Network of cyano-p-aramid nanofibres creates ultrastiff and water-rich hydrospongels.

The structure-property paradox of biological tissues, in which water-rich porous structures efficiently transfer mass while remaining highly mechanically stiff, remains unsolved. Although hydrogel/sponge hybridization is the key to understanding this phenomenon, material incompatibility makes this a challenging task. Here we describe hydrogel/sponge hybrids (hydrospongels) that behave as both ultrastiff water-rich gels and reversibly squeezable sponges. The self-organizing network of cyano-p-aramid nanofibres holds approximately 5,000 times more water than its solid content. Hydrospongels, even at a water concentration exceeding 90 wt%, are hard as cartilage with an elastic modulus of 50-80 MPa, and are 10-1,000 times stiffer than typical hydrogels. They endure a compressive strain above 85% through poroelastic relaxation and hydrothermal pressure at 120 °C. This performance is produced by amphiphilic surfaces, high rigidity and an interfibrillar, interaction-driven percolating network of nanofibres. These features can inspire the development of future biofunctional materials.

Empirical analysis of congestion spreading in Seoul traffic network.

Understanding how local traffic congestion spreads in urban traffic networks is fundamental to solving congestion problems in cities. In this work, by analyzing the high-resolution data of traffic velocity in Seoul, we empirically investigate the spreading patterns and cluster formation of traffic congestion in a real-world urban traffic network. To do this, we propose a congestion identification method suitable for various types of interacting traffic flows in urban traffic networks. Our method reveals that congestion spreading in Seoul may be characterized by a treelike structure during the morning rush hour but a more persistent loop structure during the evening rush hour. Our findings suggest that diffusion and stacking processes of local congestion play a major role in the formation of urban traffic congestion.

Global efficiency and network structure of urban traffic flows: A percolation-based empirical analysis.

Making the connection between the function and structure of networked systems is one of the fundamental issues in complex systems and network science. Urban traffic flows are related to various problems in cities and can be represented as a network of local traffic flows. To identify an empirical relation between the function and network structure of urban traffic flows, we construct a time-varying traffic flow network of a megacity, Seoul, and analyze its global efficiency with a percolation-based approach. Comparing the real-world traffic flow network with its corresponding null-model network having a randomized structure, we show that the real-world network is less efficient than its null-model network during rush hour, yet more efficient during non-rush hour. We observe that in the real-world network, links with the highest betweenness tend to have lower quality during rush hour compared to links with lower betweenness, but higher quality during non-rush hour. Since the top betweenness links tend to be the bridges that connect the network together, their congestion has a stronger impact on the network's global efficiency. Our results suggest that the spatial structure of traffic flow networks is important to understand their function.

Self-Healable Conductive Hydrogels with High Stretchability and Ultralow Hysteresis for Soft Electronics.

Stretchable sensors based on conductive hydrogels have attracted considerable attention for wearable electronics. However, their practical applications have been limited by the low sensitivity, high hysteresis, and long response times of the hydrogels. In this study, we developed high-performance poly(vinyl alcohol) (PVA)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) based hydrogels post-treated with NaCl, which showed excellent mechanical properties, fast electrical response, and ultralow hysteresis properties. The hydrogels also demonstrated excellent self-healing properties with electrical and mechanical properties comparable to those of the original hydrogel and more than 150% elongation at break after the self-healing process. The high performance of the optimized hydrogels was attributed to the enhanced intermolecular forces between the PVA matrix and PEDOT:PSS, the favorable conformational change of the PEDOT chains, and an increase in localized charges in the hydrogel networks. The hydrogel sensors were capable of tracking large human motion and subtle muscle action in real time with high sensitivity, a fast response time (0.88 s), and low power consumption (<180 µW). Moreover, the sensor was able to monitor human respiration due to chemical changes in the hydrogel. These highly robust, stretchable, conductive, and self-healing PVA/PEDOT:PSS hydrogels, therefore, show great application potential as wearable sensors for monitoring human activity.

Universal Stretchable Conductive Cellulose/PEDOT:PSS Hybrid Films for Low Hysteresis Multifunctional Stretchable Electronics.

