shapes by stereo-lithography models) are simulated by integrating spherical particles with the discrete element method. The results show that more cavities form in the spreading beds of particles with reconstructed shapes than those of spheres with blade spreading. Correspondingly, particles with reconstructed shapes have lower packing densities, leading to more uniform packing patterns. Slow propagation speeds of velocity and angular velocity lead to "right-upwards" turning boundaries for particles with reconstructed shapes and "right-downwards" turning boundaries for spherical particles. Moreover, as the blade velocity increases, the packing density decreases. Our calculation results verify each other and are in good agreement with the experiment, providing more details of the behavior of non-spherical particles before additive manufacturing. The comprehensive comparison between polymer non-spherical particles and spherical particles helps develop a reasonable map for the appropriate choice of operating parameters in real processes.

Limitations of Liquid Electrolyte RDE Experiments for the Determination of OER Catalyst Activity: The Effect of the Catalyst Layer Thickness

Developing novel oxygen evolution reaction (OER) noble metal catalysts with a low metal packing density is key for the wider large-scale implementation of polymer electrolyte membrane water electrolysis (PEMWE). OER activities of these new catalysts are commonly measured in liquid electrolytes using half-cell configurations, such as rotating-ring-disk electrodes (RDE). Recent studies in liquid electrolyte cells showed that the accumulation of microscopic oxygen bubbles within the OER catalyst layer causes shielding of active catalyst sites. In this study, three different OER catalysts were screened for their activity at different loadings in a liquid electrolyte RDE setup. Potential sweeps using bare Ir black, a commercially available IrO2/TiO2 and a homemade Ir/ATO (antimony doped tin oxide) catalyst with different loadings were performed. It was demonstrated that the mass activity of the Ir/ATO catalyst decreases by more than 50% with a catalyst loading increase, which is attributed to the accumulation of microscopic oxygen bubbles within the catalyst layer and was correlated to the coating thickness of the catalyst layer. We suggest screening the OER catalyst activity of low packing catalyst materials in a loading analysis by testing minimum three different loadings within the kinetic Tafel slope region to avoid underestimation of the catalyst activity.

Flexible Antireflection Coatings with Enhanced Durability and Antifogging Properties.

Antireflection coatings (ARCs) enhance optical clarity and improve light transmission by reducing glare and reflections. The application of conventional ARCs in flexible devices, however, is impeded by their lack of durability, particularly under bending deformation. We develop ARCs that withstand delamination and fracture, remaining intact even after 1000 bending cycles with a 5 cm bending radius. We fabricate integrated ARCs (iARCs) on a poly(methyl methacrylate) (PMMA) substrate by inducing free polymers to infiltrate the interstices of a disordered assembly of hollow silica nanochains and nanospheres. The polydispersity of PMMA creates a refractive index gradient, yielding a broadband antireflection capability. The nanochain-based iARCs are superior to the nanosphere-based coatings in both antireflection properties and mechanical durability, owing to the lower packing density and mechanical interlocking of the nanochains, respectively. Additionally, these nanochain iARCs display antifogging properties stemming from their superhydrophilicity. While our demonstrations are based on PMMA as a model substrate, this methodology is potentially extendable to other polymers, enhancing the iARC's applicability across various practical applications, including flexible and wearable devices.

Spherical Crystallization Based on Liquid-Liquid Phase Separation in a Reverse Antisolvent Crystallization Process

Vanillin crystals undergo needle-like morphology that results in poor flowability, crystal breakage, and low packing density. The spherical crystallization technology can produce particles with improved flowability and stability. A reverse antisolvent crystallization based on liquid-liquid phase separation is proposed in this work to produce vanillin spherical agglomerates. Hansen Solubility Parameters are applied to explain the liquid-liquid phase separation (LLPS) phenomenon. The Pixact Crystallization Monitoring system is applied to in-situ monitor the whole process. A six-step spherical crystallization mechanism is revealed based on the recorded photos, including the generation of oil droplets, nucleation inside oil droplets, the coalescence and split of oil droplets, crystal growth and agglomeration, breakage of oil droplets, and attrition of agglomerates. Different working conditions are tested to explore the best operation parameters and a frequency-conversion stirring strategy is proposed to improve the production of spherical crystals.

Double-Stranded DNA Immobilized in Lying-Flat and Upright Orientation on a PNIPAm-Coated Surface: A Theoretical Study.

Surface-immobilized double-stranded DNA (dsDNA) in upright orientation plays an important role in optimizing and understanding DNA-based nanosensors and nanodevices. However, it is difficult to regulate the surface density of upright DNA due to the fact that DNA usually stands vertically at a high packing density but may lie down at a low packing density. We herein report dsDNA immobilized in upright orientation on a poly(N-isopropylacrylamide) (PNIPAm)-coated surface in theory. The theoretical results reveal that the angle of upright DNA relative to the surface is larger than that of DNA immobilized on the bare surface caused by the lying-flat DNA under proper PNIPAm surface coverage at 45 °C. The surface density of upright DNA is significantly influenced by DNA concentration and DNA length. It is envisioned that the density-regulated DNA molecules immobilized in upright orientation in the present work are well suited to bottom-up construction of complex DNA-based nanostructures and nanodevices.

Using Hierarchically Structured, Nanoporous Particles as Building Blocks for NCM111 Cathodes.

