Transient Crosslinks Research Articles

Displacement Assay in a Polythiophene Sensor System Based on Supramacromolecuar Disassembly-Caused Emission Quenching.

Exploring new methodologies for simple and on-demand methods of manipulating the emission and sensing ability of fluorescence sensor devices with solid-state emission molecular systems is important for realizing on-site sensing platforms. In this regard, although conjugated polymers (CPs) are some of the best candidates for preparing molecular sensor devices owing to their luminescent and molecular recognition properties, the development of CP-based sensor devices is still in its early stages. In this study, we herein propose a novel strategy for preparing a chemical stimuli-responsive solid-state emission system based on supramacromolecular assembly-induced emission enhancement (SmAIEE). The system was spontaneously developed by mixing only the component polymers (i.e., polythiophene and a transient cross-linking polymer). The proposed strategy can be applied to the facile preparation of molecular sensor devices. The analyte-induced fluorescent response of polythiophene originated from the dynamic displacement of the transient cross-linker in the polythiophene ensemble and the generation of the polythiophene-analyte complex. Our successful demonstration of the spontaneous preparation of the fluorescence sensor system by mixing two component polymers could lead to the development of on-site molecular analyzers including the determination of multiple analytes.

Transient crosslinking controls the condensate formation pathway within chromatin networks.

The network structure of densely packed chromatin within the nucleus of eukaryotic cells acts in concert with nonequilibrium processes. Using statistical physics simulations, we explore the control provided by transient crosslinking of the chromatin network by structural-maintenance-of-chromosome (SMC) proteins over (i) the physical properties of the chromatin network and (ii) condensate formation of embedded molecular species. We find that the density and lifetime of transient SMC crosslinks regulate structural relaxation modes and tune the sol-vs-gel state of the chromatin network, which imparts control over the kinetic pathway to condensate formation. Specifically, lower density, shorter-lived crosslinks induce sollike networks and a droplet-fusion pathway, whereas higher density, longer-lived crosslinks induce gellike networks and an Ostwald-ripening pathway.

Hydrogen bonding-regulated miscibility of graphene oxide and nonionic water-soluble polymers.

The integration of graphene and nonionic water-soluble polymers has generated useful composites with high performances and rich functionalities. These attractive graphene composites are usually synthesized from the aqueous mixture of graphene oxide (GO) precursor and polymers such as synthetic polyvinyl alcohol and natural cellulose. In this widely known preparation method, the miscibility of GO and nonionic water-soluble polymers seems to be intuitive but has been disputed by some observations of gelation and aggregation. Herein, we have re-examined the miscibility of GO and nonionic water-soluble polymers and confirm their general coaggregation caused by hydrogen bonding interaction. Due to the increasing GO concentration, the property of stable miscibility is converted to aggregation by surface adsorption with transient hydrogen bond crosslinking. We have proposed a preheat mixing strategy to prepare a homogenous solution of GO and nonionic water-soluble polymers in any arbitrary ratio. The re-exploited miscibility allows the fabrication of homogeneous composite papers with renewed high performance trend. The hydrogen bonding-regulated miscibility refreshes the understanding on graphene/water-soluble polymeric composites and provides an ecofriendly interaction control method to modulate the assembly of structures and materials.

Polymer Modeling Reveals Interplay between Physical Properties of Chromosomal DNA and the Size and Distribution of Condensin-Based Chromatin Loops.

Transient DNA loops occur throughout the genome due to thermal fluctuations of DNA and the function of SMC complex proteins such as condensin and cohesin. Transient crosslinking within and between chromosomes and loop extrusion by SMCs have profound effects on high-order chromatin organization and exhibit specificity in cell type, cell cycle stage, and cellular environment. SMC complexes anchor one end to DNA with the other extending some distance and retracting to form a loop. How cells regulate loop sizes and how loops distribute along chromatin are emerging questions. To understand loop size regulation, we employed bead-spring polymer chain models of chromatin and the activity of an SMC complex on chromatin. Our study shows that (1) the stiffness of the chromatin polymer chain, (2) the tensile stiffness of chromatin crosslinking complexes such as condensin, and (3) the strength of the internal or external tethering of chromatin chains cooperatively dictate the loop size distribution and compaction volume of induced chromatin domains. When strong DNA tethers are invoked, loop size distributions are tuned by condensin stiffness. When DNA tethers are released, loop size distributions are tuned by chromatin stiffness. In this three-way interaction, the presence and strength of tethering unexpectedly dictates chromatin conformation within a topological domain.