Skin-attachable conductive materials have attracted significant attention for use in wearable devices and physiological monitoring applications. Soft, skin-like conductive films must have excellent mechanical and electrical characteristics with on-skin conformability, stretchability, and robustness to detect body motion and biological signals. In this study, a conductive, stretchable, hydro-biodegradable, and highly robust cellulose/poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) hybrid film is fabricated. Through the synergetic interplay of a conductivity enhancer, nonionic fluorosurfactant, and surface modifier, the mechanical and electrical properties of the stretchable hybrid film are greatly improved. The stretchable cellulose/PEDOT:PSS hybrid film achieves a limited resistance change of only 1.21-fold after 100 stretch-release cycles (30% strain) with exceptionally low hysteresis, demonstrating its great potential as a stretchable electrode for stretchable electronics. In addition, the film shows excellent biodegradability, promising environmental friendliness, and safety benefits. High-performance stretchable cellulose/PEDOT:PSS hybrid films, which have high biocompatibility and sensitivity, are applied to human skin to serve as on-skin multifunctional sensors. The conformally mounted on-skin sensors are capable of continuously monitoring human physiological signals, such as body motions, drinking, respiration rates, vocalization, humidity, and temperature, with high sensitivity, fast responses, and low power consumption (21 µW). The highly conductive hybrid films developed in this study can be integrated as both stretchable electrodes and multifunctional healthcare monitoring sensors. We believe that the highly robust stretchable, conductive, biodegradable, skin-attachable cellulose/PEDOT:PSS hybrid films are worthy candidates as promising soft conductive materials for stretchable electronics.

Effects of preparation routes on the physical and rheological properties of isosorbide-based thermoplastic polyurethanes.

Biomass-derived isosorbide (ISB) is a promising alternative to petroleum-based monomers in industrial plastics. In this study, ISB-based thermoplastic polyurethanes (ISB-TPUs) were prepared using ISB as a biomass chain extender, and the effects of the preparation route on the structural and physical properties of the resultant polymers were investigated. Prepolymer methods were more suitable for obtaining the desired molecular weights (MWs) and physical properties of ISB-TPUs than the one-shot method. The presence of the solvent and catalyst in the prepolymer step had significant effects on the structural and physical properties of the resultant polymer. Among several prepolymer conditions, the solvent- and catalyst-free methods were the most suitable for preparing commercial-level ISB-TPUs, with number- and weight-average MWs (M n and M w ) of 32,881 and 90,929 g mol-1, respectively, and a tensile modulus (E) and ultimate tensile strength (UTS) of 12.0 and 40.2 MPa, respectively. In comparison, the presence of a catalyst in the prepolymer step resulted in lower MWs and mechanical properties (81,033 g mol-1 and 18.3 MPa of M w and UTS, respectively). The co-existence of the catalyst/solvent led to a further decline in the properties of ISB-TPUs (26,506 and 10.0 MPa of M w and UTS, respectively). ISB-TPU prepared via the solvent- and catalyst-free methods exhibited remarkable elastic recovery when subjected to up to 1000% strain in mechanical cycling tests. Rheological characterization confirmed the thermo-reversible phase change (thermoplasticity) of the polymer. Supplementary Information: The online version contains supplementary material available at 10.1007/s13233-023-00125-w.

Achieving Both Ultrahigh Electrical Conductivity and Mechanical Modulus of Carbon Films: Templating-Coalescing Behavior of Single-Walled Carbon Nanotube in Polyacrylonitrile.