Nanoparticles have many advantages as active materials, such as a short diffusion length, low charge transfer resistance, or a reduced probability of cracking. However, their low packing density makes them unsuitable for commercial battery applications. Hierarchically structured microparticles are synthesized from nanoscale primary particles by targeted aggregation. Due to their open accessible porosity, they retain the advantages of nanomaterials but can be packed much more densely. However, the intrinsic porosity of the secondary particles leads to limitations in processing properties and increases the overall porosity of the electrode, which must be balanced against the improved rate stability and increased lifetime. This is demonstrated for an established cathode material for lithium-ion batteries (LiNi0.33Co0.33Mn0.33O2, NCM111). For active materials with low electrical or ionic conductivity, especially post-lithium systems, hierarchically structured particles are often the only way to produce competitive electrodes.

Spatially-assembled binary carbon anode synergizing directional electron transfer and enriched microbe accommodation for wastewater treatment and energy conversion: From simulation to experiments

Bioelectrochemical systems (BESs) hold prospects in wastewater energy and resource recovery. Anode optimization is important for simultaneous enhancement of wastewater energy conversion and effluent quality in BESs. In this study, a multi-physics model coupling fluid flow, organic degradation and electrochemical process was constructed to guide the design and optimization of BES anodes. Based on the multi-physics simulation, spatially-assembled binary carbon anodes composed of three-dimensional carbon mesh skeleton and granular activated carbon were proposed and established. The granular activated carbon conducive to microbe accommodation played a vital role in improving effluent water quality, while the carbon mesh skeleton favoring electron collection and transfer could enhance the bioelectricity output. With an average chemical oxygen demand (COD) removal rate of 0.442 kg m−3 d−1, a maximum power density of 20.6 W m−3 was achieved in the optimized composite anode BES, which was 25% and 154% higher than carbon mesh skeleton BES and granular activated carbon BES. Electroactive bacteria were enriched in composite anodes and performed important functions related to microbial metabolism and energy production. The spatially-assembled binary carbon anode with low carbon mesh packing density was more cost-effective with a daily energy output per anode cost of 221 J d−1 RMB−1. This study not only provides a cost-efficient alternative anode to simultaneously improve organic degradation and power generation performance, but also demonstrates the potential of multi-physics simulation in offering theoretical support and prediction for BES configuration design as well as optimization.

Controllable synthesis of star-shaped FeCoMnOx nanocrystals and their self-assembly into superlattices with low-packing densities.

We present a novel method for synthesizing monodisperse, star-shaped FeCoMnOx nanocrystals with tunable concavity. Through liquid-air interfacial assembly, these colloidal nanostars can form two-dimensional superlattices, which are characterized by low packing densities. Notably, the ability to adjust the degree of concavity of nanostars allows for the tuning of the packing symmetry of the assembled superlattices.

Mechanical properties and microstructure of coal cinder-based ultra-fine tailings cemented tailings body

Cementitious materials are the main binders used in mine filling and play a critical role in determining the mechanical properties of cemented tailings backfill (CTB). But, the materials typically account for over 60% of total filling expenses. The objective of this study is to utilize solid waste cinders as a substitute for certain cement-like materials, aiming to lower the cost of filling while maintaining the strength characteristics of CTB. Through measuring the fluidity and strength characteristics of slurry with different CC replacement levels, and the microstructure analysis of backfill, the study finds that: 1) The addition of CC can improve the fluidity of ultra-fine tailings filling slurry and adding 1 ∼ 2 mm CC can both improve the fluidity of CTB and the compressive strength of CTB. 2) The strength of the filling body can be improved by replacing 20% of the cementitious material with CC when the surface pore size of CC with porous structure is similar to the median particle size of the tailings. 3) The lower packing density of CC and the hydrophilic mineral components on the surface reduced the interfacial tension between solid and liquid, which enhanced the dispersion ability of CC in the slurry. 4) Coal cinders replace part of cement-like materials to reduce filling costs and solid waste emissions.

A bioinspired vine-like hierarchically structured PET/CA composite nanofibrous membrane with superhydrophobic and superoleophilic surface for high-efficiency cooking fumes capture

Indoor air pollution, especially from cooking oil fumes (COFs), has become a serious issue that affects human health. Obtaining filters that can offer high efficiency, high air permeability and good reusability and stability for COFs removal remains a challenge. Herein, a bioinspired vine-like polyethylene terephthalate/cellulose acetate (PET/CA) composite nanofibrous membrane with high filtration performance, high air permeability and enhanced flame retardancy for COFs removal is achieved via a one-step co-electrospinning process. The nanofibrous membrane consists of hierarchically branched nanofibers to offer small pore size (0.48 μm), high porosity (94.75 %) and low packing density (0.22 g m−3), as well as surface superhydrophobicity (water contact angle of 154°) and superoleophilicity (vegetable oil wetting time of 0.21 s). The nanofibrous filter demonstrates high-efficiency COFs removal (>99.5 %), low air resistance (<70 Pa) and good reusability and stability for actual COFs purification. By virtue of the simple fabrication technique and the superiorities in COFs capture, the bioinspired vine-like hierarchical structured nanofibrous membranes have promising applications for oily fumes filtration and air purification in the catering industry.

Shape-dependent radial segregation in rotating drum: Insights from DEM simulations

This study evaluates how particle shape affects the segregation behavior of binary mixtures in a rotating drum. The Discrete Element Method (DEM) is used to investigate radial segregation and its dependence on particle shape by varying the particle’s aspect ratio. Two scenarios are examined: one when the shape of fine particles held constant and varying shape for coarse particles, and another when the shape of coarse particles held constant and varying shape for fine particles. These scenarios help quantify the relative mixing observed in the system for the considered shapes. The SI trend in terms of aspect ratio (AR) for coarse particles is as follows: AR (5.0) > AR (2.5) > AR (1). In contrast, for fine particles, the trend is AR (5.0) > AR (1) > AR (2.5). The results indicate that coarse particles with lower packing density exhibit higher segregation. Conversely, fine particles with pronounced elongation facilitate mixing.