Gum Arabic-based three-dimensional printed hydrogel for customizable sensors

Most three-dimensional (3D) printed hydrogel exhibit non-idealized rheological properties in the process of direct ink writing and complicated curing. Therefore, accurate writability and convenient curing for 3D printed hydrogel remain a challenge. In this paper, we developed a typical 3D printed hydrogel which realized direct ink writing (DIW) at temperatures similar to human body. Silicon dioxide (SiO2) and Gum Arabic (GA) formed the Bingham fluid to ensure shape stability. The rapid initiation system of potassium persulfat (KPS) and N,N,N′,N′ -tetramethylethylenediamine (TMEDA) allowed the 3D printed hydrogel precursor solution to transiently form a hydrophobic conjoined cross-linking network structure of acrylamide (AAM) and lauryl methacrylate (LMA) after printing, resulting in preferable mechanical properties. Hydrogel precursor solution showed better rheological properties with the nature of Bingham fluids, and achieved transient cross-linking at 30 °C for 10 s in the rheological test. A variety of 3D printed hydrogel with individual strain sensing properties are prepared as customizable sensor that could monitor significant strain signals within 0–20 % strain with high sensitivity. Moreover, they were discovered excellent temperature sensitivity over a wide operating range (0–80 °C). The 3D printing hydrogel sensors were expected to have broad application prospects in flexible wearable devices and medical monitoring.

Surface forces and friction between Langmuir-Blodgett polymer layers in a nonpolar solvent

Optimization of boundary lubrication by tuning the confined molecular structures formed by surface-active additives such as surfactants and polymers is of key importance to improving energy efficiency in mechanical processes. Here, using the surface forces apparatus (SFA), we have directly measured the normal and shear forces between surface layers of a functionalised olefin copolymer (FOCP) in n-dodecane, deposited onto mica using the Langmuir-Blodgett (LB) technique. The FOCP has an olefin backbone decorated with a statistical distribution of polar-aromatic groups, with a structure that we term as “centipede”. The effect of lateral confinement, characterised by the surface pressure, Πdep, at the air–water interface at which the LB films are transferred, was examined. Normal force profiles revealed that the thickness of the LB films increased significantly with Πdep, with the film thickness (t > 20 nm) inferring a multi-layered film structure, consistent with the interfacial characterisation results from synchrotron X-ray reflectivity (XRR) measurements. The coefficient of friction, µ, between the LB films spanned two orders of magnitude from superlubricity (µ ∼ 0.002) to much higher friction (µ > 0.1) depending nonlinearly on Πdep, with the lowest friction observed at the intermediate Πdep. Molecular arrangement upon LB compression leads to the multilayer film with a structure akin to an interfacial gel, with transient crosslinking facilitated by the intra- and inter-molecular interactions between the functional groups. We attribute the differences in frictional behaviour to the different prevalence of the FOCP functional groups at the lubricating interface, which depends sensitively on the degree of compression at the air–water interface prior to the LB deposition. The LB films remain intact after repeated compression (up to pressures of 10 MPa) and shear cycles, indicating strong surface anchorage and structural robustness as a load-bearing and shear-mediating boundary layer. These unprecedented results from the friction measurements between LB films of a statistical copolymer in oil point towards new strategies for tailoring macromolecular architecture for mediating efficient energy dissipation in oil-based tribological applications.

Investigation of a Finite-Difference-Method based real-time viscous heating compensation in a nozzle viscometer for inline viscosity measurement of phenol resins

This work is motivated by the rarely available material data for thermosets and a missing inline viscosity measurement method to monitor melt property deviations. A nozzle viscometer is designed for inline viscosity measurement of phenol-formaldehyde compounds. The nozzle viscometer is mounted at the plasticizing unit of an injection molding machine. A fluid coolant circuit allows a dynamic tempering to pause the transient crosslinking reaction. A 2D FDM model is implemented, to calculate the viscous heating within an injection cycle and to compensate the temperature rising effect in the viscosity measurement. The FDM model processes the inline sensor signals in a closed loop correction in real time to determine a corrected reactive viscosity model. The signal-to-noise-ratio quantifies the reliability of the inline viscosity measurement method.