Promoting the feasibility of carbon films as electrode applications requires sufficient performances in view of both electrical and mechanical properties. Herein, carbon films with ultrahigh electrical conductivity and mechanical modulus are prepared by high temperature carbonization of polyacrylonitrile (PAN)/single-walled carbon nanotube (SWNT) nanocomposites. Achieving both performances is ascribed to remarkable graphitic crystallinity, resulting from the sequential templating-coalescing behavior of concentrated SWNT bundles (B-CNTs). While well-dispersed SWNTs (WD-CNTs) facilitate radial templating according to their tubular geometry, flattened B-CNTs sandwiched between carbonized PAN matrices induce vertical templating, where the former and latter produce concentric and planar crystallizations of the graphitic structure, respectively. After carbonization at 2500 °C with the remaining WD-CNTs as microstructural defects, the flattened B-CNTs coalesce into graphitic crystals by zipping the surrounding matrix, resulting in high crystallinity with the crystal thicknesses of 27.4 and 39.4 nm for the (002) and (10) planes, respectively. For comparison, the graphene oxide (GO) containing carbon films produce a less-ordered graphitic phase owing to irregular templating, despite the geometrical consistency. Consequently, PAN/B-CNT carbon films exhibit exceptional electrical conductivity (40.7 × 104 S m-1 ) and mechanical modulus (38.2 ± 6.4 GPa). Thus, controlling the templating-coalescing behavior of SWNTs is the key for improving final performances of carbon films.

Dual-functional alginate and collagen-based injectable hydrogel for the treatment of cancer and its metastasis.

BACKGROUND: Immunotherapies have been gaining attention for the prevention of cancer recurrence and metastasis. Cancer immunotherapy can induce memory cells to target cancer-specific antigens and, thus, selectively kill cancer cells. However, there are difficulties in inducing cancer antigen-specific immunity due to limited knowledge regarding cancer antigens. In this study, we synthesized a dual-functional hydrogel to induce antigen generation and immune activation. RESULTS: To elicit a cancer self-antigen-specific immune response, we synthesized an alginate-collagen-based injectable hydrogel, called thermally responsive hydrogel (pTRG), which was incorporated with indocyanine green and the immune stimulator polyinosinic:polycytidylic acid (poly I:C). pTRG was evaluated for its anticancer and anti-metastatic effects against CT-26 carcinoma and 4T1 breast tumor in mice by combining photothermal therapy (PTT) and immunotherapy. Near-infrared (NIR) irradiation promoted temperature elevation in pTRG, consequently exerting a therapeutic effect on mouse tumors. Lung metastasis was prevented in cured CT-26 tumor-injected mice following pTRG treatment via cancer antigen-specific T cell immunity. Moreover, pTRG successfully eliminated the original tumor in 4T1 tumor-bearing mice via PTT and protected them from lung metastasis. To further evaluate the carrier function of TRGs, different types of immunotherapeutic molecules were incorporated into TRGs, which led to the effective elimination of the first CT-26 tumor and the prevention of lung metastasis. CONCLUSIONS: Our data demonstrate that TRG is a efficient material not only for treating primary tumors but also for preventing metastasis and recurrence.

Copula-based analysis of the generalized friendship paradox in clustered networks.

A heterogeneous structure of social networks induces various intriguing phenomena. One of them is the friendship paradox, which states that on average, your friends have more friends than you do. Its generalization, called the generalized friendship paradox (GFP), states that on average, your friends have higher attributes than yours. Despite successful demonstrations of the GFP by empirical analyses and numerical simulations, analytical, rigorous understanding of the GFP has been largely unexplored. Recently, an analytical solution for the probability that the GFP holds for an individual in a network with correlated attributes was obtained using the copula method but by assuming a locally tree structure of the underlying network [Jo et al., Phys. Rev. E 104, 054301 (2021)]. Considering the abundant triangles in most social networks, we employ a vine copula method to incorporate the attribute correlation structure between neighbors of a focal individual in addition to the correlation between the focal individual and its neighbors. Our analytical approach helps us rigorously understand the GFP in more general networks, such as clustered networks and other related interesting phenomena in social networks.

Analytical approach to the generalized friendship paradox in networks with correlated attributes.

One of the interesting phenomena due to the topological heterogeneities in complex networks is the friendship paradox, stating that your friends have on average more friends than you do. Recently, this paradox has been generalized for arbitrary nodal attributes, called a generalized friendship paradox (GFP). In this paper, we analyze the GFP for the networks in which the attributes of neighboring nodes are correlated with each other. The correlation structure between attributes of neighboring nodes is modeled by the Farlie-Gumbel-Morgenstern copula, enabling us to derive approximate analytical solutions of the GFP for three kinds of methods summarizing the neighborhood of the focal node, i.e., mean-based, median-based, and fraction-based methods. The analytical solutions are comparable to simulation results, while some systematic deviations between them might be attributed to the higher-order correlations between nodal attributes. These results help us get deeper insight into how various summarization methods as well as the correlation structure of nodal attributes affect the GFP behavior, hence better understand various related phenomena in complex networks.

