Rearrangement Of Network Research Articles

4D Printing of High-Performance Shape Memory Polymer with Double Covalent Adaptive Networks

Achieving 4D printing of shape memory polymers with both high strength and high transition temperature remains challenging due to the inherent incompatibility between the rigid molecular structure required for high strength and the molecular structure that moves on demand necessary for the shape memory effect, the limitations of high-performance polymer reaction kinetics, as well as internal stress during the printing process. Here, a direct ink writing (DIW) printed high-precision cyanate ester-urethane (CU) shape memory polymer with excellent performance was accomplished by incorporating two dynamic covalent bonds (carbamate and cyanuric acid) through copolymerizing cyanate ester with polyurethane acrylates. During curing, carbamate and cyanuric acid enable stress relaxation and polymer network rearrangement, facilitating the permanent reconfiguration of CU to form a novel triazine network structure. As a result, a high mechanical properties CU with excellent strength (83 MPa) and superior Young's modulus (2.37GPa) were obtained, besides, the transition temperature (near 250 oC) is the highest in comparison to currently reported 4D-printed shape memory polymers. Furthermore, this reconfigurability was demonstrated by imprinting various surface patterns at microscopic level. Moreover, the reconfigurability of CU provides a novel strategy for smart molds in deformation and easy demolding. Overall, this study opens up a new avenue for the development of high-performance 4D printed shape memory polymers.

Crystal structure of a bacterial photoactivated adenylate cyclase determined by serial femtosecond and serial synchrotron crystallography.

OaPAC is a recently discovered blue-light-using flavin adenosine dinucleotide (BLUF) photoactivated adenylate cyclase from the cyanobacterium Oscillatoria acuminata that uses adenosine triphosphate and translates the light signal into the production of cyclic adenosine monophosphate. Here, we report crystal structures of the enzyme in the absence of its natural substrate determined from room-temperature serial crystallography data collected at both an X-ray free-electron laser and a synchrotron, and we compare these structures with cryo-macromolecular crystallography structures obtained at a synchrotron by us and others. These results reveal slight differences in the structure of the enzyme due to data collection at different temperatures and X-ray sources. We further investigate the effect of the Y6W mutation in the BLUF domain, a mutation which results in a rearrangement of the hydrogen-bond network around the flavin and a notable rotation of the side chain of the critical Gln48 residue. These studies pave the way for picosecond-millisecond time-resolved serial crystallography experiments at X-ray free-electron lasers and synchrotrons in order to determine the early structural intermediates and correlate them with the well studied picosecond-millisecond spectroscopic intermediates.

Quantum Simulations of Radiation Damage in a Molecular Polyethylene Analog.

An atomic-level understanding of radiation-induced damage in simple polymers like polyethylene is essential for determining how these chemical changes can alter the physical and mechanical properties of important technological materials such as plastics. Ensembles of quantum simulations of radiation damage in a polyethylene analog are performed using the Density Functional Tight Binding method to help bind its radiolysis and subsequent degradation as a function of radiation dose. Chemical degradation products are categorized with a graph theory approach, and occurrence rates of unsaturated carbon bond formation, crosslinking, cycle formation, chain scission reactions, and out-gassing products are computed. Statistical correlations between product pairs show significant correlations between chain scission reactions, unsaturated carbon bond formation, and out-gassing products, though these correlations decrease with increasing atom recoil energy. The results present relatively simple chemical descriptors as possible indications of network rearrangements in the middle range of excitation energies. Ultimately, the work provides a computational framework for determining the coupling between nonequilibrium chemistry in polymers and potential changes to macro-scale properties that can aid in the interpretation of future radiation damage experiments on plasticmaterials.

First-principles molecular dynamics of exciton-driven initial stage of plasma phase transition in warm dense molecular nitrogen.