Design Parameters for Injectable Biopolymeric Hydrogels with Dynamic Covalent Chemistry Crosslinks.

Dynamic covalent chemistry (DCC) crosslinks can form hydrogels with tunable mechanical properties permissive to injectability and self-healing. However, not all hydrogels with transient crosslinks are easily extrudable. For this reason, two additional design parameters must be considered when formulating DCC-crosslinked hydrogels: 1) degree of functionalization (DoF) and 2) polymer molecular weight (MW). To investigate these parameters, hydrogels comprised of two recombinant biopolymers: 1) a hyaluronic acid (HA) modified with benzaldehyde and 2) an elastin-like protein (ELP) modified with hydrazine (ELP-HYD), are formulated. Several hydrogel families are synthesized with distinct HA MW and DoF while keeping the ELP-HYD component constant. The resulting hydrogels have a range of stiffnesses, G' ≈ 10-1000Pa, and extrudability, which is attributed to the combined effects of DCC crosslinks and polymer entanglements. In general, lower MW formulations require lower forces for injectability, regardless of stiffness. Higher DoF formulations exhibit more rapid self-healing. Gel extrusion through a cannula (2 m length, 0.25 mm diameter) demonstrates the potential for minimally invasive delivery for future biomedical applications. In summary, this work highlights additional parameters that influence the injectability and network formation of DCC-crosslinked hydrogels and aims to guide future design of injectable hydrogels.

Investigation on the structural and ion transport properties of magnesium salt doped HPMC-PVA based polymer blend for energy storage applications

The effects of Mg (NO3)2. 6H2O salt on an eco-friendly biopolymer blend matrix comprising hydroxypropyl methylcellulose (HPMC) and poly (vinyl alcohol) (PVA) is presented in this work which is prepared using the solution casting method. Structural, chemical composition (functional moieties), morphological, and thermal features were investigated by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Field emission scanning electron microscopy (FE-SEM), Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). FTIR spectrum and XRD pattern confirmed that the magnesium nitrate salt was dissolved, and complexation was observed through a coordination bond and a hydrogen bond with -OH and -CH groups in the host polymer blend. The glass transition temperature (Tg) values of HPMC:PVA composites are greater than those of the pure blend, demonstrating transient cross-linking. For P0, P2, and P3 samples, the pore diameter and % porosity is calculated, and the morphology of the P4 sample is non-porous and shows ionic conductivity of P4 = 3.25 × 10−4 S/cm at 27 °C. Based on the Nyquist plot fitting and FTIR deconvolution methods, it is used to determine the transport characteristics and noticed that the carrier concentration affects the ionic conductivity. The highest conducting electrolyte has been integrated into a primary battery to demonstrate its potential use in energy storage systems.

Hybrid Hydrogels with Orthogonal Transient Cross-linking Exhibiting Highly Tunable Mechanical Properties

Compositional changes in the chemical makeup of hydrogels offer a powerful strategy for fine tuning of mechanical properties, enabling specific targeting for different applications. The chemical versatility exhibited by the tunable system introduced here can be leveraged to address a broad range of characteristics across the field of tissue engineering─from blood vessels to cartilage, for example─which demands materials with very different mechanical profiles. Furthermore, we rely exclusively on dynamic, non-covalent cross-linking to provide opportunities for 3D printing and injectability. This work describes a highly tunable system based on hydrogen bonding and ionic interactions. Single network hydrogels were made by exploiting various acrylic monomers including N-acryloyl glycinamide (NAGA) and acrylic acid (AAc). Additionally, hybrid hydrogels were explored by combining these acrylic networks with an ionically cross-linked alginate network. By combining orthogonal cross-linking strategies and altering the ratio between different components in these hybrid gels, a broad range of mechanical properties is demonstrated. The characteristics were extensively investigated using tensile testing, compression testing, and rheological measurements. The final scaffolds were also shown to be non-cytotoxic in preliminary cell viability studies for human dermal fibroblasts.

Transient and Dissipative Host-Guest Hydrogels Regulated by Consumption of a Reactive Chemical Fuel.