Rheological Percolation of Cellulose Nanocrystals in Biodegradable Poly(butylene succinate) Nanocomposites: A Novel Approach for Tailoring the Mechanical and Hydrolytic Properties.

Although biodegradable plastics are gradually emerging as an effective solution to alleviate the burgeoning plastic pollution, their performance is currently trivial for commercialization. A proposed two-pronged strategy to overcome this limitation includes (1) preparation of the nanocomposites from biorenewable nano-fillers to preserve their biodegradability and (2) tailoring their properties to meet the diverse demands in various applications. Herein, we report the preparation of biodegradable nanocomposites composed of poly(butylene succinate) (PBS) and cellulose nanocrystals (CNCs) (loading of 0.2-3.0 wt%) and propose a rheological strategy to tailor their performances. Depending on the shear frequencies, the rheological evaluation revealed two percolation thresholds at approximately 0.8 and 1.5 wt%. At high shear frequencies, the disappearance of the first threshold (0.8 wt%) and the sole persistence of the second one (1.5 wt%) indicated the collapse of the immature network of partially interconnected CNCs. The tensile and hydrolytic properties of the nanocomposites were found to undergo drastic changes at the thresholds. The tensile strength increased by 17% (from 33.3 to 39.2 MPa) up to 0.8 wt% CNC loading. However, the reinforcing efficiency of CNC decreases sharply with further incorporation, reaching nearly zero at 1.5 wt%. On the other hand, hydrolytic degradation of the nanocomposites was rapidly accelerated above 1.5 wt% CNC loading. Therefore, a thorough understanding of the rheological properties of nanocomposites is essential for the design and development of materials with tailored properties.

Biodegradable, Efficient, and Breathable Multi-Use Face Mask Filter.

The demand for face masks is increasing exponentially due to the coronavirus pandemic and issues associated with airborne particulate matter (PM). However, both conventional electrostatic- and nanosieve-based mask filters are single-use and are not degradable or recyclable, which creates serious waste problems. In addition, the former loses function under humid conditions, while the latter operates with a significant air-pressure drop and suffers from relatively fast pore blockage. Herein, a biodegradable, moisture-resistant, highly breathable, and high-performance fibrous mask filter is developed. Briefly, two biodegradable microfiber and nanofiber mats are integrated into a Janus membrane filter and then coated by cationically charged chitosan nanowhiskers. This filter is as efficient as the commercial N95 filter and removes 98.3% of 2.5 µm PM. The nanofiber physically sieves fine PM and the microfiber provides a low pressure differential of 59 Pa, which is comfortable for human breathing. In contrast to the dramatic performance decline of the commercial N95 filter when exposed to moisture, this filter exhibits negligible performance loss and is therefore multi-usable because the permanent dipoles of the chitosan adsorb ultrafine PM (e.g., nitrogen and sulfur oxides). Importantly, this filter completely decomposes within 4 weeks in composting soil.

Mechano-responsive hydrogen-bonding array of thermoplastic polyurethane elastomer captures both strength and self-healing.

Self-repairable materials strive to emulate curable and resilient biological tissue; however, their performance is currently insufficient for commercialization purposes because mending and toughening are mutually exclusive. Herein, we report a carbonate-type thermoplastic polyurethane elastomer that self-heals at 35 °C and exhibits a tensile strength of 43 MPa; this elastomer is as strong as the soles used in footwear. Distinctively, it has abundant carbonyl groups in soft-segments and is fully amorphous with negligible phase separation due to poor hard-segment stacking. It operates in dual mechano-responsive mode through a reversible disorder-to-order transition of its hydrogen-bonding array; it heals when static and toughens when dynamic. In static mode, non-crystalline hard segments promote the dynamic exchange of disordered carbonyl hydrogen-bonds for self-healing. The amorphous phase forms stiff crystals when stretched through a transition that orders inter-chain hydrogen bonding. The phase and strain fully return to the pre-stressed state after release to repeat the healing process.