Understanding the properties of molecular nitrogen N2 at extreme conditions is the fundamental problem for atomistic theory and the important benchmark for the capabilities of first-principles molecular dynamics (FPMD) methods. In this work, we focus on the connection between the dynamics of ions and electronic excitations in warm dense N2. The restricted open-shell Kohn-Sham method gives us the possibility to reach relevant time and length scales for FPMD modeling of an isolated exciton dynamics in warm dense N2. Wannier localization sheds light on the corresponding mechanisms of covalent bond network rearrangements that stand behind polymerization kinetics. FPMD results suggest a concept of energy transfer from the thermal energy of ions into the internal energy of polymeric structures that form in warm dense N2 at extreme conditions. Our findings agree with the thermobaric conditions for the onset of absorption in the optical spectroscopy study of Jiang et al. [Nat. Commun. 9, 2624 (2018)].

The effect of swelling/deswelling cycles on the mechanical behaviors of the polyacrylamide hydrogels

In practical applications, hydrogels experience swelling or deswelling in response to external stimuli, showcasing large deformation, tunable mechanical properties, and excellent biocompatibility. Previous studies focused on the effect of individual swelling or deswelling on the mechanical behaviors of hydrogels, neglecting the combined effects of both processes. The underlying mechanism of how the combined processes of swelling and deswelling affect the mechanical behaviors of hydrogels has not been systematically explored. To address this gap, polyacrylamide hydrogels with diverse initial compositions are prepared and subjected to controlled swelling-deswelling or deswelling-swelling cycles to achieve the same water content state. The mechanical properties of the hydrogel samples exposed to these cycles, including shear modulus, stretchability, Mullins effect, and fracture toughness, are experimentally evaluated and compared with those of as-prepared hydrogel samples without undergoing such cycles. Our findings reveal a significant reduction in stretchability, the Mullins effect, and fracture toughness of hydrogels exposed to either cycle. The extent of these reductions varies depending on the initial compositions of the hydrogels. This reduction in properties is primarily attributed to the rearrangement of hydrogel networks during these cycles, which becomes noticeable in hydrogels with network inhomogeneity. We also found that although the shear modulus of hydrogels varies after swelling-deswelling or deswelling-swelling cycles, it remains at relatively consistent levels compared to the as-prepared hydrogel. These findings suggest that the mechanical properties of hydrogels can be adjusted by optimizing the initial compositions and regulating the swelling-deswelling processing method. By studying the effects of swelling/deswelling cycles on the mechanical properties of hydrogels, we provide valuable insights for the application of hydrogels under dynamic environmental changes.

A Molecular Dynamics Study of the Influence of Low-Dosage Methanol on Hydrate Formation in Seawater and Pure Water Metastable Solutions of Methane

The behavior of low concentrations of methanol (0.5 and 1.0 wt% of water) as a promoter for hydrate formation in seawater or pure water metastable solutions of methane was investigated using the classical molecular dynamics method at moderate temperature and pressure. The influence of methanol on the dynamics of the re-arrangement of the hydrogen bond network in seawater and pure water solutions of methane was studied by calculating order parameters of the tetrahedral environment and intermolecular torsion angles for water molecules, as well as by calculating the number of hydrogen bonds, hydrate, and hydrate-like cavities. It was found that hydrate nucleation can be considered a collective process in which the rate of hydrate growth is faster in systems with low concentrations of methanol, and confident hydrate growth begins earlier in a metastable solution without sea salt with a small amount of methanol than in systems without methanol.

Thermadapt shape memory AB-copolymer networks exhibiting tunable properties and kinetics of topological rearrangement