The transient self-assembly of molecules under the direction of a consumable fuel source is fundamental to biological processes such as cellular organization and motility. Such biomolecular assemblies exist in an out-of-equilibrium state, requiring continuous consumption of high energy molecules. At the same time, the creation of bioinspired supramolecular hydrogels has traditionally focused on associations occurring at the thermodynamic equilibrium state. Here, hydrogels are prepared from cucurbit[7]uril host-guest supramolecular interactions through transient physical crosslinking driven by the consumption of a reactive chemical fuel. Upon action from this fuel, the affinity and dynamics of CB[7]-guest recognition are altered. In this way, the lifetime of transient hydrogel formation and the dynamic modulus obtained are governed by fuel consumption, rather than being directed by equilibrium complex formation.

Transient and Dissipative Host–Guest Hydrogels Regulated by Consumption of a Reactive Chemical Fuel

AbstractThe transient self‐assembly of molecules under the direction of a consumable fuel source is fundamental to biological processes such as cellular organization and motility. Such biomolecular assemblies exist in an out‐of‐equilibrium state, requiring continuous consumption of high energy molecules. At the same time, the creation of bioinspired supramolecular hydrogels has traditionally focused on associations occurring at the thermodynamic equilibrium state. Here, hydrogels are prepared from cucurbit[7]uril host–guest supramolecular interactions through transient physical crosslinking driven by the consumption of a reactive chemical fuel. Upon action from this fuel, the affinity and dynamics of CB[7]–guest recognition are altered. In this way, the lifetime of transient hydrogel formation and the dynamic modulus obtained are governed by fuel consumption, rather than being directed by equilibrium complex formation.

Fracture of dual crosslink gels with permanent and transient crosslinks: Effect of the relaxation time of the transient crosslinks

We investigate the fracture properties of poly(acrylamide-co-1-vinylimidazole) dual crosslink hydrogels [P(AAm-co-VIm)-M2+ gels] containing a small fraction of covalent bonds and a majority of dynamic bonds based on metal coordination bonds (Ni2+ or Zn2+). Unlike a previous study on a different dual crosslink hydrogel system having slower dynamic bonds based on poly(vinylalcohol) and borate ions (PVA-Borax gels), the presence of these faster dynamic coordination bonds has two main effects: They significantly toughen the P(AAm-co-VIm)-M2+ gels even at high stretch rates, where the dynamic bonds should in principle behave as covalent bonds at the crack tip, and they toughen the gels at very low stretch rates, where the dynamic bonds are invisible during the loading stage. We propose two additional molecular mechanisms to rationalize this behavior of P(AAm-co-VIm)-M2+ gels: we hypothesize that fast exchanging dynamic bonds remain slow compared to the characteristic time of bond scission and are, therefore, able to share the load upon covalent bond scission even at low loading rates. We also argue of the existence of longer-lived clusters of dynamic bonds that introduce a stretch rate-dependent strain hardening in uniaxial tension and stabilize and increase the size of the dissipative zone at the crack tip, thereby introducing a strain-dependent dissipative mechanism.

Zhao et al.: Fracture of dual crosslink gels with permanent and transient crosslinks: Effect of the relaxation time of the transient cross-links

Zhao <i>et al</i>.: Fracture of dual crosslink gels with permanent and transient crosslinks: Effect of the relaxation time of the transient cross-links

Modification in the microstructure of sodium carboxymethylcellulose/polyvinyl alcohol polyblend films through the incorporation of NaNO 3 for energy storage applications

In this work, the effect of NaNO3 salt concentration (0, 5, 10, 15, 20, 25, and 30 wt.%) on the structural, electrical, and mechanical properties of Na-carboxymethyl cellulose/polyvinyl alcohol polyblend electrolyte films has been studied. X-ray diffraction showed an increase in the amorphous phase of the polymer blend with increasing salt concentration up to samples containing 20 wt.% of NaNO3 supported by the scanning electron microscope studies. Fourier-transform infrared analysis confirmed the complexation of the salt via coordinate bond/hydrogen bond with –OH and –CH groups of the polymer blend. The T g of the samples have been found to increase with salt concentration indicating transient cross-links. Nyquist plot fitting has been performed to evaluate the transport properties; hence carrier concentration influences ionic conductivity. The sample complexed with 20 wt.% of NaNO3 revealed the highest room temperature conductivity of 1.75 × 10−4 S cm−1, among all other samples with suitable mechanical strength to be incorporated into energy storage devices. The highest conducting electrolyte has been incorporated into a primary battery to showcase its potential application in energy storage devices.