Highly reinforced poly(butylene succinate) nanocomposites prepared from chitosan nanowhiskers by in-situ polymerization.

Biodegradable aliphatic polyesters need to be tough for commodity-plastic applications, such as disposable bags. Herein, we show that chitosan nanowhiskers (CsWs) prepared from naturally abundant chitin is an effective nanofiller that reinforces the strength and toughness of poly(butylene succinate) (PBS). In-situ polycondensation of an aqueous solution of processed CsWs led to a PBS nanocomposite with the highest tensile strength (77 MPa) and elongation at break (530%) reported to date for all PBS types at a minimal nanofiller content of 0.2 wt%. The observed 3.2-fold increase in toughness of the CsW/PBS composite compared to neat PBS is superior to those of composites prepared using cellulose nanocrystals, chitin nanowhiskers, and unstably dispersed CsWs in 1,4-butanediol monomer. Interestingly, CsWs efficiently overcome the disadvantages of the PBS film that easily tears. The highly polar surfaces of the CsWs strongly bind to polymer chains and promote a fibrillar and micro-void structure, thereby maximizing the chain-holding ability of the nanofiller, which resists external tensile and tear stress. This sustainable all-organic nanocomposite is a promising candidate for biodegradable disposable commodities.

Malleable Hydrogel Embedded with Micellar Cargo-Expellers as a Prompt Transdermal Patch.

Although hydrogels are promising transdermal patches, they face spatiotemporal problems related to controlled drug release. From the "spatio" perspective, hydrogels are not malleable, therefore they do not fully contact curved skin, such as that found on the nose and fingers. From the "temporal" perspective, the internal network of a hydrogel retards cargo release. Herein, a malleable and rapid-cargo-releasing poly(vinyl alcohol)-borax hydrogel that embeds freely mobile poly(hydroxyethyl methacrylate) (PHEMA) micelles is prepared. The in situ polymerization of PHEMA within the matrix produces large compound micelle particles that are not bound by the matrix. The micelles act as expellers by sweeping out cargo upon exposure to wet conditions through a concentration gradient. The hydrogel embedded with the micellar cargo-expellers delivers a 25-fold larger 3-min release quantity of Nile Red (a model cargo) than the control hydrogel. The particles absorb mechanical shocks and the dynamic borate-diol bonds engender the hydrogel with self-healing properties, which results in a hydrogel that tightly contacts highly curved skin. Moreover, the hydrogel shows no toxicity in in vivo and skin irritation tests. This malleable hydrogel will inspire novel prompt skin-patch systems for pharmaceutical and cosmetics purposes.

A Self-Healing Nanofiber-Based Self-Responsive Time-Temperature Indicator for Securing a Cold-Supply Chain.

Perishable foods at undesired temperatures can generate foodborne illnesses that present significant societal costs. To certify refrigeration succession in a food-supply chain, a flexible, easy-to-interpret, damage-tolerant, and sensitive time-temperature indicator (TTI) that uses a self-healing nanofiber mat is devised. This mat is opaque when refrigerated due to nanofiber-induced light scattering, but becomes irreversibly transparent at room temperature through self-healing-induced interfibrillar fusion leading to the appearance of a warning sign. The mat monitors both freezer (-20 °C) and chiller (2 °C) successions and its timer is tunable over the 0.5-22.5 h range through control of the polymer composition and film thickness. The thin mat itself serves as both a temperature sensor and display; it does not require modularization, accurately measures localized or gradient heat, and functions even after crushing, cutting, and when weight-loaded in a manner that existing TTIs cannot. It also contains no drainable chemicals and is attachable to various shapes because it operates through an intrinsic physical response.

Aramid Nanofiber Templated In Situ SNAr Polymerization for Maximizing the Performance of All-Organic Nanocomposites.