Polycaprolactone (PCL) based thermadapt shape memory polymers (SMPs) have exhibited superiority over traditional analogues by allowing shape-editing to reconfigure permanent shapes into more complex geometrical shapes, driven by the pursuit of advanced functionalities for high-value applications. Nevertheless, although transesterification-based PCL networks exhibit impressive shape reconfigurability as prototypical thermadapt SMPs, there are still constraints in terms of the need for significant flexibility in architectural adjustment and property modulation without compromising reconfigurability, which would be relevant for practical applications. Here, we present a simple yet efficient strategy to create PCL-based thermadapt SMPs that possess a highly tunable structure and properties, as well as exceptional reconfigurability. The family of SMPs, called thermadapt shape memory AB copolymer networks (AB-CPNs), was synthesized by UV-initiated free radical polymerization between PCL diacrylate as crosslinker and 4-hydroxybutyl acrylate (HBA) as comonomer. The thermadapt AB-CPNs allow for significant structural alterations with 0 wt% to 70 wt% HBA while maintaining excellent shape memory and shape reconfigurability effects. The insertion of the polymer segment containing free hydroxyls not only promises tunable material properties but also makes network rearrangement easier since dynamic hydroxy-ester bonds are more active than dynamic ester-ester bonds. It is envisioned that the thermadapt shape memory AB-CPNs with widely tunable macroscopic properties will drive progress in the real-world applications of SMP devices with complicated geometric structures.

Bioresponsive and transformable coacervate actuated by intestinal peristalsis for targeted treatment of intestinal bleeding and inflammation

Developing an oral in situ-forming hydrogel that targets the inflamed intestine to suppress bleeding ulcers and alleviate intestinal inflammation is crucial for effectively treating ulcerative colitis (UC). Here, inspired by sandcastle worm adhesives, we proposed a water-immiscible coacervate (EMNs-gel) with a programmed coacervate-to-hydrogel transition at inflammatory sites composed of dopa-rich silk fibroin matrix containing embedded inflammation-responsive core-shell nanoparticles. Driven by intestinal peristalsis, the EMNs-gel can be actuated forward and immediately transform into a hydrogel once contacting with the inflamed intestine to yield strong tissue adhesion, resulting from matrix metalloproteinases (MMPs)-triggered release of Fe3+ from embedded nanoparticles and rearrangement of polymer network of EMNs-gel on inflamed intestine surfaces. Extensive in vitro experiments and in vivo UC models confirmed the preferential hydrogelation behavior of EMNs-gel to inflamed intestine surfaces, achieving highly effective hemostasis, and displaying an extended residence time (> 48 h). This innovative EMNs-gel provides a non-invasive solution that accurately suppresses severe bleeding and improves intestinal homeostasis in UC, showcasing great potential for clinical applications.

Applying the SPP nonlinear rheology framework to characterize the effect of fermentation time and the gluten-to-chickpea flour ratio in yeasted bread

In this work, doughs made with gluten add chickpea composite flour were mixed to reach the 500BU standard and baked into bread products. Chickpea flour was substituted at the level of 20%, 30%, and 40% by wheat gluten to provide structural support for the dough. Higher gluten concentrations improved gas bubble retention as determined by crumb image analysis, resulting in higher final loaf volume. Dough samples were taken out of the fermentation chamber at 0, 30, 60, and 90 min to study the effect of fermentation on rheology. Utilizing SPP deltoids (Gt′ vs Gt″ plot), the intracycle and intercycle network rearrangement of dough were studied in details. Obtaining deltoids as a function of fermentation time offers an insight into the impact of fermentation on dough structure. It is found that longer fermentation time makes gluten-chickpea composite dough more elastic in the linear region (<1% strain) and less elastic in the nonlinear region. This work helps to demonstrate an application of SPP analysis in facilitating the development of innovative bread products made with a mixture of pulse flour and wheat gluten.

A Biobased Vitrimer: Self-Healing, Shape Memory, and Recyclability Induced by Dynamic Covalent Bond Exchange.

Plant oil-based vitrimer is an innovative and sustainable polymer with wide-ranging potential applications in the field of advanced materials. However, its restricted application is caused by the poor mechanical properties and the need for catalysts during preparation. Using renewable cardanol as the raw material, epoxy cardanol glycidyl ether (ECGE) with an end epoxide group was obtained by the clicking reaction and epoxidation reaction. After the application of citric acid (CA), ECGE was successfully cured, resulting in the production of fully biobased ECGE-CA vitrimers. This material does not require a catalyst, possesses self-healing properties, and exhibits high mechanical strength. On account of the introduction of hydroxyl groups in citric acid, plenty of hydrogen bonds are formed, allowing the topological network rearrangement of the material in the absence of a catalyst. Recyclable adhesives and repairable materials, vitrimer polymers have good shape memory, self-healing, and recyclability since of their dynamic ester and hydroxyl bonds.