Non-Covalent Interaction on the Self-Healing of Mechanical Properties in Supramolecular Polymers.

Supramolecular polymers are widely utilized and applied in self-assembly or self-healing materials, which can be repaired when damaged. Normally, the healing process is classified into two types, including extrinsic and intrinsic self-healable materials. Therefore, the aim of this work is to review the intrinsic self-healing strategy based on supramolecular interaction or non-covalent interaction and molecular recognition to obtain the improvement of mechanical properties. In this review, we introduce the main background of non-covalent interaction, which consists of the metal–ligand coordination, hydrogen bonding, π–π interaction, electrostatic interaction, dipole–dipole interaction, and host–guest interactions, respectively. From the perspective of mechanical properties, these interactions act as transient crosslinking points to both prevent and repair the broken polymer chains. For material utilization in terms of self-healing products, this knowledge can be applied and developed to increase the lifetime of the products, causing rapid healing and reducing accidents and maintenance costs. Therefore, the self-healing materials using supramolecular polymers or non-covalent interaction provides a novel strategy to enhance the mechanical properties of materials causing the extended cycling lifetime of products before replacement with a new one.

Dynamics of Hydrogels with a Variable Ratio of Permanent and Transient Cross-Links: Constitutive Model and Its Molecular Interpretation

Dynamics of Hydrogels with a Variable Ratio of Permanent and Transient Cross-Links: Constitutive Model and Its Molecular Interpretation

Tough and self-healing hydrogels based on transient crosslinking by nanoparticles.

In this investigation, transient crosslinking was constructed to obtain a hydrogel with excellent mechanical and self-healing properties. Firstly, core-shell particles with hydrophilic amino groups were prepared by emulsion polymerization and subsequently dispersed into hydrophobic association polyacrylamide hydrogels. Transient crosslinking was constructed through hydrogen bonding between core-shell particles and polyacrylamide. As a result, the hydrogels exhibited a tensile strength of 1.4 MPa and self-healing efficiency of 98% at 24 h. Furthermore, reconstruction of the transient crosslinking was confirmed from rheological measurements. Therefore, the essential reinforcement principle based on transient crosslinking would open a novel strategy to obtain hydrogels with superior toughness and self-healing properties.

Mechanically robust, shape memory, self-healing and 3D printable thermoreversible cross-linked polymer composites toward conductive and biomimetic skin devices applications

The current work demonstrates excellent thermal, mechanical, shape memory, and self-healing properties of 3D printable, thermoreversible, cross-linked network composites. The thermoreversible cross-linked networks are composed of Diels-Alder (DA) reversible covalent and transient cross-links, which are formed by thermoplastic polyurethane (TPU) and poly(ε-caprolactone) (PCL). Also, cellulose nanocrystalline (CNC) is utilized as a cross-linking agent. The incorporated CNC, modified with furan (CNC-FA) and maleic anhydride groups (CNC-MAH), exhibits excellent compatibility with TPU/PCL matrix, forming physical and chemical cross-linking structures in the composites. Also, the mechanical properties, thermal stability, and self-healing properties are significantly improved after the addition of modified CNC. In addition, the mechanism of performance enhancement is further analyzed by molecular dynamics simulations. One should note that the mechanically robust and 3D printable self-healing composites enable the fabrication of durable conductive devices and biomimetic skin devices with high mechanical integrity, excellent electrical healing and superior strain-induced fluorescence properties, showing promise in next-generation flexible electronics, encryption devices and electronic skins, and may broaden the variety and applications of 3D-printable materials. • The thermoreversible composites are composed of DA reversible covalent and transient crosslinks. • The CNC modified with furan and maleic anhydride groups, exhibit compatibility with polymer matrix. • The mechanism of performance enhancement is further analyzed by molecular dynamics simulations. • The damage could be healed due to the good self-healing capability, thanks to the shape memory effect.

Time–strain inseparability in multiaxial stress relaxation of supramolecular gels formed via host–guest interactions

Time and strain effects on stress are not separable in supramolecular gels utilizing host–guest interactions in contrast to a dual cross-link gel with covalent and transient cross-links in which the separability was validated by the same assessment.