The performance limits of conventional super engineering plastics with inorganic nanofillers are surpassed by all-organic nanocomposites prepared via in situ SNAr polymerization of polysulfone (PSU) in the presence of a highly dispersed aramid nanofiber (ANF) solution. The latter is directly used, bypassing the energy-consuming, nanostructure-damaging workup process. Using only a 0.15 wt % nanofiller, the all-organic nanocomposite shows an ultimate tensile strength 1.6× higher and 3.4× tougher than neat PSU and its blending counterpart due to the mutually interactive filler and maximally homogenized matrix. The exceptional toughness of the ANF/PSU nanocomposite originates from the grafted PSU on the surface of ANF; it drives stress-delocalized deformation, as revealed by stress-absorbable viscoelastic behavior and ductile elongation of materials. This material is a promising candidate for use as a filler-interactive, high-performance nanocomposite.

Rediscovery of nylon upgraded by interactive biorenewable nano-fillers.

Inorganic nanomaterials can only stiffen nylon with a significant loss of its toughness and ductility. Furthermore, they are not eco-friendly. In this study, the facile tuning of nylon's mechanical properties from stiff to tough was achieved, using cellulose nanocrystals (CNC) and chitosan nanowhiskers (CSW) as biorenewable fillers. The interaction between the matrix and filler was controlled by varying the types of fillers and the employed processing methods, including in situ interfacial polymerization and post-solution blending. Particularly with CSW, the in situ-incorporated filler with a 0.4 wt% loading strengthened nylon and led to a 1.9-fold increase in its Young's modulus (2.6 GPa) and a 1.7-fold increase in its ultimate tensile strength (106 MPa), whereas the solution-blended filler with a 0.3 wt% loading toughened the polymer with a 2.1-fold increase (104 MJ m-3). Compared with inorganic nanocomposites, these interactive biofiller-nanocomposites are unrivaled in their reinforcing performance when normalized by filler content. This stiff-to-tough tuning trend is more pronounced in the CSW system than in the CNC system. Covalent polymer grafts on the amine surface of CSW enhanced interfacial interactions in the in situ method, whereas its cationic surface charges plasticized the polymer matrix in the blending method. This proteinaceous composite-mimicking all-organic nylon nanocomposite opens new possibilities in the field of reinforced engineering plastics.

Extremely Fast Self-Healable Bio-Based Supramolecular Polymer for Wearable Real-Time Sweat-Monitoring Sensor.

Sensors with autonomous self-healing properties offer enhanced durability, reliability, and stability. Although numerous self-healing polymers have been attempted, achieving sensors with fast and reversible recovery under ambient conditions with high mechanical toughness remains challenging. Here, a highly sensitive wearable sensor made of a robust bio-based supramolecular polymer that is capable of self-healing via hydrogen bonding is presented. The integration of carbon fiber thread into a self-healing polymer matrix provides a new toolset that can easily be knitted into textile items to fabricate wearable sensors that show impressive self-healing efficiency (>97.0%) after 30 s at room temperature for K+/Na+ sensing. The wearable sweat-sensor system-coupled with a wireless electronic circuit board capable of transferring data to a smart phone-successfully monitors electrolyte ions in human perspiration noninvasively in real time, even in the healed state during indoor exercise. Our smart sensors represent an important advance toward futuristic personalized healthcare applications.

Impact of perception models on friendship paradox and opinion formation.

Topological heterogeneities of social networks have a strong impact on the individuals embedded in those networks. One of the interesting phenomena driven by such heterogeneities is the friendship paradox (FP), stating that the mean degree of one's neighbors is larger than the degree of oneself. Alternatively, one can use the median degree of neighbors as well as the fraction of neighbors having a higher degree than oneself. Each of these reflects on how people perceive their neighborhoods, i.e., their perception models, hence how they feel peer pressure. In our paper, we study the impact of perception models on the FP by comparing three versions of the perception model in networks generated with a given degree distribution and a tunable degree-degree correlation or assortativity. The increasing assortativity is expected to decrease network-level peer pressure, while we find a nontrivial behavior only for the mean-based perception model. By simulating opinion formation, in which the opinion adoption probability of an individual is given as a function of individual peer pressure, we find that it takes the longest time to reach consensus when individuals adopt the median-based perception model compared to other versions. Our findings suggest that one needs to consider the proper perception model for better modeling human behaviors and social dynamics.