Sandwich‐Type Single‐Molecule Magnets Complexes of Er(III) with Ansa‐Cyclooctatetraenyl Ligands†

Comprehensive SummaryMany sandwich‐type lanthanide complexes show extremely high energy barriers (Ueff) for the reversal of magnetization and high blocking temperatures, being the star molecules in the research area of single‐molecule magnets. Herein, the preparation, structural determination, and magnetic property studies of two ansa‐bridged Er‐COT (COT = cyclooctatetraenyl dianion) complexes [KDME2][Er((η8‐COT‐SiMe2)2O)] (1) and [KDME2][Er((η8‐COT‐SiiPr2)2O)]K[Er((η8‐COT‐SiiPr2)2O)] (2) were reported. The Er(III) ions in both complexes are sandwiched by two COT rings which are ansa‐bridged by a [Si‐O‐Si] group. Magnetic studies reveal both complexes display slow magnetic relaxations with comparable energy barriers (228(5) K for 1, and 196(4) K for 2) and blocking temperatures (10.5 K for both complexes). The difference in the relaxation times (τ) for the two complexes was studied in details: different molecular vibrations induced by the substituents are the main reason for τ for 1 being about 10 times longer than for 2 at the same temperature above 10 K, while the quantum tunnelling of magnetization relaxation time (τQTM) for 2 is about 10 times longer than for 1 below 8 K, probably owing to the different dipolar interactions. Further rearrangement of molecular network with such ansa‐bridged SMMs is promising to design molecular magnetic materials with enhanced properties or new properties.

Covalent adaptable polymer networks with CO2-facilitated recyclability

Cross-linked polymers with covalent adaptable networks (CANs) can be reprocessed under external stimuli owing to the exchangeability of dynamic covalent bonds. Optimization of reprocessing conditions is critical since increasing the reprocessing temperature costs more energy and even deteriorates the materials, while reducing the reprocessing temperature via molecular design usually narrows the service temperature range. Exploiting CO2 gas as an external trigger for lowering the reprocessing barrier shows great promise in low sample contamination and environmental friendliness. Herein, we develop a type of CANs incorporated with ionic clusters that achieve CO2-facilitated recyclability without sacrificing performance. The presence of CO2 can facilitate the rearrangement of ionic clusters, thus promoting the exchange of dynamic bonds. The effective stress relaxation and network rearrangement enable the system with rapid recycling under CO2 while retaining excellent mechanical performance in working conditions. This work opens avenues to design recyclable polymer materials with tunable dynamics and responsive recyclability.

Adaptative survival of Aspergillus fumigatus to echinocandins arises from cell wall remodeling beyond β−1,3-glucan synthesis inhibition

Antifungal echinocandins inhibit the biosynthesis of β−1,3-glucan, a major and essential polysaccharide component of the fungal cell wall. However, the efficacy of echinocandins against the pathogen Aspergillus fumigatus is limited. Here, we use solid-state nuclear magnetic resonance (ssNMR) and other techniques to show that echinocandins induce dynamic changes in the assembly of mobile and rigid polymers within the A. fumigatus cell wall. The reduction of β−1,3-glucan induced by echinocandins is accompanied by a concurrent increase in levels of chitin, chitosan, and highly polymorphic α−1,3-glucans, whose physical association with chitin maintains cell wall integrity and modulates water permeability. The rearrangement of the macromolecular network is dynamic and controls the permeability and circulation of the drug throughout the cell wall. Thus, our results indicate that echinocandin treatment triggers compensatory rearrangements in the cell wall that may help A. fumigatus to tolerate the drugs’ antifungal effects.

Bio-Based Epoxy Vitrimers with Excellent Properties of Self-Healing, Recyclability, and Welding.

The development of more recyclable materials is a key requirement for a transition towards a more circular economy. Thanks to exchange reactions, vitrimer, an attractive alternative for recyclable materials, is an innovative class of polymers that is able to change its topology without decreasing its connectivity. In this work, a bisphenol compound (VP) was prepared from saturated cardanol, i.e., 3-pentadecylphenol and vanillyl alcohol. Then, VP was epoxidized to obtain epoxide (VPGE). Finally, VPGE and citric acid (CA) were polymerized in the presence of catalyst TBD to prepare a fully bio-based vitrimer based on transesterification. The results from differential scanning calorimetry (DSC) showed that the VPGE/CA system could be crosslinked at around 163 °C. The cardanol-derived vitrimers had good network rearrangement properties. Meanwhile, because of the dynamic structural elements in the network, the material was endowed with excellent self-healing, welding, and recyclability.

Ultra-Fast-Healing Glassy Hyperbranched Plastics Capable of Restoring 26.4 MPa Tensile Strength within One Minute at Room Temperature.

The growing concern regarding widespread plastic pollution has propelled the development of sustainable self-healing plastics. Although considerable efforts have been dedicated to fabricating self-healing plastics, achieving rapid healing at room temperature is extremely challenging. Herein, we have developed an ultra-fast-healing glassy polyurethane (UGPU) by designing a hyperbranched molecular structure with a high density of multiple hydrogen bonds (H-bonds) on compliant acyclic heterochains and introducing trace water to form water bridge across the fractured surfaces. The compliant acyclic heterochains allow the dense multiple hydrogen bonds to form a frozen network, enabling tensile strength of up to 70 MPa and storage modulus of 2.5 GPa. The hyperbranched structure can drive the reorganization of the H-bonding network through the high mobility of the branched chains and terminals, thereby leading to self-healing ability at room temperature. Intriguingly, the presence of trace water vapor facilitates the formation of activated layers and the rearrangement of networks across the fractured UGPU sections, thereby enabling ultra-fast self-healing at room temperature. Consequently, the restored tensile strength after healing for 1 minute achieves a historic-record of 26.4 MPa. Furthermore, the high transparency (>90 %) and ultra-fast healing property of UGPU make it an excellent candidate for advanced optical and structural materials.

Ultra‐Fast‐Healing Glassy Hyperbranched Plastics Capable of Restoring 26.4 MPa Tensile Strength within One Minute at Room Temperature

AbstractThe growing concern regarding widespread plastic pollution has propelled the development of sustainable self‐healing plastics. Although considerable efforts have been dedicated to fabricating self‐healing plastics, achieving rapid healing at room temperature is extremely challenging. Herein, we have developed an ultra‐fast‐healing glassy polyurethane (UGPU) by designing a hyperbranched molecular structure with a high density of multiple hydrogen bonds (H‐bonds) on compliant acyclic heterochains and introducing trace water to form water bridge across the fractured surfaces. The compliant acyclic heterochains allow the dense multiple hydrogen bonds to form a frozen network, enabling tensile strength of up to 70 MPa and storage modulus of 2.5 GPa. The hyperbranched structure can drive the reorganization of the H‐bonding network through the high mobility of the branched chains and terminals, thereby leading to self‐healing ability at room temperature. Intriguingly, the presence of trace water vapor facilitates the formation of activated layers and the rearrangement of networks across the fractured UGPU sections, thereby enabling ultra‐fast self‐healing at room temperature. Consequently, the restored tensile strength after healing for 1 minute achieves a historic‐record of 26.4 MPa. Furthermore, the high transparency (&gt;90 %) and ultra‐fast healing property of UGPU make it an excellent candidate for advanced optical and structural materials.

Cost‐Effective Conductive Paste for Radiofrequency Devices Using Carbon‐Based Materials

With the increasing demand for compact, lightweight, cost‐effective, and high‐performance radiofrequency (RF) devices, the development of low‐profile antennas becomes crucial. This article presents a study of a novel carbon–cellulose‐based paste intended for screen printing RF devices. The investigation specifically explores the application of high‐reactivity carbon mixture (HRCM) particles as conductive fillers. The results demonstrate that optimal electrical conductivity values and discrete electromagnetic dipole performances can be achieved at lower concentrations of solid conductive material compared to conventional pastes, for similar applications. This offers benefits in terms of total cost, material consumption, and environmental impact. The paste formulation showcases a complex non‐Newtonian behavior, where yielding flow and thixotropicity are found to be independent and dependent on preshear conditions, respectively. This behavior can be attributed to the network orientation and rearrangement of filler structures within the paste system, which in turn are responsible for filler pattern uniformity and overall printing quality. Compared to traditional conductive materials, HRCM pastes are proven to be a viable alternative for RF devices fabrication, including printed Wi‐Fi antennas.

Extracellular vesicles released from microglia after palmitate exposure impact brain function

Dietary patterns that include an excess of foods rich in saturated fat are associated with brain dysfunction. Although microgliosis has been proposed to play a key role in the development of brain dysfunction in diet-induced obesity (DIO), neuroinflammation with cytokine over-expression is not always observed. Thus, mechanisms by which microglia contribute to brain impairment in DIO are uncertain. Using the BV2 cell model, we investigated the gliosis profile of microglia exposed to palmitate (200 µmol/L), a saturated fatty acid abundant in high-fat diet and in the brain of obese individuals. We observed that microglia respond to a 24-hour palmitate exposure with increased proliferation, and with a metabolic network rearrangement that favors energy production from glycolysis rather than oxidative metabolism, despite stimulated mitochondria biogenesis. In addition, while palmitate did not induce increased cytokine expression, it modified the protein cargo of released extracellular vesicles (EVs). When administered intra-cerebroventricularly to mice, EVs secreted from palmitate-exposed microglia in vitro led to memory impairment, depression-like behavior, and glucose intolerance, when compared to mice receiving EVs from vehicle-treated microglia. We conclude that microglia exposed to palmitate can mediate brain dysfunction through the cargo of shed EVs.

Transcription factor network dynamics during the commitment to oncogene-induced senescence

Aberrant oncogenic signaling causes cells to transition into oncogene-induced senescence (OIS) to limit uncontrolled proliferation. Despite being a potent tumor suppressor mechanism, OIS is an unstable cell state susceptible to reprogramming that can promote tumorigenesis. Therefore, elucidating the underlying gene regulatory mechanisms that commit cells to OIS is critical to identifying actionable targets to modulate the senescence state. We previously showed that timely execution of the OIS program is governed by hierarchical transcription factor (TF) networks. However, the gene regulatory mechanisms that prime cells to commit to the OIS fate early upon oncogene hyperactivation are currently not known. Here, we leveraged our time-resolved multi-omic profiling approach to generate TF networks during the first 24 h of oncogenic HRASG12V activation. Using this approach, we demonstrate that the commitment to OIS requires the rearrangement of the TF network on a pre-established epigenomic landscape, priming the cells for the substantial chromatin remodeling that underpins the transition to OIS. Our results provide a detailed map of the chromatin landscape before cells transition to OIS thus offering a platform for manipulation of senescence outcomes of potentially therapeutic value.

‘Rewritable’ and ‘liquid-specific’ recognizable wettability pattern

Bio-inspired surfaces with wettability patterns display a unique ability for liquid manipulations. Sacrificing anti-wetting property for confining liquids irrespective of their surface tension (γLV), remains a widely accepted basis for developing wettability patterns. In contrast, we introduce a ‘liquid-specific’ wettability pattern through selectively sacrificing the slippery property against only low γLV (<30 mN m−1) liquids. This design includes a chemically reactive crystalline network of phase-transitioning polymer, which displays an effortless sliding of both low and high γLV liquids. Upon its strategic chemical modification, droplets of low γLV liquids fail to slide, rather spill arbitrarily on the tilted interface. In contrast, droplets of high γLV liquids continue to slide on the same modified interface. Interestingly, the phase–transition driven rearrangement of crystalline network allows to revert the slippery property against low γLV liquids. Here, we report a ‘rewritable’ and ‘liquid-specific’ wettability pattern for high throughput screening, separating, and remoulding non-aqueous liquids.